CA2125015C - Proportional-integral-derivative controller having adaptive control capability - Google Patents
Proportional-integral-derivative controller having adaptive control capabilityInfo
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- CA2125015C CA2125015C CA002125015A CA2125015A CA2125015C CA 2125015 C CA2125015 C CA 2125015C CA 002125015 A CA002125015 A CA 002125015A CA 2125015 A CA2125015 A CA 2125015A CA 2125015 C CA2125015 C CA 2125015C
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- 239000003570 air Substances 0.000 description 12
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Classifications
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F11/00—Control or safety arrangements
- F24F11/30—Control or safety arrangements for purposes related to the operation of the system, e.g. for safety or monitoring
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24F—AIR-CONDITIONING; AIR-HUMIDIFICATION; VENTILATION; USE OF AIR CURRENTS FOR SCREENING
- F24F11/00—Control or safety arrangements
- F24F11/62—Control or safety arrangements characterised by the type of control or by internal processing, e.g. using fuzzy logic, adaptive control or estimation of values
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B11/00—Automatic controllers
- G05B11/01—Automatic controllers electric
- G05B11/36—Automatic controllers electric with provision for obtaining particular characteristics, e.g. proportional, integral, differential
- G05B11/42—Automatic controllers electric with provision for obtaining particular characteristics, e.g. proportional, integral, differential for obtaining a characteristic which is both proportional and time-dependent, e.g. P. I., P. I. D.
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05B—CONTROL OR REGULATING SYSTEMS IN GENERAL; FUNCTIONAL ELEMENTS OF SUCH SYSTEMS; MONITORING OR TESTING ARRANGEMENTS FOR SUCH SYSTEMS OR ELEMENTS
- G05B13/00—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion
- G05B13/02—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion electric
- G05B13/04—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion electric involving the use of models or simulators
- G05B13/042—Adaptive control systems, i.e. systems automatically adjusting themselves to have a performance which is optimum according to some preassigned criterion electric involving the use of models or simulators in which a parameter or coefficient is automatically adjusted to optimise the performance
-
- G—PHYSICS
- G05—CONTROLLING; REGULATING
- G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
- G05D23/00—Control of temperature
- G05D23/19—Control of temperature characterised by the use of electric means
- G05D23/1917—Control of temperature characterised by the use of electric means using digital means
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- Engineering & Computer Science (AREA)
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Automation & Control Theory (AREA)
- General Engineering & Computer Science (AREA)
- Mechanical Engineering (AREA)
- Combustion & Propulsion (AREA)
- Chemical & Material Sciences (AREA)
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- Medical Informatics (AREA)
- Health & Medical Sciences (AREA)
- Computer Vision & Pattern Recognition (AREA)
- Artificial Intelligence (AREA)
- Feedback Control In General (AREA)
- Control Of Temperature (AREA)
Abstract
Apparatus for controlling at least one variable output parameter in response to a variable predetermined input parameter in a process system, such as a digital thermostat.
The apparatus provides adaptive control of the output variable by utilizing a controller means that includes an adaptive controller means, an identifier means and a tuner means. The identifier means defines a model having parameters which represent the operational characteristics of the process system, and the identifier means monitors the operation of the adaptive controller means and selectively changes the parame-ters of said model to improve the operation of the adaptive controller means. The tuner means receives the model parame-ters from the identifier means and calculating robust and reliable values of said predetermined gain factors and applying the same to the adaptive controller means for use thereby.
The apparatus provides adaptive control of the output variable by utilizing a controller means that includes an adaptive controller means, an identifier means and a tuner means. The identifier means defines a model having parameters which represent the operational characteristics of the process system, and the identifier means monitors the operation of the adaptive controller means and selectively changes the parame-ters of said model to improve the operation of the adaptive controller means. The tuner means receives the model parame-ters from the identifier means and calculating robust and reliable values of said predetermined gain factors and applying the same to the adaptive controller means for use thereby.
Description
` 2125015 6 Field of the Invention 7 The present invention generally relates to a process 8 controller that has either proportional-integral control 9 functionality or proportional-integral-derivative control functionality, and more particularly to such a controller that 11 has adaptive control capability.
12 There has been a need for controllers for control-13 ling a single variable in many kinds of processes that pro-14 vides effective control. One of the applications for such controllers is readily apparent to all individuals in an 16 indoor environment is that of temperature control. Ineffec-17 tive temperature control of an indoor environment is readily 18 apparent to those who are uncomfortable, and there is a 19 continuing need for effective control of heating, ventilating and air conditioning systems in all types of buildings.
21 Controllers have been developed which are increas-22 ingly more sophisticated, and with advancements in electronic 23 technology, more robust control capability can be achieved and 24 implemented at reasonable cost. Controllers which control a 1 single loop, i.e., control a single variable such as tempera-- 2 ture, humidity or the like, by controlling an output have been 3 implemented, and improved control has been achieved by imple-4 menting control sch~me which include three separate factors or components. These include a proportional gain factor, an 6 integral gain factor and a derivative gain factor. Such PID
7 controllers can provide better control because they determine 8 the derivative as well as the integral of change of the error 9 over time, in addition to the error that is determined at a particular time, to control the controlled variable.
11 While such PID controllers offer many advantages 12 over controllers which merely provide proportional control, 13 there is a need for improved PID controllers for particular 14 applications and uses.
Accordingly, it is a primary object of the present 16 invention to provide an improved PID controller that has 17 adaptive control capability that has many possible appli-18 cations.
l9 Another object of the present invention is to provide an improved PID controller having adaptive control 21 capability that is particularly suited for controlling a 22 single control loop, i.e., a single variable is controlled and 23 provides a single output.
24 Yet another object of the present invention is to provide such an improved adaptive controller for controlling 26 a single loop, but also has the capability of operating in 27 series with other single control loops.
28 Still another object of the present invention is to 29 provide such an improved adaptive controller that has the capability of operating in a cascaded configuration of control 31 loops.
32 Another object of the present invention is to pro-33 vide such an improved adaptive controller that utilizes an 34 internal model of the application that is to be controlled, which model matches the expected application, and which during 1 operation, tunes itself in response to load, equipment or time 2 changes.
3 A related object lies in the provision of ~m;n;ng 4 the input, comparing the input with what it should be and then S changes the parameters within the internal model to move 6 actual conditions closer to the desired condition, and provide 7 control of the output in accordance with the changed internal 8 model.
g A detailed object of the present invention is to provide an improved thermostat which also has the capability 11 of providing adaptive control, i.e., during operation, it will 12 monitor itself in terms of its effectiveness in control, and 13 will generate more effective operating parameters within 14 specific algorithms to provide more accurate control.
lS Other objects and advantages will become apparent 16 from the ensuing detailed description, while referring to the 17 attached drawings, in which:
18 FIGURE 1 is a perspective view of a thermostat 19 embodying the present invention;
FIG. 2 is a schematic diagram of a unit ventilator 21 shown with a thermostat embodying the present invention;
22 FIG. 3 is a perspective view of internal structure 23 of the thermostat shown in FIG. l;
24 FIGS. 4a, 4b and 4c together comprise a detailed electrical schematic diagram of the circuitry of a thermostat 26 embodying the present invention;
27 FIG. 5 is a block diagram of the adaptive loop 28 control system showing the relationship between the control 29 system and the room;
FIG. 6 is a block diagram of the adaptive con-31 troller;
32 FIG. 7 is a detailed flow chart of the adaptive 33 controller, and particularly illustrating the controller shown 34 in FIG. 6;
FIG. 8 is a detailed flow chart of the adaptive `
1 control system and particularly illustrating the identifier 2 shown in FIG. 6.
3 Detailed Description 4 The present invention is directed to a PID control-ler that has adaptive control capability. The controller may 6 be operated in many PID process control applications, and is 7 ideally suited for various applications in the HVAC art. It 8 is adapted for use in controlling a single loop, i.e., 9 controlling one variable with one output, and can be optimized for a particular application such as room temperature control.
11 Other examples of use where a single adaptive loop is desir-12 able and for which the present invention is suited are: room 13 temperature control of a unit ventilator or a constant volume 14 damper application; humidity control in a duct or room;
discharge air temperature control by controlling a valve, coil 16 or bypass damper; flow control; mixed air/water control; and 17 static pressure control.
18 Single adaptive loops can be strung together in 19 series. For example, one adaptive loop can control the air temperature in a supply duct, while another can control the 21 temperature of a room by modulating a damper in the supply 22 duct. Such series loops are not interlocked and can be 23 controlled by two separate control algorithms. Single 24 adaptive loops can be interlocked in a cascade arrangement.
For example, a unit ventilator uses discharge temperature 26 control, and one adaptive loop can control the discharge air 27 temperature by modulating a coil valve or bypass damper.
28 Another adaptive loop can control the room temperature by 29 setting the discharge air temperature setpoint for the inner adaptive loop. Such cascaded adaptive loops can also be used 31 in dual duct control, and can be controlled by one controller 32 running both adaptive algorithms.
33 While the present invention is suited for the above 34 applications, as well as others, the present detailed descrip-212501~
1 tion describes an application of the controller in a thermo-2 stat of the type which can be used in a unit ventilator of the 3 type which has pneumatic controls.
