Rotor short-circuit slip control system and control method for high-power pulse generator set

Abstract

This invention belongs to the field of motor system control technology, specifically relating to a rotor short-circuit slip control system and method for a high-power pulse generator set. It includes: an 8500kW motor, a slip device, a main monitoring PC, a PLC master station, a slip control cabinet, and several sets of slip control devices installed within the slip control cabinet. The 8500kW motor is connected to both the slip device and the slip control cabinet. Each slip control device includes: a frequency converter, a slip PLC substation, a communication control module, and a current measurement device. This invention achieves high-parameter and high-precision slip start control, meeting the technical requirements of frequent starting of high-power pulse generator sets and interlocking control of multiple slip control devices. It also ensures safe start-up of the unit and stable acceleration according to a given current.

Description

Technical Field

[0001] The invention belongs to the technical field of motor system control, and in particular relates to a rotor short-circuit slip control system and a control method for a high-power pulse generator set. Background Art

[0002] The traditional motor rotor series resistance starting control method is used in low-power applications. It maintains a constant torque starting of the rotor circuit series resistance by changing the slip resistance to maintain a constant stator current. The control parameters and accuracy requirements are low. The traditional control system only supports starting from a stop state to the maximum speed, and the maximum speed that can be achieved by accelerating the motor using the traditional slip control system is low, which cannot meet the discharge requirements of the device experiment. In addition, the existing slip control method has large fluctuations in the stator current during the acceleration process, and cannot stably accelerate the unit according to the given current.

[0003] The motor power of a high-power vertical pulse generator set is as high as 8500kW, the motor starting torque is large, and the starting time is long. According to the experimental requirements of the 2M device, the unit needs to start quickly within the specified time, and discharge and re-accelerate frequently during the experiment. The high-power pulse generator set uses a liquid slip regulator (here referred to as slip) to control the unit. The slip device is equipped with four travel switches of high position, pre-position, low position, and pre-low position, including three operating modes of quick lifting, high position, and acceleration. During the experiment, the slip device needs to frequently move between pre-positioning and low position to realize the discharge and re-acceleration process of the unit. The resistance liquid spacing between the low-position plates of the slip device is only 2mm. In order to further increase the speed of the unit, a short-circuit operation is required after reaching the low position to further reduce the resistance of the rotor. How to ensure that there is no stator overcurrent requires an improved system control method. The generator set has extremely high requirements for acceleration time, current fluctuation, and torque stability parameters. Therefore, it is necessary to design a slip control system and control method that can control high parameters and high precision in a high-power pulse generator set to solve the above-mentioned existing technical problems. Summary of the invention

[0004] The present invention proposes a rotor short-circuit slip control system and control method for a high-power pulse generator set, which are used to solve the technical problem in the prior art that frequent starting of the set cannot meet the safety and stability of the set starting. In addition, the control method of the existing slip control device has a large stator current fluctuation during the acceleration process and cannot stably accelerate the set according to a given current.

[0005] The technical solution of the present invention is:

[0006] A short-circuit slip control system for a high-power pulse generator set, comprising: an 8500kw motor, a slip device, a main monitoring PC, a PLC master station and a slip control cabinet and several sets of slip control devices arranged in the slip control cabinet; the 8500kw motor is connected to the slip device and the slip control cabinet respectively, and each set of slip control devices comprises: a frequency converter, a slip PLC substation, a communication control module and a current measuring device;

[0007] The slip frequency converter in the slip control device is connected to the slip PLC substation, the slip frequency converter includes a PID regulator, the communication control module is arranged in the slip PLC substation, and the current measuring device is connected to the PID regulator in the slip frequency converter.

[0008] The main monitoring PC is connected to the PLC master station, and the PLC master station is also connected to the slip control cabinet.

[0009] The slip PLC substations in each slip control device are connected to the PLC master station through the slip control cabinet.

[0010] The slip device contains a liquid resistor.

[0011] The 8500KW motor is started by means of a liquid resistor in a rotor series slip device.

