JPS59119077A - Apparatus for controlling the number of compressors to be operated - Google Patents

Abstract

PURPOSE:To avoid superfluous starting and stopping operation, by employing such an arrangement that operation of compressors operated at its full load is switched successively to partial-load operation in case that the discharge pressure of a compressor operated under capacity-controlled mode becomes higher than a value preset for partial-load operation of the compressor. CONSTITUTION:An apparatus 9 for controlling the number of compressors to be operated, which produces a signal for starting or stopping operation of four compressors 1a-1d successively so that the discharge pressure satisfies a set value on the basis of the output signal of a pressure detector 6, a signal for making one compressor operate under capacity-controlled mode, and a signal for operating a required number of compressors at its full load is connected to control boards 3a-3d. Thus, since operation of the compressors operated at its full load is switched successively to partial-load operation in case that the discharge pressure becomes higher than a set pressure, it is enabled to attain a required discharge pressure with minimum energy and to avoid superfluous starting and stopping operation.

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a device for controlling the number of compressors, and more specifically, for starting, stopping, and operating a plurality of compressors at full load so that the discharge pressure satisfies a set value. The present invention relates to a device for controlling the number of compressors that operate under one partial load.

[Prior art]

Conventionally, controlling the number of multiple compressors involves starting and stopping multiple compressors so that the discharge pressure satisfies a set value, and adjusting the capacity of one compressor in response to minute changes in discharge pressure. It was operated under control.

FIG. 1 shows a block diagram of conventional number control.

In FIG. 1, 1a to 1d are compressors, 2a to 2d are electric motors, 3a to 3d are control panels, and 4a to 4d are each compressor 1a.
This is a pressure detector for capacity control for ~1d. Reference numeral 5 denotes a discharge pipe that combines the discharged air from these four compressors 1a to 1d and sends the combined air to the plant. This discharge pipe 5 is provided with a pressure detector 6 for controlling the number of units for detecting the pressure of the discharged air. Reference numeral 7 denotes a number control device which additionally starts and stops four compressors 1a to 1d, and also controls one compressor, based on the detection signal of the pressure detector 6, so that the discharge pressure of the discharge pipe 5 satisfies the set value. This compressor is used as a capacity regulator to perform capacity control operation, and the other compressors in operation are operated at full load.

Capacity control operation of the conditioner is performed by commands 8a to 8d from each control panel 3a to 3d.

FIG. 2 shows the relationship between the set value of the pressure detector for controlling the number of units and the control operation for controlling the number of units. The set value of the discharge pressure is divided into five regions as shown on this screen. Control operations are determined by detecting where the discharge pressure of each compressor 1a to 1d is in this region using a plurality of pressure detectors 6.

In the number control device shown in FIGS. 1 and 2 described above,
If the discharge pressure is higher than PUH and the compressor under capacity control performs partial load operation, the discharge pressure does not decrease and the set pressure is higher than PUH, the operating compressor A control operation for additional compressor shutdown is performed to sequentially stop the compressors and forcibly reduce the discharge pressure. At this time, depending on the degree of change in the discharge pressure, the discharge pressure may drop rapidly due to this additional compressor stop control operation, and the discharge pressure may drop below the set pressure POL, causing the compressor that is controlling the capacity to reach full load. If the discharge pressure does not rise even after the operation control operation and the set pressure POL is low, the compressor additional start control starts the stopped compressors one after another and forcibly increases the discharge pressure. Have them do the action. In particular, when load fluctuations are large, it is necessary to repeat the control operations of additional stops and additional starts as described above, which makes it impossible to precisely control the discharge pressure to the set value and has a negative impact on the life of the machine. It is undesirable because it causes

[Purpose of the invention]

The present invention was made in order to solve these problems.The present invention is a compression method that enables a predetermined discharge pressure to be achieved with the least amount of energy and avoids unnecessary starting and stopping operations. The purpose is to provide a device for controlling the number of machines.