4 It is well known that many building heating, ven-5 tilating and air conditioning systems are controlled through 6 the use of pneumatic controls wherein the pressure in the 7 pneumatic lines are controlled and the variable pressure in 8 turn controls pneumatic control valves. The control valves 9 are then used to control the position of dampers, as well as valves which admit heat to heating coils and the like. Prior 11 art thermostats for such systems have the capability of 12 adjusting the temperature set point for the room or other 13 enclosed area which the thermostats are intended to control, 14 and the thermostats normally operate to provide a controlled 15 pressure in a pneumatic line which is connected to control 16 elements such as dampers, valves and the like and such ther-17 mostats operate to admit increased pressure from a pneumatic 18 supply line for the purpose of increasing the temperature and 19 to decrease the pressure in the control line when the tempera-20 ture is to be reduced. The controlled pneumatic pressure 21 typically adjusts the position of the valves, dampers and the 22 like to regulate the temperature in the controlled area.
23 Additionally, there are many buildings which are controlled by 24 pneumatic thermostats which control the operation of unit 25 ventilators, such as are often used in schools. Such unit 26 ventilators are typically stand-alone units and have a fan for 27 circulating air, a heating coil through which steam or hot 28 water may circulate with the amount of flow therethrough being 29 regulated by a valve. While such mechanical pneumatic thermo-30 stats adequately control the temperature in the area which 31 they are located, they are generally stand-alone units from a 32 system standpoint, except for the capability of being switched 33 between day/night operation by changing the pressure in the 34 supply pneumatic lines, as is well known in the art.
The controller embodying the present invention can ~ 2125015 1 be incorporated into a digital thermostat which is capable of 2 use in a pneumatically controlled temperature control system 3 of the type which has a pneumatic supply line which extends to 4 various components of the control system and wherein the control elements of the system are controlled by varying the 6 control pressure that is communicated to such elements. For 7 example, pressure within pneumatic control lines may vary to 8 adjust the position of dampers, control valves or the like 9 which control the volume of steam, air and water to heating coils, radiators or the like, or in the case of dampers, 11 controlling the amount of air that is forced into the space 12 that is being controlled.
13 Such systems generally have been controlled by a 14 pneumatic thermostat that is essentially mechanical in nature and wherein adjustment of the set point for the desired 16 temperature has been performed by manual manipulation and 17 except for the capability of providing day/night modes of 18 operation, very little control is possible through the thermo-19 stat. The thermostat embodying the present invention is intended to be operable with such a pneumatic control system 21 and is capable of stand-alone operation or with an integrated 22 supervisory and control system if desired. Because of its 23 superior design, it is capable of being merely substituted for 24 a prior pneumatic thermostat without any other alterations or modifications to the control elements or the heating appa-26 ratus.
27 The thermostat embodying the present invention can 28 be substituted for a pneumatic mechanical thermostat which 29 controls a unit ventilator of the type which has been commonly used in school systems and the like. Such unit ventilators 31 generally have a fan, a heating coil of which the heating 32 element is steam, hot water or electrical. Such unit ventila-33 tors generally do not provide air conditioning in the true 34 sense, but have outside dampers which are capable of admitting outside air which may often be cooler than air in the room.
212501~
1 Typically, such unit ventilators are operable in a stand-alone 2 mode and do not have system-wide capabilities which are 3 extremely desirable in terms of efficient energy usage.
4 Another advantage of the thermostat is that it can 5 be either battery powered or can be connected to an inde-6 pendent power source and it can also be connected via a two 7 wire cable to a com~l~nication network, commonly a local area 8 network or LAN, so that it can be operated as a part of a 9 total supervisory and control system. The thermostat embody-ing the present invention includes a processing means having 11 internal memory and is therefore capable of running relatively 12 complex control algorithms which are capable of providing 13 proportional control, integral control, as well as derivative 14 control, among other control schemes, such as a Smith predic-tor type of control scheme.
16 Day/night and heat/cooling modes of operation can be 17 achieved, with different temperature set points for each mode 18 of operation. The thermostat is manually adjustable so that 19 its set point can be adjusted at the location of the thermo-20 stat to suit individual needs if desired, or it can be pro-21 grammed so that it is not responsive to such individual con-22 trols during certain time periods or the like.
23 Turning now to the drawings, and particularly FIG.
24 1, a thermostat embodying the present invention, indicated 25 generally at 10, is illustrated and includes an outer enclo-26 sure 12 having opposite end walls 14, opposite sidewalls 16 27 and a front wall 18. The sidewalls preferably have a plural-28 ity of openings 20 therein through which air may pass so that 29 a temperature sensing device located within the enclosure will measure the temperature of ambient air in the area which the 31 thermostat is intended to control. In the front face 18 of 32 the thermostat 10, a display 22 is shown.
33 The display is preferably a liquid crystal display 34 which will illustrate the time and current temperature, but 35 may display other information, including the temperature set 1 point of the thermostat, whether it is operating in one of the 2 day or night control modes and the like. The thermostat 3 preferably has a pair of switches 24 and 26, which are illus-4 trated to be up and down arrows and are provided to enable the temperature set point of the thermostat to be either increased 6 or decreased upon pushing the appropriate pushbutton.
7 Since the thermostat must effectively interface 8 pneumatic lines and electrical circuitry, it is preferred that 9 the electronic components be constructed using a printed cir-cuit board such as is shown in FIG. 3. A processing means 2811 is provided, as is a temperature sensing device, preferably a 12 pair of thermistors 30 and other electrical components, which 13 are illustrated in FIG. 4, and which are mounted on a printed 14 circuit board 32, but which are not shown in detail in FIG. 3.
15 Connectors 33 are provided for connection to the display 22 16 and switches 24 and 26, with the number illustrated in FIG. 3 17 not being the total number of such connectors but being 18 diagrammatic of the intended construction. It should be 19 understood that a ribbon or zebra connector 35 may be utilized 20 or other appropriate conductors and connectors which are well 21 known in the art.
22 The connectors 34 are intended to connect the cir-23 cuitry of the printed circuit board 32 with the electrical 24 pneumatic components that are attached to a base 36 and addi-tional connectors 38 are provided to provide connection to the 2 6 local area network and to a source of power. The base 36 has 27 a number of openings, not shown, through which the power and 28 LAN connectors may pass. The base plate also has internal 29 ports to which pneumatic lines can be attached, and to this 30 end, the pneumatic supply port 44 is shown connected to an 31 electropneumatic valve 46 to which another pneumatic port 48 32 is attached and which comprises the controlled output. The 33 port 48 is also connected to a second valve 50 which in turn 34 is connected to a bleed port 52. It should be understood 35 that the electropneumatic valves 46 and 50 are shown to be ~125015 -1 generally cylindrical and may be in the form of conventional 2 solenoid valves. However, it should be understood that any 3 suitable control device may be used which is operable in 4 response to appropriate electrical signals being applied thereto. It is conventional practice that the pneumatic 6 pressure in the control port 48 is variable within the range 7 of the supply pressure and atmospheric pressure, and the 8 controlled pressure may be adjusted by operating one or the 9 other of the control valves 46 and 50.
The valves operate to selectively communicate air 11 among the ports 44, 48 and 52 when they are open and isolate 12 one from another when they are closed. In this regard, the 13 pressure in the controlled output port 48 may be increased by 14 opening the valve 46 which communicates the higher supply pressure to the controlled output port. Similarly, if it is 16 intended to decrease the control pressure within the port 48, 17 the valve 50 may be opened to bleed pressure to atmosphere via 18 port 52. The output port 48 may have a small molded manifold 19 piece which is in communication with port 48 and which also includes a pneumatic transducer element, diagrammatically 21 illustrated at 54, for providing an electrical signal to the 22 circuitry of FIG. 4 which is indicative of the controlled 23 pressure in port 48.
24 The thermostat 10 is adapted for use with apparatus such as a unit ventilator, the schematic diagram of which is 26 shown in FIG. 2, and which has a fan 60 and a pneumatic elec-27 tric switch 62, for turning the fan on when it is otherwise 28 placed in condition for operation. The thermostat 10 is shown 29 with power lines 64 and LAN lines 66 which can be connected to a remote central control station 67. The thermostat 10 has a 31 pneumatic supply line 44' attached to port 44 and an output 32 line 48~ attached to port 48, which line 48' extends to a 33 valve 68 that admits hot water, steam or the like to a heating 34 coil 70. The pneumatic line 48' also extends to a pneumatic-ally controlled damper control 72 and to another valve 74 212~015 1 which controls the flow of steam, hot water or the like to an 2 auxiliary radiation coil 76.
3 With respect to the electrical schematic circuitry 4 of the thermostat 10, and referring to FIGS. 4a, 4b and 4c, the circuit components which have been previously identified 6 have been given the same reference numerals in this figure for 7 consistency. The circuitry is driven by the processing means 8 28, (FIG. 4a) which is preferably a model 68HCll micro-9 controller manufactured by Motorola. The micro-controller is driven by a clock circuit comprising a crystal 80 that is 11 connected to pins 7 and 8. Pins 9-15 extend to the display 12 22, via a display driver integrated circuit of conventional 13 design which is not shown.
14 The valves 46 and 50 are illustrated in FIG. 4a-as being solenoid valves and the solenoid which increases the 16 pressure 46 is driven by lines from pins 37 and 38, through a 17 driver circuit 82, while lines from pins 35 and 36 operate the 18 pressure reducing solenoid 50. In this regard, when the 19 solenoid is initially actuated, the up line from pin 37 is activated and it is held by a signal on line from pin 38. The 21 circuitry also includes a power up/down reset circuit 84.