[0012] The control logic of the slip PLC substation in each slip control device includes: slip control system raising position operation mode, slip control system fast raising operation mode and slip control system accelerating operation mode;

[0013] When the slip control system operates in the fast lifting mode, the slip inverter in the slip control device has a given frequency of 50HZ, and the slip device quickly rises to the pre-position one in about 10s;

[0014] When the slip control system operates in the high position operation mode, the slip inverter controls the given frequency to 50HZ, and the slip device is raised to the high position;

[0015] When the slip control system runs in acceleration mode, the slip inverter in the slip control device sets the given frequency to a maximum of 100Hz and a minimum of 20Hz; the stator side current of the unit is introduced as a feedback signal for PID adjustment, and the slip device drops from a high position or pre-position to a low position.

[0016] The number of the plurality of slip control devices is three, and the names of the three slip control devices are respectively slip control device number one, slip control device number two, and slip control device number three.

[0017] The communication between the slip PLC substation and the PLC master station adopts the PROFIBUS DP communication protocol; the communication between the main monitoring PC and the PLC master station adopts the MPI communication protocol.

[0018] The master station PLC controls the three slip control devices to accelerate in sequence according to a preset acceleration sequence. The preset acceleration sequence of the three slip control devices is slip control device number three, slip control device number one and slip control device number two, thereby ensuring that only one slip control device is accelerated at the same time, avoiding multiple slip control devices from working at the same time.

[0019] Each slip control device has two control modes: local control and computer control. The computer control mode is to control the PLC master station through the main monitoring PC, and control the slip PLC substation connected to the PLC master station;

[0020] The local control mode directly controls the slip PLC substation through the slip control cabinet;

[0021] Of the two control modes mentioned above, local control and computer control, computer control has priority.

[0022] When the slip control system is running in acceleration operation, the startup phase has a time delay function; the PID regulator is numerically set to a stator current stop value and a stator current start value.

[0023] Each of the slip control system raising position operation mode, slip control system quick raising operation mode and slip control system accelerating operation mode has three different operation methods, and the three different operation methods are manual, automatic-button, and automatic-WinCC operation modes.

[0024] A control method for the slip control system of the high-power pulse generator set as described above comprises the following control steps:

[0025] Step 1: When the PLC substation in the slip control device meets the start-up conditions of the slip control system and the PLC substation receives the computer control command of the main monitoring PC or the local control command, the unit starts, the slip control device starts after a delay, and the slip inverter starts to work, executing the acceleration operation mode of the slip control system;

[0026] Step 2: The stator current is introduced into the PID regulator to receive the stator current signal of the 8500KW motor, and control the electrode descent speed. After the motor reaches the low position, the electrode start-up is completed.

[0027] Step 3: If the unit is discharged during step 2, the slip control system starts the fast lifting operation mode, the slip motor is lifted to the preset position 1, and the acceleration operation is performed again after the discharge is completed. The PID regulator feedbacks the control work, the motor reaches the low position, and the acceleration is completed. When the unit is shut down during step 2, the slip control system executes the high position operation mode, the slip inverter set frequency is 50HZ, and the slip device is lifted to the high position.

[0028] Beneficial effects of the present invention:

[0029] The slip control system and control method designed in the present invention realize high-parameter and high-precision slip starting mode control, can meet the technical requirements of frequent starting of large-power pulse generator sets and interlocking control of multiple slip control devices, can meet the unit starting safety and stable acceleration according to a given current.

[0030] In addition, the slip control device designed in the present invention has the following specific technical advantages:

[0031] 1) The slip control system designed in the present invention takes into account that when multiple slip control devices work at the same time, the multiple slip control devices are operated by a linkage control method. Through the linkage control between different slip control devices, the multiple slip control systems are accelerated in sequence, avoiding simultaneous acceleration. It is ensured that only one slip device is accelerated at the same time, thereby improving reliability and operating parameters.

[0032] 2) The slip control device in the slip control system designed by the present invention adopts three control operation modes, namely, quick lift, increase position, and acceleration operation modes. Given different control parameters, each operation mode has three operation modes: manual, automatic-button, and automatic-WinCC.

[0033] 3) The control strategy of the slip control device is optimized, and a time delay is added to the startup phase of the acceleration operation mode of the slip control device to prevent overcurrent of the stator current of the generator set system during startup.

