JP4043184B2 - Compressor control method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for controlling a compressor including a plurality of compressor main bodies arranged in parallel whose rotational speed is controlled by an inverter.
[0002]
[Prior art]
Conventionally, a compressor having a plurality of compressor main bodies arranged in parallel whose rotation speed is controlled by an inverter is known (Japanese Patent Laid-Open No. 11-343986). In this compressor, in order to maintain the discharge pressure in one main discharge flow path that joins the discharge flow paths of the compressor main body at a predetermined target value, a plurality of, for example, four compressor main bodies Of these, only one compressor body is controlled by the inverter, and the other three compressor bodies are either fully loaded (at 100% of the rated speed) or stopped ( One of the 0% rotation speed states with respect to the rated rotation speed) is selected.
[0003]
That is, the one compressor body is a rotational speed controller, and the other three compressor bodies are on-off machines, for example, the amount of compressed air used from the main discharge flow path is reduced, When the discharge pressure in the main discharge flow path rises and it is sufficient to reduce the number of operating compressor main bodies by one, one of the on-off machines is stopped. On the other hand, for example, the amount of compressed air used increases, the discharge pressure in the main discharge flow path drops, and the discharge pressure is reduced even if all the compressor main bodies in operation are operated at full load. When the target value cannot be maintained and the on-off machine that is stopped remains, the on-off machine is newly operated at full load.
[0004]
[Problems to be solved by the invention]
In the case of the conventional compressor described above, one of the four compressor main bodies is a rotational speed controller, the remaining three are on-off machines, and the rotation controlled by the inverter is reduced. The number has a lower limit and is not controlled below a predetermined minimum rotational speed (eg, 20% of the rated rotational speed). For this reason, as the amount of compressed air used, that is, the amount of air used decreases, the rotational speed of the rotational speed controller decreases from a value of 100% of the rated rotational speed, and the minimum rotational speed (20% value). When this value is reached, the value of this minimum rotation speed is not maintained, and when the number of operating compressor bodies changes, the full load operation state (steps from 4 to 3 or 3 to 2 or It becomes a stop state (when switching from 1 to 0) when switching from 2 to 1). When the amount of air used increases, the rotational speed of the rotational speed controller follows the opposite change.
[0005]
Therefore, the relationship between the amount of air used and the power consumption by the operating compressor main body is represented by a line that rises to the right and protrudes at the portion corresponding to the minimum rotational speed, as shown in FIG. In FIG. 5, the numbers in the circles are symbols indicating the compressor main body in operation. Specifically, “1” indicates the rotational speed controller, and “2”, “3”, “ 4 "indicates each of the on-off machines. In addition, each of the grids with hatching on the inner periphery in FIG. 5 indicates the compressor body during full load operation. Corresponding to FIG. 5, the relationship between the amount of air used and the discharge pressure is, as shown in FIG. 6, the discharge pressure is maintained at the target value and is constant while the minimum rotational speed is not reached. However, the discharge pressure is represented by a broken line protruding from the target value while the rotation speed of the rotation speed controller maintains the minimum rotation speed.
[0006]
As described above, in the case of the above-described conventional compressor, there are a problem that the discharge pressure cannot be kept constant and a problem that the discharge pressure is higher than the target value, and there is a problem that the power consumption is increased accordingly. is there.