22 Power lines 64 (FIG. 4c) are preferably 24 volt alternating 23 current lines that are applied to a full wave rectifier, 24 indicated generally at 86, (FIG. 4c) which is applied to a switching mode power supply circuit 88, preferably a Model 26 MC34129 manufactured by Motorola. It supplies plus and minus 27 5 Volts D.C. (VDC) on lines 90 and 92, respectively, which are 28 distributed to various portions of the circuitry as illU8-29 trated.
Additionally, lines 90 and 92 are connected to an 31 integrated circuit 94 which provides a reference voltage of 1-32 1/2 VDC on line 96 and a 4.1 VDC reference voltage on line 98, 33 both of which are respectively connected to pins 51 and 52 of 34 the micro-controller 28. The switches 24 and 26 are connected to pins 49 and 47, respectively, for adjusting the set point ~12501S
1 of the thermostat and lines 100 are provided as spares for 2 other functional input signals that may be desired. The 3 temperature measuring function is performed by the pair of 4 thermistors 30 connected in parallel with one another which provide an electrical output to the micro-controller at pin 45 6 that is proportional to the temperature that is sensed. In 7 this regard, two thermistors are used to provide an average 8 value for use by the micro-controller 28.
9 The pressure transducer 54 has positive and negative outputs which are c~nnected to an amplifier circuit, indicated 11 generally at 102, which provides an amplified signal to pin 43 12 of the micro-controller. Communication with a LAN network via 13 line 66 is provided by circuitry associated with a RS485 14 transmission receiver integrated circuit 103 which has lines 104 that extend to pins 20 and 21 of the micro-controller and 16 a select line 106 that extends to pin 42 thereof.
17 The flow chart for the adaptive control algorithm 18 that controls the operation of the thermostat is shown in FIG.
19 5 and has a room temperature set point applied by a control dial switch on the thermostat itself or is supplied by a 21 remote control station via the LAN communication. The 22 adaptive controlling algorithm continuously calculates robust 23 controller gains required for accurate temperature control in 24 a room. As the properties and characteristics of the room change, the algorithm adjusts the controller gains appro-26 priately to maintain robust control. The algorithm adapts 27 particularly well to gradual changes in room parameters.
28 Sudden changes, such as a large rise or drop in the tempera-29 ture of the water going to a heating or cooling coil, cause temporary fluctuations in room temperature, as they would with 31 any controller, but the adaptive controller retunes itself and 32 returns the room to good control.
33 The algorithm is a single loop controller. One 34 input, Yq(n), from the room temperature sensor 108 is applied via line 110 to the controller 112 and it provides an output -1 U(n) on line 114 to block 116 which represents the dynamics of 2 the room and the actuator. The output X(t) represents the 3 temperature rise or fall in the room due to the operation of 4 the actuator. The room model symbolically has a summing junction 118 which receives the units of temperature X(t) and 6 the load and the room temperature is represented by Y(t) on 7 line 120 which is sensed by the sensor 108. The load is 8 defined as any temperature effect in the room which is not a 9 direct re-sult of the control efforts as applied through the actuator. The room temperature Y(t) is sampled by the sensor 11 and quantized by no more than 0.25 degrees F, generating 12 signal Yq(n).
13 As is shown in FIG. 6, the adaptive controller 112 14 itself consists of three primary blocks, which consist of a controller block 122, a tuner block 124 and an identifier 16 block 126. These blocks define an algorithm for room tempera-17 ture control. The controller 122 uses the room temperature 18 setpoint r(n) on line 128 and the measured room temperature 19 Yq(n) to create a control signal U(n). This signal drives an actuator in such a way as to keep the measured room tempera-21 ture at the setpoint. The identifier 126 uses the control 22 signal from the controller and the actual room temperature 23 signal to recursively calculate appropriate parameters for a 24 second order room model, and outputs the parameters in the form of a vector Qa~, identified at 130, and a factor k on 26 line 132 which represents the number of controller sampling 27 periods in the calculated room time delay. Each room has 28 different model parameters, and these parameters can change 29 over time. The identifier is able to zero in on these parameters and track them as they move. The tuner block 124 31 uses the room model parameter estimates generated by the 32 identifier and calculates appropriate controller gains, i.e., 33 the proportional gain factor Kp on line 134, the integral gain 34 factor Ki on line 136 and the derivative gain factor Kd on line 138, for the controller 122 to use.
-1 Referring to FIG. 7, the controller 122 is illus-2 trated and comprises a Smith Predictor structure with an 3 imbedded PID controller. The estimated room model is used in 4 the structure, but it is divided into two parts. The first 5 part contains the dynamic elements of the model and the second 6 part contains only a time delay. The principle of the Smith 7 Predictor is simple; if the estimated room model is exactly 8 right, then the signal C(n) will be equal to the output of the 9 room, X(n). The signal (Yq(n)-C(n)) will then be equal to the load. The problem of controlling the room, with its time 11 delay, is then reduced to the problem of controlling the 12 dynamic part of the estimated room model with no time delay.
13 The Smith Predictor limits if not eliminates the effects of a 14 time delay.
The structure of the controller 122 is shown in FIG.
16 7 to have a PID controller 140, a room dynamic model 142 and 17 a room delay model 144 interconnected as shown. The output 18 U(n) is applied via line 114 to the room dynamic model 142 and 19 the model block 142 provides an output Atn) on line 146 that 20 iS applied to the room delay model 144 and to a summing 21 junction 148. The output of the room delay model 144 is C(n) 22 on line 150 and it is compared with the sensed room tempera-23 ture Yq(n) on line 110 and the difference determined by 24 summing junction 152 is applied to the summing junction 148 via line 154. The output of the summing junction 148 appears 26 on line 156 that is compared with temperature set point r(n) 27 from line 128 at summing junction 158 to provide an error 28 signal e(n) on line 158 that is applied to the PID controller 29 140.
The PID in the controller is a standard digital PID.
31 The P, I and D terms are calculated separately and added 32 together and limited between given high and low limits to 33 create the output U(n). The formulas are as follows:
34 P-term = Kp * e(n) -1I-term(n) = (Ki * e(n) * Ts) + I-term(n-1) 2D-term = Kd* (e(n) - e(n-l) ) 3U(n) = (P-term + I-term + D-term) limited between 4given high and low values where e(n) = input error signal, (temp., setpoint, r(n), minus 6 the prediction error (line 156, FIG. 7)), T9 = controller 7 sampling period. The foregoing discussion relating to the 8 controller shown in FIG. 7 also applies to a controller having 9 only proportional-integral control functionàlity. In such a controller, the above defined D-term would not be present.
11 The room model includes effects from the actuator, 12 the temperature sensor, and the room itself. The dynamic part 13 of the room model is represented by the second order equation:
14 A(z)= b1p*z-1 + b2p*z-2 U(z) 1 + alQ*z~l + a2Q*z~2 which can be rewritten into the following vector equation:
16 A(n) = (-A(n-1) -A(n-2) U(n-1) U(n-2)) * Qa~
17 where Qa~ = (a1Q a2Q blQ b2Q) T, a vector containing the room 18 parameters.
19 The room delay model simply delays the signal A(n) by the time k*T8. The formula is:
21 C(n) = A(n-k) 22 where k is the time delay length in sample periods.
23 The tuner 124 calculates PID gains for the control-24 ler using the Zeigler-Nichols tuning formulas. Instead of -1 going through the painstaking and time-consuming process of 2 raising the P-gain in successive trials in order to find the 3 "ultimate gain" (K~x) and the associated period of oscillation 4 (To)~ as the classic tuning procedure requires, the ultimate gain and the period of oscillation are calculated analyti-6 cally, directly from the auxillary room model parameters. The 7 formulas for these calculations are:
~nax b2p 9 h = 0.5 * (alQ + K~x * blQ) O To = Ts* (2 *~) tan~~ h 2 ) 11 The following formulas are then used to produce robust PID
12 gains:
13 ~ = 0.6 * K~x 14 2 K~
o Kd =0.125 * Kp * To 16 In the event a proportional-integral controller is employed, 17 the following formulas are then used to produce robust PI
18 gains:
19 ~ = 0-45 * K~x Ki = 1.2 * Kp/To 21The identifier shown in FIG. 8 is comprised of six 212501~
-1blocks: the two difference operators 160, 162, a time delay 2identifier 164, a functional coefficients identifier 166, a 3coefficients filter 168, and a stability supervisor 170.
4The difference operator blocks 160, 162 simply subtract the previous value from the current value. These 6 blocks are required because the two identifier blocks 164 and 7 166 require only the change in a value from sample time to 8 sample time, not the actual value itself. The signals which 9 pass through the difference operators are the output from the controller tU(n)), and the measured room temperature (Yq(n)).
11 The equations used are:
12 Ui(n) = U(n) - U(n-l) 13 Yi(n) = Yq(n) - Yq(n-1) 14 The coefficients identifier determines recursively the values of a set of model parameters which cause predicted 16 model outputs to most closely match the room response to the 17 controller's action.