[0034] The present invention can effectively improve the stability of the unit startup, avoid the impact of unstable startup on the unit structure, increase the unit startup current, effectively shorten the unit startup time, and take into account the requirements of shortening the startup time and startup stability, meet the rotor resistance short-circuit operation, and will not cause the unit stator current to overcurrent, avoiding the unit from tripping during startup. This device can meet the high-parameter pulse discharge requirements of the 2M Tokamak device, and can shorten the discharge time interval from 20 minutes to 15 minutes. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural schematic diagram of the slip control system of the present invention;

[0036] Figure 2 A schematic diagram of a configuration network connection of multiple slip control devices in the slip control system of the present invention;

[0037] Figure 3 It is a control flow chart of the slip PLC substation in the slip control device of the present invention;

[0038] Figure 4 A flow chart of the PID regulator adjustment process in the slip control device designed for the present invention;

[0039] Figure 5 It is a waveform diagram of the generator set speed increase, the set stator current, the set rotor current and the set rotor voltage; DETAILED DESCRIPTION

[0040] A high-power pulse generator rotor short-circuit slip control system and control method of the present invention are described in detail below in conjunction with the accompanying drawings and embodiments.

[0041] A short-circuit slip control system for a high-power pulse generator set includes: an 8500kw motor, a slip device, a main monitoring PC, a PLC master station, a slip control cabinet, and several sets of slip control devices arranged in the slip control cabinet; the 8500kw motor is connected to the slip device and the slip control cabinet respectively, and each set of slip control devices includes: a frequency converter, a slip PLC substation, a communication control module, and a current measuring device.

[0042] The slip frequency converter in the slip control device is connected to the slip PLC substation, the slip frequency converter includes a PID regulator, the communication control module is arranged in the slip PLC substation, and the current measuring device is connected to the PID regulator in the slip frequency converter.

[0043] The main monitoring PC is connected to the PLC master station, and the PLC master station is also connected to the slip control cabinet.

[0044] The slip PLC substations in each slip control device are connected to the PLC master station through the slip control cabinet.

[0045] The slip device contains a liquid resistor.

[0046] The 8500KW motor is started by means of a liquid resistor in a rotor series slip device.

[0047] The control logic of the slip PLC substation in each slip control device includes: slip control system raising position operation mode, slip control system fast raising operation mode and slip control system accelerating operation mode;

[0048] When the slip control system operates in the fast lifting mode, the slip inverter in the slip control device has a given frequency of 50HZ, and the slip device quickly rises to the pre-position one in about 10s;

[0049] When the slip control system operates in the high position operation mode, the slip inverter controls the given frequency to 50HZ, and the slip device is raised to the high position;

[0050] When the slip control system runs in acceleration mode, the slip inverter in the slip control device sets the given frequency to a maximum of 100Hz and a minimum of 20Hz; the stator side current of the unit is introduced as a feedback signal for PID adjustment, and the slip device drops from a high position or pre-position to a low position.

[0051] The number of the plurality of slip control devices is three, and the names of the three slip control devices are respectively slip control device number one, slip control device number two, and slip control device number three.

[0052] The communication between the slip PLC substation and the PLC master station adopts the PROFIBUS DP communication protocol; the communication between the main monitoring PC and the PLC master station adopts the MPI communication protocol.

[0053] The master station PLC controls the three slip control devices to accelerate in sequence according to a preset acceleration sequence. The preset acceleration sequence of the three slip control devices is slip control device number three, slip control device number one and slip control device number two, thereby ensuring that only one slip control device is accelerated at the same time, avoiding multiple slip control devices from working at the same time.

[0054] Each slip control device has two control modes: local control and computer control. The computer control mode is to control the PLC master station through the main monitoring PC, and control the slip PLC substation connected to the PLC master station;

[0055] The local control mode directly controls the slip PLC substation through the slip control cabinet;

[0056] Of the two control modes mentioned above, local control and computer control, computer control has priority.

[0057] When the slip control system is running in acceleration operation, the startup phase has a time delay function; the PID regulator is numerically set to a stator current stop value and a stator current start value.

[0058] Each of the slip control system raising position operation mode, slip control system quick raising operation mode and slip control system accelerating operation mode has three different operation methods, and the three different operation methods are manual, automatic-button, and automatic-WinCC operation modes.

[0059] A control method for the slip control system of the high-power pulse generator set as described above comprises the following control steps:

[0060] Step 1: When the PLC substation in the slip control device meets the start-up conditions of the slip control system and the PLC substation receives the computer control command of the main monitoring PC or the local control command, the unit starts, the slip control device starts after a delay, and the slip inverter starts to work, executing the acceleration operation mode of the slip control system;

[0061] Step 2: The stator current is introduced into the PID regulator to receive the stator current signal of the 8500KW motor, and control the electrode descent speed. After the motor reaches the low position, the electrode start-up is completed.

[0062] Step 3: If the unit is discharged during step 2, the slip control system starts the fast lifting operation mode, the slip motor is lifted to the preset position 1, and the acceleration operation is performed again after the discharge is completed. The PID regulator feedbacks the control work, the motor reaches the low position, and the acceleration is completed. When the unit is shut down during step 2, the slip control system executes the high position operation mode, the slip inverter set frequency is 50HZ, and the slip device is lifted to the high position.

[0063] The optimization control strategy designed in the present invention is to add a time delay in the starting phase of the acceleration operation mode of the slip control system to prevent the stator current of the unit system from overcurrent during startup. The slip device will not perform the descending operation until the delay time is expired, and slope control is added in the descending starting phase. The given frequency of the inverter increases according to the slope, and there will be an acceleration process in the descending process.

[0064] Set the stator current stop setting value and start setting value of the PID regulator. When the stator current exceeds the stop setting value, the inverter stops. When the stator current drops to the start setting value, the inverter restarts to protect the speed regulation mechanism from descending operation mode, improve the unit operation status, and avoid frequent starting and stopping of the speed regulation motor.

[0065] Before the electrode reaches the low position, the inverter is switched to feedback the given current to reduce the stator current of the unit, so as to solve the problem that when the electrode drops to the low position, the resistance between the three-phase plates is unbalanced, causing the stator current to suddenly increase and exceed the protection value. After the electrode reaches the low position, the short-circuit operation is delayed to further increase the motor speed.

[0066] The specific implementation operations include:

[0067] In the automatic operation mode, the computer control mode is operated through the host computer, and the local control is operated on-site through the slip control cabinet, and the computer control has priority. After receiving the acceleration command, each slip system accelerates after comprehensive pre-positioning, instructions, return orders and other conditions, including the acceleration of other units and the condition of its own electrodes as the interlocking conditions of acceleration. When switching to manual mode, all operations are manually operated in the local slip control cabinet.

[0068] The slip control device sets two speed parameters to drive the electrode action, corresponding to the two operating modes of the slip device: lifting and lowering.

[0069] When the slip device is in the lifting operation mode, a 20s time delay is added in the starting stage to prevent the stator current from overcurrent. After the delay time is up, the slip device will perform the descending operation. At the beginning of the descent, the inverter set frequency rises from 0Hz to 100Hz within 2s according to the given slope. Set the stator current stop setting value and start setting value of the PID regulator. The stator current is inversely proportional to the inverter set frequency. When the current is 0, the electrode descends at full speed according to the inverter set frequency 100Hz setting parameter. When the current reaches the current stop setting value of 848A, the inverter set frequency is 20Hz. After exceeding 848A, the inverter set frequency is 20Hz, and the electrode stops descending. When the current drops to the stop start value of 845V, the inverter set frequency is 20Hz, and the electrode descends again.

[0070] The minimum given frequency of the inverter is 20Hz instead of 0Hz, which can effectively ensure that the unit can run closer to the maximum stator current value of 848A and shorten the motor starting time. There is a difference of 3A between the stator current stop setting value and the start setting value, which avoids frequent starting and stopping of the speed regulating motor.

[0071] Introduce the electrode position into feedback control, increase the plate position as the feedback control amount of the inverter, add a pre-low position travel switch, and when the control system receives the pre-low position signal, reduce the current stop setting value from 848A to 700A. After the change, the unit operating current is reduced, which can effectively prevent low-position current fluctuations and overcurrent alarms. Since the stator current is reduced after reaching the low position, it is very conducive to subsequent graded short-circuit operations. Eliminate system protection risks.

[0072] After the slip electrode reaches the low position, it delays for 20 seconds, waiting for the motor stator current to decrease. When the delay time reaches the short-circuit switch action, the slip resistor is connected to a solid resistor, and then delayed for another 10 seconds to directly short-circuit the slip resistor. The motor rotor series resistance becomes 0, further increasing the unit operating speed.