[Summary of the invention]

The present invention is characterized by starting and stopping multiple compressors so that the discharge pressure reaches a predetermined value, and operating one compressor under capacity control while operating the necessary number of compressors at full load. When controlling the number of compressors to be used, if the discharge pressure exceeds the value that causes the compressors operating under capacity control to operate at partial load, the compressors operating at full load are sequentially switched to partial load operation. This is what I did.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described in more detail with reference to the drawings.

FIG. 3 is a block diagram showing a system for controlling the number of devices equipped with an example of the device for controlling the number of devices according to the present invention. In Figure 3, the first
Components with the same reference numerals as those in the figure are the same parts. In the present invention, the number control device 9 uses the detection signal of the pressure detector 6 to
Four compressors 1a to 1 are installed so that the discharge pressure satisfies the set value.
d, a signal to start and stop one compressor in sequence, a signal to cause one compressor to perform capacity control operation, and four compressors 1a to 1a.
It has a function of outputting a signal to the control panels 32 to 3d to cause a necessary number of compressors 1d to operate at full load.

The control operation of this number control device 9 will be explained using the fourth example. If the discharge pressure is higher than the set pressure PUH and the compressor that is under capacity control performs partial load operation, but the discharge pressure does not decrease and the set pressure PUH is higher than the set pressure PUH, full load operation is started. The compressors that are running are sequentially operated at partial load. In this method, when the discharge pressure is higher than the set pressure FOR, one of the compressors A, which is operating at full load, is operated at partial load. As a result, if the discharge pressure is lower than the set pressure PUH, either return the compressor A to full load operation or lower the discharge pressure to the set pressure Po.
When the discharge pressure is still lower than the set pressure POL even if the compressor is operated at full load due to a decrease in pressure L, this compressor A
Return to full load operation. On the other hand, if the discharge pressure is still higher than the set pressure PUB even if compressor A is operated at partial load, then one compressor B of the compressors operating at full load is operated at partial load. let As a result, if the discharge pressure falls below the set pressure PUB, either compressor B should be returned to full load operation or the discharge pressure should be lower than the set pressure PUB.
Even if the pressure L is lowered and the volumetric machine is operated at full load, when the discharge pressure is still lower than the set pressure PoL, the compressor B is returned to full load operation. At this time, the discharge pressure is set pressure PUN
If the discharge pressure is still lower than the set pressure POL, return the compressor A to full load operation, or if the discharge pressure is still lower than the set pressure POL, return the compressor A to full load operation. A, BeThe discharge pressure remains the set pressure P even during partial load operation.
The same applies if UII is still high. In this way, the discharge pressure changes from the set pressure PIIIH to the set pressure P.
If the pressure is fluctuating between R, the compressors that are operating at full load are sequentially operated at partial load to lower the discharge pressure. Also, if the discharge pressure fluctuates between the set pressure POL and the set pressure Pun as a result of this, or if it fluctuates between the set pressure and the set pressure POL, partial load operation is performed as described above. The compressors are operated at full load one after another to increase the discharge pressure. Therefore, starting the compressor,
The discharge pressure can be controlled between the set pressure PL and the set pressure Pg, more precisely between the set pressure Pot and the set pressure PUN, without performing a stop operation.

Figure 5 shows how the discharge pressure changes from the set pressure PITH to the set pressure P.
This shows another control method in the case of fluctuations between H. In this control method, the range between the set pressure Paw and the set pressure Pm is divided into several levels, and the number of compressors that are operated at full load and operated at partial load is determined according to the level of discharge pressure. The higher the discharge pressure, the greater the number of units, and when the pressure is higher than the set pressure Pa, all units are operated under partial load. On the other hand, from the set pressure POL to the set pressure PU
It is also possible to divide the HO interval into several levels and determine the number of compressors that are operating at partial load to operate at full load depending on the level of discharge pressure. The lower the discharge pressure is, the more the number of the pipes is increased, and when the pressure is below the set pressure POL, all the pipes are operated at full load. Of course, depending on the load level, the number of compressors in operation will fluctuate due to control operations such as additional start-up and stop of the compressors, and the relationship with discharge pressure is not uniquely determined as shown in Figure 5, but in this case Similar control effects can be obtained by understanding FIG. 5 as a relative control operation. For example, if only two out of four compressors are responding to the load, if the discharge pressure rises above the set pressure PUH and these two compressors go into partial load operation, the
Since there is no partial load operation for the second unit, the control operation in this case is to additionally stop the compressor as described below.

