Control method during hard commutation of motor

Abstract

A control method for hard commutation of a motor belongs to the field of electronic technology and motor control, and is characterized in that real-time monitoring analysis and control are carried out on the duty ratio of speed regulation PWM (Pulse Width Modulation); when the duty ratio of the speed regulation PWM is larger than a preset threshold, the motor driving controller is switched to a lower arm MOS PWM mode from a lower arm MOS normally-on mode; and delaying the closing of the lower arm PWM, so that the closing of the lower arm MOS switching tube is delayed by one or more time periods compared with the closing of the upper arm MOS switching tube. The drive current obtained from the bus during hard commutation of the motor drive controller can be effectively reduced, the conduction pressure of a three-phase bridge lower arm MOS switch tube is reduced, and energy consumed from the bus during commutation of the drive controller can be supplemented in time through energy feedback.

Description

Technical Field

[0001] The invention belongs to the field of electronic technology and motor control, and in particular relates to a control method during hard commutation of a motor. Background Art

[0002] BLDC motors are widely used in industry, military, aerospace and other fields. BLDC motor drive controllers are key components of BLDC motor control. At present, mainstream BLDC motor drive controllers are mainly composed of three-phase MOS bridges, Hall commutation logic control and MOS bridge drive components. In some application fields with high mobility requirements, the BLDC drive controller is required to have fast response capabilities, and the servo is required to output extremely large torque. Therefore, the BLDC motor drive controller used in this field generally does not have a separate braking mechanism, but uses reverse drive for hard commutation.

[0003] When the motor drive controller drives the motor in reverse, the bus voltage of the drive controller and the induced electromotive force of the motor winding are in series, and a huge drive current will be formed on the motor winding in a very short time. The driving force generated by the drive current prevents the motor from continuing to rotate in the original direction of rotation. Therefore, this part of the kinetic energy and the energy consumed by the bus current will be completely converted into magnetic energy on the motor winding. If the current of the motor winding continues to increase, the MOS bridge of the motor and the drive controller will eventually burn out. Therefore, when the current reaches a certain threshold value, the current protection circuit of the motor drive controller will cut off the upper arm MOS switch tube of the drive controller, thereby limiting the continuous increase of current on the motor winding.

[0004] In a general BLDC motor drive controller, the lower arm of the MOS bridge is continuously turned on according to the Hall commutation logic control, or is turned on by PWM according to the speed control, which are respectively called the lower arm MOS normally-on mode and the lower arm MOS PWM mode.

[0005] In the lower arm MOS normally-on mode, during hard commutation, the MOS switch tube of the lower arm bears a huge current impact and dissipates energy. At the same time, the motor drive controller needs to obtain a larger current from the bus than during normal drive, resulting in excessive bus power supply pressure. On the contrary, the MOS PWM mode feeds back the kinetic energy of the motor rotor and load to the bus through the body diode, thereby realizing energy recovery. However, for systems that are not powered by secondary rechargeable batteries, when the fed-back energy is too large, it will cause the bus voltage to rise sharply and even cause damage to the power supply system. Therefore, both working modes cannot solve the problem of high working pressure on the drive controller caused by the inertial kinetic energy of the motor rotor and load during hard commutation. Summary of the invention

[0006] The present invention aims to solve the above problems and provides a control method for absorbing kinetic energy and feeding it back to a busbar during hard commutation of a motor.

[0007] The control method for hard commutation of the motor of the present invention performs real-time monitoring, analysis and control on the duty cycle of the speed regulation PWM; When the duty cycle of the speed regulation PWM is greater than a preset threshold, the motor drive controller is switched from the lower arm MOS normal-on mode to the lower arm MOS PWM mode; The closing of the lower arm PWM is delayed so that the closing of the lower arm MOS switch tube is delayed by a time period t compared with the upper arm MOS switch tube. The selection of the time period t is related to the bus energy storage capacitor, the static inductance of the motor winding and the frequency of controlling PWM. Different delay periods have an impact on the bus voltage fluctuation amplitude. The specific selection needs to be determined according to the actual engineering needs. Practitioners in this industry can complete the selection of the time period based on experience and professional knowledge without additional creative work; thereby, the motor drive controller can switch between the lower arm MOS normal mode and the lower arm MOS PWM in a timely manner, which can reduce the drive current obtained by the motor drive controller from the bus during hard commutation, and at the same time reduce the conduction pressure of the lower arm MOS switch tube of the three-phase bridge. Energy feedback can timely replenish the energy consumed from the bus when commutating the drive controller.