[0073] Figure 4This is the functional diagram of the PID regulator. The traditional slip speed regulation only controls the start and stop of the electrode by introducing a switch node signal, and the speed is adjusted by frequent actions of the electrode operating mechanism or the speed regulating motor. This device introduces PID regulation, measures the motor stator current through a 1500 / 5 current transformer, and then uses a current transmitter to convert the current into a 0-20mA signal, and connects to the inverter feedback port as a feedback signal to compare with the given parameters. The feedback signal is also switched using a pre-low signal, and the output frequency is calculated through the internal PID algorithm, driving the speed regulating motor to control the slip electrode descent speed, thereby changing the water resistance value to adjust the stator current.

[0074] The slip resistance changes with the displacement of the slip electrode, and the descent process of the slip electrode is a closed-loop control process. The stator current of the motor outputs a secondary current through the current transformer, and the current sensor converts the secondary current into a DC voltage output proportional to it. After comparing the stator current setting signal with the DC signal output by the current sensor, the signal integrated and amplified by the PID feedback control unit controls the output frequency of the inverter. This output controls the speed of the electrode descending motor to make the liquid resistance change with the stator current.

[0075] The slip resistance changes with the displacement of the slip active electrode, where the descent process of the slip electrode is a closed-loop control process. The stator current of the motor outputs a secondary current through the current transformer, and the current sensor converts the secondary current into a DC voltage output proportional to it. After comparing the stator current setting signal with the DC signal output by the current sensor, the signal integrated and amplified by the PID feedback control unit controls the inverter output. This output controls the speed of the electrode descent motor to make the liquid resistance change with the stator current.

[0076] like Figure 5 As shown in the figure, the unit quickly starts to 490rpm within 15 minutes. The stator current is stable and close to the maximum value of 848A during the entire startup process, reflecting that the unit startup process is smooth and fast. The rotor voltage decreases at a certain slope and the rotor current is stable, reflecting that the resistance of the slip device decreases steadily and the speed control system is stable.

[0077] In the device of the present invention, multiple slip control devices are interlocked through the master station PLC, and the three units are accelerated in the order of sequence number 3-1-2, and multiple slip control systems are interlocked through the master station PLC, and the three units are accelerated in the order of 3-1-2 to avoid multiple slip systems working at the same time. After the slip control system receives the acceleration command, when the slip control system receives the pole plate position is in the pre-position one, the central control command release signal, the return command condition signal, and the other slip control device does not accelerate signal, the system starts acceleration, and when the slip control system receives the low position signal, it stops accelerating. When the speed reaches 485rpm, the system sends an acceleration completion signal. When the previous slip control system sends an acceleration completion signal, the other slip control devices meet their own acceleration conditions, and the slip control system starts the acceleration process.

[0078] Through the PLC substation, the slip control cabinet can realize on-site monitoring, and can also be remotely monitored and controlled through the main monitoring PC during the operation of the unit. The PROFIBUS DP communication protocol is used to replace a large amount of long-distance wiring and calibration work; fieldbus communication greatly simplifies system maintenance, reduces fault points, and increases system reliability.

[0079] The signal calls between the various slip systems are realized through the program, which is convenient for reading and writing programs and improves the readability of the programs; at the same time, the execution status of the variables and statements in the program can be monitored online in real time, and the status of each parameter and each device can be directly displayed dynamically. The main monitoring PC not only realizes the working status monitoring of the slip system, but also has the functions of alarm display and data archiving.

[0080] In addition, the slip control system designed in the present invention introduces a time delay function in the acceleration mode starting phase to prevent the stator current of the unit system from overcurrent during startup. The slip device performs the descending operation after the delay time is up, and slope control is added in the descending starting phase. The given voltage of the DC speed regulator increases according to the slope, and there will be an acceleration process in the descending process.

[0081] The embodiments of the present invention are described in detail above, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the field without departing from the purpose of the present invention.

Claims

1. A short-circuit slip control system for a high-power pulse generator set, characterized in that: include: 8500kW motor, slip device, main monitoring PC, PLC master station and slip control cabinet and several sets of slip control devices installed in the slip control cabinet; The 8500kW motor is connected to the slip device and the slip control cabinet respectively. Each slip control device includes: a frequency converter, a slip PLC substation, a communication control module and a current measuring device. The slip frequency converter in the slip control device is connected to the slip PLC substation, the slip frequency converter includes a PID regulator, the communication control module is arranged in the slip PLC substation, and the current measuring device is connected to the PID regulator in the slip frequency converter; The main monitoring PC is connected to the PLC master station, and the PLC master station is also connected to the slip control cabinet.

