Motor positive and negative rotation control device and control method thereof

Abstract

The invention relates to a motor forward and reverse rotation control device and a control method thereof. The motor forward and reverse rotation control device comprises a phase detection module, a thyristor control module, a short-circuit protection module and a controller, the thyristor control module comprises a plurality of thyristors; the controller is electrically connected with the phase detection module, the thyristor control module and the short-circuit protection module. The phase detection module comprises an open-phase detection circuit and a phase detection unit. The open-phase detection circuit is provided with a plurality of lines; each line is provided with at least two detection members. According to the invention, the controller controls the phase detection module to carry out phase detection on the three-phase power, and the thyristor is used for replacing a contactor, so that no large transient current is generated during opening or closing, and the device is prevented from being damaged. The controller is used for controlling the phase detection module to detect the phase of the input power grid, and the opening of the thyristor is adjusted according to the detected phase condition, so that the phenomenon of errors in positive and negative rotation of the motor is avoided. When the power grid is detected to be abnormal, the fault is reported and the motor is not started, thereby preventing the motor from being damaged.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and more specifically, to a motor forward and reverse rotation control device and a control method thereof. Background Art

[0002] In the electric hoist industry, two contactors are generally used to interlock to control the forward and reverse rotation of the motor. When the motor needs to rotate forward, the first contactor is turned on and the second contactor is turned off. When the motor needs to reverse, the second contactor is turned on and the first contactor is turned off.

[0003] However, this solution has the following problems: When the contactor is either opened or closed, the current passing through the contactor will be relatively large, which can easily cause the contactor to arc or be damaged. When the user connects the three-phase power, because they are not clear about the specific phase of the input three-phase power, there will be phase errors in the wiring. If the motor is commanded to run forward at this time, the motor will reverse, and vice versa. When the phase is connected incorrectly, the user needs to manually adjust the wiring of the input three-phase power to ensure that the motor runs in the normal direction. It is impossible to detect whether the three-phase input is missing a phase. When the phase is missing, the motor will still be powered on and run, which can easily cause damage to the motor. When the motor has a short circuit fault or is blocked, the motor cannot be protected from overcurrent, which can easily cause the motor to burn out. Summary of the invention

[0004] The technical problem to be solved by the present invention is that the prior art will generate a large transient current, which is easy to damage the device; it is easy to connect the wrong phase, resulting in the wrong direction of motor rotation, and it is impossible to detect whether the three-phase input is missing a phase. It will still run when there is a phase missing, which is easy to cause damage to the motor. In view of the above-mentioned defects of the prior art, a motor forward and reverse control device and a control method thereof are provided.

[0005] The technical solution adopted by the present invention to solve its technical problem is:

[0006] A motor forward and reverse control device is constructed, wherein the device comprises a phase detection module, a thyristor control module, a short-circuit protection module and a controller, wherein one end of the thyristor control module is connected to the phase detection module, and the other end is connected to the short-circuit protection module; the thyristor control module comprises a plurality of thyristors; the thyristors are interlocked; the controller is electrically connected to the phase detection module, the thyristor control module and the short-circuit protection module respectively, and is used to detect the phase of the input current and adjust the opening positions of the plurality of thyristors; the phase detection module comprises a phase loss detection circuit and a phase detection unit; the phase loss detection circuit is provided with a plurality of circuits, and the input ends of the circuits are respectively connected to three-phase alternating current; each of the circuits is provided with at least two detection components, and the detection components are used to detect whether the circuit is phase-lost; wherein the input current passes through the phase detection module, the thyristor control module and the short-circuit protection module in sequence, and is output to the motor.

[0007] Furthermore, when the circuit is missing a phase, the detection element corresponding to the circuit is not conducting.

[0008] Furthermore, the phase detection unit includes a plurality of phase lines and phase detection points; each of the phase lines corresponds to each of the phase detection points.

[0009] Furthermore, the thyristor control module includes a thyristor drive circuit for driving the thyristor and a control unit for controlling the opening or closing of the thyristor; the thyristor drive circuit includes at least a driver and a thyristor, the driver is used to control the signal from the input end to the trigger end of the thyristor; the input end is connected to the output end of the controller.