The control operations shown in FIGS. 4 and 5 relate to full-load operation and partial-load operation of the compressor during operation, and these control operations and additional stop operations are related as follows. Immediately stopping the compressor just because the discharge pressure rises above the set pressure PUH is not preferable in terms of the lifespan of the compressor and the control accuracy of the discharge pressure. For this reason, the method of controlling the discharge pressure by partial load operation as described above is effective.

However, during partial load operation, the energy efficiency of the compressor is poor, so it is a good idea to stop the compressor as much as possible to save power. The following method can be considered as a criterion for performing this additional stop control operation.

(1) Time 2 judgment value 2 (11) of partial load operation of volumetric machine
Time 2 judgment value of other compressors with longest partial load operation 2 610 Sum of all times of compressors in partial load operation ≧ judgment value 3 (1■) Number of compressors operating with partial load 2 judgment value The operating compressor is stopped only when these individual conditions or a combination of conditions are satisfied. This determination value is determined as appropriate depending on the characteristics of the compressor equipment and the load conditions. Moreover, this determination value can also be determined as a function of discharge pressure.

〔Effect of the invention〕

As explained above, according to the present invention, when the discharge pressure exceeds the value for full load operation of the compressor operating under capacity control, the compressor operating under full load is sequentially operated under partial load. At the same time, additional pressure machines can be stopped as necessary. Therefore, a predetermined discharge pressure can be achieved with the least amount of energy, and unnecessary starting and stopping operations can be avoided.

[Brief explanation of the drawing]

Fig. 1 is a control system diagram in a conventional compressor control device, and Fig. 2 is an explanatory diagram showing the relationship between the setting value of a pressure detector for controlling the number of compressors used in the conventional control device and the compressor control operation. , FIG. 3 is a control system diagram of a compressor number control device having an example of the present invention, and FIGS. 4 and 5 are explanatory diagrams for explaining the control operation of the control device of the present invention. 1a to 1d...Compressor, 2a to 2d...Electric motor, 3
a to 3d... Control panel, 4a to 4d... Pressure detector for capacity control, 5... Discharge pipe, 6... Pressure detector for number control, 9... Number control device. 1st entry ¥12 3rd drawing

Claims (1)

[Claims] 1. Starting and stopping a plurality of compressors so that the discharge pressure reaches a predetermined value, and operating one compressor under capacity control, and operating the necessary number of compressors at full load. 1. An apparatus for controlling the number of compressors, comprising: a number control section for controlling the number of compressors by sequentially operating compressors operating at full load at partial load and additionally stopping the compressors. 2. The number control unit switches the compressors operating at full load to partial load operation in sequence when the discharge pressure exceeds the value that causes the compressors operating at capacity control to operate at partial load. A compressor number control device characterized by comprising: 3. The number control unit determines the number of compressors that are operating at full load to be operated at partial load, depending on the discharge pressure that is greater than the value that causes the compressors operating at capacity control to operate at partial load. In the compressor number control device 4 according to claim 1, the number control unit controls the number of compressors when the number of compressors operating at partial load or the time thereof exceeds a predetermined value. 2. The compressor number control device according to claim 1, wherein the compressor number control device stops the compressor in operation. 5. The number control unit is designed to sequentially bring the compressors that are operating at partial load to full load operation if the discharge pressure falls below the value that causes the compressors that are operating at capacity control to operate at partial load. A compressor number control device according to claim 1, characterized in that: