CN112865616B - PWM control method for inhibiting torque ripple of brushless direct current motor - Google Patents

Abstract

The invention discloses a PWM control method for suppressing torque ripple of a brushless direct current motor. When the brushless direct current motor works in a 120-degree two-phase conduction mode, by inverting the non-conductive phase in the brushless direct current motor control system The bridge switch tube and the conductive phase inverter bridge switch tube perform complementary PWM control, so that the average current of the non-conductive phase freewheeling current is greatly reduced; the advantages are that the switching loss is small, the current fluctuation is small, and there is no need to detect the over-voltage of the back EMF. At the same time of zero point, low cost and simple control, it can significantly reduce the average current of non-conducting phase freewheeling, greatly improve the torque ripple of brushless DC motor caused by non-conducting phase freewheeling, and greatly improve the brushless DC motor. Control performance of DC motors.

Description

A PWM Control Method for Suppressing Torque Ripple of Brushless DC Motor

technical field

The invention relates to a PWM control method, in particular to a PWM control method for suppressing torque ripple of a brushless DC motor.

Background technique

Brushless DC motors and their control systems are widely used in various fields due to their advantages of good speed regulation performance, high efficiency, simple control and low cost. The brushless DC motor control system is usually implemented with a three-phase full-bridge inverter structure. The existence of torque ripple greatly affects the control performance of the brushless DC motor. Especially when running at low speed, equipment noise and vibration are caused by torque ripple. , so the torque ripple suppression technology has always been a hot issue in the study of brushless DC motors.

The torque ripple of brushless DC motor is divided into torque ripple caused by commutation and torque ripple caused by non-conducting phase freewheeling. The torque ripple caused by commutation can be improved by the current loop control method, and the torque ripple caused by the non-conducting phase freewheeling is related to the PWM modulation method. When the brushless DC motor works in the 120-degree two-phase conduction mode, there are six common PWM modulation modes: ⑴PWM_ON; ⑵ON_PWM; ⑶H_PWM_L_ON; ⑷H_ON_L_PWM; ⑸H_PWM_L_PWM; ⑹PWM_ON_PWM. These 6 PWM modulation methods are all unipolar control (only one switch is used for PWM control on the upper and lower switches of the same bridge arm, and the other switch is always off), and these 6 PWM modulation methods have corresponding bipolar PWM modulation (that is, PWM complementary control is performed at the same time with the upper and lower switches of the bridge arm), the torque ripple caused by the non-conducting phase freewheeling of each bipolar PWM modulation mode is similar to its corresponding unipolar PWM modulation mode. Among the above 6 PWM modulation methods, H_PWM_L_PWM and PWM_ON_PWM do not have non-conducting phase freewheeling, but H_PWM_L_PWM has the disadvantages of large switching loss and large current fluctuation. PWM_ON_PWM needs to detect the zero-crossing point of the back EMF, the cost is relatively high, and the control is complicated. Therefore, these two modulation methods are rarely used and are not suitable for popularization and application. PWM_ON, ON_PWM, H_PWM_L_ON, H_ON_L_PWM have the advantages of small switching loss, small current fluctuation, no need to detect the zero-crossing point of back EMF, relatively low cost and simple control, and are currently mainly used several PWM modulation methods. However, as shown in Table 1, the four modulation methods of PWM_ON, ON_PWM, H_PWM_L_ON, and H_ON_L_PWM all have non-conductive phase freewheeling, and the control performance of the brushless DC motor still has a large room for improvement.

Table 1 Non-conducting phase freewheeling interval under four PWM modulation modes

In Table 1, (+) indicates that a positive freewheeling current flows in the non-conducting phase winding, (-) indicates that a negative freewheeling current flows in the non-conducting phase winding, and × indicates that there is no freewheeling current.

SUMMARY OF THE INVENTION

The technical problem to be solved by the present invention is to provide a PWM control method for suppressing the torque ripple of a brushless DC motor. At the same time, it can significantly reduce the average current of the non-conducting phase freewheeling current, greatly improve the torque ripple of the brushless DC motor caused by the non-conducting phase freewheeling current, and greatly improve the control performance of the brushless DC motor.

