JPH09126176A - Variable capacity compressor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To operate the variable capacity compressor stably without responding to very small input and disturbance, which are developed at the time of stable normal rotation, by comparing discharge pressure received from a pressure sensor with a target pressure given in advance by a control device, and thereby determining its revolution speed. SOLUTION: When the pressure of the inside of an air tank 10 is lowered with the amount of compressed air consumption increased, which is sensed by a pressure sensor 11, a control device 5 directs a command to accelerate the revolution speed of a rotor. Upon receiving the command, an inverter 4 increases its output frequency, an electric motor 3 is accelerated, and the rotor of a compressor main body 2 is thereby accelerated. Since a compressor is a capacity type compressor, the more the revolution speed is increased, the more the amount of discharge is increased, its discharge pressure is thereby restored to a specified value. When the amount of compressed air consumption is decreased, the aforesaid operations are reversed so as to allow the compressor to cope with a situation with the revolution speed of a rotor decelerated, discharge pressure having been increased once is thereby lowered, and it comes close to a set value. Thus as mentioned above, discharge pressure can thereby be kept constant regardless of the amount of compressed air consumption.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compressor, and more particularly to a variable displacement compressor having a function of controlling a discharge pressure to be substantially constant even if a consumption amount of compressed gas is increased or decreased.

[0002]

2. Description of the Related Art The basic function of a compressor is to inhale, compress, and discharge gas. The gas to be compressed (hereinafter, referred to as compressed gas) is often air, but the air conditioning refrigeration compressor may compress a refrigerant gas, and the chemical plant compressor may compress another gas. It is easiest to operate a compressor with a constant capacity, but the consumption of compressed gas is not always constant. When the consumption amount of the compressed gas exceeds the discharge amount, the discharge pressure decreases, and conversely, when the consumption amount is less than the discharge amount, the discharge pressure becomes excessive, and the discharge pressure varies depending on the consumption amount. In many cases where compressed gas is used, the discharge pressure is desired to be constant, so a capacity control function for maintaining the discharge pressure constant even if the consumption amount changes is required. The capacity control function includes on / off control by stopping the operation of the compressor that combines compressed gas containers, suction throttle control that throttles the suction of the compressor body with a valve, and slide valve control that adjusts the suction volume of the screw compressor body. , Several methods have been put to practical use. Recently, as the technology of the frequency converter has been improved and the price has been reduced, and the variable speed control of the electric motor has become easy, the following method disclosed in Japanese Patent Laid-Open No. 164792/55 has been put into practical use.

In this known example, when the consumption amount increases, a phenomenon such as a decrease in the discharge pressure appears. Therefore, it is detected that the rotor rotation speed is accelerated to increase the discharge amount to keep the discharge pressure constant. Has been. On the contrary, when the amount of compressed gas consumed decreases and the discharge pressure becomes excessive, the rotor rotation speed is reduced to reduce the discharge amount and prevent the discharge pressure from increasing. As described above, a method of continuously changing the rotor rotation speed by the inverter is described. However, even when the discharge pressure approaches the target pressure and becomes almost stable, there is no mention of a phenomenon in which the rotational speed fluctuates due to a slight difference between the target pressure and the discharge pressure, and a solution thereto.

An example of a solution to the unstable phenomenon associated with capacity control is disclosed in Japanese Patent Laid-Open No. 3-124993. The capacity control of the compressor described in this known example is a method by limiting the intake air amount by an intake throttle valve, and is different from the method of the present invention in which the rotor rotation speed is adjusted. The occurrence of the unstable phenomenon is limited to the transient time following the load fluctuation, and is different from the phenomenon that occurs in the steady state, which is a problem of the present invention. The solution is to reduce the response gain by inserting an orifice, and the control system is linear and stabilized by changing the system constant. Therefore, it is not helpful as a solution to the unstable phenomenon which is a problem in the present invention.

Japanese Laid-Open Patent Publication No. 61-265382 discloses a method in which a dead zone is provided near the target value so as not to respond to small fluctuations or disturbances one by one and avoid frequent and minute control commands.
The compressor capacity control method described in this known example is a method of controlling the suction volume by a slide valve,
This is different from the method of the present invention for controlling the rotation speed. The unstable phenomenon which is a problem in the present invention is self-excited due to a quantization error or the like depending on the amount of compressed gas used. Causes different. Therefore, although the stabilizing means uses the same dead zone, the cause of the phenomenon and the action and effect of the stabilizing means are different. The object of the invention is also to prolong the life of the slide valve, which is different from the first purpose of reducing noise.

[0006]

Although the required accuracy of the discharge pressure depends on the user, in many cases, it is not necessary to strictly match the target pressure, and it is sufficient if it is within a certain range including the target pressure. . For example, when compressed air is used for power or as a coating spray medium, a gauge pressure of 7 atm ± 0.3 atm and its accuracy are sufficient. ± 0 at this time.
The allowable pressure range is 6.7 to 7.3 atm, which is the range of 3 atm, and the allowable pressure range is 0.6 atm.

However, the variable displacement compressor which feeds back the discharge pressure and changes the rotor rotation speed to control the discharge pressure at a constant level has a function of bringing the discharge pressure closer to the target pressure, so that the following problems occur. The discharge pressure is close to the target pressure,
Even if the discharge pressure is within the allowable pressure range, as long as there is a difference between the discharge pressure and the target pressure, even if the difference is small, the control device reacts and gives an instruction for acceleration or deceleration. Therefore, it takes time for the discharge pressure to settle even if the amount of compressed gas used does not change. Occasionally, minute fluctuations in the discharge pressure remain without complete settling. In addition, if there is a slight change in the amount of compressed gas used or electromagnetic disturbance, an instruction to change the rotation speed is issued, and the discharge pressure changes each time.
In order to prevent these fluctuations by the conventional technique, there is a method of lowering the ratio by which the difference of the discharge pressure from the target pressure is reduced to slow the response, but this is not a good idea because the response is sacrificed.

In particular, when a microcomputer (commonly known as a microcomputer) composed of a digital electronic circuit is used as the control means, which is the control means, the rotational speed fluctuation is remarkable as follows. The pressure sensor, which is the pressure detecting means, detects the discharge pressure, which is an analog amount, and the control device handles it as a digital amount. Therefore, an analog / digital converter (commonly called A / D converter, hereinafter abbreviated as ADC) is used in the middle. Convert. At this time, a quantization error occurs due to the convenience of converting the analog value, which is a continuous quantity, into a stepwise digital quantity. For example, even if only a slight pressure increase occurs in the analog amount, the digital value may increase by one step (1 bit) near the boundary value. As a result, the control device instructs the deceleration of the compressor body in a reaction corresponding to one step (1 bit), and the deceleration amount becomes excessive. On the other hand, if the pressure does not exceed the boundary value, there is a phenomenon that even if there is a slight insufficient pressure increase in one step, it will not be detected, but it is not a problem.

The above-mentioned operation causes the control device to instruct one-step deceleration, which is excessive deceleration, so that the discharge pressure gradually decreases, and continues to decrease even if the discharge pressure becomes equal to or lower than the target pressure. Under normal operating conditions, when the discharge pressure decreases, the flow rate decreases, so the amount of non-compressed air used also decreases, and it becomes less than or equal to the target pressure but gradually becomes constant. However, when the difference from the target pressure falls below one step of ADC, the control device instructs the acceleration, and the discharge pressure starts increasing again. Since the above operation is repeated, the discharge pressure and the rotor rotation speed are not stable, and increase and decrease are repeated. This phenomenon is particularly noticeable in the sound and gives the user anxiety as unstable noise. Further, frequent acceleration and deceleration may adversely affect the reliability and life of the compressor because the burden on each part is increased as compared with steady rotation.

The above rotation fluctuation can be ignored with a margin of error with respect to a sufficient acceleration or deceleration instruction amount when the discharge pressure is separated from the target pressure, but the amount of compressed gas used is substantially constant and stable. It is especially problematic when you are

The one-step increase in output may also occur due to another cause, for example, electromagnetic noise generated from a power line or the like entering the control device. The level is usually small enough to be ignored, but is affected when the discharge pressure value is in the vicinity of the boundary value of whether to increase by one step.

