TWI861177B - Method of determining speed control coefficients for an elevator - Google Patents

Abstract

A method of determining speed control coefficients for an elevator is provided. Preferred values for control coefficients to be used in a PI controller could be derived based on magnitude of the frequency response and phase shift in a closed loop control model of the elevator and boundary conditions set by the engineers.

Description

Method for determining elevator speed control coefficient

The present invention relates to a method for determining or adjusting an elevator speed control coefficient, and more particularly to a method for determining or adjusting an elevator speed control coefficient.

In the technical field of elevator control, the motor can generally be controlled by a proportional integral (PI) controller or a proportional integral differential (PID) controller to control the speed of the elevator car. For relevant technical documents, please refer to, for example, US US4684856, US5880416, CN109477479A, CN103079978A, etc.

The operating principle of a typical PI or PID controller is to feedback the system output signal through a closed loop control system, compare it with the control command signal, generate an error signal to correct the system input signal, and achieve the control command target requirement. This method can effectively improve system accuracy and reduce external noise interference, and has an automatic error compensation effect.

It should be noted that if the control coefficients in the PI or PID controller are set improperly, it will affect the stability of the control system. When applied to the field of elevator control, it will directly affect the comfort and safety of passengers.

Generally speaking, there are two ways to determine the control coefficients in PI or PID controllers, such as the "guess and check" method and the Ziegler Nichols method. The former requires engineers to explore for a long time, while the latter is similar to the former. Although the exploration time can be shortened to a limited extent based on the general empirical rules, the general empirical rules used in the Ziegler Nichols method are not based on the environment and purpose of elevator control. Therefore, the results of its application may not necessarily meet the above-mentioned requirements for the comfort and safety of elevator passengers.

As mentioned above, since the Ziegler Nichols method is not suitable for elevator control, the traditional method of determining or adjusting the speed control coefficient of an elevator must mostly be tested in an elevator research tower to simulate the operation under different loads. Engineering testers must move various counterweights into the car and prepare various instruments to detect feedback signals of the elevator operation. Then, based on experience and feedback signals, testers use "guess and check" (or trial and error) to adjust or determine the speed control coefficient. This method consumes a lot of manpower and time. Moreover, as long as there is any change in the elevator system (such as changes in the motor system and load weight), it is necessary to re-test in the elevator research tower.

In view of this, this case proposes a method for determining or adjusting the elevator speed control coefficient. In brief, first, a closed-loop control model is established based on the proportional integral (PI) controller to be used for speed control of the elevator device, and the relevant physical quantities of the mechanical system and electrical drive system of the elevator device are introduced, such as the elevator imbalance, the weight of the pulley, the weight of the steel cable, the weight of the motor, the suspension ratio, and the current and torque ratio of the motor controller. Finally, according to the frequency response gain and phase oscillation of the closed-loop control model and the boundary conditions set by the engineers, the best value or optimal value of the control coefficient in the PI controller can be obtained by reverse deduction.

According to one aspect of the present invention, a method for determining an elevator speed control coefficient, wherein an elevator device has a proportional integral (PI) controller for elevator speed control, the method comprising: ● establishing a closed-loop control model, the closed-loop control model comprising the PI controller and a controlled body, the PI controller being connected in series with the controlled body, wherein the PI controller outputs a motor torque quantity to the controlled body, and the controlled body outputs a motor speed quantity, and the difference between the motor speed quantity and an initial speed quantity is fed back as an input of the PI controller; ● obtaining a transfer function of the PI controller, wherein the transfer function of the PI controller has a proportional gain coefficient ( _Kp ) and an integral gain coefficient ( _Ki ); ● ● Obtaining the transfer function of the controlled object based on the transfer function of a mechanical system and the transfer function of an electrical drive system in the elevator device; ● Obtaining the transfer function of the closed-loop control model composed of the transfer function of the PI controller and the transfer function of the controlled object; ● Generating a frequency response Bode diagram of the transfer function of the closed-loop control model, the frequency response Bode diagram comprising a gain Bode diagram and a phase Bode diagram; ● Setting upper and lower limits of a frequency range based on the gain Bode diagram, wherein the frequency value corresponding to 0 decibel in the gain Bode diagram is within the frequency range; ● According to the phase Bode diagram, set the upper and lower limits of a phase interval, wherein the frequency value corresponding to 0 dB in the gain Bode diagram and its corresponding phase value in the phase Bode diagram are located in the phase interval; and ● determine the values of the proportional gain coefficient and the integral gain coefficient according to the upper and lower limits of the frequency interval and the upper and lower limits of the phase interval.

In one embodiment, the above method can be performed through computer software, such as ^MATLAB® or ^LabVIEW® , to perform modeling and numerical calculations based on input operations by engineers.