The technical solution adopted by the present invention to solve the above technical problems is: a PWM control method for suppressing the torque ripple of the brushless DC motor. When the brushless DC motor works in the 120-degree two-phase conduction mode, In the control system, the non-conducting phase inverter bridge switch tube and the conductive phase inverter bridge switch tube perform complementary PWM control, so that the average current of the non-conducting phase freewheeling current is greatly reduced.

During the conduction period of two phases in the brushless DC motor control system, under the condition that the switch tube of the upper bridge arm of the inverter bridge of the current inflow phase is turned on, and the switch tube of the lower bridge arm of the inverter bridge of the current outflow phase is PWM controlled, the non-conduction phase is controlled by PWM. The switch tube of the upper arm of the inverter bridge performs PWM control complementary to the switch tube of the lower arm of the inverter bridge of the current outflow phase, and the dead time is set; during the conduction period of two phases in the brushless DC motor control system, the When the switch tube of the upper arm of the inverter bridge is controlled by PWM, and the switch tube of the lower arm of the inverter bridge of the current outflow phase is turned on, the switch tube of the lower arm of the non-conducting phase inverter bridge is connected to the upper bridge of the inverter bridge of the non-conducting phase. Complementary PWM control of arm switches and set dead time.

Compared with the prior art, the advantage of the present invention is that when the brushless DC motor works in the 120-degree two-phase conduction mode, the non-conductive phase inverter bridge switch tube in the brushless DC motor control system is connected with the conduction phase. The inverter bridge switch tube performs complementary PWM control, so that the average current of the non-conducting phase freewheeling current is greatly reduced, thereby improving the torque ripple of the brushless DC motor caused by the non-conducting phase freewheeling current. It has the advantages of small switching loss, small current fluctuation, no need to detect the zero-crossing point of back EMF, low cost and simple control. The torque pulsation of the brushless DC motor caused by the current can greatly improve the control performance of the brushless DC motor.

Description of drawings

1 is a circuit diagram of a brushless DC motor control system of a PWM control method for suppressing torque ripple of a brushless DC motor according to the present invention;

FIG. 2 is a waveform diagram 1 of the PWM control method for suppressing the torque ripple of the brushless DC motor according to the present invention;

3 is a waveform diagram 2 of the PWM control method for suppressing the torque ripple of the brushless DC motor according to the present invention;

Fig. 4 is the PWM waveform that adopts the existing method of H_PWM_L_ON modulation mode;

Fig. 5 is the PWM waveform that adopts H_PWM_L_ON modulation mode in conjunction with the PWM control method of the present invention;

FIG. 6 is a phase current waveform diagram of a brushless DC motor using an existing method of H_PWM_L_ON modulation;

FIG. 7 is a phase current waveform diagram of a brushless DC motor using the H_PWM_L_ON modulation method combined with the PWM control method of the present invention.

Detailed ways

The present invention will be further described in detail below with reference to the embodiments of the accompanying drawings.

Embodiment: A PWM control method for suppressing torque ripple of a brushless DC motor. When the brushless DC motor works in a 120-degree two-phase conduction mode, the non-conducting phase inverter bridge in the brushless DC motor control system is controlled. The complementary PWM control of the switch tube and the conduction-phase inverter bridge switch tube can greatly reduce the average current of the non-conductive phase freewheeling current, thereby improving the torque ripple of the brushless DC motor caused by the non-conducting phase freewheeling current. , to greatly improve the control performance of the brushless DC motor.

In this embodiment, during the conduction period of two phases in the brushless DC motor control system, in the case that the current inflow phase inverter bridge upper arm switch tube is turned on, and the current outflow phase inverter bridge lower arm switch tube performs PWM control, Perform PWM control complementary to the switch tube of the upper arm of the non-conducting phase inverter bridge and the switch tube of the lower arm of the inverter bridge of the current outflow phase, and set the dead time; in the brushless DC motor control system, during the conduction period of two phases , when the current inflow phase inverter bridge upper arm switch tube is PWM controlled, and the current outflow phase inverter bridge lower arm switch tube is turned on, the non-conducting phase inverter bridge lower arm switch tube is connected to the current inflow phase. Complementary PWM control of the switch tube of the upper arm of the inverter bridge, and set the dead time.