An object of the present invention is to provide a variable capacity variable compressor capable of stable operation without responding to a minute input or disturbance generated during stable steady rotation in a compressor whose rotor rotational speed changes in accordance with the addition. To realize a compact compressor.

[0013]

Means for Solving the Problems A first method for solving the above problems is described below.
A variable capacity compressor is configured as follows as a means.

The control device which is the control means compares the target pressure given in advance with the discharge pressure received from the pressure sensor which is the pressure detection means. For the comparison, the difference is calculated, or the progress record of the discharge pressure is referred to as necessary, and the time differential value or the time integrated value of the difference is calculated. An appropriate coefficient is multiplied from these values to obtain the sum, and the rotation speed is determined so that the discharge pressure approaches the target pressure. Means is provided for transmitting the value to the variable speed means, and the variable speed means guides the rotational speed of the compressor body to the determined value. The rotational speed does not instantly match the determined value due to the rotational inertia, but it approaches the determined rotational speed in a short time. The discharge amount of the compressed gas per unit time changes due to the change in the rotation speed, and the discharge pressure approaches the target pressure.

Normally, the allowable pressure range is set for the target pressure, and it is not necessary to strictly match the discharge pressure with the target pressure, but it is sufficient if it is within the allowable pressure range. The target pressure is set inside, and a dead zone narrower than this allowable pressure range is set. When the discharge pressure is in the dead zone, the controller is provided with a criterion for maintaining the current rotational speed even if the error is not zero.

As a second means for solving the above problems, the following structure is further added to the variable capacity compressor.

The drive means of the compressor body is an induction type electric motor, and the variable speed means is a frequency converter (also called an inverter) for supplying electric power to the electric motor. The control means is a digital electronic circuit (commonly known as a microcomputer) in which a control algorithm is programmed in advance, which is mainly composed of a microprocessor that performs digital control. Since the discharge pressure, which is an analog amount, is input to the digital control device, an analog / digital converter (ADC) is inserted in the middle of the information transmission path.

The width of the dead zone is set to be wider than twice the pressure corresponding to one unit (1 bit) when converting the pressure sensor output into a digital value. Therefore, the control device does not respond to a pressure fluctuation of 1 bit from the target pressure, and neither acceleration nor deceleration is instructed.

As a third means for solving the above problems, an algorithm provided in the control means of the variable capacity compressor may be configured as follows.

Instead of the dead zone in the first or second means, a narrow insensitive zone included in the allowable range is set. When the discharge pressure is in the insensitive zone, the degree of acceleration or deceleration instruction is relaxed and the tendency of maintaining the current rotation speed is strengthened as compared with the method of determining the rotation speed when the discharge pressure is out of the range. Therefore, no instruction for acceleration / deceleration is issued in the dead zone, whereas a small instruction for acceleration / deceleration is issued in the insensitive zone. Alternatively, a dull zone may be provided outside the narrow dead zone so that the response to the pressure error gradually increases.

In embodying the second means, the use of the fourth means facilitates implementation.

The control algorithm subtracts the discharge pressure from the target pressure, and calculates the acceleration or deceleration instruction by taking into consideration the operating condition of the compressor such as the record of the calculated value from the past and the rotor rotation speed. To do. Regarding the latest value of the calculated value, first, the part that exceeds the upper limit of the dead zone or the part that falls below the lower limit is obtained. If the discharge pressure is close to the target pressure and in the dead zone, the calculated value is set to no acceleration / deceleration. The value proportional to the amount exceeding the upper limit or falling below the lower limit is the amount to be decelerated or accelerated. If necessary, this value is corrected according to the operating condition of the compressor such as the record of the calculated value from the past and the rotor rotation speed, and the transmission is instructed as an instruction for acceleration or deceleration.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of the present invention based on claim 1 will be described below with reference to FIGS. 1 and 2. As the gas to be compressed, the air having the highest possibility in carrying out the present invention is targeted, but other gases have the same action and effect.

FIG. 1 is a system diagram of a variable capacity air compressor according to this embodiment. The compressor 1 is composed of a compressor body 2 and some auxiliary machines. The compressor body 2 is a positive displacement rotary compressor such as a screw type or a scroll type, and has a property that the discharge amount increases or decreases in proportion to the rotation speed. The compressor body 2 operates by being supplied with rotational power by the induction motor 3, sucks air from the suction port 8, compresses it, and then discharges it from the discharge port 9. The electric motor 3 is supplied with a three-phase alternating current from the inverter 4 and rotates. The inverter 4 has a capability of receiving the rotation speed command value from the control device 5 inside the compressor 1, converting the commercial AC power 6 supplied from the outside into a commanded frequency and voltage, and outputting the commanded frequency and voltage.

The piping from the discharge port 9 to the air tank 10 continues,
The air tank 10 is provided with a pressure sensor 11 that detects the internal pressure. The output information of the pressure sensor 11 is wired so as to be sent to the control device 5 as an electric signal. An air pipe 12 is guided from the air tank 10 to the outside of the compressor 1 and sends out compressed air.

The output of the pressure sensor 11 is converted into an analog amount into a digital amount by the A / D converter 13 and input to the control device 5. The output of the switch 14, which is the target pressure input means by the compressor user, is also input to the control device 5.

Next, the control algorithm of the control device 5 is shown in FIG.
This will be described with reference to FIG. Although FIG. 2 shows the data flow in a block diagram, it is actually programmed software. In some cases, it may be an electronic circuit configured by a dedicated logic circuit.

The value of the discharge pressure 21 is subtracted 31 from the value of the target pressure 22 to calculate the residual 23. If the value of the residual 23 is positive, it means that the discharge pressure is insufficient, and if it is negative, it is excessive. Conventionally, the residual 23 is multiplied by a constant K _p for the proportional element 32, and the integral element is a constant K _i for a value obtained by time integration.
And the differential element is multiplied by a constant K _d , and the sum is added by the adder 35. The calculation result becomes the value of the rotation speed command 25. The above relationship is shown in Equation 1.

[0029]

(Equation 1)

The input / output relationship of the proportional element 32 at this time is shown in FIG.
It has a simple linear relationship as shown in. In the present invention, FIG.
Although there is no change in the control algorithm shown in FIG. 5, a dead zone is provided in the input / output relationship of the proportional element 32 as shown in FIG. The width of the dead zone is narrower than the allowable range of discharge pressure as the performance of the compressor.

The air compressor according to this embodiment operates as follows. FIG. 3 is a time graph of the analog output of the pressure sensor 11 and the digital amount after conversion by the A / D converter 13.

The present compressor basically operates as follows. The commercial AC power 6 is converted in voltage and frequency by the inverter 5 to drive the electric motor 3. The compressor main body 2 which receives power from the electric motor 3 and rotates rotates in and sucks in air from the suction port 8, compresses it, and discharges it from the discharge port 9. The compressed air discharged from the discharge port 9 is discharged to the outside from the discharge pipe 10. The discharge pressure at that time is constantly monitored by the pressure sensor 11, and the obtained discharge pressure data is sent to the control device 5.

The control system for keeping the discharge pressure constant operates as follows. When the consumption of compressed air increases and the pressure inside the air tank 10 decreases, the pressure sensor 11 senses it, and the control device 5 commands the acceleration of the rotor rotation speed. In response to this, the inverter 4 increases the output frequency, accelerates the electric motor 3, and accelerates the rotor of the compressor body 2. Since it is a positive displacement compressor, the amount of discharge increases as the rotation speed increases, and the discharge pressure recovers to a specified value. When the amount of compressed air used decreases, it works in reverse, and the rotor rotation speed is reduced to respond. Therefore, the discharge pressure that has risen once decreases and approaches the set value. In this way, the discharge pressure becomes constant regardless of the amount of compressed air consumed.

When the air consumption amount fluctuates drastically and the compressor rotation speed also fluctuates in accordance with it, the conventional technique has no problem (range A in FIG. 3). However, when the air consumption is almost constant and the rotation speed is also almost constant, there are the following problems.

When in the range B in FIG. 3, there is a slight change in the discharge pressure, and even if there is a slight change in the pressure sensor output, the A / D converter 13 does not change the output and the rotation speed remains constant. Is. On the other hand, in the range C, the output of the A / D converter 13 rises by one step even with a slight pressure fluctuation,
It will instruct to reduce the rotation speed that matches it. This is an excessive reaction, and tends to cause instability of the system. At the same time, even if the amount of air used does not change, if the rotation speed changes by a small amount, the rotation sound changes and the user feels uneasy. Further, if acceleration and deceleration occur frequently, the equipment will be burdened, and there is a concern that energy efficiency will be reduced and life will be shortened.

In the present invention, a dead zone is provided, and a one-step fluctuation is ignored. Therefore, unnecessary rotation fluctuation does not occur and the above-mentioned problem does not occur. Even when there is an unexpected disturbance in the control system, such as electromagnetic noise, it can be ignored in the same way, so it does not spread to an unstable phenomenon due to an excessive response.

Incidentally, in the present embodiment, the auxiliary equipment such as a separating device for the lubricating oil injected into the compressed air and a heat exchanger for cooling the air whose temperature has risen due to the compression are omitted, which are not directly related to the present theory. .

[0038]

According to the present invention, when the amount of compressed gas used is substantially constant and the rotation speed is stable, even if a slight variation in discharge pressure or electromagnetic noise occurs, it is ignored and stable. You can continue to drive.

[Brief description of the drawings]

FIG. 1 is a system diagram of a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of control of the control circuit according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of an example of a signal indicating a discharge pressure.

FIG. 4 is a graph showing an input / output relationship of a conventional proportional element.

FIG. 5 is a graph showing the input / output relationship of the proportional element according to the first embodiment of the present invention.

[Explanation of symbols]

1 ... Compressor, 2 ... Compressor body, 3 ... Electric motor, 4 ... Inverter, 5 ... Control circuit, 6 ... Commercial AC power, 8 ... Suction port,
9 ... Discharge port, 10 ... Air tank, 11 ... Pressure sensor, 12 ...
Compressed air pipe, 13 ... A / D converter, 14 ... Switch.

Claims (2)

[Claims] 1. A control means comprising a compressor main body which is a positive displacement rotary compressor represented by a screw type or a scroll type, a driving means for the compressor body, and a speed changing means, and having a function of instructing a rotation speed to the speed changing means. And a compressor having a pressure detection means for detecting the discharge pressure of the compressed gas discharged from the compressor body, wherein the pressure detection means has a function of transmitting pressure information to the control means. The target pressure obtained is compared with the discharge pressure received from the pressure detecting means, and if necessary, the progress record of the discharge pressure and the current rotation speed are referred to, and a new rotation speed is set to bring the discharge pressure close to the target pressure. And determines the value to the speed change means, the speed change means guides the rotation speed of the compressor body to the determined value, and changes the discharge amount of the compressed gas per unit time, By continuing the above series of operations, the discharge pressure is limited to a narrower range within the allowable pressure range while having the function of keeping the discharge pressure within the allowable pressure range that is the limited range including the target pressure. When the dead zone including the target pressure is set and the discharge pressure is within the dead zone, the control means is provided with a criterion for maintaining the current rotation speed even if the discharge pressure does not match the target pressure. A variable capacity compressor characterized in that 2. The driving means for the compressor body is an induction type AC electric motor, the speed changing means is a frequency converter for supplying electric power to the electric motor, and the control means is a microprocessor for performing digital control. , A digital electronic circuit in which a control algorithm is programmed in advance, the pressure detecting means is a pressure sensor having a voltage output proportional to the detected pressure, and the dead zone for maintaining the rotation speed at present is an analog amount. 1 when converting the output of the pressure sensor into a digital value
A variable capacity compressor with a range that is wider than twice the pressure equivalent to the unit.