[0008] Furthermore, in the control method for hard commutation of the motor described in the present invention, the process of delaying the shutdown of the lower arm PWM includes: when the falling edge of the speed regulation PWM arrives, or when the driving current reaches the protection threshold due to hard commutation, the V-phase upper arm MOS switch tube is immediately turned off according to the driving control signal, and the U-phase lower arm MOS switch tube is turned off after a delay of a time period t.

[0009] Furthermore, in the control method for hard commutation of the motor described in the present invention, when the V-phase upper arm MOS switch tube is turned off and the U-phase lower arm MOS switch tube has not yet been turned off, the working state of the motor drive controller is the same as the state of the lower arm MOS normally-on mode, and the kinetic energy of the motor rotor forms a loop through the body diodes of the U-phase lower arm MOS switch tube and the V-phase lower arm MOS switch tube, and the energy is consumed in the internal resistance of the motor winding, the internal resistance of the MOS switch tube, the body diode of the V-phase lower arm MOS switch tube, and the resistance in the loop.

[0010] Furthermore, in the control method for hard commutation of the motor described in the present invention, after the U-phase lower arm MOS switch tube is delayed for a time period t and turned off, the working state of the motor drive controller is the same as the working state of the lower arm MOS PWM mode. If the inertial kinetic energy of the motor rotor and the load has not been completely discharged, or the magnetic energy stored in the motor winding has not been completely discharged, the body diode of the U-phase upper arm MOS switch tube and the body diode of the V-phase lower arm MOS switch tube form a loop, and the inertial kinetic energy of the motor rotor and the load and the magnetic energy stored in the motor winding feed back energy to the bus through the loop.

[0011] The control method for motor hard commutation of the present invention monitors the duty cycle of the speed regulation PWM. When the speed is high, the motor drive controller will switch to the lower arm MOS PWM mode, or when the motor is hard commutated, it is necessary to quickly switch the rotation direction of the motor, and the speed regulation PWM is also in a high duty cycle state. At this time, the motor will also switch to the lower arm MOS PWM mode. At this time, the shutdown of the lower arm MOS switch tube lags behind the shutdown of the upper arm MOS switch tube by a time period t, so that the motor drive controller can switch between the lower arm MOS normally-on mode and the lower arm MOS PWM in a timely manner, which can effectively reduce the drive current obtained by the motor drive controller from the bus during hard commutation, reduce the conduction pressure of the lower arm MOS switch tube of the three-phase bridge, and energy feedback can timely replenish the energy consumed from the bus when the commutation drive controller is used. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a schematic diagram of the principle of the control method for hard commutation of a motor according to an embodiment of the present invention; Figure 2 This is a schematic diagram of current flow when the forward drive and PWM are at a high level according to an embodiment of the present invention; Figure 3 A schematic diagram of the current flow direction of the lower arm MOS normally-on mode when the forward drive and PWM are at a low level according to an embodiment of the present invention; Figure 4 A schematic diagram of the current flow direction of the lower arm MOS PWM mode when the forward drive and PWM are at a low level according to an embodiment of the present invention; Figure 5 A schematic diagram of current flow when reverse driving after commutation and PWM is at a high level according to an embodiment of the present invention; Figure 6 A schematic diagram of the current flow direction of the lower arm MOS in the normally-on mode when reverse driving after commutation and PWM is at a low level according to an embodiment of the present invention; Figure 7 A schematic diagram of current flow in the lower arm MOS PWM mode when reverse driving after commutation and PWM is at a low level according to an embodiment of the present invention; Figure 8It is a schematic diagram of the principle of low-side PWM operation according to an embodiment of the present invention; Among them, E ω represents the induced electromotive force of the motor winding, the U-phase end is positive and the V-phase end is negative; VCC is the power supply bus voltage, GND is the power supply bus ground loop; UH and HL are the U-phase upper arm MOS switch tube and lower arm switch tube respectively; VH and VL are the V-phase upper arm switch tube and lower arm switch tube respectively; Moto is the motor. DETAILED DESCRIPTION

[0013] The control method for hard commutation of the motor according to the present invention is described in detail below through the accompanying drawings and embodiments.

[0014] The specific implementation principle of the control method for hard commutation of the motor described in this embodiment is as follows: Figure 1 As shown, for the BLDC motor drive controller, the Hall commutation logic operation circuit, the MOS drive signal generation circuit, the three-phase MOS bridge and the current protection circuit are all conventional necessary circuits. The present invention does not adjust these circuits, but only improves the control PWM of the lower arm MOS switch tube, that is, the control method for hard commutation of the motor described in this embodiment is realized through low-side PWM operation.

[0015] Usually, the three-phase MOS bridge of the BLDC driver is composed of three MOS half-bridges, namely U phase, V phase and W phase, each of which is composed of an upper arm MOS switch tube and a lower arm MOS switch tube. The U, V, W three-phase half-bridges and the Hall sensors Ha, Hb and Hc of the BLDC motor correspond one to one. The BLDC motor drive controller performs decoding operations based on the motor rotor position information collected by the Hall sensor, and turns on the upper arm MOS switch tube or the lower arm MOS switch tube of the three-phase MOS bridge according to a certain logical relationship to replace the brush in the brushed motor to achieve commutation operation. If speed adjustment is required, PWM can be used to modulate the conduction time of the upper arm or lower arm MOS switch tube to achieve speed or torque control of the BLDC motor.

[0016] The Hall commutation logic relationship has little to do with the change in motor current when the speed regulation PWM works, and it only controls the operation of different MOS switches. In order to simplify the description, this embodiment is described with a fixed Hall commutation relationship unless otherwise specified, that is, the current Hall commutation relationship is: when the drive rotates forward, the commutation logic is that the current flows from phase U to phase V, such as Figure 2 As shown, the U-phase upper arm MOS switch tube and the V-phase lower arm MOS switch tube are turned on, the U-phase lower arm MOS switch tube and the V-phase upper arm MOS switch tube are turned off, and VCC drives the motor to rotate forward after overcoming Eω; when driving reverse rotation, the commutation logic is that the current flows from the V phase to the U phase.

[0017] Usually, the PWM control method of the BLDC motor drive controller adopts the upper arm MOS switch tube to control the opening and closing according to the speed regulation PWM, and the lower arm MOS switch tube can be selected to be continuously turned on during the commutation cycle, which is called the lower arm MOS normally-on mode; the control method in which the lower arm MOS is turned on and off according to the speed regulation PWM is called the lower arm MOS PWM mode.

[0018] The motor winding has a certain inductance. When current flows through the winding, an inductor energy storage effect is generated. During commutation, or when the speed regulation PWM control turns off the upper arm MOS switch tube, the current on the inductor cannot change suddenly. Therefore, at the node where the MOS switch tube is turned off, a freewheeling diode is required to discharge the current on the inductor. Power MOS devices are usually used as motor drive control power devices. Since the MOS's own diode can achieve freewheeling, there is no need to add additional diodes for freewheeling.

[0019] In actual applications, there are also motor drive controllers that use IGBT as a power device. When IGBT is used as a power device, an additional diode needs to be added for freewheeling. There is no essential difference in the use of these two types of power devices. Therefore, in this embodiment, the use of IGBT power devices is not separately described, and only the motor drive controller using MOS as the power device is described. Such description will not affect the control measures used in the present invention and its ultimate control effect.

[0020] When the motor rotates normally, the rotation of the rotor will generate an induced electromotive force on the motor winding, which is opposite to the direction of the driving voltage. The higher the speed, the higher the induced electromotive force. Under the same conditions, the current flowing through the winding is also smaller. Normally, the induced electromotive force of the motor winding will not be higher than the supply voltage of the drive controller bus.

[0021] When the motor drive controller works in the lower arm MOS normally on mode, when the speed regulation PWM is at a high level, the U-phase upper arm MOS switch tube is turned on, and the V-phase lower arm MOS switch tube is also in the on state, and remains on continuously during the Hall commutation cycle; when the speed regulation PWM is converted to a low level, the U-phase upper arm MOS switch tube is turned off, and the current in the motor winding continues to flow in the original direction until the magnetic energy stored in the motor winding is consumed. Figure 3 As shown in the figure, in this case, the V-phase lower arm MOS is in the normally on mode, and the energy stored in the motor winding needs to overcome the induced electromotive force Eω generated by the motor winding, and form a loop through the body diode of the U-phase lower arm MOS switch tube for freewheeling, further converting the magnetic energy stored in the motor winding into kinetic energy for the rotation of the motor rotor, and continuing to drive the motor to rotate in the forward direction.

[0022] When the motor drive controller works in the lower arm MOS PWM mode, when the speed PWM is high, the U-phase upper arm MOS switch tube is turned on, and the V-phase lower arm MOS switch tube is turned on at the same time; when the speed PWM is converted to a low level, the U-phase upper arm MOS switch tube will be turned off, and the V-phase lower arm MOS switch tube is also controlled to be turned off; at this time, the current in the motor winding continues to flow in the original direction until the magnetic energy stored in the motor winding is consumed. In this case, if Figure 4 As shown, the energy stored in the motor winding needs to overcome the induced electromotive force Eω generated by the motor winding, and a loop is formed through the body diode of the U-phase lower arm MOS switch tube and the body diode of the V-phase upper arm MOS switch tube for continuous flow, so as to feed back energy to the bus, and divide the magnetic energy stored in the motor winding into two parts. One part is converted into the kinetic energy of the motor rotor rotation to drive the motor to continue to rotate in the forward direction, and the other part is fed back to the bus.

[0023] Therefore, during normal rotation, when the lower arm MOS normally-on mode is driven by the speed regulation PWM with the same duty cycle, the proportion of electrical energy converted into kinetic energy is higher than that of the lower arm MOS PWM mode, especially when the rotation is at low speed or the speed regulation PWM duty cycle is relatively small; the advantage of the lower arm MOS PWM mode is that through the body diode of the MOS switch tube, energy feedback can be achieved, the power supply pressure of the bus can be reduced, and the working pressure of the lower arm MOS switch tube can also be reduced.

[0024] When the motor drive controller performs hard commutation, the drive current after commutation flows from phase V to phase U. Due to the inertia of the motor rotor and the inertia of the load, the motor rotor still rotates in the original direction of rotation, and the polarity of the induced electromotive force in the motor winding remains consistent with that before commutation until the motor speed drops to 0.

[0025] When the motor drive controller works in the lower arm MOS normally on mode, when PWM is high level, after hard commutation, the V upper arm MOS switch tube and the U phase lower arm MOS switch tube are both in the on state, such as Figure 5 As shown, the induced electromotive force of the motor winding and VCC are superimposed in series and loaded onto the motor winding. After the current passes through the winding, the motor is prevented from rotating in the forward direction. The energy provided by the busbar and the reduced kinetic energy of the motor rotor and load are all converted into magnetic energy in the motor winding.

[0026] At this time, the bus voltage and the induced electromotive force of the motor winding are in the same direction, which is a series relationship. After the voltage of the two is superimposed and acts on the motor winding, the current of the motor winding will increase sharply. Maintaining this state for a long time will cause the motor drive controller and the motor to burn out. Usually, the motor drive controller will be equipped with an overcurrent protection circuit. When the bus current rises sharply and exceeds a certain threshold, the protection circuit will turn off the speed regulation PWM signal, and then turn off the V-phase upper arm MOS switch tube. Since the current in the motor winding cannot change suddenly, the energy stored in the winding will continue to make the current flow in the original direction under the action of the inductor. At this time, the voltage generated by the inductor and the induced electromotive force on the motor winding are in the same direction and are in a series relationship. After superposition, the body diodes of the U-phase lower arm MOS switch tube and the V-phase lower arm MOS switch tube form a loop, such as Figure 6 As shown, in this current loop, except for the body diode of the MOS switch tube that will produce a conduction voltage drop, the other parts in the loop are all resistance characteristics (the inductance characteristics and the voltage generated by the induced electromotive force of the winding have been considered in the total voltage after series connection). When the motor rotates at high speed, the induced electromotive force in the winding is close to the bus voltage. After being connected in series with the induced voltage generated by the winding inductance, the total voltage is much higher than the bus voltage, and the DC resistance of the motor winding and the resistance of the connecting cable are very small. The superimposed voltage instantly generates a huge loop current, and the magnetic energy stored in the winding is converted into heat energy and consumed; therefore, when the hard commutation is at a low level of the speed regulation PWM or the overcurrent protection circuit is in effect, it works in the lower arm MOS normally on mode, and a large phase current will be formed in the loop of the lower arm MOS switch tube. This current is often several to dozens of times the normal working current. In order to prevent the power device from being damaged due to overcurrent, overheating and other factors during the hard commutation process, the motor drive controller often needs to reserve a larger working margin for the power device when designing.

[0027] When the motor drive controller works in the lower arm MOS PWM mode, when PWM is high level, after hard commutation, the V-phase upper arm MOS switch tube and the U-phase lower arm MOS switch tube are both in the on state. At this time, the polarity of the bus voltage and the induced electromotive force of the motor winding are in a series relationship. The superposition of the two voltages acts on the motor winding, which will cause the current of the motor winding to rise sharply. When the bus current rises sharply and exceeds a certain threshold, such as Figure 7As shown, the protection circuit turns off the speed regulation PWM signal, and then turns off the V-phase upper arm MOS switch tube and the U-phase lower arm MOS switch tube. Since the current in the motor winding cannot change suddenly, the energy stored in the winding will continue to make the current flow in the original direction under the action of the inductor. At this time, the voltage generated by the inductor and the induced electromotive force on the motor winding are in the same direction and are in a series relationship. The body diode of the U-phase upper arm MOS switch tube and the body diode of the V-phase lower arm MOS switch tube are used for continuous flow to form a loop. In this current loop, the induced electromotive force in the winding and the induced voltage generated by the winding inductance are connected in series to feed back energy to the bus. Obviously, when the motor drive controller works in the lower MOS PWM mode, the induced electromotive force generated by the motor rotor winding will not exceed the bus voltage. The current of energy feedback during hard commutation mainly depends on the magnetic energy stored in the motor winding inductance and the inductance of the motor winding. In this mode, the current flowing through the winding is much smaller than when the motor drive controller works in the lower arm MOS normally on mode. Therefore, the lower arm MOS PWM mode has much lower requirements on the power dissipation and overcurrent capacity of the power devices of the motor drive controller.

[0028] The lower arm MOS PWM mode will cause the kinetic energy of the motor rotor and load inertia during hard commutation to be fed back to the bus when the speed regulation PWM is at a low level. When the kinetic energy is large, the fed-back energy will increase the bus voltage. For some application scenarios, reverse current is not allowed to flow into the power supply bus, so the bus voltage is not allowed to increase too much; the increase in bus voltage will also lead to higher voltage resistance requirements for power devices and other components of the motor driver.

[0029] This embodiment combines the working characteristics of the lower arm MOS normally-on mode and the lower arm MOS PWM mode to perform real-time monitoring, analysis and control of the duty cycle of the speed regulation PWM; when the duty cycle of the speed regulation PWM is greater than a preset threshold, the motor drive controller is switched from the lower arm MOS normally-on mode to the lower arm MOS PWM mode; the shutdown of the lower arm PWM is delayed so that the shutdown of the lower arm MOS switch tube is delayed by a time period t compared with the upper arm MOS switch tube.

[0030] When the falling edge of the speed regulation PWM arrives, or the driving current reaches the protection threshold due to hard commutation, the V-phase upper arm MOS switch tube is immediately turned off according to the driving control signal, and the U-phase lower arm MOS switch tube is turned off after a delay of a time period t; during the period when the V-phase upper arm MOS switch tube is turned off and the U-phase lower arm MOS switch tube has not yet been turned off, the working state of the motor drive controller is the same as the state of the lower arm MOS normally on mode, and the kinetic energy of the motor rotor forms a loop through the body diodes of the U-phase lower arm MOS switch tube and the V-phase lower arm MOS switch tube, and the energy is consumed in the internal resistance of the motor winding, the internal resistance of the MOS switch tube, the body diode of the V-phase lower arm MOS switch tube, and the resistance in the loop; after the U-phase lower arm MOS switch tube is delayed for a time period t and turned off, the working state of the motor drive controller is the same as the state of the lower arm MOS The working state of the PWM mode is the same. If the inertial kinetic energy of the motor rotor and the load has not been completely discharged, or the magnetic energy stored in the motor winding has not been completely discharged, the body diode of the U-phase upper arm MOS switch tube and the body diode of the V-phase lower arm MOS switch tube form a loop, and the inertial kinetic energy of the motor rotor and the load and the magnetic energy stored in the motor winding feed back energy to the bus through the loop.

[0031] In the embodiments of the present disclosure, Figure 8 As shown, discrete components are used to implement Figure 1 The low-side PWM operation shown in the figure completes the detection of the PWM duty cycle and the low-side PWM shutdown delay; PWM_Hi is the high-side PWM control signal of the motor drive controller. Usually, the current protection circuit constrains the input PWM, that is, the input PWM will be cut off during overcurrent protection. The constrained signal is PWM_Hi, which is used to drive the upper-arm MOS switch tube of the three-phase MOS bridge after performing an AND operation with the upper-arm drive signal output by the Hall commutation logic. PWM_Low is the low-side PWM drive signal. After the PWM_Low signal and the lower-arm drive signal output by the Hall commutation logic are ANDed, it is used to drive the lower-arm MOS switch tube of the three-phase MOS bridge.

[0032] like Figure 8As shown, R1 and C1 form a low-pass filter to perform simple filtering on PWM_Hi. The time constant is appropriately selected so that the input PWM_Hi becomes a DC level with smaller pulsation after filtering. The level is proportional to the duty cycle of PWM_Hi. The Schmitt trigger of U1 is used to detect the level. When the input level is higher than the high-level flip threshold of the Schmitt trigger, U1 outputs a low level. When the input level is lower than the low-level flip threshold of the Schmitt trigger, U1 outputs a high level. D1, D2 and R2 form an OR gate logic. When the outputs of PWM_Hi and U1 have a high level, the input of U2 is a high level. Therefore, when the duty cycle of PWM_Hi is higher than a certain threshold, the input of U2 is the same as PWM_Hi. When the duty cycle of PWM_Hi is lower than a certain threshold, the input of U2 is always a high level, thereby realizing the detection of PWM pulse width.

[0033] C2 is used for delay. When the input of U2 is converted to a high level, D1 or D2 is directly turned on to charge C2. There is no delay on the rising edge of U2. When the left ends of D1 and D2 are all flipped to a low level, C2 can only discharge through R2. After being shaped by the Schmitt trigger of U2, a falling edge lags behind a certain time period at the output end. The lag time is related to the low-level flip threshold of U2 and the time constant of R2 and C2. By adjusting the parameters appropriately, the required lag time period can be obtained.

[0034] The PWM_Low and PWM_Hi output by U2 are related to the duty cycle of its input. When the duty cycle is less than a certain threshold, PWM_Low outputs a normally high level. When the PWM_Hi duty cycle is higher than a certain threshold, the rising edge of PWM_Low is synchronized with PWM_Hi, and the falling edge of PWM_Low lags behind the falling edge of PWM_Hi.

[0035] The control method for hard commutation of the motor described in this embodiment can be realized by performing an AND operation on PWM_Low and the upper arm drive signal output by the Hall commutation logic and then using the signal to drive the lower arm MOS switch tube of the three-phase MOS bridge.

[0036] Obviously, the described embodiments are only some embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention.

Claims

1. A control method for hard commutation of a motor, characterized in that: Real-time monitoring, analysis and control of the duty cycle of the speed regulation PWM; When the duty cycle of the speed regulation PWM is greater than a preset threshold, the motor drive controller is switched from the lower arm MOS normal-on mode to the lower arm MOS PWM mode; The closing of the lower arm PWM is delayed so that the closing of the lower arm MOS switch tube is delayed by a time period t compared with the closing of the upper arm MOS switch tube.

2. The control method for hard commutation of a motor according to claim 1, characterized in that: The process of delaying the shutdown of the lower arm PWM includes: when the falling edge of the speed regulation PWM arrives, or when the driving current reaches the protection threshold due to hard commutation, the V-phase upper arm MOS switch tube is immediately turned off according to the driving control signal, and the U-phase lower arm MOS switch tube is turned off after a delay of a time period t.

3. The control method for hard commutation of a motor according to claim 2, characterized in that: During the period when the V-phase upper arm MOS switch tube is turned off and the U-phase lower arm MOS switch tube has not yet been turned off, the working state of the motor drive controller is the same as the state of the lower arm MOS normally-on mode, and the kinetic energy of the motor rotor forms a loop through the body diodes of the U-phase lower arm MOS switch tube and the V-phase lower arm MOS switch tube, and the energy is consumed in the internal resistance of the motor winding, the internal resistance of the MOS switch tube, the body diode of the V-phase lower arm MOS switch tube, and the resistance in the loop.

4. The control method for hard commutation of a motor according to claim 2, characterized in that: After the U-phase lower arm MOS switch tube is delayed for a time period t and turned off, the working state of the motor drive controller is the same as the working state of the lower arm MOS PWM mode. If the inertial kinetic energy of the motor rotor and the load has not been completely discharged, or the magnetic energy stored in the motor winding has not been completely discharged, the body diode of the U-phase upper arm MOS switch tube and the body diode of the V-phase lower arm MOS switch tube form a loop, and the inertial kinetic energy of the motor rotor and the load and the magnetic energy stored in the motor winding feed back energy to the bus through the loop.

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