2. According to claim 1, a high-power pulse generator set rotor short-circuit slip control system is characterized in that: The slip PLC substations in each slip control device are connected to the PLC master station through the slip control cabinet.

3. A high-power pulse generator rotor short-circuit slip control system according to claim 2, characterized in that: The slip device contains a liquid resistor.

4. A high-power pulse generator rotor short-circuit slip control system according to claim 3, characterized in that: The 8500kW motor is started by means of a liquid resistor in a rotor series slip device.

5. A high-power pulse generator rotor short-circuit slip control system according to claim 4, characterized in that: The control logic of the slip PLC substation in each slip control device includes: slip control system raising position operation mode, slip control system fast raising operation mode and slip control system accelerating operation mode; When the slip control system operates in the fast lifting mode, the slip inverter in the slip control device has a given frequency of 50HZ, and the slip device quickly rises to the pre-position one in about 10s; When the slip control system operates in the high position operation mode, the slip inverter controls the given frequency to 50HZ, and the slip device is raised to the high position; When the slip control system runs in acceleration mode, the slip inverter in the slip control device has a given frequency of up to 100Hz and a minimum of 20Hz; the stator side current of the unit is introduced as a feedback signal for PID adjustment, and the slip device drops from a high position or pre-position to a low position.

6. A high-power pulse generator rotor short-circuit slip control system according to claim 5, characterized in that: The number of the plurality of slip control devices is three, and the names of the three slip control devices are respectively slip control device number one, slip control device number two, and slip control device number three.

7. A high-power pulse generator rotor short-circuit slip control system according to claim 6, characterized in that: The communication between the slip PLC substation and the PLC master station adopts the PROFIBUS DP communication protocol; the communication between the main monitoring PC and the PLC master station adopts the MPI communication protocol.

8. A high-power pulse generator rotor short-circuit slip control system according to claim 7, characterized in that: The master station PLC controls the three slip control devices to accelerate in sequence according to a preset acceleration sequence. The preset acceleration sequence of the three slip control devices is slip control device number three, slip control device number one and slip control device number two, thereby ensuring that only one slip control device is accelerated at the same time, avoiding multiple slip control devices from working at the same time.

9. A high-power pulse generator rotor short-circuit slip control system according to claim 8, characterized in that: Each slip control device has two control modes: local control and computer control. The computer control mode is to control the PLC master station through the main monitoring PC, and control the slip PLC substation connected to the PLC master station; The local control mode directly controls the slip PLC substation through the slip control cabinet; Of the two control modes mentioned above, local control and computer control, computer control has priority.

10. A rotor short-circuit slip control system for a high-power pulse generator set according to claim 9, characterized in that: When the slip control system is running in acceleration operation, the startup phase has a time delay function; the PID regulator is numerically set to a stator current stop value and a stator current start value.

11. A high-power pulse generator rotor short-circuit slip control system according to claim 10, characterized in that: Each of the slip control system raising position operation mode, slip control system quick raising operation mode and slip control system accelerating operation mode has three different operation methods, and the three different operation methods are manual, automatic-button, and automatic-WinCC operation modes.

12. A control method for a slip control system of a high-power pulse generator set according to any one of claims 1 to 11, characterized in that The control steps include: Step 1: When the PLC substation in the slip control device meets the start-up conditions of the slip control system and the PLC substation receives the computer control command of the main monitoring PC or the local control command, the unit starts, the slip control device starts after a delay, and the slip inverter starts to work, executing the acceleration operation mode of the slip control system; Step 2: The stator current is introduced into the PID regulator to receive the stator current signal of the 8500kW motor and control the electrode descent speed. After the motor reaches the low position, the electrode start-up is completed; Step three: If the unit is discharged during step two, the slip control system starts the fast-lift operation mode, the slip motor is lifted to the preset position one, and the acceleration operation is performed again after the discharge is completed. The PID regulator feedbacks the control work, the motor reaches the low position, and the acceleration is completed; when the unit is shut down during step two, the slip control system executes the high-position operation mode, the slip inverter set frequency is 50HZ, and the slip device is lifted to the high position.

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