The present invention has been made in order to eliminate such a conventional problem, and intends to provide a compressor control method capable of suppressing an excessive increase in discharge pressure and reducing wasteful power consumption. Is.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the present invention provides a plurality of compressor bodies arranged in parallel whose rotation speed is controlled by an inverter, and a single main discharge in which the discharge passages of these compressor bodies are merged. And a compressor operating method that is controlled so as to keep the discharge pressure in the main discharge flow path constant. In order to adjust the discharge pressure, the compressor body is in an operating state. The number of revolutions of the compressor main body N is 1, the discharge pressure exceeds the upper limit set pressure, and the inverter command rotational speed is When the compressor body is lower than a predetermined rated rotational speed, and when the operating compressor body number N is 2 or more, the discharge pressure is a lower limit set pressure or more, and the command rotational speed is the above Rated speed (N-1) In either case the N and less than or equal to the value obtained by multiplying the 1 less margin ratio, the driving compressor body number decreases 1, when the discharge pressure is lower than the limit set pressure, and said discharge pressure limit setting In any case where the pressure is equal to or higher than the pressure and the command rotational speed is equal to or higher than the rated rotational speed, the number of operating compressor main bodies is increased by one.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows a compressor 1 to which a control method according to the present invention is applied. The compressor 1 includes a plurality of, for example, NO. 1-NO. 4 four compressor bodies 11, for example, a screw type compressor body. Each of the compressor main bodies 11 is driven by a motor 14 whose rotational speed is controlled by an inverter 13 connected to a power source 12. That is, the rotation speed of each of the compressor main bodies 11 as well as the motor 14 is controlled by the inverter 13.
[0009]
A suction passage 15 is connected to one of the compressor main bodies 11, and a discharge passage 16 extends to the other. The four discharge flow paths 16 merge with one main discharge flow path 17. In addition, a reservoir tank 18 for storing compressed gas, for example, compressed air, is interposed in the main discharge flow path 17, and the reservoir tank 18 is provided with a pressure detector 19 for detecting the internal pressure thereof. The pressure detected by the pressure detector 19, that is, a pressure signal indicating the discharge pressure is input to a control device 21 having a PID control circuit. The pressure detector 19 is not necessarily provided in the reservoir tank 18 and may be provided at any position of the main discharge flow path 17.
On the other hand, a target value P _{T of} discharge pressure, an upper limit set pressure P _U , a lower limit set pressure P _L , a rated rotational speed S _R of the motor 14 and the like are input in advance to the control device 21. Then, based on these input data and the pressure signal from the pressure detector 19, the details will be described below through calculation in the control device 21 or control signals from the control device 21 to each of the inverters 13, for example, an operation signal and a command rotational speed signal. The control described is performed. The operation signal is a signal indicating whether or not to operate, and the command rotation speed signal is a signal for determining how many rotations the inverter 13 rotates the motor 14.
[0010]
Next, a control method according to the present invention applied to the compressor 1 described above will be described with reference to FIG.
When the operation of the compressor is started, the control is started. First, in S1 (step 1), the number N of the compressor main bodies 11 in operation is set to 1, and one starting machine, for example, the compressor main body 11 (NO. The operation 1) is started.
In S2 (Step 2), it is determined whether or not an all-machine stop command has been issued. If NO, the process proceeds to S3 (Step 3) to continue the operation of the compressor main body 11. If YES, Then, the process proceeds to S7 (step 7) in order to stop the operation of the compressor body 11.
[0011]
In S3, with respect to the compressor body 11 during operation, the inverter 13, the pressure detector 19, the control system including the controller 21, so as to eliminate the difference between the detected discharge pressure P _D and the target value P _T Rotational speed control is performed. That is, when the detected discharge pressure P _D is higher than the target value P _T is the command speed signal which causes lowering the rotational speed of the motor 14 to the inverter 13 from the control unit 21 is output, the discharge pressure is above When it is lower than the target value P _T , a command rotational speed signal for causing the inverter 13 to increase the rotational speed of the motor 14 is output from the control device 21. When the discharge pressure is equal to the target value P _T , a command rotational speed signal that maintains the current operation state is output.
[0012]
The S4 (Step 4), the detected discharge pressure P _D is determined whether lower than the lower limit set pressure P _L to a predetermined, if NO, whether is room to reduce the number in operation there Therefore, the process proceeds to S5 (step 5), and in the case of YES, the process proceeds to S6 (step 6) because it is necessary to add the number of operating compressor main bodies 11 unconditionally.
In S5, it is determined whether or not the command rotational speed S _O output from the control device 21 to the inverter 13 is smaller than the rated rotational speed S _R of the motor 14, and in the case of NO, the operating compressor body 11 is in operation. Since it is already in the full load operation state or the overload state, the process proceeds to S6. In the case of YES, the process proceeds to S8 (step 8) in order to check whether there is room for reducing the number of the compressor main bodies 11 in operation. .
[0013]
The command rotation speed S _O is a value determined by the control device 21 and is input to each inverter 13.
In S6, an operation signal and a command rotation speed signal are newly output from the control device 21 to the inverter 13, and one operation unit of the compressor body 11 is added, and then the process returns to S2.
[0014]
On the other hand, since the all-machine stop command is issued in S7, the number N of the compressor main bodies 11 in operation is set to 0 by the stop signal from the control device 21 to the inverter 13, that is, all the machines are stopped. Control ends.
Further, in S8, it is determined whether or not the number N of the compressor main bodies 11 in operation is one, and in the case of YES, in order to determine whether or not the supply amount of compressed air is excessive, S9 ( In step 9), in the case of NO, in order to check whether or not the command rotational speed S _O for the compressor main body 11 has reached the rotational speed at which the number N of the operating compressor main bodies 11 can be decreased by one. To S11 (step 11).
[0015]
In the control method according to the present invention, as shown in FIG. 3, the rotational speed of the compressor main body 11 in operation is always controlled to be equal, and the number of compressor main bodies 11 in operation is as small as possible. The number control is performed as described above. Therefore, when this number is N, as the amount of air used decreases, the command rotation speed S _O from the control device 21 to the inverter 13 also decreases, and this command rotation speed S _O becomes the rated rotation speed S _R of the motor 14. When the value (S _R · (N−1) / N) is multiplied by (N−1) / N, the number N is reduced to the number (N−1). Conversely, as the amount of air used increases, the command rotational speed S _O increases, and when the command rotational speed S _O reaches the rated rotational speed S _R of the motor 14, the number N of operating compressor bodies 11 is 1. Added units.
[0016]
In addition, this figure shows, as an example, the startup sequence of the compressor main body 11 due to an increase in the amount of air used. 1 → NO. 2 → NO. 3 → NO. 4 and, on the contrary, when there are four compressor main bodies 11 in operation, the stop order of the compressor main bodies 11 due to the decrease in the amount of air used is NO. 4 → NO. 3 → NO. 2 → NO. Although represented as 1, the present invention is not limited to this order.
[0017]
In S9, whether higher than the upper limit set pressure PU the detected discharge pressure P _D is predetermined are determined, in the case of YES, the supply of compressed air is excessive, while driving the compressor body The process proceeds to S10 (step 10) in order to decrease the number N of 11 and, in the case of NO, there is no need to increase or decrease the number N of operating compressors, and only the rotation speed control is sufficient, so the process returns to S2.
In S10, and the number N of the compressor body 11 during operation from the controller 21 to 0, after all aircraft stopped, it returns to step S4 in order to examine the change again the discharge pressure P _D.
In FIG. 2, the * marks mean that they are connected to each other.
[0018]
In S11, under the condition that the N compressor bodies 11 are in operation, the command rotational speed S _O is a value obtained by multiplying the rated rotational speed S _R by (N−1) / N (S _R · (N−1) / N) is determined, and if YES, the number of compressor main bodies 11 in operation cannot be reduced, so the number of compressor main bodies 11 in operation is not changed. Returning to S2, in the case of NO, there is room for reducing the number of compressor main bodies 11 in operation, and therefore the process proceeds to S12 (step 12) for controlling the number of compressor main bodies 11 in operation.
As a condition for stopping the number of units, instead of the formula S _O = S _R · (N−1) / N, a formula S _O = α · S _R · (N− 1) / N may be adopted.
In S12, the number N of the compressor main bodies 11 in operation is reduced to (N-1) by a stop signal from the control device 21 to the inverter 13, and then the process returns to S2.
According to the control flow described above, the above steps are executed until the control is completed.