18 The algorithm used is the Recursive Instrumental 19 Variables algorithm. The actual algorithm used, in vec-tor/matrix formulation, is as follows:
21T = (-Yi(n-1) -Yi(n-2) Ui(n-k-1) Ui(n-k-2))T
22W = (-h(n-1) -h(n-2) Ui(n-k-1) Ui(n-k-2))T
23h(n) = WT * Qaux 24e(n) = Yi(n) - TT * Q
P(n-l) *W
25(~+ TT*P(n-l) *W) 212501~
1 Q(n) = Q(n-l) + K * e(n) 2 P(n) = (1/~) * (I-(K * WT)) * P(n-l) (covariance 3 matrix update) 4 where ~ is a forgetting factor.
The coefficients filter 168 filters each of the 6 estimated model parameters held in vector Q. The filter 168 7 is required to ensure that model estimates change very 8 smoothly, which will allow the controller to control more 9 smoothly. The filter 168 used is as follows:
Qa~(n) = (1 - r) * Qa~(n-l) + r* (Q(n)) 11 where r is the filter factor, initially set to 0.01.
12 The coefficients stability supervisor 170 checks the 13 parameter estimates coming out of the coefficients identifier 14 166 to make sure that the estimated model is stable. It also checks that K~, coming from the tuner 124 is positive, a 16 necessary condition for loop stability.
17 A stability test is performed according to the 18 following criteria. The model is unstable if any of the 19 following occurs:
20 1) l+alo+a2Q
21 2) l-alQ+a2Q~0 22 3) 23 4) K~0 24 where the subscript Q indicates a parameter from Q vector (not the Qa~ vector).
1 If any one of these conditions is satisfied, the 2 supervisor does three things:
3 1. Resets the covariance matrix to all zeros with 4 0.1 on the major diagonal;
2. Sets the new Qaux to the old Qaux/ skipping the 6 coefficients filter's Q update;
7 3. Sets the new K~x to the old K~x, skipping the 8 tuner's K~x update for (K~x s O only).
9 The time delay identifier 164 estimates the time delay by evaluating a cost function, J(kt), for different 11 values of kt. The value of kt which results in the lowest J
12 is selected as the estimated time delay, k.
13 The cost function is evaluated for all integers 14 between the predefined k~x and kmin. The cost function is:
J(kt,n) = ~k * J(kt,n-1) + (Yi(n) - Yi(n,kt) )2 16 where ~k = forgetting factor and Yi(n,kt) = predicted output 17 difference for given possible delay time.
18 The cost functions run constantly, each evaluating 19 using a different possible time delay, kt. The value for the time delay which is selected and used for parameter estimation 21 and control is the value which results in the lowest J.
22 From the foregoing, it should be understood that a 23 controller has been shown and described which has many 24 desirable attributes and advantages. The adaptive capability of the controller enables it to be installed in an applica-26 tion, such as the thermostat that has been described, and it 27 will be self-starting and self-tuning in the sense that the 28 parameters of its internal model will be modified in response 29 to load, equipment or time changes. Such capability ensures effective control without external manipulation.
31 While various embodiments of the present invention 32 have been shown and described, it should be understood that 33 various alternatives, substitutions and equivalents can be 1 used, and the present invention should only be limited by the 2 claims and equivalents thereof.
3 Various features of the present invention are set 4 forth in the following claims.
12 There has been a need for controllers for control-13 ling a single variable in many kinds of processes that pro-14 vides effective control. One of the applications for such controllers is readily apparent to all individuals in an 16 indoor environment is that of temperature control. Ineffec-17 tive temperature control of an indoor environment is readily 18 apparent to those who are uncomfortable, and there is a 19 continuing need for effective control of heating, ventilating and air conditioning systems in all types of buildings.
21 Controllers have been developed which are increas-22 ingly more sophisticated, and with advancements in electronic 23 technology, more robust control capability can be achieved and 24 implemented at reasonable cost. Controllers which control a 1 single loop, i.e., control a single variable such as tempera-- 2 ture, humidity or the like, by controlling an output have been 3 implemented, and improved control has been achieved by imple-4 menting control sch~me which include three separate factors or components. These include a proportional gain factor, an 6 integral gain factor and a derivative gain factor. Such PID
7 controllers can provide better control because they determine 8 the derivative as well as the integral of change of the error 9 over time, in addition to the error that is determined at a particular time, to control the controlled variable.
11 While such PID controllers offer many advantages 12 over controllers which merely provide proportional control, 13 there is a need for improved PID controllers for particular 14 applications and uses.
Accordingly, it is a primary object of the present 16 invention to provide an improved PID controller that has 17 adaptive control capability that has many possible appli-18 cations.
l9 Another object of the present invention is to provide an improved PID controller having adaptive control 21 capability that is particularly suited for controlling a 22 single control loop, i.e., a single variable is controlled and 23 provides a single output.
24 Yet another object of the present invention is to provide such an improved adaptive controller for controlling 26 a single loop, but also has the capability of operating in 27 series with other single control loops.
28 Still another object of the present invention is to 29 provide such an improved adaptive controller that has the capability of operating in a cascaded configuration of control 31 loops.
32 Another object of the present invention is to pro-33 vide such an improved adaptive controller that utilizes an 34 internal model of the application that is to be controlled, which model matches the expected application, and which during 1 operation, tunes itself in response to load, equipment or time 2 changes.
3 A related object lies in the provision of ~m;n;ng 4 the input, comparing the input with what it should be and then S changes the parameters within the internal model to move 6 actual conditions closer to the desired condition, and provide 7 control of the output in accordance with the changed internal 8 model.
g A detailed object of the present invention is to provide an improved thermostat which also has the capability 11 of providing adaptive control, i.e., during operation, it will 12 monitor itself in terms of its effectiveness in control, and 13 will generate more effective operating parameters within 14 specific algorithms to provide more accurate control.
lS Other objects and advantages will become apparent 16 from the ensuing detailed description, while referring to the 17 attached drawings, in which:
18 FIGURE 1 is a perspective view of a thermostat 19 embodying the present invention;
FIG. 2 is a schematic diagram of a unit ventilator 21 shown with a thermostat embodying the present invention;
22 FIG. 3 is a perspective view of internal structure 23 of the thermostat shown in FIG. l;
24 FIGS. 4a, 4b and 4c together comprise a detailed electrical schematic diagram of the circuitry of a thermostat 26 embodying the present invention;
27 FIG. 5 is a block diagram of the adaptive loop 28 control system showing the relationship between the control 29 system and the room;
FIG. 6 is a block diagram of the adaptive con-31 troller;
32 FIG. 7 is a detailed flow chart of the adaptive 33 controller, and particularly illustrating the controller shown 34 in FIG. 6;
FIG. 8 is a detailed flow chart of the adaptive `
1 control system and particularly illustrating the identifier 2 shown in FIG. 6.
3 Detailed Description 4 The present invention is directed to a PID control-ler that has adaptive control capability. The controller may 6 be operated in many PID process control applications, and is 7 ideally suited for various applications in the HVAC art. It 8 is adapted for use in controlling a single loop, i.e., 9 controlling one variable with one output, and can be optimized for a particular application such as room temperature control.
11 Other examples of use where a single adaptive loop is desir-12 able and for which the present invention is suited are: room 13 temperature control of a unit ventilator or a constant volume 14 damper application; humidity control in a duct or room;
discharge air temperature control by controlling a valve, coil 16 or bypass damper; flow control; mixed air/water control; and 17 static pressure control.
18 Single adaptive loops can be strung together in 19 series. For example, one adaptive loop can control the air temperature in a supply duct, while another can control the 21 temperature of a room by modulating a damper in the supply 22 duct. Such series loops are not interlocked and can be 23 controlled by two separate control algorithms. Single 24 adaptive loops can be interlocked in a cascade arrangement.
For example, a unit ventilator uses discharge temperature 26 control, and one adaptive loop can control the discharge air 27 temperature by modulating a coil valve or bypass damper.
28 Another adaptive loop can control the room temperature by 29 setting the discharge air temperature setpoint for the inner adaptive loop. Such cascaded adaptive loops can also be used 31 in dual duct control, and can be controlled by one controller 32 running both adaptive algorithms.
33 While the present invention is suited for the above 34 applications, as well as others, the present detailed descrip-212501~
1 tion describes an application of the controller in a thermo-2 stat of the type which can be used in a unit ventilator of the 3 type which has pneumatic controls.
4 It is well known that many building heating, ven-5 tilating and air conditioning systems are controlled through 6 the use of pneumatic controls wherein the pressure in the 7 pneumatic lines are controlled and the variable pressure in 8 turn controls pneumatic control valves. The control valves 9 are then used to control the position of dampers, as well as valves which admit heat to heating coils and the like. Prior 11 art thermostats for such systems have the capability of 12 adjusting the temperature set point for the room or other 13 enclosed area which the thermostats are intended to control, 14 and the thermostats normally operate to provide a controlled 15 pressure in a pneumatic line which is connected to control 16 elements such as dampers, valves and the like and such ther-17 mostats operate to admit increased pressure from a pneumatic 18 supply line for the purpose of increasing the temperature and 19 to decrease the pressure in the control line when the tempera-20 ture is to be reduced. The controlled pneumatic pressure 21 typically adjusts the position of the valves, dampers and the 22 like to regulate the temperature in the controlled area.
23 Additionally, there are many buildings which are controlled by 24 pneumatic thermostats which control the operation of unit 25 ventilators, such as are often used in schools. Such unit 26 ventilators are typically stand-alone units and have a fan for 27 circulating air, a heating coil through which steam or hot 28 water may circulate with the amount of flow therethrough being 29 regulated by a valve. While such mechanical pneumatic thermo-30 stats adequately control the temperature in the area which 31 they are located, they are generally stand-alone units from a 32 system standpoint, except for the capability of being switched 33 between day/night operation by changing the pressure in the 34 supply pneumatic lines, as is well known in the art.
The controller embodying the present invention can ~ 2125015 1 be incorporated into a digital thermostat which is capable of 2 use in a pneumatically controlled temperature control system 3 of the type which has a pneumatic supply line which extends to 4 various components of the control system and wherein the control elements of the system are controlled by varying the 6 control pressure that is communicated to such elements. For 7 example, pressure within pneumatic control lines may vary to 8 adjust the position of dampers, control valves or the like 9 which control the volume of steam, air and water to heating coils, radiators or the like, or in the case of dampers, 11 controlling the amount of air that is forced into the space 12 that is being controlled.
13 Such systems generally have been controlled by a 14 pneumatic thermostat that is essentially mechanical in nature and wherein adjustment of the set point for the desired 16 temperature has been performed by manual manipulation and 17 except for the capability of providing day/night modes of 18 operation, very little control is possible through the thermo-19 stat. The thermostat embodying the present invention is intended to be operable with such a pneumatic control system 21 and is capable of stand-alone operation or with an integrated 22 supervisory and control system if desired. Because of its 23 superior design, it is capable of being merely substituted for 24 a prior pneumatic thermostat without any other alterations or modifications to the control elements or the heating appa-26 ratus.
27 The thermostat embodying the present invention can 28 be substituted for a pneumatic mechanical thermostat which 29 controls a unit ventilator of the type which has been commonly used in school systems and the like. Such unit ventilators 31 generally have a fan, a heating coil of which the heating 32 element is steam, hot water or electrical. Such unit ventila-33 tors generally do not provide air conditioning in the true 34 sense, but have outside dampers which are capable of admitting outside air which may often be cooler than air in the room.
212501~
1 Typically, such unit ventilators are operable in a stand-alone 2 mode and do not have system-wide capabilities which are 3 extremely desirable in terms of efficient energy usage.
4 Another advantage of the thermostat is that it can 5 be either battery powered or can be connected to an inde-6 pendent power source and it can also be connected via a two 7 wire cable to a com~l~nication network, commonly a local area 8 network or LAN, so that it can be operated as a part of a 9 total supervisory and control system. The thermostat embody-ing the present invention includes a processing means having 11 internal memory and is therefore capable of running relatively 12 complex control algorithms which are capable of providing 13 proportional control, integral control, as well as derivative 14 control, among other control schemes, such as a Smith predic-tor type of control scheme.
16 Day/night and heat/cooling modes of operation can be 17 achieved, with different temperature set points for each mode 18 of operation. The thermostat is manually adjustable so that 19 its set point can be adjusted at the location of the thermo-20 stat to suit individual needs if desired, or it can be pro-21 grammed so that it is not responsive to such individual con-22 trols during certain time periods or the like.
23 Turning now to the drawings, and particularly FIG.
24 1, a thermostat embodying the present invention, indicated 25 generally at 10, is illustrated and includes an outer enclo-26 sure 12 having opposite end walls 14, opposite sidewalls 16 27 and a front wall 18. The sidewalls preferably have a plural-28 ity of openings 20 therein through which air may pass so that 29 a temperature sensing device located within the enclosure will measure the temperature of ambient air in the area which the 31 thermostat is intended to control. In the front face 18 of 32 the thermostat 10, a display 22 is shown.
33 The display is preferably a liquid crystal display 34 which will illustrate the time and current temperature, but 35 may display other information, including the temperature set 1 point of the thermostat, whether it is operating in one of the 2 day or night control modes and the like. The thermostat 3 preferably has a pair of switches 24 and 26, which are illus-4 trated to be up and down arrows and are provided to enable the temperature set point of the thermostat to be either increased 6 or decreased upon pushing the appropriate pushbutton.
7 Since the thermostat must effectively interface 8 pneumatic lines and electrical circuitry, it is preferred that 9 the electronic components be constructed using a printed cir-cuit board such as is shown in FIG. 3. A processing means 2811 is provided, as is a temperature sensing device, preferably a 12 pair of thermistors 30 and other electrical components, which 13 are illustrated in FIG. 4, and which are mounted on a printed 14 circuit board 32, but which are not shown in detail in FIG. 3.
15 Connectors 33 are provided for connection to the display 22 16 and switches 24 and 26, with the number illustrated in FIG. 3 17 not being the total number of such connectors but being 18 diagrammatic of the intended construction. It should be 19 understood that a ribbon or zebra connector 35 may be utilized 20 or other appropriate conductors and connectors which are well 21 known in the art.
22 The connectors 34 are intended to connect the cir-23 cuitry of the printed circuit board 32 with the electrical 24 pneumatic components that are attached to a base 36 and addi-tional connectors 38 are provided to provide connection to the 2 6 local area network and to a source of power. The base 36 has 27 a number of openings, not shown, through which the power and 28 LAN connectors may pass. The base plate also has internal 29 ports to which pneumatic lines can be attached, and to this 30 end, the pneumatic supply port 44 is shown connected to an 31 electropneumatic valve 46 to which another pneumatic port 48 32 is attached and which comprises the controlled output. The 33 port 48 is also connected to a second valve 50 which in turn 34 is connected to a bleed port 52. It should be understood 35 that the electropneumatic valves 46 and 50 are shown to be ~125015 -1 generally cylindrical and may be in the form of conventional 2 solenoid valves. However, it should be understood that any 3 suitable control device may be used which is operable in 4 response to appropriate electrical signals being applied thereto. It is conventional practice that the pneumatic 6 pressure in the control port 48 is variable within the range 7 of the supply pressure and atmospheric pressure, and the 8 controlled pressure may be adjusted by operating one or the 9 other of the control valves 46 and 50.
The valves operate to selectively communicate air 11 among the ports 44, 48 and 52 when they are open and isolate 12 one from another when they are closed. In this regard, the 13 pressure in the controlled output port 48 may be increased by 14 opening the valve 46 which communicates the higher supply pressure to the controlled output port. Similarly, if it is 16 intended to decrease the control pressure within the port 48, 17 the valve 50 may be opened to bleed pressure to atmosphere via 18 port 52. The output port 48 may have a small molded manifold 19 piece which is in communication with port 48 and which also includes a pneumatic transducer element, diagrammatically 21 illustrated at 54, for providing an electrical signal to the 22 circuitry of FIG. 4 which is indicative of the controlled 23 pressure in port 48.
24 The thermostat 10 is adapted for use with apparatus such as a unit ventilator, the schematic diagram of which is 26 shown in FIG. 2, and which has a fan 60 and a pneumatic elec-27 tric switch 62, for turning the fan on when it is otherwise 28 placed in condition for operation. The thermostat 10 is shown 29 with power lines 64 and LAN lines 66 which can be connected to a remote central control station 67. The thermostat 10 has a 31 pneumatic supply line 44' attached to port 44 and an output 32 line 48~ attached to port 48, which line 48' extends to a 33 valve 68 that admits hot water, steam or the like to a heating 34 coil 70. The pneumatic line 48' also extends to a pneumatic-ally controlled damper control 72 and to another valve 74 212~015 1 which controls the flow of steam, hot water or the like to an 2 auxiliary radiation coil 76.
3 With respect to the electrical schematic circuitry 4 of the thermostat 10, and referring to FIGS. 4a, 4b and 4c, the circuit components which have been previously identified 6 have been given the same reference numerals in this figure for 7 consistency. The circuitry is driven by the processing means 8 28, (FIG. 4a) which is preferably a model 68HCll micro-9 controller manufactured by Motorola. The micro-controller is driven by a clock circuit comprising a crystal 80 that is 11 connected to pins 7 and 8. Pins 9-15 extend to the display 12 22, via a display driver integrated circuit of conventional 13 design which is not shown.
14 The valves 46 and 50 are illustrated in FIG. 4a-as being solenoid valves and the solenoid which increases the 16 pressure 46 is driven by lines from pins 37 and 38, through a 17 driver circuit 82, while lines from pins 35 and 36 operate the 18 pressure reducing solenoid 50. In this regard, when the 19 solenoid is initially actuated, the up line from pin 37 is activated and it is held by a signal on line from pin 38. The 21 circuitry also includes a power up/down reset circuit 84.
22 Power lines 64 (FIG. 4c) are preferably 24 volt alternating 23 current lines that are applied to a full wave rectifier, 24 indicated generally at 86, (FIG. 4c) which is applied to a switching mode power supply circuit 88, preferably a Model 26 MC34129 manufactured by Motorola. It supplies plus and minus 27 5 Volts D.C. (VDC) on lines 90 and 92, respectively, which are 28 distributed to various portions of the circuitry as illU8-29 trated.
Additionally, lines 90 and 92 are connected to an 31 integrated circuit 94 which provides a reference voltage of 1-32 1/2 VDC on line 96 and a 4.1 VDC reference voltage on line 98, 33 both of which are respectively connected to pins 51 and 52 of 34 the micro-controller 28. The switches 24 and 26 are connected to pins 49 and 47, respectively, for adjusting the set point ~12501S
1 of the thermostat and lines 100 are provided as spares for 2 other functional input signals that may be desired. The 3 temperature measuring function is performed by the pair of 4 thermistors 30 connected in parallel with one another which provide an electrical output to the micro-controller at pin 45 6 that is proportional to the temperature that is sensed. In 7 this regard, two thermistors are used to provide an average 8 value for use by the micro-controller 28.
9 The pressure transducer 54 has positive and negative outputs which are c~nnected to an amplifier circuit, indicated 11 generally at 102, which provides an amplified signal to pin 43 12 of the micro-controller. Communication with a LAN network via 13 line 66 is provided by circuitry associated with a RS485 14 transmission receiver integrated circuit 103 which has lines 104 that extend to pins 20 and 21 of the micro-controller and 16 a select line 106 that extends to pin 42 thereof.
17 The flow chart for the adaptive control algorithm 18 that controls the operation of the thermostat is shown in FIG.
19 5 and has a room temperature set point applied by a control dial switch on the thermostat itself or is supplied by a 21 remote control station via the LAN communication. The 22 adaptive controlling algorithm continuously calculates robust 23 controller gains required for accurate temperature control in 24 a room. As the properties and characteristics of the room change, the algorithm adjusts the controller gains appro-26 priately to maintain robust control. The algorithm adapts 27 particularly well to gradual changes in room parameters.
28 Sudden changes, such as a large rise or drop in the tempera-29 ture of the water going to a heating or cooling coil, cause temporary fluctuations in room temperature, as they would with 31 any controller, but the adaptive controller retunes itself and 32 returns the room to good control.
33 The algorithm is a single loop controller. One 34 input, Yq(n), from the room temperature sensor 108 is applied via line 110 to the controller 112 and it provides an output -1 U(n) on line 114 to block 116 which represents the dynamics of 2 the room and the actuator. The output X(t) represents the 3 temperature rise or fall in the room due to the operation of 4 the actuator. The room model symbolically has a summing junction 118 which receives the units of temperature X(t) and 6 the load and the room temperature is represented by Y(t) on 7 line 120 which is sensed by the sensor 108. The load is 8 defined as any temperature effect in the room which is not a 9 direct re-sult of the control efforts as applied through the actuator. The room temperature Y(t) is sampled by the sensor 11 and quantized by no more than 0.25 degrees F, generating 12 signal Yq(n).
13 As is shown in FIG. 6, the adaptive controller 112 14 itself consists of three primary blocks, which consist of a controller block 122, a tuner block 124 and an identifier 16 block 126. These blocks define an algorithm for room tempera-17 ture control. The controller 122 uses the room temperature 18 setpoint r(n) on line 128 and the measured room temperature 19 Yq(n) to create a control signal U(n). This signal drives an actuator in such a way as to keep the measured room tempera-21 ture at the setpoint. The identifier 126 uses the control 22 signal from the controller and the actual room temperature 23 signal to recursively calculate appropriate parameters for a 24 second order room model, and outputs the parameters in the form of a vector Qa~, identified at 130, and a factor k on 26 line 132 which represents the number of controller sampling 27 periods in the calculated room time delay. Each room has 28 different model parameters, and these parameters can change 29 over time. The identifier is able to zero in on these parameters and track them as they move. The tuner block 124 31 uses the room model parameter estimates generated by the 32 identifier and calculates appropriate controller gains, i.e., 33 the proportional gain factor Kp on line 134, the integral gain 34 factor Ki on line 136 and the derivative gain factor Kd on line 138, for the controller 122 to use.
-1 Referring to FIG. 7, the controller 122 is illus-2 trated and comprises a Smith Predictor structure with an 3 imbedded PID controller. The estimated room model is used in 4 the structure, but it is divided into two parts. The first 5 part contains the dynamic elements of the model and the second 6 part contains only a time delay. The principle of the Smith 7 Predictor is simple; if the estimated room model is exactly 8 right, then the signal C(n) will be equal to the output of the 9 room, X(n). The signal (Yq(n)-C(n)) will then be equal to the load. The problem of controlling the room, with its time 11 delay, is then reduced to the problem of controlling the 12 dynamic part of the estimated room model with no time delay.
13 The Smith Predictor limits if not eliminates the effects of a 14 time delay.
The structure of the controller 122 is shown in FIG.
16 7 to have a PID controller 140, a room dynamic model 142 and 17 a room delay model 144 interconnected as shown. The output 18 U(n) is applied via line 114 to the room dynamic model 142 and 19 the model block 142 provides an output Atn) on line 146 that 20 iS applied to the room delay model 144 and to a summing 21 junction 148. The output of the room delay model 144 is C(n) 22 on line 150 and it is compared with the sensed room tempera-23 ture Yq(n) on line 110 and the difference determined by 24 summing junction 152 is applied to the summing junction 148 via line 154. The output of the summing junction 148 appears 26 on line 156 that is compared with temperature set point r(n) 27 from line 128 at summing junction 158 to provide an error 28 signal e(n) on line 158 that is applied to the PID controller 29 140.
The PID in the controller is a standard digital PID.
31 The P, I and D terms are calculated separately and added 32 together and limited between given high and low limits to 33 create the output U(n). The formulas are as follows:
34 P-term = Kp * e(n) -1I-term(n) = (Ki * e(n) * Ts) + I-term(n-1) 2D-term = Kd* (e(n) - e(n-l) ) 3U(n) = (P-term + I-term + D-term) limited between 4given high and low values where e(n) = input error signal, (temp., setpoint, r(n), minus 6 the prediction error (line 156, FIG. 7)), T9 = controller 7 sampling period. The foregoing discussion relating to the 8 controller shown in FIG. 7 also applies to a controller having 9 only proportional-integral control functionàlity. In such a controller, the above defined D-term would not be present.
11 The room model includes effects from the actuator, 12 the temperature sensor, and the room itself. The dynamic part 13 of the room model is represented by the second order equation:
14 A(z)= b1p*z-1 + b2p*z-2 U(z) 1 + alQ*z~l + a2Q*z~2 which can be rewritten into the following vector equation:
16 A(n) = (-A(n-1) -A(n-2) U(n-1) U(n-2)) * Qa~
17 where Qa~ = (a1Q a2Q blQ b2Q) T, a vector containing the room 18 parameters.
19 The room delay model simply delays the signal A(n) by the time k*T8. The formula is:
21 C(n) = A(n-k) 22 where k is the time delay length in sample periods.
23 The tuner 124 calculates PID gains for the control-24 ler using the Zeigler-Nichols tuning formulas. Instead of -1 going through the painstaking and time-consuming process of 2 raising the P-gain in successive trials in order to find the 3 "ultimate gain" (K~x) and the associated period of oscillation 4 (To)~ as the classic tuning procedure requires, the ultimate gain and the period of oscillation are calculated analyti-6 cally, directly from the auxillary room model parameters. The 7 formulas for these calculations are:
~nax b2p 9 h = 0.5 * (alQ + K~x * blQ) O To = Ts* (2 *~) tan~~ h 2 ) 11 The following formulas are then used to produce robust PID
12 gains:
13 ~ = 0.6 * K~x 14 2 K~
o Kd =0.125 * Kp * To 16 In the event a proportional-integral controller is employed, 17 the following formulas are then used to produce robust PI
18 gains:
19 ~ = 0-45 * K~x Ki = 1.2 * Kp/To 21The identifier shown in FIG. 8 is comprised of six 212501~
-1blocks: the two difference operators 160, 162, a time delay 2identifier 164, a functional coefficients identifier 166, a 3coefficients filter 168, and a stability supervisor 170.
4The difference operator blocks 160, 162 simply subtract the previous value from the current value. These 6 blocks are required because the two identifier blocks 164 and 7 166 require only the change in a value from sample time to 8 sample time, not the actual value itself. The signals which 9 pass through the difference operators are the output from the controller tU(n)), and the measured room temperature (Yq(n)).
11 The equations used are:
12 Ui(n) = U(n) - U(n-l) 13 Yi(n) = Yq(n) - Yq(n-1) 14 The coefficients identifier determines recursively the values of a set of model parameters which cause predicted 16 model outputs to most closely match the room response to the 17 controller's action.
18 The algorithm used is the Recursive Instrumental 19 Variables algorithm. The actual algorithm used, in vec-tor/matrix formulation, is as follows:
21T = (-Yi(n-1) -Yi(n-2) Ui(n-k-1) Ui(n-k-2))T
22W = (-h(n-1) -h(n-2) Ui(n-k-1) Ui(n-k-2))T
23h(n) = WT * Qaux 24e(n) = Yi(n) - TT * Q
P(n-l) *W
25(~+ TT*P(n-l) *W) 212501~
1 Q(n) = Q(n-l) + K * e(n) 2 P(n) = (1/~) * (I-(K * WT)) * P(n-l) (covariance 3 matrix update) 4 where ~ is a forgetting factor.
The coefficients filter 168 filters each of the 6 estimated model parameters held in vector Q. The filter 168 7 is required to ensure that model estimates change very 8 smoothly, which will allow the controller to control more 9 smoothly. The filter 168 used is as follows:
Qa~(n) = (1 - r) * Qa~(n-l) + r* (Q(n)) 11 where r is the filter factor, initially set to 0.01.
12 The coefficients stability supervisor 170 checks the 13 parameter estimates coming out of the coefficients identifier 14 166 to make sure that the estimated model is stable. It also checks that K~, coming from the tuner 124 is positive, a 16 necessary condition for loop stability.
17 A stability test is performed according to the 18 following criteria. The model is unstable if any of the 19 following occurs:
20 1) l+alo+a2Q
21 2) l-alQ+a2Q~0 22 3) 23 4) K~0 24 where the subscript Q indicates a parameter from Q vector (not the Qa~ vector).
1 If any one of these conditions is satisfied, the 2 supervisor does three things:
3 1. Resets the covariance matrix to all zeros with 4 0.1 on the major diagonal;
2. Sets the new Qaux to the old Qaux/ skipping the 6 coefficients filter's Q update;
7 3. Sets the new K~x to the old K~x, skipping the 8 tuner's K~x update for (K~x s O only).
9 The time delay identifier 164 estimates the time delay by evaluating a cost function, J(kt), for different 11 values of kt. The value of kt which results in the lowest J
12 is selected as the estimated time delay, k.
13 The cost function is evaluated for all integers 14 between the predefined k~x and kmin. The cost function is:
J(kt,n) = ~k * J(kt,n-1) + (Yi(n) - Yi(n,kt) )2 16 where ~k = forgetting factor and Yi(n,kt) = predicted output 17 difference for given possible delay time.
18 The cost functions run constantly, each evaluating 19 using a different possible time delay, kt. The value for the time delay which is selected and used for parameter estimation 21 and control is the value which results in the lowest J.
22 From the foregoing, it should be understood that a 23 controller has been shown and described which has many 24 desirable attributes and advantages. The adaptive capability of the controller enables it to be installed in an applica-26 tion, such as the thermostat that has been described, and it 27 will be self-starting and self-tuning in the sense that the 28 parameters of its internal model will be modified in response 29 to load, equipment or time changes. Such capability ensures effective control without external manipulation.
31 While various embodiments of the present invention 32 have been shown and described, it should be understood that 33 various alternatives, substitutions and equivalents can be 1 used, and the present invention should only be limited by the 2 claims and equivalents thereof.
3 Various features of the present invention are set 4 forth in the following claims.
Claims (39)
- Claim 1. Apparatus for controlling at least one variable output parameter in response to a variable predeter-mined input parameter in a process system, said apparatus comprising:
means for sensing said variable input parameter and generating a signal that is indicative of said sensed input parameter;
means for sensing the output parameter and generat-ing a signal that is indicative of the sensed output parame-ter;
processing means including memory means for storing instructions and data relating to the operation of the apparatus, said processing means being adapted to receive said signals indicative of said sensed input and output parameters and generate an output control signal for controlling said output parameter;
said processing means including instructions and data which define a controller means for controlling the operation of said apparatus, said controller means including an adaptive controller means, an identifier means and a tuner means;
said identifier means defining a model having parameters which represent the operational characteristics of the process system, said identifier means operating to monitor the operation of the adaptive controller means and selectively change the parameters of said model to improve the operation of the adaptive controller means;
said adaptive controller means being adapted to receive said electrical signal from said input sensing means and said electrical signal from said output sensing means and producing said output control signal utilizing predetermined gain factors received from said tuner means;
said tuner means receiving said model parameters from said identifier means and calculating appropriate values of said predetermined gain factors and applying the same to said adaptive controller means for use by said adaptive controller means; and, means operatively connected to said processing means for adjusting the value of said variable input parameter. - Claim 2. Apparatus as defined in claim 1 further including means operatively connected to said processing means for communicating with a remote controlling means.
- Claim 3. Apparatus as defined in claim 1 wherein said adaptive controller means further comprises a proportion-al-integral (PI) controller means producing an output control signal that comprises the sum of a proportional term and an integral term, with the respective terms having associated gain constants Kp and Ki.
- Claim 4. Apparatus as defined in claim 3 wherein said gain constant Ki is defined by the equation Ki = 1.2 * Kp/To where Kp = 0.45 * Kmax and and a2Q and b2Q are predetermined input parameters.
- Claim 5. Apparatus as defined in claim 1 wherein said adaptive controller means further comprises a proportion-al-derivative-integral (PID) controller means producing an output control signal that comprises the sum of a proportional term, a derivative term and an integral term, with the respective terms having associated gain constants Kp, Kd and Ki.
- Claim 6. Apparatus as defined in claim 5 wherein said output control signal from said PID controller means is applied to a dynamic model means that has a dynamic model output applied to a delay model means that has a delay model output that is summed with said signal indicative of said sensed output parameter to provide a first error signal, said first error signal being summed with said dynamic model output to provide a second error signal that is summed with said value of said variable input parameter to provide an input error signal that is applied to said PID controller means.
- Claim 7. Apparatus as defined in claim 6 wherein said adaptive controller means operates to produce an output control signal recursively each predetermined sample period.
- Claim 8. Apparatus as defined in claim 7 wherein said proportional term of said output control signal of said PID controller means is defined by the equation P-term = Kp * e(n) where e(n) is said input error signal.
- Claim 9. Apparatus as defined in claim 7 wherein said derivative term of said output control signal of said PID
controller means is defined by the equation D-term = Kd * (e(n) - e(n-1))/Ts where: e(n) is said input error signal at sample time n;
e(n-1) is said input error signal at the previous sample time; and Ts is the sampling period. - Claim 10. Apparatus as defined in claim 7 wherein said integral term of said output control signal of said PID
controller means is defined by the equation I-term = (Ki * e(n) * Ts) + I-term(n-1) where: e(n) is said input error signal at sample time n;
I-term(n-1) is the I-term calculated at the previous sample time; and Ts is the sampling period. - Claim 11. Apparatus as defined in claim 7 wherein said dynamic model output is defined by the equation A(n) = (-A(n-1) -A(n-2) U(n-1) U(n-2)) * Qaux where Qaux = (a1Q a2Q b1Q b2Q)T, a vector containing the model parameters.
- Claim 12. Apparatus as defined in claim 7 where said delay model output comprises the dynamic model output from a previous number of sample periods and is defined by the equation C(n) = A(n-k) where k is the time delay length in a predetermined number of sample periods.
- Claim 13. Apparatus as defined in claim 11 wherein said tuner means determines a maximum proportional gain factor prepatory to providing said appropriate values of said predetermined gain factors.
- Claim 14. Apparatus as defined in claim 13 wherein said maximum proportional gain factor Kmax is determined analytically from said model parameters in accordance with the following equations h = 0.5 * (a1Q + Kmax * b1Q) and the gain factors are determined in accordance with the following equations Kp = 0.6 * Kmax Kd =0.125 * Kp * To.
- Claim 15. Apparatus as defined in claim 1 wherein said predetermined input parameter is a temperature set point and said output parameter represents a temperature value.
- Claim 16. An electronic digital thermostat for use in a pneumatically controlled temperature control system of the type which has a pneumatic source line and pneumatic output control lines, the pressure in each control line of which controls the temperature of a particular indoor area, said thermostat being adapted to maintain a desired ambient temperature in an indoor area, said thermostat comprising:
means for determining and adjusting the temperature set point of the thermostat;
valve means being adapted to be operatively connect-ed to the pneumatic source line and to an exhaust and having a pneumatic output line, said valve means controlling the pressure in said pneumatic output line in response to electri-cal control signals being applied to said valve means, said controlled pressure being within the range defined by the pressures of said source line and said exhaust;
means for sensing the ambient temperature and generating an electrical signal that represents the sensed temperature;
means for sensing the pneumatic pressure in said pneumatic output line and generating an electrical signal that represents the sensed pressure;
processing means including memory means for storing instructions and data relating to the operation of the thermostat, said processing means being adapted to receive electrical signals representing sensed temperature and sensed pressure, and to generate said electrical control signals for controlling said valve means;
said memory means of said processing means includ-ing instructions and data which define a controller means for controlling the operation of said thermostat, said controller means including an adaptive controller means, an identifier means and a tuner means;
said identifier means defining a model having parameters which represent the operational characteristics of the temperature control system as it controls the temperature of said indoor area, said identifier means operating to monitor the operation of the adaptive controller means and selectively change the parameters of said model to improve the operation of the adaptive controller means;
said adaptive controller means being adapted to receive said electrical signal representing said sensed temperature and said electrical signal representing said sensed pressure and producing said output control signal utilizing predetermined gain factors received from said tuner means;
said tuner means receiving said model parameters from said identifier means and calculating appropriate values of said predetermined gain factors and applying the same to said adaptive controller means for use by said adaptive controller means; and, means for providing power for operating the thermo-stat. - Claim 17. A thermostat as defined in claim 16 further including means operatively connected to said process-ing means for communicating with a remote controlling means.
- Claim 18. Apparatus as defined in claim 16 further including means operatively connected to said processing means for communicating with a remote controlling means.
- Claim 19. Apparatus as defined in claim 16 wherein said adaptive controller means further comprises a proportion-al-derivative-integral (PID) controller means producing an output control signal that comprises the sum of a proportional term, a derivative term and an integral term, with the respective terms having associated gain constants Kp, Kd and Ki.
- Claim 20. Apparatus as defined in claim 19 wherein said output control signal from said PID controller means is applied to a dynamic model means that has a dynamic model output applied to a delay model means that has a delay model output that is summed with said signal indicative of said sensed output parameter to provide a first error signal, said first error signal being summed with said dynamic model output to provide a second error signal that is summed with said value of said variable input parameter to provide an input error signal that is applied to said PID controller means.
