TWI674360B - Multiple Variable Frequency Pump Controller And Control Method - Google Patents

Abstract

This case proposes a plurality of variable frequency pump controllers and control methods. The controller includes a signal frequency conversion module and a decision module. The signal frequency conversion module receives and converts a pressure signal into a pressure to frequency signal. The pressure-to-frequency signal and the output signal of the PLC unit are output to output an output voltage signal to control at least one inverter. In particular, when the pressure-to-frequency signal falls within the stop deviation range, the decision-making module performs stop detection to decide to shut down at least one inverter or resume controlling the inverter by outputting the output voltage signal, and the decision-making module can According to the motor status signal, frequency parameter and time parameter returned by the inverter to judge the operation mode of the inverter.

Description

Multiple frequency conversion pump controllers and control methods

This case is about a variable pump controller, especially a variable frequency pump controller that controls multiple variable frequency pumps.

A motor is a mechanical device that generates kinetic energy, and a pump is a mechanical device that converts kinetic energy into potential energy and contains at least one motor. At present, pumps are widely used in hydraulic control, air pressure control, wind pressure control, etc., even in the field of industrial manufacturing and electric vehicles. With the development of variable frequency control technology, the frequency conversion pump combined with the frequency conversion control technology and pump technology can achieve excellent constant pressure and constant temperature control performance, and make the application of the motor more extensive.

In different application fields, the motors are designed with various specifications, so the variable frequency pump controller has developed various special inverters in order to adapt to different specifications of the motors. Please refer to the first figure, which is a traditional special inverter 120 Block diagram.

First, external signals are converted into electrical signals through the pressure sensor 110. Please note that this case is not limited to the pressure sensor 110. For example, it can be replaced with other sensors such as a temperature sensor. The Proportional-Integral-Derivative (PID) control unit 121 receives the pressure signal detected by the pressure sensor 110, and compares the detected pressure value with a preset pressure set value. Yes, through feedback control to dynamically adjust the frequency, you can control the motor acceleration, deceleration or constant speed, so that the detected pressure value can approach the pressure set value.

Furthermore, a Programmable Logic Controller (PLC) unit 123 receives the output signal of the PID control unit 121, and the PLC unit 122 is based on software programming to control the Insulated Gate Bipolar Transistor of the inverter (IGBT) output module 123, whereby the IGBT output module 123 can control the rotation speed of the motor 130, and the motor 130 can be controlled by frequency conversion to maintain the pressure near the pressure set value.

However, in addition to the high cost of using a dedicated inverter 120 to control the motor 130, since different dedicated inverters 120 need to be replaced when different motors 130 are replaced, the pump system design has low flexibility and high modification costs. In particular, the traditional special-purpose inverter 120 has disadvantages in operation. When the traditional special-purpose inverter 120 is under a slight voltage drop, the motor often cannot be turned off normally, resulting in the special-purpose inverter 120 causing the motor to continuously increase Pressure and burst (the pressure is greater than the tolerable pressure of the pipe) occurs.

In addition, the current dedicated inverter can only control two motors at the same time. Under actual conditions, two motors often cannot meet the needs of the environment. At the same time, more than one dedicated inverter can be controlled at the same time because of different brands. There are different control methods for the special-purpose inverters, and when there is any abnormality in the controlled inverters, it is more difficult to adjust the scheduling and use in time. Based on the above problems, it is still difficult to control multiple inverter pumps at the same time.

To solve the foregoing problems, this case proposes a universal variable frequency pump controller, which can be applied to ordinary inverters of various specifications. The ordinary inverters do not include PID control units and PLC units. It only has simple PLC function. Multiple inverter pump controllers are connected between ordinary inverters and (pressure) sensors to directly control the inverters, so it can effectively reduce costs, especially when it is necessary to Use multiple inverters.