[0010] The present invention also provides a control method according to the motor forward and reverse control device, comprising the following steps:

[0011] Controlling a preset phase detection module through a preset controller to detect the phase of the input current to obtain a phase detection result;

[0012] Adjusting the states of the preset multiple thyristors according to the phase detection result through a preset thyristor control module; wherein the states include an on state and a off state;

[0013] Detecting the output current through a preset controller, and determining whether the output current exceeds a preset range;

[0014] If not, the output current is input to the motor.

[0015] Furthermore, the step of controlling a preset phase detection module to detect the phase of the input current through a preset controller to obtain a phase detection result includes:

[0016] Determine whether the input current is abnormal; wherein the abnormal conditions include phase loss and voltage abnormality;

[0017] If so, a fault is reported and the machine is shut down.

[0018] Furthermore, the step of determining whether the input current is abnormal includes:

[0019] If not, inputting the first phase detection flag or the second phase detection flag to the thyristor control module;

[0020] If so, the third phase detection flag is input to the thyristor control module, and all the thyristors are turned off.

[0021] Further, when the first phase detection flag or the second phase detection flag is input, it is determined whether the input command is forward rotation;

[0022] If yes, some of the thyristors are turned on, and the motor rotates forward;

[0023] If not, some of the thyristors are turned on and the motor is reversed.

[0024] Further, the input current includes a first phase line, a second phase line and a third phase line;

[0025] When the phase of the first phase line is 0, the phase of the second phase line lags behind the phase of the first phase line by 120°, and the phase of the third phase line lags behind the phase of the first phase line by 240°, inputting the first phase detection flag;

[0026] When the phase of the second phase line lags behind the phase of the first phase line by 240° and the phase of the third phase line lags behind the phase of the first phase line by 120°, the second phase detection flag is input.

[0027] Furthermore, the step of detecting the output current by a preset controller and determining whether the output current exceeds a preset range includes:

[0028] If so, the thyristors are turned off simultaneously through a preset short-circuit protection module.

[0029] The beneficial effects of the present invention are:

[0030] The controller controls the phase detection module to perform phase detection on the user's input three-phase electricity, and uses thyristors instead of contactors. The thyristors use software interlocking to avoid large transient currents when turned on or off, thus avoiding device damage.

[0031] The controller controls the phase detection module to detect the phase of the input power grid, and adjusts the opening of the thyristor according to the detected phase to avoid the phenomenon of motor forward and reverse errors. In addition, the phase detection module can detect whether the input power grid is missing a phase and whether the voltage is normal. When an abnormality in the power grid is detected, the fault will be reported and the motor will not be started to avoid damage to the motor. The input current of the motor can be detected in real time, and when the current exceeds the set range, the power supply to the motor will be cut off in time to protect the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is a structural schematic diagram of a motor forward and reverse rotation control device in one embodiment of the present invention;

[0033] Figure 2 This is a schematic diagram of current flow in a motor forward and reverse rotation control device according to an embodiment of the present invention;

[0034] Figure 3 is a circuit diagram of a phase loss detection circuit in the present invention;

[0035] Figure 4 is a schematic diagram of a phase detection unit in the present invention;

[0036] Figure 5 is a circuit diagram of a thyristor driving circuit in the present invention;

[0037] Figure 6 is a schematic diagram of a control unit in the present invention;

[0038] Figure 7 The present invention is a schematic diagram of the method steps of a control method of a motor forward and reverse control device in one embodiment of the present invention.

[0039] Description of reference numerals: phase detection module 10 , thyristor control module 20 , short circuit protection module 30 , controller 40 . DETAILED DESCRIPTION

[0040] In order to make the purpose, technical solution and advantages of the present application more clearly understood, the present application is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

[0041] Please refer to Figure 1The present invention proposes a motor forward and reverse control device, including a phase detection module 10, a thyristor control module 20, a short-circuit protection module 30 and a controller 40, one end of the thyristor control module 20 is connected to the phase detection module 10, and the other end is connected to the short-circuit protection module 30; the thyristor control module 20 includes a plurality of thyristors; the thyristors are interlocked; the controller 40 is electrically connected to the phase detection module 10, the thyristor control module 20 and the short-circuit protection module 30 respectively, and is used to detect the phase of the input current and adjust the opening position of the plurality of thyristors; the phase detection module 10 includes a phase loss detection circuit and a phase detection unit; the phase loss detection circuit is provided with a plurality of circuits, and the input ends of the circuits are respectively connected to three-phase alternating current; each circuit is provided with at least two detection components, and the detection components are used to detect whether the circuit is phase-deficient; wherein the input current passes through the phase detection module 10, the thyristor control module 20 and the short-circuit protection module 30 in sequence, and is output to the motor.

[0042] In this embodiment, a phase detection module 10, a thyristor control module 20, a short circuit protection module 30 and a controller 40 are provided. The controller 40 is electrically connected to the phase detection module 10, the thyristor control module 20 and the short circuit protection module 30 respectively; the controller 40 can control the phase detection module 10 to detect the phase of the input current. Figure 2 As shown, the three-phase input AC power passes through the phase detection module 10, the thyristor control module 20 and the short-circuit protection module 30 in sequence, and is finally output to the motor. During this period, the controller 40 controls the phase detection module 10 to detect the three-phase input AC power and the output current.

[0043] Specifically, the controller 40 is an MCU, Microcontroller Unit. The present application uses an MCU to perform phase detection on the user's input three-phase power, and can detect whether the input three-phase power is missing a phase and whether the voltage is normal. When a missing phase or abnormal voltage is detected, the fault is reported and the motor is not started.

[0044] More specifically, the thyristor control module 20 includes a plurality of thyristors, thyristors are used to replace contactors, and the thyristors are interlocked by software, so that no transient large current will be generated when they are turned on or off, and damage to the device can be avoided. Among them, software interlock refers to the way in which software is mutually restricted or interdependent, such as input verification and authority control. In a specific embodiment, the logical conditions between thyristors are pre-set, such as when one thyristor is turned on, the other associated thyristor is turned off. After the MCU controls the phase detection module 10 to detect the phase of the input power grid, the thyristors that need to be turned on are adjusted according to the phase of the power grid, and there will be no error in the forward and reverse rotation of the motor, and the user does not need to consider the phase problem of the input power grid when wiring.

[0045] In one embodiment, the phase loss detection circuit is provided with a plurality of circuits, each circuit is provided with an input terminal for receiving AC power, and each circuit is provided with at least two detection elements for detecting whether the circuit is phase-lost. When the circuit is phase-lost, the detection element corresponding to the circuit is not conducting.

[0046] In specific implementation: the phase loss detection circuit is provided with an R input terminal, an S input terminal and a T input terminal, the detection element is a diode, and the phase loss detection circuit can detect the missing phase in the three-phase alternating current. Specifically, Figure 3 As shown, the phase loss detection circuit is provided with R input terminal, S input terminal and T input terminal, which can be connected to three-phase AC respectively. The R input terminal is provided with resistors R5 and R6; the S input terminal is provided with resistors R7 and R8; the T input terminal is provided with resistors R9 and R10; multiple resistors are provided to protect the circuit to prevent the input signal voltage from being too high and causing damage to the components. The R input terminal is provided with diodes V1 and V2; the S input terminal is provided with diodes V3 and V4; the T input terminal is provided with diodes V5 and V6. When a phase is missing, the diode of the phase will not be turned on, and the output of the phase is 0, thereby detecting whether the phase is missing.

[0047] In addition, the phase loss detection circuit is also equipped with a capacitor C2, which can smooth the pulsating DC signal after rectification and form a stable DC voltage. When the three-phase voltage is normal, the rectified signal will be relatively stable. If one phase is missing, the rectified signal will become asymmetric. In this way, it can also be seen whether there is any abnormality in the three-phase current.

[0048] Equipped with PC, optocoupler, it can perform signal isolation, isolate the rectified and filtered voltage signal from the control circuit, and prevent high voltage from being directly transmitted to the low voltage control circuit. When the signal strength reaches a certain threshold, the LED inside the optocoupler will light up, activate the phototransistor to turn on, and output a low-level signal. If the signal level of a phase is low or missing, the output signal of the optocoupler will become abnormal, and the phase loss state can be detected. The circuit finally outputs the Fre signal, which can be used to notify the system or monitoring device. When the voltage of one of the three phases is missing, an alarm is triggered.

[0049] In one embodiment, the phase detection unit includes a plurality of phase lines and phase detection points; each phase line corresponds to each phase detection point.

[0050] Specifically, Figure 4As shown, each phase line is respectively set corresponding to each phase detection point. The first phase line L1 is connected to phase detection point 1, the second phase line L2 is connected to phase detection point 2, and the third phase line L3 is connected to phase detection point 3. The phase detection points set on the phase lines detect the phase lines, the first phase line L1 is detected at phase detection point 1, the second phase line L2 is detected at phase detection point 2, and the third phase line L3 is detected at phase detection point 3. In a specific embodiment, the first phase line L1 is detected at phase detection point 1, and the detection result is Phase_L1=0, that is, the phase of the first phase line is 0.

[0051] In one embodiment, the thyristor control module 20 includes a thyristor driving circuit for driving the thyristor and a control unit for controlling the opening or closing of the thyristor; the thyristor driving circuit includes at least a driving component and a thyristor, and the driving component is used to control the signal from the input end to the trigger end of the thyristor; the input end is connected to the output end of the controller 40.

[0052] In specific implementation: Figure 5 As shown, VCC is the power supply end, which is powered by a 5V power supply and can provide the required operating voltage for the thyristor drive circuit. The thyristor drive circuit includes a driver. In a specific embodiment, the driver is PS, an optical coupler, which is used to control the signal from the input end to the trigger end of the thyristor to turn on the thyristor. Among them, the input end of the optical coupler is connected by pin 1, pin 2 and pin 3, and the output end is a phototransistor, which is connected by pin 4, pin 5 and pin 6. When the input signal is transmitted to the LED of the optical coupler through resistor R1, the LED emits light and activates the phototransistor, thereby transmitting the signal. PC_A is the input end of the thyristor drive circuit, which can be connected to the controller 40 (MCU) to control the LED part of the optical coupler, and then control the switch of the thyristor. Further, the resistor R1 is connected in series with the input end of the optical coupler, which can limit the current of the LED and ensure its safe operation. Thyristor Q, when the trigger end of the thyristor receives the signal, the thyristor is turned on and starts to conduct current.

[0053] Specifically, when PC_A is activated, current flows into the LED of the optocoupler through the resistor R1, and then the LED emits light, activating the phototransistor, turning on the phototransistor, and then turning on the thyristor to achieve driving of the thyristor.

[0054] like Figure 6 As shown, the control unit includes three phases L1, L2 and L3, and is provided with 5 thyristors. The output ends of the three phases L1, L2 and L3 are respectively connected to the thyristors, and the output ends of the thyristors are respectively connected to the input ends of the motors. The input of the three-phase current is controlled by controlling the switches of the thyristors.

[0055] Furthermore, by controlling the conduction time of the thyristor, the speed of the motor can be adjusted, the start and stop control or the rotation direction of the motor can be changed.

[0056] Please refer to Figure 7 The present invention provides a control method according to the above motor forward and reverse control device, comprising the following steps:

[0057] S1, controlling a preset phase detection module 10 through a preset controller 40 to detect the phase of an input current to obtain a phase detection result;

[0058] S2, adjusting the states of the preset multiple thyristors according to the phase detection result through the preset thyristor control module 20; wherein the states include an on state and a off state;

[0059] S3, detecting the output current through a preset controller 40, and determining whether the output current exceeds a preset range;

[0060] S4, if not, input the output current to the motor.

[0061] In this embodiment, the phase detection module 10 is first controlled by the controller 40 to detect the phase of the input current to obtain a phase detection result; then the thyristor control module 20 adjusts the opening or closing of the thyristor according to the phase detection result, and then the output current is detected by the controller 40 to determine whether the output current exceeds a preset range. If so, the output current is input to the motor.

[0062] In one embodiment, the step of controlling the preset phase detection module 10 to detect the phase of the input current by the preset controller 40 to obtain the phase detection result includes:

[0063] Determine whether the input current is abnormal; the abnormal conditions include phase loss and voltage abnormality;

[0064] If so, a fault is reported and the machine is shut down.

[0065] In specific implementation: determine whether there is a phase loss or voltage abnormality in the three phases of the input current. If so, report the fault and turn off all thyristors.

[0066] In one embodiment, the step of determining whether the input current is abnormal includes:

[0067] If not, input the first phase detection flag or the second phase detection flag to the thyristor control module 20;

[0068] If yes, the third phase detection flag is input to the thyristor control module 20 and all thyristors are turned off.

[0069] In specific implementation: whether the input current is abnormal is judged, if not, the first phase detection flag or the second phase detection flag is input to the thyristor control module 20. When performing phase detection, taking phase detection point 1 as the reference point, Phase_L1=0, indicating that the phase value of the first phase line L1 is 0. Then the phase of the second phase line L2 and the third phase line L3, when the phase of L2 lags the phase of L1 by 120°, Phase_L2=120, indicating the phase value of the second phase line L2; the phase of the third phase line L3 lags the phase of L1 by 240°, Phase_L3=240, then the first phase detection flag det_phase=0 is input. If the phase of L2 is detected to lag the phase of L1 by 240°, Phase_L2=240, the phase of L3 lags the phase of L1 by 120 degrees, Phase_L3=120, then the second phase detection flag det_phase=1 is input. If there is a situation of input phase loss or input voltage abnormality, the third phase detection flag det_phase=2 is input.

[0070] In one embodiment, when the first phase detection flag or the second phase detection flag is input, it is determined whether the input command is forward rotation;

[0071] If so, some of the thyristors are turned on and the motor rotates forward;

[0072] If not, some thyristors are turned on and the motor reverses.

[0073] In specific implementation: when the first phase detection flag det_phase=0 is input, the input command is judged. Figure 6 As shown in the figure, when the input command is forward rotation, thyristor 1, thyristor 2 and thyristor 3 are turned on. At this time, the three-phase input of the motor is A=L1, B=L2, C=L3, and the three-phase power input phase of the motor is: Phase_A=0, Phase_B=120, Phase_C=240, and the motor rotates forward. Among them, Phase_A represents the phase of A, Phase_B represents the phase of B, and Phase_C represents the phase of C.

[0074] When the input command is reverse, thyristor 1, thyristor 4 and thyristor 5 are turned on. At this time, the three-phase input of the motor is A=L1, B=L3, C=L2, and the input phase of the motor's three-phase power supply is: Phase_A=0, Phase_B=240, Phase_C=120, and the motor reverses.

[0075] Table 1:

[0076]

[0077]

[0078] It can be seen from Table 1 that the input current includes the first phase line, the second phase line and the third phase line; when the phase of the first phase line is 0, the phase of the second phase line lags behind the phase of the first phase line by 120°, and the phase of the third phase line lags behind the phase of the first phase line by 240°, the first phase detection flag is input; when the phase of the second phase line lags behind the phase of the first phase line by 240° and the phase of the third phase line lags behind the phase of the first phase line by 120°, the second phase detection flag is input.

[0079] In specific implementation: when the first phase detection flag is used as the reference point, Phase_L1=0, then the phases of the second phase line and the third phase line are detected, if the second phase detected lags the first phase by 120°, Phase_L2=120, and the third phase lags the first phase by 240°, Phase_L3=240, then the first phase detection flag det_phase=0 is input. Wherein, det_phase represents the demodulated phase, which is the phase value obtained through the demodulation process.

[0080] If the detected second phase lags the first phase by 240°, Phase_L2=240, and the third phase lags the first phase by 120°, Phase_L3=120, then the second phase detection flag det_phase=1 is input.

[0081] If a phase loss or abnormality is detected, the third phase detection flag det_phase=2 is input, at which time the fault is reported and the machine is shut down, and all thyristors are turned off to protect the motor.

[0082] In one embodiment, the step of detecting the output current by a preset controller 40 and determining whether the output current exceeds a preset range includes:

[0083] If so, the thyristors are turned off simultaneously through the preset short-circuit protection module 30 .

[0084] In specific implementation: the present application performs real-time detection on the input current of the motor, and can promptly cut off the power supply to the motor and turn off the thyristor at the same time to protect the motor when the current exceeds the allowable range of the motor.

[0085] Specifically, the short-circuit protection module 30 may include a current sensor that can monitor the current in real time and transmit it to the MCU. A thyristor is used to cut off the power supply. When the current is transmitted to the MCU, the MCU will judge whether the current exceeds the allowable range. When it exceeds the allowable range, the thyristor is controlled to close to cut off the power supply, thereby protecting the motor. In addition, the short-circuit protection module 30 can also be provided with a capacitor for filtering and noise reduction to prevent high-frequency noise from affecting the judgment result.

[0086] It is worth mentioning that, in addition to the current sensor and thyristor mentioned in the embodiment, other components with the same function, such as a relay, can also be used to cut off the power supply.

[0087] It should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, device, article or method including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, device, article or method. In the absence of further restrictions, an element defined by the sentence "includes a ..." does not exclude the presence of other identical elements in the process, device, article or method including the element.

[0088] The above are only preferred embodiments of the present application, and are not intended to limit the patent scope of the present application. Any equivalent structure or equivalent process transformation made using the contents of the present application specification and drawings, or directly or indirectly used in other related technical fields, are also included in the patent protection scope of the present application.

Claims

1. A motor forward and reverse control device, characterized in that: It includes a phase detection module, a thyristor control module, a short-circuit protection module and a controller, wherein one end of the thyristor control module is connected to the phase detection module, and the other end is connected to the short-circuit protection module; The thyristor control module comprises a plurality of thyristors; the thyristors are interlocked; The controller is electrically connected to the phase detection module, the thyristor control module and the short-circuit protection module respectively, and is used to detect the phase of the input current and adjust the opening positions of the plurality of thyristors; The phase detection module includes a phase loss detection circuit and a phase detection unit; The phase loss detection circuit is provided with a plurality of circuits, and the input ends of the circuits are respectively connected to three-phase alternating current; Each of the circuits is provided with at least two detection components, and the detection components are used to detect whether the circuit is missing a phase; The input current passes through the phase detection module, the thyristor control module and the short-circuit protection module in sequence and is output to the motor.

2. The motor forward and reverse control device according to claim 1, characterized in that: When the circuit is missing a phase, the detection element corresponding to the circuit is not conducting.

3. The motor forward and reverse control device according to claim 1, characterized in that: The phase detection unit includes a plurality of phase lines and phase detection points; Each of the phase lines corresponds to each of the phase detection points.

4. The motor forward and reverse control device according to claim 1, characterized in that: The thyristor control module includes a thyristor drive circuit for driving the thyristor and a control unit for controlling the on or off of the thyristor; The thyristor drive circuit at least comprises a driver and a thyristor, wherein the driver is used to control the signal to be transmitted from an input end to a trigger end of the thyristor; The input end is connected to the output end of the controller.

5. A control method for a motor forward and reverse control device according to any one of claims 1 to 4, characterized in that: The following steps are involved: Controlling a preset phase detection module through a preset controller to detect the phase of the input current to obtain a phase detection result; Adjusting the states of the preset multiple thyristors according to the phase detection result through a preset thyristor control module; wherein the states include an on state and a off state; Detecting the output current through a preset controller, and determining whether the output current exceeds a preset range; If not, the output current is input to the motor.

6. The control method according to claim 5, characterized in that: The step of controlling a preset phase detection module to detect the phase of the input current through a preset controller to obtain a phase detection result includes: Determine whether the input current is abnormal; wherein the abnormal conditions include phase loss and voltage abnormality; If so, a fault is reported and the machine is shut down.

7. The control method according to claim 6, characterized in that: The step of determining whether the input current is abnormal includes: If not, inputting the first phase detection flag or the second phase detection flag to the thyristor control module; If so, the third phase detection flag is input to the thyristor control module, and all the thyristors are turned off.

8. The control method according to claim 7, characterized in that: When the first phase detection flag or the second phase detection flag is input, determining whether the input command is forward rotation; If yes, some of the thyristors are turned on, and the motor rotates forward; If not, some of the thyristors are turned on and the motor is reversed.

9. The control method according to claim 8, characterized in that: The input current includes a first phase line, a second phase line and a third phase line; When the phase of the first phase line is 0, the phase of the second phase line lags behind the phase of the first phase line by 120°, and the phase of the third phase line lags behind the phase of the first phase line by 240°, inputting the first phase detection flag; When the phase of the second phase line lags behind the phase of the first phase line by 240° and the phase of the third phase line lags behind the phase of the first phase line by 120°, the second phase detection flag is input.

10. The control method according to claim 5, characterized in that: The step of detecting the output current by a preset controller and determining whether the output current exceeds a preset range includes: If so, the thyristors are turned off simultaneously through a preset short-circuit protection module.

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