Other aspects of the present invention will be described in the following description, and some can be easily known from the description, or can be known from the implementation of the present invention. Various aspects of the present invention can be understood and achieved by using the components and combinations specifically pointed out in the attached patent scope. It should be understood that the above general description and the following detailed description are only for exemplification and are not used to limit the present invention.

<Basic Introduction to Elevator Control>: Elevator devices usually have a control module to control the operation of the elevator device, especially the ascent, descent or stationary movement of the elevator car, thereby transporting passengers to the destination floor.

The control module mainly contains the elevator program controller and actuator (generally called inverter). The inverter has a power converter, a microprocessor, a motor drive circuit, a motor current sampling circuit, an encoder speed detection circuit, etc. The power converter is used to convert external AC power into DC power. The inverter microprocessor mainly uses the encoder speed detection module and the motor current sampling circuit to calculate the elevator speed and current and the S-curve velocity profile generated by the elevator program controller, calculates and outputs the voltage command required for the motor drive, and drives the elevator up and down.

Generally speaking, the inverter is divided into a current loop and a speed loop in terms of elevator operation control strategy, as shown in Figure 1. In the current loop, the current controller C1 controls the controlled body G1 according to the motor current sampling. In the speed loop, the speed controller C2 controls the controlled body G2 according to the encoder speed detection.

The above basic introduction to elevator control should be known to those skilled in the art and will not be elaborated here. For the above related technologies, reference may be made to the descriptions of, for example, US Pat. No. 4,684,856, US Pat. No. 5,880,416, CN109477479A, and CN103079978A.

FIG. 2 is a flow chart showing a method for adjusting the frequency response coefficient of elevator speed control according to an embodiment of the present disclosure.

In step 200, a closed loop control model is established, and the closed loop control model includes a PI controller C and a controlled body G, as shown in FIG3. The PI controller C is connected in series with the controlled body G, wherein the PI controller C outputs a motor torque to the controlled body G, and the controlled body G outputs a motor speed, and the difference between the motor speed and an initial speed is fed back as an input of the PI controller C. In another embodiment, the controller C can also be implemented as a PID controller.

In step 202, the transfer function _Kp + _Ki /s of the PI controller C is obtained, where _Kp is the proportional gain coefficient and _Ki is the integral gain coefficient, as shown in FIG3. This part is known in the field of control and will not be elaborated here. As mentioned above, in the absence of other data for reference, the setting or adjustment of the proportional gain coefficient _Kp and the integral gain coefficient _Ki also needs to obtain their optimal or better values through subsequent steps to ensure the stability of the control system.

In step 204, a transfer function of the controlled body G is obtained. In one embodiment, the transfer function of the controlled body G is formed by combining a transfer function J of a mechanical system and a transfer function _Kv of an electrical drive system in the elevator device. For example, the transfer function of the controlled body G can be set to _Kv /J, but the present invention is not intended to be limited to this specific embodiment.

The transfer function J of the mechanical system can be designed according to the physical quantities related to the inertia of the mechanical system in the elevator device. For example, the transfer function J can be set according to any combination of mechanical coefficients such as the passenger base load, car weight, counterweight, cable weight, balance chain weight, steering wheel weight, main machine weight, and suspension ratio of the elevator device, but the present invention is not intended to be limited to any specific combination.

In one embodiment, the transfer function J can be set as a constant, that is, the sum of any combination of the above mechanical coefficients. For example, the transfer function J can be set as the sum of seven coefficients, namely, the passenger base load (e.g., 1150 kg), the car weight (e.g., 1400 kg), the counterweight (e.g., 2000 kg), the cable weight (e.g., 300 kg), the balance chain weight (e.g., 250 kg), the steering wheel weight (e.g., 30 kg), and the main machine weight (e.g., 100 kg). However, it should be noted that the present invention is not intended to limit the transfer function J to any mathematical operation between any mechanical coefficients.

The transfer function _Kv of the electric drive system can be designed according to the relevant physical quantities of the electric drive system in the elevator device. For example, the transfer function _Kv can be set according to any combination of the rated current of the inverter power board, the main machine torque current ratio, the main machine speed coefficient, and the speed sampling time, but the present invention is not intended to be limited to any specific combination.

In one embodiment, the transfer function _Kv can be set as the product of any combination of the above electrical drive coefficients. For example, the transfer function _Kv can be set as the product of the inverter power board rated current (e.g., 100 amperes), the host torque current ratio (e.g., 25 Newtons/amperes), the host speed coefficient (e.g., 30,000 Hz or 300 Hz), and the speed sampling time (e.g., 1 millisecond). It should be understood that the present invention is not intended to limit the transfer function _Kv to any mathematical operation between electrical drive coefficients.