The brushless DC motor is a three-phase brushless DC motor with A-phase, B-phase and C-phase. Correspondingly, the structure of the brushless DC motor control system is a three-phase full-bridge inverter, and its circuit diagram is shown in Figure 1. In Figure 1, the switch VT1, the switch VT4, the diode VD1 and the diode VD4 constitute the A-phase inverter bridge of the three-phase full-bridge inverter, and the switch VT3, the switch VT6, the diode VD3 and the diode VD6 constitute the three-phase full bridge. The B-phase inverter bridge of the inverter, the switch tube VT5, the switch tube VT2, the diode VD5 and the diode VD2 constitute the C-phase inverter bridge of the three-phase full-bridge inverter, V _a is the voltage of A relative to ground, and V _b is B Phase-to-ground voltage, V _c is the relative-to-ground voltage of C, i _a is the A-phase current, i _b is the B-phase current, _ic is the C-phase current, e _a is the A opposite electromotive force, e _b is the B opposite electromotive force, e _c is the opposite electromotive force of C, R is the stator winding resistance, L is the equivalent inductance of the stator winding, V _n is the central node voltage of the armature winding of the brushless DC motor, and U _dc is the DC bus voltage. The implementation method of the present invention applied to the brushless DC motor control system is described as follows:

When the A-B phase is energized, during this period, the C phase is a non-conducting phase, the C-phase inverter bridge is a non-conducting phase inverter bridge, the switch tube VT5 is a non-conducting phase inverter bridge upper arm switch tube, and VT2 is a non-conducting phase inverter bridge. The switch tube of the lower bridge arm of the on-phase inverter bridge, the A-phase and the B-phase are two conductive phases. There are two situations at this time. The first situation is that the current flows from the A-phase into the B-phase and flows out, and the A-phase is the current inflow. Phase, B phase is the current outflow phase, A phase inverter bridge is the current inflow phase inverter bridge, B phase inverter bridge is the current outflow phase inverter bridge, switch tube VT1 is the current inflow phase inverter bridge upper arm switch tube , the switch tube VT4 is the switch tube of the lower bridge arm of the current inflow phase inverter bridge, the switch tube VT3 is the switch tube of the upper bridge arm of the current outflow phase inverter bridge, and the switch tube VT6 is the switch tube of the lower bridge arm of the current outflow phase inverter bridge. The two cases are that the current flows from the B phase into the A phase, the A phase is the current outflow phase, the B phase is the current inflow phase, the A phase inverter bridge is the current outflow phase inverter bridge, and the B phase inverter bridge is the current inflow phase reverse. Switching bridge, the switch tube VT1 is the switch tube of the upper arm of the current outflow phase inverter bridge, the switch tube VT4 is the switch tube of the lower arm arm of the current outflow phase inverter bridge, and the switch tube VT3 is the switch tube of the upper arm arm of the current inflow phase inverter bridge , the switch tube VT6 is the switch tube of the lower bridge arm of the current inflow phase inverter bridge. In the first case, if the switch tube VT1 is turned on, the switch tube VT6 performs PWM control with a set duty cycle. In this PWM control mode, the method of the present invention controls the non-conductive phase inverter bridge lower bridge The arm switch VT2 is turned off, and the upper arm switch VT5 of the non-conducting phase inverter bridge is controlled for PWM control, and a complementary PWM output control mode is formed with the switch VT6 (the appropriate dead time needs to be set according to the actual use situation) , The waveform diagram of PWM control of the switch VT5 and the switch VT6 is shown in Figure 2; if the switch VT1 is PWM controlled with the set duty cycle, the switch VT6 is turned on. Under this PWM control mode, The method of the invention controls the switch tube VT5 of the upper bridge arm of the non-conducting phase inverter bridge to be turned off, controls the switch tube VT2 of the lower bridge arm of the non-conducting phase inverter bridge to perform PWM control, and forms a complementary PWM output control mode with the switch tube VT1 (According to the actual use, it is necessary to set an appropriate dead time), and the waveform of the PWM control of the switch VT1 and the switch VT2 is shown in Figure 3. In the second case, if the switch tube VT3 is turned on, the switch tube VT4 performs PWM control with a set duty cycle. In this PWM control mode, the method of the present invention controls the non-conductive phase inverter bridge lower bridge The arm switch VT2 is turned off, and the upper arm switch VT5 of the non-conducting phase inverter bridge is controlled for PWM control, and a complementary PWM output control mode is formed with the switch VT4 (the appropriate dead time needs to be set according to the actual use situation) If the switch tube VT3 performs PWM control with the set duty ratio, the switch tube VT4 is turned on, and under this PWM control mode, the method of the present invention controls the non-conduction phase inverter bridge upper bridge arm switch tube VT5 to be turned off , control the switch tube VT2 of the lower arm of the non-conducting phase inverter bridge to perform PWM control, and form a complementary PWM output control mode with the switch tube VT3 (set appropriate dead time according to actual use needs).