[0019]
As described above, in particular, as shown in FIG. 3, in the control method according to the present invention, the number N of the compressor main bodies 11 in operation is 1, and the compressor main body 11 reaches the above-described minimum rotational speed. As shown in FIG. 5, the rotational speed control of the compressor main body 11 during operation is always performed equally and the number of compressor main bodies 11 to be operated is controlled according to the increase or decrease in the amount of air used. Thus, the discharge pressure is kept constant regardless of the increase or decrease in the amount of air used, except when the amount of air used approaches zero.
In addition, about the compressor mentioned above and its control method, although working gas was demonstrated as air, this invention does not limit working gas to air.
[0020]
【The invention's effect】
As is clear from the above description, according to the present invention, a plurality of compressor bodies arranged in parallel whose rotation speed is controlled by an inverter, and one discharge passage of these compressor bodies are joined together. In the compressor operating method controlled so as to keep the discharge pressure in the main discharge flow path constant in order to adjust the discharge pressure. The rotational speed control is always performed equally to all of the compressor main bodies in the state, the number N of operating compressor main bodies is 1, the discharge pressure exceeds the upper limit set pressure, and the inverter command When the rotational speed is lower than a predetermined rated rotational speed of the compressor body, and when the operating compressor body number N is 2 or more, the discharge pressure is not less than a lower limit set pressure, and the command rotation Number above the rated speed N-1) / N and in any case less than the value obtained by multiplying the 1 less margin ratio, the driving compressor body number decreases 1, when the discharge pressure is lower than the limit set pressure, and, the In any case where the discharge pressure is equal to or higher than the lower limit set pressure and the command rotational speed is equal to or higher than the rated rotational speed, the number of operating compressor bodies is increased by one.
[0021]
For this reason, regardless of increase / decrease in the amount of gas used, there is an effect that the discharge pressure can be kept substantially constant without being excessively increased and wasteful power consumption can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration of a compressor to which a control method according to the present invention is applied.
FIG. 2 is a control flow chart for performing a control method according to the present invention applied to the compressor shown in FIG. 1;
FIG. 3 is a diagram showing the relationship between the amount of air used and power consumption when the compressor shown in FIG. 1 is used.
4 is a diagram showing the relationship between the amount of air used and the discharge pressure when the compressor shown in FIG. 1 is used.
FIG. 5 is a diagram showing the relationship between the amount of air used and power consumption when a conventional compressor is used.
FIG. 6 is a diagram showing the relationship between the amount of air used and the discharge pressure when a conventional compressor is used.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Compressor 11 Compressor main body 12 Power supply 13 Inverter 14 Motor 15 Suction flow path 16 Discharge flow path 17 Main discharge flow path 18 Reservoir tank 19 Pressure detector 21 Control device N Number of operation compressor main bodies P _D Discharge pressure (detection value)
_PT target value P _U upper limit set pressure P _L lower limit set pressure S _O command speed S _R motor rated speed

Claims (1)

A plurality of compressor main bodies arranged in parallel whose rotation speed is controlled by an inverter, and a single main discharge flow path that joins the discharge flow paths of these compressor main bodies, In the control method of the compressor that is controlled so as to keep the discharge pressure constant, the adjustment of the discharge pressure is performed so that the compressor body is constantly and equally applied to all of the compressor bodies in the operating state within the compressor body. While controlling the rotation speed,
When the number N of operating compressor bodies is 1, the discharge pressure exceeds the upper limit set pressure, and the command rotation speed of the inverter is lower than a predetermined rated rotation speed of the compressor body, and the operation The number N of compressor main bodies is 2 or more, the discharge pressure is not less than the lower limit set pressure, and the command rotational speed is (N-1) / N and a margin ratio of 1 or less to the rated rotational speed. In any case where the value is less than the multiplied value, the number of operating compressor bodies is decreased by 1,
In both cases where the discharge pressure is lower than the lower limit set pressure and the discharge pressure is equal to or higher than the lower limit set pressure and the command rotational speed is equal to or higher than the rated rotational speed, the number of operating compressor main bodies is reduced. A method for controlling a compressor, wherein the number is increased by one.

Images