Next, in step 206, the transfer function of the closed-loop control model (also called the whole system) formed by combining the transfer function _Kp + _Ki /s of the PI controller C and the transfer function _Kv /J of the controlled body G is obtained, and a frequency response Bode diagram of the transfer function of the whole system is generated. The frequency response Bode diagram includes a gain Bode diagram and a phase Bode diagram, as shown in FIG4. The vertical axis of the gain Bode diagram is decibel (db), and the horizontal axis is frequency, and the unit is rad/second (sec). The vertical axis of the phase Bode diagram is angle (degree), and the horizontal axis is also frequency, and the unit is rad/second (sec). If this step is performed using computer software such as MATLAB ^® or LabVIEW ^® , the built-in commands for drawing Bode plots in MATLAB ^® or LabVIEW ^® can be used.

The following is an example of instructions related to the above steps using ^MATLAB® . The transfer functions _Kv and J are constants, and their values are only used as examples. ASR_Kp % (Coefficient setting unit:%) ASR_KI % (Coefficient setting unit:sec) Kv=31.38 % System speed loop constant Elevator_J=56.61 % Elevator inertia Elevator_TF=tf([Kv],[Elevator_J 0]) % Elevator system/controlled body transfer function ASR_TF=tf([ASR_KP ASR_KI],[1 0]) % PI controller transfer function TotalSystem_TF= Elevator_TF*ASR_TF % Total system/closed loop control model transfer function margin(TotalSystem_TF) % Total system – Bode diagram

Then, in step 208, according to the gain Bode diagram in FIG. 4, a lower limit A and an upper limit B of a frequency range are set, wherein the frequency value corresponding to 0 dB in the gain Bode diagram is located in the frequency range, that is, the intersection point of the gain curve and 0 dB is between frequency A and frequency B. The selection of the frequency A and B values is related to the speed of the dynamic response of the elevator running design, and can be set by engineers based on experience or predetermined rules. In one embodiment, the lower limit A is set to 50 rad/second, and the upper limit B is set to 100 rad/second, that is, a frequency range with an interval of 50 rad/second is defined. In another embodiment, the lower limit A is set to 45 rad/second, and the upper limit B is set to 105 rad/second, which defines a frequency interval of 60 rad/second. In yet another embodiment, the lower limit A is set to 55 rad/second, and the upper limit B is set to 95 rad/second, which defines a frequency interval of 40 rad/second.

In step 210, according to the phase Bode diagram in FIG. 4, a lower limit C and an upper limit D of a phase interval are set, wherein the frequency value corresponding to 0 dB in the gain Bode diagram corresponds to a phase value in the phase Bode diagram that is within the phase interval. The selection of the phase margins C and D values is related to the stability of the elevator speed loop design, and can be set by engineers based on experience or predetermined rules. In one embodiment, the lower limit C is set to -135 degrees, and the upper limit D is set to -115 degrees, which defines a phase interval of 20 degrees. In another embodiment, the lower limit C is set to -135 degrees, and the upper limit D is set to -90 degrees, which defines a phase interval of 45 degrees. In another embodiment, the lower limit C is set to -135 degrees, and the upper limit D is set to -100 degrees, which defines a phase interval of 35 degrees.

Finally, in step 212, a frequency value F is further selected from the lower limit A and the upper limit B of the frequency range in the gain Bode plot. The selection of the frequency value F can be based on experience or predetermined rules by engineers. In one embodiment, the frequency value F can be the middle value between the lower limit A and the upper limit B, that is, (A+B)/2. In another embodiment, the frequency value F can be (2A+B)/3. In one embodiment, the frequency value F can be (A+3B)/4.

Similarly, in step 212, a phase value P is also selected from the lower limit C and the upper limit D of the phase interval of the phase Bode diagram. The selection of the phase value P can be based on experience or predetermined rules by engineers. In one embodiment, the phase value P can be the middle value between the lower limit A and the upper limit B, that is, (C+D)/2. In another embodiment, the phase value P can be (C+2D)/3. In one embodiment, the phase value P can be (3C+D)/4.

Once the frequency value F and the phase value P are selected, they can be used as two related boundary conditions, and the proportional gain coefficient _Kp and the integral gain coefficient _Ki can be further inferred from the transfer function of the whole system. Specifically, the selected frequency value F and the phase value P are used as known numbers, and the system gain is also used as a known number and set to 0, and then substituted into the equation 20log|transfer function of the whole system|=0 (that is, the system gain is substituted with 0dB), and the proportional gain coefficient _Kp and the integral gain coefficient _Ki can be inferred.

As the selected frequency value F and phase value P are different, the obtained proportional gain coefficient _Kp and integral gain coefficient _Ki will also be different. The engineer can further make a final selection or slight adjustment to the proportional gain coefficient _Kp and integral gain coefficient _Ki based on other factors or simple simulation experiments. The selected value can then be transmitted to the speed controller in the speed loop of the inverter in the elevator device (i.e., the speed controller C2 shown in Figure 1, for example) to set or adjust the proportional gain coefficient _Kp and integral gain coefficient _Ki .

Compared to the traditional practice of relying heavily on actual tests in elevator research towers, the approach proposed in this case can save considerable manpower and time. Although it may not be possible to completely eliminate the need for testers to use trial and error to fine-tune the speed control coefficient to the optimal value, the approach in this case is still much more efficient and saves engineers time to explore from scratch.

In addition, the approach of this case is to add the transfer function of the mechanical system and the transfer function of the electrical drive system in the elevator device into the control model. Therefore, compared with the Ziegler Nichols method which is not used for the environment and purpose of elevator control, the control coefficient obtained by this approach can better meet the needs of elevator control.

Although the present invention is disclosed as above with various embodiments, they are not intended to limit the scope of the present invention. Any person with ordinary knowledge in the relevant technical field can make some changes and modifications without departing from the spirit and scope of the present invention. The scope of protection of the present invention shall be determined by the scope of the attached patent application.

C:PI controller C1:current controller C2:speed controller G:controlled body G1:controlled body G2:controlled body 200:step 202:step 204:step 206:step 208:step 210:step 212:step

The present invention will be more fully understood and appreciated from the detailed description of the embodiments of the present invention in conjunction with the accompanying drawings, wherein the drawings are as follows:

FIG. 1 shows the current loop and speed loop used in elevator control in the prior art;

FIG2 shows a flow chart of a method according to an embodiment of the present invention;

FIG3 shows a closed loop control model according to an embodiment of the present invention;

FIG. 4 shows a Bode diagram of the frequency response of the transfer function of the entire system according to an embodiment of the present invention.

200:Step

202: Step

204: Step

206: Step

208: Step

210: Steps

212: Step

Claims (9)

A method for determining an elevator speed control coefficient, wherein an elevator device has a proportional integral (PI) controller for elevator speed control, the method comprising: a) establishing a closed loop control model, the closed loop control model comprising the PI controller and a controlled body, the PI controller being connected in series with the controlled body, wherein the PI controller outputs a motor torque quantity to the controlled body, and the controlled body outputs a motor speed quantity, and the difference between the motor speed quantity and an initial speed quantity is fed back as an input of the PI controller; b) obtaining a transfer function of the PI controller, wherein the transfer function of the PI controller has a proportional gain coefficient ( _Kp ) and an integral gain coefficient ( _Ki ); c) obtaining a transfer function of the controlled object according to a transfer function of a mechanical system and a transfer function of an electrical drive system in the elevator device; d) obtaining a transfer function of the closed-loop control model formed by combining the transfer function of the PI controller and the transfer function of the controlled object, and generating a frequency response Bode diagram of the transfer function of the closed-loop control model, the frequency response Bode diagram including a gain Bode diagram and a phase Bode diagram; e) setting f) setting upper and lower limits of a frequency interval according to the phase Bode diagram, wherein the frequency value corresponding to 0 dB in the gain Bode diagram is located in the frequency interval; g) determining the values of the proportional gain coefficient and the integral gain coefficient according to the upper and lower limits of the frequency interval and the upper and lower limits of the phase interval. The method as described in item 1 of the patent application scope further includes setting the proportional integral (PI) controller with the determined values of the proportional gain coefficient and the integral gain coefficient. The method as described in item 1 of the patent application scope, wherein the controlled system transfer function includes a transfer function of a mechanical system of the elevator device and a transfer function of an electrical drive system. As described in item 3 of the patent application, the transfer function of the mechanical system is set according to any combination of mechanical coefficients such as the passenger base load, car weight, counterweight, cable weight, balance chain weight, steering wheel weight, main machine weight, and suspension ratio of the elevator device. As described in item 3 of the patent application scope, the transfer function of the electrical drive system is set according to any combination of the inverter power board rated current, the host torque-current ratio, the host speed coefficient, and the speed sampling time of the elevator device. As described in item 1 of the patent application, step (g) further includes: selecting a frequency value between the upper and lower limits of the frequency range, and selecting a phase value between the upper and lower limits of the phase range, so as to determine the values of the proportional gain coefficient and the integral gain coefficient according to the frequency value and the phase value. The method as described in item 6 of the patent application scope, wherein the frequency value is the middle value of the upper and lower limits of the frequency interval, and the phase value is the middle value of the upper and lower limits of the phase interval. The method as described in item 1 of the patent application, wherein the upper and lower limits of the frequency range define a frequency range with an interval of 50 rad/second. As described in item 1 of the patent application, the upper and lower edges of the phase interval define a phase interval of 45 degrees.

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