In addition, multiple variable frequency pump controllers include signal frequency conversion modules and decision-making modules. By comparing the output results of the PLC unit and the output results of the frequency conversion module, the shutdown detection is performed to determine whether there is still a situation of use. This method effectively judges whether the machine needs to be stopped, which can avoid the situation where the inverter controls the motor to continue to pressurize and burst the pipe.

Furthermore, the decision-making module can further control at least one inverter, and receive a signal from the motor status of each inverter, which can be used to coordinate and control the operation of each inverter and operate with a precisely controlled motor.

This case proposes a multiple frequency conversion pump controller that can be used to control multiple frequency converters. The multiple frequency conversion pump controller can include a signal frequency conversion module and a decision module, where the signal frequency conversion module receives the pressure signal and converts it. The pressure signal is a pressure-to-frequency signal. The decision module compares the pressure-to-frequency signal with the calculated output frequency signal, outputs multiple output voltage signals to control each inverter, and receives a motor status signal from each of the inverters.

In particular, the operation output frequency signal is related to the comparison result between the pressure signal and a pressure set value, and the decision-making module changes and controls each of the frequency converters according to the motor status signal and the pressure to frequency signal of each of the frequency converters. This output voltage signal of the converter.

This case also proposes a method for controlling multiple inverters. The method includes: receiving a pressure signal through a signal frequency conversion module and converting the pressure signal into a pressure-to-frequency signal; and comparing the pressure-to-frequency signal with a decision-making module. The output frequency signal is calculated to output at least one output voltage signal to control each of the inverters, and a motor status signal can be received from each of the inverters.

In particular, the operation output frequency signal is a comparison result between the pressure signal and a pressure set value, and the decision module controls each of the inverters according to the motor status signal and the pressure-to-frequency signal change of each of the inverters. The output voltage signal.

101, 210‧‧‧ Pressure Sensor

120‧‧‧ special inverter

123‧‧‧IGBT output module

220‧‧‧Multiple inverter pump controllers

121, 221‧‧‧PID control unit

122, 222‧‧‧PLC units

223‧‧‧Signal Frequency Conversion Module

224‧‧‧ Decision Module

2241‧‧‧Frequency comparison module

2242‧‧‧One-to-many control module

231‧‧‧Main Inverter

232, 233‧‧‧Auxiliary inverter

301 ~ 306, 401 ~ 407‧‧‧ steps

The first figure is a block diagram of a traditional special-purpose inverter.

The second figure is a block diagram of multiple variable frequency pump controllers proposed in this case.

The third figure is a flow chart of multiple inverter pump controllers to perform shutdown detection.

The fourth diagram is a flowchart of a plurality of variable frequency pump controllers for alternately operating the motors.

The fifth diagram A is a schematic diagram of actual pressure values of a plurality of variable-frequency pumping controllers for alternately operating motors.

The fifth diagram B is a schematic diagram of the variable frequency of the output of the main motor which is proposed by multiple variable frequency pump controllers to perform alternate motor operation.

The fifth C diagram is a schematic diagram of the auxiliary motor operation in which multiple frequency conversion pump controllers perform alternate motor operation.

This case proposes a universal inverter pump controller that can be applied to ordinary inverters of various specifications. A single inverter pump controller can be used to control multiple ordinary inverters. The inverter may not include a PID control unit and a PLC unit, or only has a simple PLC function, so it can effectively reduce costs, especially if multiple inverters and motors are used at the same time.

Multiple inverter pump controllers include a signal frequency conversion module and a frequency comparison module, which can be used to perform stop detection. After stopping the inverter or motor for a while, the output results and frequency conversion of the PLC unit are compared. The output result of the module is based on the comparison result to further determine whether the shutdown is required. In addition, multiple variable frequency pump controllers can receive the motor status signal of each frequency converter, and change the speed of each frequency converter according to the motor status signal.

The multiple frequency conversion pump controllers proposed in this case include a signal frequency conversion module and a frequency comparison module to ensure that even if there is a slight change in pressure or temperature, the frequency comparison module comparison step can correctly determine whether there is currently In the case of still being used, this method effectively judges whether the machine needs to be stopped to completely avoid the situation where the inverter controls the motor to continue to pressurize and burst the pipe.

Those skilled in the art can understand that the pressure sensor disclosed in this case is merely an example and does not limit the scope of application of this case. For example, the pressure sensor may be replaced by a temperature sensor, and the pressure sensor may be Further applied in the range of water pressure and air pressure. In addition, the pump controller can be used to control the pump motor, and multiple inverter pump controllers can also be directly applied to the motor control, or any communication interface device can be added between the pump controller and the motor and the transmission. Connect multiple devices. Therefore, any change mentioned above does not depart from the protection scope of this case.

Please refer to the second figure, and propose a block diagram of a plurality of variable frequency pump controllers 220 for this case. Multiple variable frequency pump controllers 220 receive pressure signals from the pressure sensor 210 and output multiple output voltage signals after conversion, comparison, and judgment to control multiple frequency converters to change the speed of the motor. The inverter can be configured as a main inverter 231 and auxiliary inverters 232 and 233. Multiple inverter pump controllers 220 receive motor status signals from each of the inverters 231, 232, and 233, and can change the output voltage signal according to the motor status signals. To change the way the motor works. The plurality of variable frequency pump controllers 220 include a PID control unit 221, a PLC unit 222, a signal frequency conversion module 223, and a decision module 224.

First, the signal frequency conversion module 223 receives the pressure signal to convert it into a pressure-to-frequency signal, and the magnitude of the frequency change of the pressure-to-frequency signal can correspond to the magnitude of the voltage or current of the pressure signal. The frequency signal can be a frequency signal of 0 to 60 Hz, and the pressure signal can be a voltage signal of 0 to 10 volts or a current signal of 4 to 20 milliamps, and the frequency of the frequency of the pressure-to-frequency signal will follow the pressure signal. Variation and distribution of voltage or current.

On the other hand, the pressure signal is received by the PID control unit 221 and subjected to feedback control to dynamically adjust the frequency, and the output signal of the PID control unit 221 is changed so that the pressure signal can follow the preset pressure set value. In addition, the PLC unit 222 receives the output signal of the PID control unit 221 and calculates it into an operation output frequency signal that can control the operation of the motor. Therefore, the operation output frequency signal is related to the comparison result of the pressure signal and the pressure setting value. For example, The operational output frequency signal can be a frequency signal of 0-60 Hz, that is, its frequency range is equal to the frequency range of the pressure-to-frequency signal.

Both the pressure-to-frequency signal and the frequency-to-frequency signal are input to the decision-making module 224. The pressure-to-frequency signal can be expressed as the current actual pressure value, and the arithmetic output frequency signal can be expressed as the PID control unit 221 to determine that the speed of the motor is adjusted to accelerate. Or slow down. Therefore, the decision-making module 224 can be used to determine the current use situation based on the comparison of the two frequency signals, and then generate an appropriate output voltage signal to control the main inverter 231 and the auxiliary inverters 232 and 233. In addition, the decision-making module 224 receives the motor status signals output from the main inverter 231 and the auxiliary inverters 232 and 233, can know the operating status of each controlled motor, and changes the motor operation according to the motor status signals.

In detail, the decision module 224 may further include a frequency comparison module 2241 and a one-to-many control module 2242. The frequency comparison module 2241 can determine whether the current pumping system is to be pressurized according to the pressure-to-frequency signal and the calculated output frequency signal. For example: during stop detection, the frequency comparison module 2241 can compare the operation output frequency signal with the pressure-to-frequency signal, decide to shut down the main inverter 231 and auxiliary inverters 232, 233, or resume outputting the output voltage signal to control the Inverter. On the other hand, one-to-many control The control module 2242 can receive the motor status signals output by the main inverter 231 and the auxiliary inverters 232 and 233, and can know the operating status of each controlled motor, for example: according to the operating status, increase or decrease the running motor Or, make multiple motors in operation perform alternate operation to improve the service life of the motor.

In addition, the decision module 224 can store multiple frequency and time parameter settings, and judge the operation modes of the main inverter 231 and the auxiliary inverters 232 and 233 based on the frequency parameters and time parameters. The frequency parameters and Time parameters can include:

The decision module 224 may include a high-speed detection level P1 and a high-speed detection time T1. The high-speed detection level P1 may be the maximum speed of the motor. When the motor status signal indicates that the motor is operating at the high-speed detection level P1, And maintaining this running state for high-speed detection time T1, it means that all The pressurizing capacity of the rotating motor is insufficient. Therefore, the one-to-many control module 2242 turns on an auxiliary inverter 232 or 233.

Conversely, the decision module 224 may include a low-speed detection level P2 and a low-speed duration T2. The low-speed detection level P2 may be 50% of the maximum speed of the motor. When the motor status signal indicates that the motor is running at low speed When detecting the level P2 and maintaining this running state for a low speed duration T2, it means that the current pressurizing capacity of all running motors is sufficient and the running motors are running at low efficiency. Therefore, the one-to-many control mode Group 2242 turns off an auxiliary frequency converter 232 or 233.

The decision module 224 may include an alternate operation time T3 and an alternate interlock time T4. The alternate operation time T3 may be three hours, and the alternate interlock time T4 may be ten seconds. When a motor has been running continuously for up to three hours, excessively long running time may cause rapid loss of the motor and reduce the service life. The one-to-many control module 2242 will control the inverter of an unused motor to take over the continuous operation. Pressurization of the motor that has reached the alternate operation time T3. Therefore, the one-to-many control module 2242 shuts down the motor that has reached the alternate operation time T3. After the alternate interlock time T4 has passed, an auxiliary inverter 232 is turned on Perform pressure work.

In addition, the decision module 224 may include a stop frequency level P5 and a stop frequency detection time T5. The stop frequency level P5 may be set to 50%, which is substantially equal to 50% of the set value. When the operation outputs a frequency signal When the stop frequency level P5 is reached, it means that the actual pressure value is too low. The PID calculation is stopped and the motor is turned off to stop pressurization after the stop frequency detection time T5 has passed. For example, the range of the pressure signal is 0 to 10 volts (equal to 0 to 10 bar). The set value of the pressure is 5 bar. When the output frequency signal of the operation is 30 Hz, the set value is reached, so when the operation output When the frequency signal falls at 15 Hz, it means that the current actual pressure value is 2.5 bar and reaches the stop frequency level P5. After 1 second set by the stop frequency detection time T5, control the inverters 231, 232, and 233 to turn off All motors.

The decision module 224 may include a shutdown detection deviation value P6 and a shutdown detection detection time T6. The shutdown detection deviation value P6 can be set to 3%, which is equivalent to a range of plus or minus 3% of the set value. The detection time T6 can be 30 seconds. It is used to determine whether pressure is still needed (the pressure is still falling). When multiple variable frequency pump controllers 220 follow the actual pressure into the range of the stop deviation, the decision module 224 Carry out shutdown detection to turn off the motor and pressurize it for a period of time. You can turn off one inverter (motor) or all inverters (motors), or set the motor to run at a very low speed for a period of time, and then compare the calculated output frequency signal and Pressure to frequency signal, shut down the inverter or resume controlling the inverter by outputting the output voltage signal. For example, the range of the pressure signal is 0 to 10 volts (equal to 0 to 10 bar), the set pressure is 5 volts (equal to 5 bar), and the deviation is 3%. When the pressure-to-frequency signal and the arithmetic output frequency signal are both 30 Hz, it means that the follow-up is successful, and the deviation value ranges from 29.1 Hz to 30.9 Hz. Therefore, when the pressure-to-frequency signal (the actual pressure value) falls within the range of the deviation value, the multiple frequency conversion pump controllers 220 enter the shutdown detection.

In addition, the decision-making module 224 may include a restart level P7, and the restart level P7 may be set to 95%, which is equivalent to 95% of the set value. Understandably, when the operation output frequency signal falls at 28.5 At Hertz, it means that when the current actual pressure value is 4.75 bar, the motor is started again to pressurize when stopped.

Those skilled in the art can understand that the frequency parameters proposed in this case are all percentage values. When the user changes the setting value or replaces the motor, there is no need to reset all parameter values, but it will follow the new setting value or the maximum speed of the motor. Unified modulation.

This case further proposes a control flowchart, please refer to the third figure, which is a flowchart of a multi-frequency pump controller 220 to perform shutdown detection. This method is used when multiple multi-frequency pump controllers 220 cause the actual pressure to fall. The pressure-to-frequency signal falls within the range of the deviation of the stop and performs stop detection.

First, step 301 is that the pressure-to-frequency signal falls within the range of the deviation of the stop. Then proceed to step 302. First delay the operation output frequency signal to control the main inverter 231 and the auxiliary inverter 232 for a period of time, so that the main inverter 231 and Auxiliary inverter 232 is off or running at low speed for a period of time, for example, output The voltage signal is maintained at 0 volts for a period of time, so that the motor is temporarily pressurized, and the PID control unit 221 and the PLC unit 222 continue to calculate.

Then, the stop judgment of step 304 is performed. If no one is currently used, the calculation result of the continuous calculation by the PID control unit 221 and the PLC unit 222 will consider that no pressure is needed, so the frequency of the pressure-to-frequency signal (current actual pressure value) will be higher than or It is equal to the frequency of the operation output frequency signal (currently, pressurization frequency is needed), so the stop judgment result is "Yes", and then step 305 is executed to gradually turn off the inverters, so that the motors controlled by each inverter gradually stop running.

Conversely, if it is currently in continuous use, the calculation result of the PID control unit 221 and PLC unit 222's continuous calculation will consider that the pressure needs to be increased, so the frequency of the pressure-to-frequency signal (current actual pressure value) will be lower than the frequency of the operation output frequency signal ( Currently, the pressurization frequency is required), so the judgment result of the shutdown is "No", and then step 306 is performed to convert the output frequency signal into an output voltage signal according to the calculation for the constant voltage tracking operation.

Based on the above steps, even under a slight pressure change, the multiple variable frequency pump controllers 220 can still make the difference between the pressure-to-frequency signal and the calculated output frequency signal after a period of stoppage, and then clearly determine the current Is anyone using it and stopping it properly to avoid continuous pressure and bursting the tube, effectively and accurately controlling the inverter.

This case also proposes a control flow chart. Please refer to the fourth figure. For this case, a flow chart of multiple motors with variable frequency pump controllers 220 to perform alternate motor operation is provided. The main frequency converter 231 and auxiliary frequency converter can be judged based on frequency parameters and time parameters. 232, 233 mode of operation.

At the beginning of motor operation 401, at least the speed and state of the motor in operation can be known through the motor status signals transmitted by the main inverter 231 or the auxiliary inverters 232 and 233. If the motor reaches the high-speed operation level P1 (step 402) ), And the motor runs to maintain high-speed detection level P1 for high-speed duration T1 (Step 403), it means that the result of the current motor pressurization may not be sufficient to meet the needs of the existing conditions, or it is just just to meet the requirements of the existing conditions, but the continuous maintenance of high-speed operation may accelerate the motor wear. Therefore, a pair of The multi-control module 2242 will turn on the non-running motor (step 404), increasing the system's ability to pressurize.

Conversely, if the motor runs to the low-speed detection level P2 (step 405), and the motor runs to maintain the low-speed detection level P2 after reaching the low-speed duration T1 (step 406), it means that the current running motor is pressurized. It may meet and exceed the requirements of the current situation, which may cause excessive energy consumption. Therefore, the one-to-many control module 2242 will turn on the non-running motor (step 404), increasing the system's ability to pressurize.

Those skilled in the art can understand that the main motor controlled by the main inverter can also alternate with the auxiliary motor controlled by the auxiliary inverter to avoid excessive wear of the main motor and short life.

In order to clearly explain that the decision-making module 224 can change the operation mode of the main inverter 231 and the auxiliary inverters 232 and 233 based on the stored frequency parameters and time parameters, please refer to FIGS. 5A to 5C and [Table] One], it can be understood that the present case proposes an actual pressure value when multiple frequency conversion pump controllers 220 perform alternate motor operations, and the main inverter 231 and auxiliary inverters 232 and 233 control the operation modes of the main motor and the auxiliary motor. Among them, the fifth diagram A is a schematic diagram of the actual pressure values of multiple frequency conversion pump controllers 220 for the alternate operation of the motor, and the fifth diagram B is a main motor of multiple frequency conversion pump controllers 220 for the alternate operation of the motor. The output variable frequency schematic diagram and the fifth C diagram are a schematic diagram of the auxiliary motor operation in which multiple variable frequency pump controllers 220 perform alternate motor operation.

Please refer to the fifth chart A to fifth chart C, where the vertical axis of the fifth chart A indicates the current actual pressure value, and the vertical axis of the fifth chart B indicates the current output frequency of the motor (it can be understood that the main control of the main inverter 231) The rotation speed of the motor), and the horizontal axes of the fifth A to fifth C graphs are expressed as time.

Assuming that no motor is pressurized, at time t1, the pressure value drops to the restart level P7, then the main motor is started and the output frequency is continuously increased in order to achieve the pressure set value. At time t2, the main motor has reached the high-speed detection level P1, and at time t3, the output frequency of the main motor has reached the high-speed detection level P1 and maintained the high-speed duration T1. One-to-many control mode Group 2242 controls the auxiliary inverter 232 to turn on the auxiliary motor 2 to increase the number of motors in operation.

However, after the two motors are running at the same time, at time t4, the main motor is still at the high-speed detection level P1 and continued for the high-speed duration T1. Therefore, the one-to-many control module 2242 controls the auxiliary inverter 233 to turn on the auxiliary motor. 3 to increase the number of motors in operation. As a result, the three motors continued to operate, and the pressure value reached the range of the deviation value.

Due to changes in usage, at time t5, the output frequency of the main motor is at the low-speed detection level P2 and maintained at the low-speed duration T2. The one-to-many control module 2242 controls the auxiliary inverter 232 to turn off the auxiliary motor 3 to Reduce system power consumption.

At time t6, when the auxiliary motor 2 has been running continuously for the alternate operation time T3, the one-to-many control module 2242 controls the auxiliary inverter 232 to turn off the auxiliary motor 2 and turns off after reaching the alternate reciprocating time T4. At time, the one-to-many control mode 2242 controls the auxiliary inverter 233 to turn on the auxiliary motor 3 to take over the pressurizing work of the auxiliary motor 2.

Those skilled in the art can understand that the above content is only a simple explanation, but does not limit the technical content of this case, and can be flexibly configured according to the system requirements. For example, the auxiliary motor and the main motor can be replaced with each other based on the alternate operating time.

Claims (16)

A multiple frequency conversion pump controller for controlling multiple frequency converters includes: a signal frequency conversion module that receives a pressure signal and converts the pressure signal into a pressure-to-frequency signal; and a decision-making module for comparison The pressure-to-frequency signal and an operational output frequency signal output a plurality of output voltage signals to control each of the inverters, and receive a motor status signal from each of the inverters; wherein the operational output frequency signal is related to the pressure A comparison result between the signal and a pressure set value; and wherein the decision-making module changes and controls the output voltage signal of each inverter according to the motor status signal and the pressure-to-frequency signal of each inverter. The plurality of variable frequency pump controllers as described in the first item of the patent application scope, wherein: the decision module calculates a stopping deviation range based on the pressure setting value, and when the pressure-to-frequency signal falls within the stopping deviation range After shutting down the inverter for a period of time, according to the comparison result of the pressure-to-frequency signal and the calculated output frequency signal, to continue to shut down the inverter or resume controlling the inverter by outputting the output voltage signal. For example, if there are multiple variable frequency pump controllers in the scope of the patent application, when the decision module shuts down the frequency converter for a period of time, if the frequency of the pressure-to-frequency signal is higher than or equal to the operation output frequency signal At the frequency, the decision-making module continues to shut down the inverters. For example, there are multiple variable frequency pump controllers in the scope of patent application, among which: When the decision module turns off the inverter for a period of time, if the frequency of the pressure-to-frequency signal is lower than the frequency of the operation output frequency signal, the decision module resumes outputting the output voltage signal to control the inverter. For example, if there are multiple variable frequency pump controllers in the second scope of the patent application, the stopping deviation range is based on the plus or minus of the pressure setting value and a stopping deviation value, and the stopping deviation value is a percentage value. According to the plurality of variable frequency pump controllers described in item 1 of the scope of patent application, wherein the decision module outputs the outputs according to the motor status signal, at least one frequency parameter and at least one time parameter of each of the inverters. Voltage signals to control the operation of each of the inverters. According to the plurality of variable frequency pump controllers described in the sixth item of the patent application scope, wherein: the frequency parameter is a percentage value of the motor speed. The plurality of variable frequency pump controllers described in item 6 of the scope of patent application, wherein the operation mode may include increasing or decreasing the number of motors controlled by each of the frequency converters in operation, or causing multiple motors in operation to execute Alternate operation. A method for controlling multiple frequency converters, comprising: receiving a pressure signal and converting the pressure signal into a pressure-to-frequency signal; and comparing the pressure-to-frequency signal with an operational output frequency signal to output a plurality of output voltages Signals to control each of the inverters, and receive a motor status signal from each of the inverters; wherein the arithmetic output frequency signal is related to a comparison result of the pressure signal and a pressure set value; and wherein The motor status signal and the pressure-to-frequency signal of the inverter change and control the output voltage signal of each inverter. The method according to item 9 of the scope of patent application, wherein: a stopping deviation range is calculated based on a set value, and when the pressure-to-frequency signal falls within the stopping deviation range, after the inverter is turned off for a period of time, The comparison result of the rotating frequency signal and the operation output frequency signal is used to shut down the inverter or resume controlling the inverter by outputting the output voltage signal. The method as described in item 10 of the scope of patent application, wherein when the frequency converter is turned off for a period of time, if the frequency of the pressure-to-frequency signal is higher than or equal to the frequency of the operational output frequency signal, the frequency converters are further turned off. Device. The method as described in item 10 of the scope of patent application, wherein when the frequency converter is turned off for a period of time, if the frequency of the pressure-to-frequency signal is lower than the frequency of the operation output frequency signal, the output voltage signal is restored to output Control the drive. The method according to item 10 of the scope of patent application, wherein: the stoppage deviation range is based on the positive and negative of the pressure setting value and a stoppage deviation value, and the stoppage deviation value is a percentage value. The method according to item 9 of the scope of patent application, wherein: according to the motor status signal, at least one frequency parameter and time parameter of each inverter, outputting the output voltage signals to control the operation mode of each inverter. The method according to item 14 of the scope of patent application, wherein: the frequency parameter is a percentage value of the motor speed. The method according to item 14 of the patent application scope, wherein the operation mode may include increasing or decreasing the number of motors controlled by each of the frequency converters in operation, or causing multiple motors in operation to perform alternate operations.