Brushless direct current motor control system and control method thereof

Abstract

The invention discloses a brushless direct current motor control system and a control method thereof, and relates to the technical field of brushless direct current motors, and the system comprises a controlled motor, a three-phase inverter, a motor control terminal, a current controller, a current difference reduction module, a rotating speed calculation module, a commutation angle calculation module, a commutation logic module, and a logic AND gate module. The current difference reduction module is used for subtracting a current instruction output by the motor control terminal from the three-phase detection current and then outputting a current difference signal, and the current difference signal is converted into a current amplitude signal for controlling the controlled motor by the current controller; the commutation angle calculation module outputs commutation angle data matched with the three-phase current detection signal and the rotating speed signal according to the commutation meter; the commutation logic module generates a commutation logic signal according to the commutation angle signal and the rotor position information, and the logic AND gate module performs logic AND on the commutation logic signal and a current amplitude signal output by the current controller and then outputs a three-phase driving current of the three-phase inverter.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of brushless DC motor, in particular to a brushless DC motor control system and a control method thereof. BACKGROUND

[0002] The brushless DC motor has the excellent characteristics of both DC motor and AC motor, and has high reliability and excellent speed regulation performance, so it has been widely used in electric vehicles, aerospace and high-performance servo systems.

[0003] Similar to the design of DC motor, the air gap magnetic field of the brushless DC motor is trapezoidal wave, and the no-load electromotive force is approximately trapezoidal wave. The three-phase armature currents of the existing brushless DC motor in a period are controlled by current hysteresis loop. The conduction and turn-off of the power switching device are controlled according to the Hall position signal and the electromotive force. The non-conduction phase electromotive force zero-crossing point is again through 30 0 The commutation starts, and the current is approximately trapezoidal, which matches the trapezoidal electromotive force.

[0004] When the load runs, the armature winding generates a stepping rotating armature reaction magnetic field, which is superimposed with the rotor permanent magnet magnetic field, and the electromotive force generated in the winding is severely distorted. The conduction and turn-off of the power switching device and the freewheeling of the freewheeling diode aggravate this distortion. For the motor, the electromotive force phase advances under load; for the generator, the electromotive force phase lags under load. This causes the winding of the turn-off phase and the turn-on phase to form a circulating current through the freewheeling diode, resulting in increased winding copper loss, decreased efficiency, and increased torque ripple. On the other hand, the use of traditional control leads to weak armature reaction, which limits the high-speed operation of the motor. SUMMARY

[0005] In view of the defects in the prior art, the technical problem to be solved by the present application is to provide a brushless DC motor control system and a control method thereof, which can reduce the circulating current between windings at medium and low speeds, reduce the excitation current at high speeds, and maintain reliable operation with constant power.

[0006] In order to solve the above technical problems, the brushless DC motor control system provided by the present application comprises a controlled motor, a three-phase inverter, a motor control terminal and a current controller. The controlled motor is a brushless DC motor. The three-phase output ports of the three-phase inverter are connected to the three-phase stator windings of the controlled motor. The controlled motor is provided with a position sensor for detecting the rotor position information thereof and a three-phase winding current sensor for detecting the three-phase stator winding current thereof. The motor control terminal is used to output a current instruction for controlling the operation of the controlled motor. The current controller is used to convert the current instruction received by the current instruction input port into a current amplitude signal for controlling the controlled motor.

[0007] It is characterized in that: it further includes a current difference reduction module, a rotating speed calculation module, a commutation angle calculation module, a commutation logic module, a logic AND gate module;

[0008] The current difference reduction module is provided with a current instruction input port and a three-phase detection current input port, wherein the current instruction input port is connected to the current instruction output port of the motor control terminal, and the three-phase detection current input port is connected to the three-phase detection current output port of the three-phase winding current sensor on the controlled motor; the output port of the current difference reduction module is connected to the current instruction input port of the current controller; the current difference reduction module is used for subtracting the current received by the current instruction input port from the current received by the three-phase detection current input port and outputting a current difference value signal;

[0009] The input port of the rotating speed calculation module is connected to the position sensor on the controlled motor, and is used for converting the rotor position information output by the position sensor into the rotating speed data of the controlled motor;

[0010] The commutation angle calculation module is provided with a three-phase current detection signal input port and a rotating speed signal input port, wherein the three-phase current detection signal input port is connected to the three-phase detection current output port of the three-phase winding current sensor on the controlled motor, and the rotating speed signal input port is connected to the output port of the rotating speed calculation module; the commutation angle calculation module is internally provided with a commutation table of the controlled motor; the commutation table contains a plurality of records; each record contains three-phase stator winding current data, rotor rotating speed data and commutation angle data matched with the three-phase stator winding current data and the rotor rotating speed data in the record; the commutation angle calculation module outputs the commutation angle data matched with the three-phase current detection signal and the rotating speed signal received by the three-phase current detection signal input port and the rotating speed signal input port according to the internally provided commutation table;

[0011] The commutation logic module is provided with a commutation angle signal input port, a position signal input port and a three-phase logic signal output end, wherein the commutation angle signal input port is connected to the commutation angle signal output port of the commutation angle calculation module, and the position signal input port is connected to the position sensor on the controlled motor; the commutation logic module generates the commutation logic signal according to the received commutation angle signal and rotor position information and then outputs the commutation logic signal from the three-phase logic signal output end;

[0012] The logic AND gate module has three AND gates; the first input ends of the three AND gates are respectively connected to the current amplitude signal output end of the current controller; the second input ends of the three AND gates are respectively connected to the three-phase logic signal output end of the commutation logic module; and the three output ends of the three AND gates are respectively connected to the three-phase control current input end of the three-phase inverter through operational amplifiers.

[0013] The current control method of the brushless DC motor control system provided by the present invention is characterized by: using a position sensor and a winding current sensor to detect the real-time position of the rotor and the real-time current of the three-phase stator windings of the controlled motor.

[0014] The speed calculation module converts the real-time rotor position of the controlled motor into the real-time speed data of the controlled motor and then sends it to the commutation angle calculation module.

[0015] The commutation angle calculation module uses a lookup table to find the commutation angle data that matches the real-time current and real-time speed data of the three-phase stator winding of the controlled motor from the built-in commutation table, and then outputs the found commutation angle data to the commutation logic module.

[0016] If the controlled motor is an electric motor and the controlled motor is in a load operation state, the commutation angle data output by the commutation angle calculation module is the degree of leading commutation angle;

[0017] If the controlled motor is a generator and the controlled motor is in a load operation state, the commutation angle data output by the commutation angle calculation module is the degree of the lag commutation angle;

[0018] The leading commutation angle is the angle by which the position where the electromotive force of the off-phase and the conducting phase are equal when the controlled motor is under load leads the position where the electromotive force of the off-phase and the conducting phase are equal when the controlled motor is under no-load.

[0019] The commutation lag angle is the angle by which the position where the electromotive force of the off phase and the conducting phase are equal when the controlled motor is under load lags behind the position where the electromotive force of the off phase and the conducting phase are equal when the controlled motor is under no-load.

[0020] The commutation logic module generates a commutation logic signal output based on the received commutation angle data and the real-time rotor position information of the controlled motor.

[0021] The current difference module subtracts the current command output by the motor control terminal from the real-time current of the three-phase stator winding of the controlled motor and outputs the current difference signal to the current controller.

[0022] The current controller outputs a corresponding current amplitude signal based on the received current command;

[0023] The current amplitude signal output by the current controller and the commutation logic signal output by the commutation logic module are processed by a logic AND gate to generate the corresponding three-phase drive current. After being amplified by an operational amplifier, the drive current is input to the three-phase inverter, thereby controlling the three-phase output terminals of the three-phase inverter to output the corresponding three-phase current to the three-phase stator windings of the controlled motor, thus realizing the operation control of the controlled motor.

[0024] Furthermore, if the controlled motor is an electric motor, its commutation angle under high-speed load operation is forward compared to its commutation angle under medium- and low-speed load operation.

[0025] If the controlled motor is a generator, its commutation angle under high-speed load operation is lagging behind that under medium- and low-speed load operation.

[0026] High-speed load operation of a controlled motor refers to the controlled motor operating at a load exceeding its rated speed, while medium- and low-speed load operation of a controlled motor refers to the controlled motor operating at a load not exceeding its rated speed.

[0027] The brushless DC motor control system and its control method provided by this invention control the armature winding current by obtaining the leading or lagging commutation angle from a table based on the speed and load current. When the speed is below the rated speed, the commutation angle is advanced, which can reduce the circulating current between the windings, reduce copper losses, and at the same time improve output power and efficiency, and reduce torque pulsation and vibration noise. When the speed is above the rated speed, the commutation angle is advanced or lagging, which can effectively reduce the excitation current, expand the speed range, improve efficiency, and achieve constant power safe and reliable operation. Attached Figure Description

[0028] Figure 1 This is a structural block diagram of the brushless DC motor control system according to an embodiment of the present invention;

[0029] Figure 2 (a) is a waveform diagram of the phase electromotive force of the three-phase stator windings during one cycle when the motor is unloaded;

[0030] Figure 2 (b) is a waveform diagram of the back electromotive force of the three-phase stator windings within one cycle when the motor is operating under low-speed load.

[0031] Figure 2 (c) is a waveform diagram of the phase electromotive force of the three-phase stator windings within one cycle when the motor is operating under low-speed load as a generator;

[0032] Figure 3 It is a graph showing the relationship between the magnetic field magnetomotive force and the current commutation angle during one armature reaction cycle when the motor is running at high speed. Detailed Implementation

[0033] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings. However, these embodiments are not intended to limit the present invention. Any similar structures or variations thereof that adopt the present invention should be included in the protection scope of the present invention. The commas in the present invention all indicate a relationship between and.

[0034] like Figure 1 As shown, the brushless DC motor control system provided in this embodiment of the invention includes a controlled motor M1, a three-phase inverter U1, a motor control terminal U8, a current differential module U7, a current controller U5, a speed calculation module U2, a commutation angle calculation module U3, a commutation logic module U4, and a logic AND gate module U6.

[0035] The controlled motor M1 is a brushless DC motor. The three-phase output ports of the three-phase inverter U1 are respectively connected to the three-phase stator windings of the controlled motor M1. The controlled motor is equipped with a position sensor C1 for detecting its rotor position information and a three-phase winding current sensor (not shown in the figure) for detecting its three-phase stator winding current.

[0036] The motor control terminal U8 is used to output current commands to control the operation of the controlled motor M1;

[0037] The current difference reduction module U7 is provided with a current command input port and a three-phase detection current input port. The current command input port is connected to the current command output port of the motor control terminal U8, and the three-phase detection current input port is connected to the three-phase detection current output port of the three-phase winding current sensor on the controlled motor M1. The output port of the current difference reduction module U7 is connected to the current command input port of the current controller U5. The current difference reduction module U7 is used to subtract the current received by the current command input port from the current received by the three-phase detection current input port and output the current difference signal.

[0038] The current controller U5 is used to convert the current command (current difference signal output by the current difference module) received by the current command input port into a current amplitude signal for controlling the controlled motor M1.

[0039] The input port of the speed calculation module U2 is connected to the position sensor C1 on the controlled motor, and is used to convert the rotor position information output by the position sensor into the speed data of the controlled motor.

[0040] The commutation angle calculation module U3 is equipped with a three-phase current detection signal input port and a speed signal input port. The three-phase current detection signal input port is connected to the three-phase current detection output port of the three-phase winding current sensor on the controlled motor M1, and the speed signal input port is connected to the output port of the speed calculation module U2. The commutation angle calculation module has a built-in commutation table of the controlled motor. The commutation table is preset according to the electrical parameters of the controlled motor. The commutation table contains multiple records. Each record contains three-phase stator winding current data, rotor speed data, and commutation angle data that matches the three-phase stator winding current data and rotor speed data in the record. The commutation angle data includes leading commutation angle data and / or lagging commutation angle data. The commutation angle calculation module outputs commutation angle data that matches the three-phase current detection signal and speed signal received by the three-phase current detection signal input port and the speed signal input port according to the built-in commutation table.

[0041] The commutation logic module U4 is provided with a commutation angle signal input port, a position signal input port, and a three-phase logic signal output terminal. The commutation angle signal input port is connected to the commutation angle signal output port of the commutation angle calculation module U3, and the position signal input port is connected to the position sensor C1 on the controlled motor. The commutation logic module generates a commutation logic signal based on the received commutation angle signal and rotor position information and outputs it from the three-phase logic signal output terminal.

[0042] The logic AND gate module U6 has three AND gates. The first input terminals of the three AND gates are respectively connected to the current amplitude signal output terminal of the current controller U5. The second input terminals of the three AND gates are respectively connected to the three-phase logic signal output terminal of the commutation logic module U4 (the second input terminal of each AND gate is connected to one phase signal, and the second input terminals of the three AND gates are respectively connected to the three-phase signals). The three output terminals of the three AND gates are each connected to the three-phase control current input terminal of the three-phase inverter U1 via operational amplifiers (A1, A2, A3).

[0043] The control method of the brushless DC motor control system provided in this embodiment of the invention is as follows:

[0044] During the operation of the controlled motor M1, the real-time position of the rotor and the real-time current of the three-phase stator windings of the controlled motor are detected by the position sensor C1 and the winding current sensor.

[0045] The speed calculation module U2 converts the real-time rotor position of the controlled motor into the real-time speed data of the controlled motor and then sends it to the commutation angle calculation module U3.

[0046] The commutation angle calculation module U3 uses a lookup table to find the commutation angle data that matches the real-time current and real-time speed data of the three-phase stator winding of the controlled motor from the built-in commutation table, and then outputs the found commutation angle data to the commutation logic module U4.

[0047] If the controlled motor is an electric motor and the controlled motor is in a load operation state, the commutation angle data output by the commutation angle calculation module is the degree of leading commutation angle;

[0048] If the controlled motor is a generator and the controlled motor is in a load operation state, the commutation angle data output by the commutation angle calculation module is the degree of the lag commutation angle;

[0049] The leading commutation angle is the angle by which the position where the electromotive force of the off-phase and the conducting phase are equal when the controlled motor is under load leads the position where the electromotive force of the off-phase and the conducting phase are equal when the controlled motor is under no-load.

[0050] The commutation lag angle is the angle by which the position where the electromotive force of the off phase and the conducting phase are equal when the controlled motor is under load lags behind the position where the electromotive force of the off phase and the conducting phase are equal when the controlled motor is under no-load.

[0051] If the controlled motor is an electric motor, its commutation angle under high-speed load operation is forward compared to its commutation angle under medium and low-speed load operation.

[0052] If the controlled motor is a generator, its commutation angle under high-speed load operation is lagging behind that under medium- and low-speed load operation.

[0053] High-speed load operation of a controlled motor refers to the controlled motor operating at a load exceeding its rated speed, while medium- and low-speed load operation of a controlled motor refers to the controlled motor operating at a load not exceeding its rated speed.

[0054] The commutation logic module U4 generates a commutation logic signal output based on the received commutation angle data and the real-time rotor position information of the controlled motor (from position sensor C1);

[0055] The current difference module U7 subtracts the current command output by the motor control terminal U8 from the real-time current of the three-phase stator winding of the controlled motor and outputs the current difference signal to the current controller U5.

[0056] The current controller U5 outputs a corresponding current amplitude signal based on the received current command (the current difference signal output by the current differential module);

[0057] The current amplitude signal output by the current controller U5 and the commutation logic signal output by the commutation logic module U4 are processed by the logic AND gate U6 to generate the corresponding three-phase drive current. After being amplified by operational amplifiers A1, A2, and A3, the current is input to the three-phase inverter U1, thereby controlling the three-phase output terminals of the three-phase inverter U1 to output the corresponding three-phase current to the three-phase stator windings of the controlled motor M1, thus realizing the operation control of the controlled motor.

[0058] In this embodiment of the invention, the three-phase inverter, current differential module, current controller, speed calculation module, commutation angle calculation module, and commutation logic module are all existing technologies.

[0059] The leading / lagging commutation angle and the winding current of the three-phase stator winding are approximately linearly related. In this embodiment of the invention, the relationship between them is determined through simulation / experiment to establish the commutation table in the commutation angle calculation module.

[0060] Figure 2 (a) is a waveform diagram of the phase electromotive force of the three-phase stator windings during one cycle when the motor is under no-load. The vertical axis of the figure is... The horizontal axis represents the electromotive force. For electrical angle, The electromotive force curve for phase A stator winding is shown. The electromotive force curve for phase B stator winding is shown. This is the electromotive force (EMF) curve of the C-phase stator winding. The EMF is generated by the three-phase stator winding cutting the permanent magnet field, and it is close to a trapezoidal wave with a phase difference of 120°. 0 Electrical angle, the stator winding of phase A and the stator winding of phase B are at 30 degrees. 0 The electrical angle positions are equal. The existing control switches phases at this position. During the switching, the stator winding of phase A is turned on and the stator winding of phase B is turned off.

[0061] Figure 2 (b) is a waveform diagram of the back electromotive force of the three-phase stator windings during one cycle when the motor is operating under a low-speed (not exceeding the rated speed) load. The vertical axis of the figure is... The horizontal axis represents the electromotive force. For electrical angle, The curve shows the back electromotive force of the stator winding in phase A. The curve shows the back electromotive force of the B-phase stator winding. The curve shows the back electromotive force of the C-phase stator winding. The current control signal for phase A stator winding (the current control signals for phase B and phase C stator windings are delayed by 120° sequentially). 0 (Electrical angle, not shown in the diagram) The magnetic field inside the motor includes the permanent magnet magnetic field and the armature reaction magnetic field. The back electromotive force waveform is significantly distorted. At the same time, the position of the back electromotive force of phase A stator winding and phase B stator winding is shifted forward by an angle compared with the no-load state. The current commutation angle of phase A stator winding and phase B stator winding is advanced;

[0062] Figure 2 (c) is a waveform diagram of the phase electromotive force of the three-phase stator windings during one cycle when the motor is operating under low-speed (not exceeding the rated speed) load conditions as a generator. The vertical axis of the figure is... The horizontal axis represents the electromotive force. For electrical angle, The phase electromotive force curve of phase A stator winding is shown. The phase electromotive force curve for phase B stator winding is shown. The phase electromotive force curve of the C-phase stator winding is shown. The current control signal for phase A stator winding (the current control signals for phase B and phase C stator windings are delayed by 120° sequentially). 0 (Electrical angle, not shown in the diagram) The magnetic field inside the motor includes the permanent magnet magnetic field and the armature reaction magnetic field. The phase electromotive force waveform is significantly distorted. At the same time, the electromotive force of phase A stator winding is equal to that of phase B stator winding, and lags behind by an angle compared to the no-load state. The commutation angle of the stator windings in phase A and phase B lags behind.

[0063] Figure 3This graph shows the relationship between the magnetomotive force of the magnetic field and the commutation angle of the current during one armature reaction cycle of a motor operating at high speed (above rated speed) under load. Figure 3 (a) indicates the motor is in motor operating mode. Figure 3 (b) shows the motor operating as a generator. The arrow S in the figure indicates the direction of rotor rotation. When the motor is running at high speed, the armature reaction is used to weaken the magnetic field inside the motor, so that the electromotive force does not continue to increase with the increase of speed.

[0064] like Figure 3 As shown in (a), when the motor is in motor operation, the armature reaction magnetomotive force is... The initial permanent magnetomotive force remains unchanged. With termination of permanent magnet magnetomotive force The difference is 60 degrees along the direction of rotation 0 Electric angle, and simultaneously the initial permanent magnetomotive force Lag Angle Starting Line 30 0 Electrical angle;

[0065] like Figure 3 As shown in (b), when the motor is operating as a generator, the armature reaction magnetomotive force... The initial permanent magnetomotive force remains unchanged. With termination of permanent magnet magnetomotive force The difference is 60 degrees along the direction of rotation 0 Electric angle, and simultaneously the initial permanent magnetomotive force Leading angle starting line 30 0 Electrical angle.

[0066] This invention, without increasing motor manufacturing costs or altering the main structure, considers armature reaction and can adjust the commutation angle by setting parameters of the commutation table. In the low-to-medium speed range, this reduces circulating current between windings, decreases copper losses, increases output power and efficiency, and reduces torque pulsation and vibration noise. In the high-speed range, the commutation angle is further advanced / retarded to expand the speed range, improve efficiency, and achieve constant power safe and reliable operation.

Claims

1. A brushless DC motor control system, comprising a controlled motor, a three-phase inverter, a motor control terminal, and a current controller, wherein the controlled motor is a brushless DC motor, the three-phase output ports of the three-phase inverter are respectively connected to the three-phase stator windings of the controlled motor, the controlled motor is provided with a position sensor for detecting its rotor position information and a three-phase winding current sensor for detecting its three-phase stator winding current; the motor control terminal is used to output a current command for controlling the operation of the controlled motor; the current controller is used to convert the current command received by the current command input port into a current amplitude signal for controlling the controlled motor; Its features are: It also includes a current differential reduction module, a speed calculation module, a commutation angle calculation module, a commutation logic module, and a logic AND gate module; The current difference reduction module is provided with a current command input port and a three-phase detection current input port. The current command input port is connected to the current command output port of the motor control terminal, and the three-phase detection current input port is connected to the three-phase detection current output port of the three-phase winding current sensor on the controlled motor. The output port of the current difference reduction module is connected to the current command input port of the current controller. The current difference reduction module is used to subtract the current received by the current command input port from the current received by the three-phase detection current input port and output the current difference signal. The input port of the speed calculation module is connected to the position sensor on the controlled motor, and is used to convert the rotor position information output by the position sensor into the speed data of the controlled motor. The commutation angle calculation module is equipped with a three-phase current detection signal input port and a speed signal input port. The three-phase current detection signal input port is connected to the three-phase current detection output port of the three-phase winding current sensor on the controlled motor, and the speed signal input port is connected to the output port of the speed calculation module. The commutation angle calculation module has a built-in commutation table of the controlled motor. The commutation table contains multiple records. Each record contains three-phase stator winding current data, rotor speed data, and commutation angle data that matches the three-phase stator winding current data and rotor speed data in the record. The commutation angle calculation module outputs commutation angle data that matches the three-phase current detection signal and speed signal received by the three-phase current detection signal input port and the speed signal input port according to the built-in commutation table. The commutation logic module is provided with a commutation angle signal input port, a position signal input port, and a three-phase logic signal output terminal. The commutation angle signal input port is connected to the commutation angle signal output port of the commutation angle calculation module, and the position signal input port is connected to the position sensor on the controlled motor. The commutation logic module generates a commutation logic signal based on the received commutation angle signal and rotor position information and outputs it from the three-phase logic signal output terminal. The logic AND gate module has three AND gates. The first input terminals of the three AND gates are respectively connected to the current amplitude signal output terminal of the current controller. The second input terminals of the three AND gates are respectively connected to the three-phase logic signal output terminal of the commutation logic module. The three output terminals of the three AND gates are each connected to the three-phase control current input terminal of the three-phase inverter via operational amplifiers.

2. The current control method of the brushless DC motor control system according to claim 1, characterized in that: The real-time position of the rotor and the real-time current of the three-phase stator windings of the controlled motor are detected by using position sensors and winding current sensors. The speed calculation module converts the real-time rotor position of the controlled motor into the real-time speed data of the controlled motor and then sends it to the commutation angle calculation module. The commutation angle calculation module uses a lookup table to find the commutation angle data that matches the real-time current and real-time speed data of the three-phase stator winding of the controlled motor from the built-in commutation table, and then outputs the found commutation angle data to the commutation logic module. If the controlled motor is an electric motor and the controlled motor is in a load operation state, the commutation angle data output by the commutation angle calculation module is the degree of leading commutation angle; If the controlled motor is a generator and the controlled motor is in a load operation state, the commutation angle data output by the commutation angle calculation module is the degree of the lag commutation angle; The leading commutation angle is the angle by which the position where the electromotive force of the off-phase and the conducting phase are equal when the controlled motor is under load leads the position where the electromotive force of the off-phase and the conducting phase are equal when the controlled motor is under no-load. The commutation lag angle is the angle by which the position where the electromotive force of the off phase and the conducting phase are equal when the controlled motor is under load lags behind the position where the electromotive force of the off phase and the conducting phase are equal when the controlled motor is under no-load. The commutation logic module generates a commutation logic signal output based on the received commutation angle data and the real-time rotor position information of the controlled motor. The current difference module subtracts the current command output by the motor control terminal from the real-time current of the three-phase stator winding of the controlled motor and outputs the current difference signal to the current controller. The current controller outputs a corresponding current amplitude signal based on the received current command; The current amplitude signal output by the current controller and the commutation logic signal output by the commutation logic module are processed by a logic AND gate to generate the corresponding three-phase drive current. After being amplified by an operational amplifier, the drive current is input to the three-phase inverter, thereby controlling the three-phase output terminals of the three-phase inverter to output the corresponding three-phase current to the three-phase stator windings of the controlled motor, thus realizing the operation control of the controlled motor.

3. The current control method of the brushless DC motor control system according to claim 2, characterized in that: If the controlled motor is an electric motor, its commutation angle under high-speed load operation is forward compared to its commutation angle under medium and low-speed load operation. If the controlled motor is a generator, its commutation angle under high-speed load operation is lagging behind that under medium- and low-speed load operation. High-speed load operation of a controlled motor refers to the controlled motor operating at a load exceeding its rated speed, while medium- and low-speed load operation of a controlled motor refers to the controlled motor operating at a load not exceeding its rated speed.

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