- Claim 21. Apparatus as defined in claim 20 wherein said adaptive controller means operates to produce an output control signal recursively each predetermined sample period.
- Claim 22. Apparatus as defined in claim 21 wherein said proportional term of said output control signal of said PID controller means is defined by the equation P-term = Kp * e(n) where e(n) is said input error signal.
- Claim 23. Apparatus as defined in claim 21 wherein said derivative term of said output control signal of said PID
controller means is defined by the equation D-term = Kd * (e(n) - e(n-1))/Ts where: e(n) is said input error signal at sample time n;
e(n-1) is said input error signal at the previous sample time; and Ts is the sampling period. - Claim 24. Apparatus as defined in claim 21 wherein said integral term of said output control signal of said PID
controller means is defined by the equation I-term = (Ki * e(n) * Ts) + I-term(n-1) where: e(n) is said input error signal at sample time n;
I-term(n-1) is the I-term calculated at the previous sample time; and Ts is the sampling period. - Claim 25. Apparatus as defined in claim 21 wherein said dynamic model output is defined by the equation A(n) = (-A(n-1) -A(n-2) U(n-1) U(n-2))* Qaux where Qaux = (a1Q a2Q b1Q b2Q)T, a vector containing the model parameters.
- Claim 26. Apparatus as defined in claim 21 where said delay model output comprises the dynamic model output from a previous number of sample periods and is defined by the equation C(n) = A(n-k) where k is the time delay length in a predetermined number of sample periods.
- Claim 27. Apparatus as defined in claim 25 wherein said tuner means determines a maximum proportional gain factor prepatory to providing said appropriate values of said predetermined gain factors.
- Claim 28. Apparatus as defined in claim 27 wherein said maximum proportional gain factor Kmax is determined analytically from said model parameters in accordance with the following equations Kmax = h = 0.5 * (a1Q + Kmax * b1Q) To = and the gain factors are determined in accordance with the following equations Kp = 0.6 * Kmax Kd = 0.125 * Kp * To.
- Claim 29. An electronic digital thermostat adapted for use in a pneumatically controlled temperature control system of the type which has at least one pneumatic source line and at least one pneumatic output control line, the pressure in each output control line controlling the tempera-ture of a particular indoor area, said thermostat being adapted to maintain a desired ambient temperature in at least one particular indoor area, said thermostat comprising:
a housing for containing the various means of the thermostat, said housing having a compact overall size;
means for determining and adjusting the temperature set point of the thermostat;
valve means being adapted to be operatively connect-ed to one pneumatic source line and to an exhaust and having a pneumatic output line, said valve means controlling the pressure in said pneumatic output line in response to electri-cal control signals being applied to said valve means, said controlled pressure being within the range defined by the pressures that exist in said source line and said exhaust;
means for sensing the ambient temperature and generating an electrical signal that is indicative of the sensed temperature;
means for sensing the pneumatic pressure in said pneumatic output line and generating an electrical signal that is indicative of the sensed pressure;
processing means including memory means for storing instructions and data relating to the operation of the thermostat, said processing means being adapted to receive electrical signals that are indicative of sensed temperature and sensed pressure and said temperature set point, and to generate said electrical control signals for controlling said valve means;
said memory means of said processing means includ-ing instructions and data which define a controller means for controlling the operation of said thermostat, said controller means including an adaptive controller means being adapted to receive said electrical signal representing said sensed temperature and said electrical signal representing said sensed pressure and producing said output control signal utilizing predetermined gain factors;
means operatively connected to said processing means for communicating with a remote controlling means; and, means for providing power for operating the thermo-stat. - Claim 30. A thermostat as defined in claim 29 wherein said controller further includes an identifier means and a tuner means;
said identifier means defining a model having parameters which represent the operational characteristics of the temperature control system as it controls the temperature of said indoor area, said identifier means operating to monitor the operation of the adaptive controller means and selectively change the parameters of said model to improve the operation of the adaptive controller means;
said tuner means receiving said model parameters from said identifier means and calculating appropriate values of said predetermined gain factors and applying the same to said adaptive controller means for use by said adaptive controller means;
said adaptive controller means utilizing said predetermined gain constants received from said tuner means. - Claim 31. Apparatus as defined in claim 30 wherein said tuner means determines a maximum proportional gain factor prepatory to providing said appropriate values of said predetermined gain factors.
- Claim 32. Apparatus as defined in claim 31 wherein said adaptive controller means further comprises a proportion-al-derivative-integral (PID) controller means producing an output control signal that comprises the sum of a proportional term, a derivative term and an integral term, with the respective terms having associated gain constants Kp, Kd and Ki.
- Claim 33. Apparatus as defined in claim 32 wherein said output control signal from said PID controller means is applied to a dynamic model means that has a dynamic model output applied to a delay model means that has a delay model output that is summed with said signal indicative of said sensed output parameter to provide a first error signal, said first error signal being summed with said dynamic model output to provide a second error signal that is summed with said value of said variable input parameter to provide an input error signal that is applied to said PID controller means.
- Claim 34 Apparatus as defined in claim 33 wherein said adaptive controller means operates to produce an output control signal recursively each predetermined sample period.
- Claim 35. Apparatus as defined in claim 34 wherein said proportional term of said output control signal of said PID controller means is defined by the equation P-term = Kp * e(n) where e(n) is said input error signal.
- Claim 36. Apparatus as defined in claim 34 wherein said derivative term of said output control signal of said PID
controller means is defined by the equation D-term = Kd * (e(n) - e(n-1))/Ts where: e(n) is said input error signal at sample time n;
e(n-1) is said input error signal at the previous sample time; and Ts is the sampling period. - Claim 37. Apparatus as defined in claim 34 wherein said integral term of said output control signal of said PID
controller means is defined by the equation I-term = (Ki * e(n) * Tg) + I-term(n-1) where: e(n) is said input error signal at sample time n;
I-term(n-1) is the I-term calculated at the previous sample time; and Ts is the sampling period. - Claim 38. Apparatus as defined in claim 34 wherein said dynamic model output is defined by the equation A(n) = (-A(n-1) -A(n-2) U(n-1) U(n-2)) * Qaux where Qaux = (a1Q a2Q b1Q b2Q)T, a vector containing the model parameters.
- Claim 39. Apparatus as defined in claim 34 where said delay model output comprises the dynamic model output from a previous number of sample periods and is defined by the equation C(n) = A(n-k) where k is the time delay length in a predetermined number of sample periods.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US7873393A | 1993-06-16 | 1993-06-16 | |
| US078,733 | 1993-06-16 |
Publications (2)
| Publication Number | Publication Date |
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| CA2125015A1 CA2125015A1 (en) | 1994-12-17 |
| CA2125015C true CA2125015C (en) | 1997-01-28 |
Family
ID=22145897
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002125015A Expired - Fee Related CA2125015C (en) | 1993-06-16 | 1994-06-02 | Proportional-integral-derivative controller having adaptive control capability |
Country Status (5)
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|---|---|
| JP (1) | JP3095199B2 (en) |
| KR (1) | KR950001442A (en) |
| AU (1) | AU683053B2 (en) |
| CA (1) | CA2125015C (en) |
| TW (1) | TW332874B (en) |
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| KR101478450B1 (en) | 2013-07-19 | 2014-12-31 | 재단법인대구경북과학기술원 | Design method of variable pid gains for multivariable nonlinear systems |
| CN103439882B (en) * | 2013-09-02 | 2016-08-17 | 北京经纬恒润科技有限公司 | The method of adjustment of a kind of controller parameter and device |
| CN105259756B (en) * | 2015-10-20 | 2018-05-04 | 广东电网有限责任公司电力科学研究院 | Power plant's control loop identification Method and system |
| JP2025008355A (en) * | 2023-07-05 | 2025-01-20 | 学校法人早稲田大学 | Air conditioner performance measuring method, air conditioner performance measuring device, and condition generator control method |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4388692A (en) * | 1980-09-03 | 1983-06-14 | Texas Instruments Incorporated | Electronically controlled programmable digital thermostat having variable threshold hysteresis with time |
| JPS63109503A (en) * | 1986-10-28 | 1988-05-14 | Japan Tobacco Inc | Automatic controller |
| US4897798A (en) * | 1986-12-08 | 1990-01-30 | American Telephone And Telegraph Company | Adaptive environment control system |
| JPH0277801A (en) * | 1988-09-14 | 1990-03-16 | Yokogawa Electric Corp | Self-tuning controller |
| US4942613A (en) * | 1988-12-02 | 1990-07-17 | Heil-Quaker Corporation | Service thermostat |
-
1994
- 1994-06-02 CA CA002125015A patent/CA2125015C/en not_active Expired - Fee Related
- 1994-06-09 AU AU64643/94A patent/AU683053B2/en not_active Ceased
- 1994-06-15 KR KR1019940013458A patent/KR950001442A/en not_active Withdrawn
- 1994-06-16 JP JP06134524A patent/JP3095199B2/en not_active Expired - Fee Related
- 1994-08-02 TW TW083107052A patent/TW332874B/en active
Also Published As
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| JPH0756604A (en) | 1995-03-03 |
| KR950001442A (en) | 1995-01-03 |
| JP3095199B2 (en) | 2000-10-03 |
| CA2125015A1 (en) | 1994-12-17 |
| AU683053B2 (en) | 1997-10-30 |
| AU6464394A (en) | 1994-12-22 |
| TW332874B (en) | 1998-06-01 |
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