When the A-C phase is energized, during this period, the B phase is a non-conducting phase, the B-phase inverter bridge is a non-conducting phase inverter bridge, the switch tube VT3 is the non-conducting phase inverter bridge upper arm switch tube, and VT6 is a non-conducting phase inverter bridge. The switch tube of the lower bridge arm of the on-phase inverter bridge, the A-phase and the C-phase are two conductive phases. There are two situations at this time. The first situation is that the current flows from the A-phase into the C-phase and flows out, and the A-phase is the current inflow. Phase, C-phase is the current outflow phase, A-phase inverter bridge is the current inflow-phase inverter bridge, C-phase inverter bridge is the current outflow-phase inverter bridge, and switch tube VT1 is the current inflow-phase inverter bridge upper arm switch tube , the switch tube VT4 is the switch tube of the lower bridge arm of the current inflow phase inverter bridge, the switch tube VT5 is the switch tube of the upper bridge arm of the current outflow phase inverter bridge, and the switch tube VT2 is the switch tube of the lower bridge arm of the current outflow phase inverter bridge. The two cases are that the current flows from the C phase into the A phase, the A phase is the current outflow phase, the C phase is the current inflow phase, the A phase inverter bridge is the current outflow phase inverter bridge, and the C phase inverter bridge is the current inflow phase reverse. Switching bridge, switch tube VT1 is the switch tube of the upper bridge arm of the current outflow phase inverter bridge, switch tube VT4 is the switch tube of the lower bridge arm of the current outflow phase, and switch tube VT5 is the switch tube of the upper bridge arm of the current inflow phase inverter bridge , the switch tube VT2 is the switch tube of the lower bridge arm of the current inflow phase inverter bridge. In the first case, if the switch VT1 is turned on, the switch VT2 performs PWM control with a set duty cycle. In this PWM control mode, the method of the present invention controls the non-conducting phase inverter bridge lower bridge The arm switch VT6 is turned off, and the upper arm switch VT3 of the non-conducting phase inverter bridge is controlled for PWM control, and a complementary PWM output control mode is formed with the switch VT2 (the appropriate dead time needs to be set according to the actual use situation) ; If the switch tube VT1 is PWM controlled with the set duty ratio, the switch tube VT2 is turned on, in this PWM control mode, the method of the present invention controls the non-conduction phase inverter bridge upper arm switch tube VT3 to be turned off , control the switch tube VT6 of the lower arm of the non-conducting phase inverter bridge to perform PWM control, and form a complementary PWM output control mode with the switch tube VT1 (set appropriate dead time according to the actual use situation). In the second case, if the switch tube VT5 is turned on, the switch tube VT4 performs PWM control with a set duty ratio. In this PWM control mode, the method of the present invention controls the non-conductive phase inverter bridge lower bridge The arm switch VT6 is turned off, and the upper arm switch VT3 of the non-conducting phase inverter bridge is controlled for PWM control, and a complementary PWM output control mode is formed with the switch VT4 (the appropriate dead time needs to be set according to the actual use situation) If the switch tube VT5 performs PWM control with the set duty ratio, the switch tube VT4 is turned on, and under this PWM control mode, the method of the present invention controls the non-conduction phase inverter bridge upper arm switch tube VT3 to be turned off , control the switch tube VT6 of the lower arm of the non-conducting phase inverter bridge to perform PWM control, and form a complementary PWM output control mode with the switch tube VT5 (set appropriate dead time according to the actual use situation).

When the B-C phase is energized, during this period, the A phase is a non-conducting phase, the A-phase inverter bridge is a non-conducting phase inverter bridge, the switch tube VT1 is a non-conducting phase inverter bridge upper arm switch tube, and VT4 is a non-conducting phase inverter bridge. The switch tube of the lower bridge arm of the on-phase inverter bridge, the B-phase and the C-phase are two on-phase phases. At this time, there are two situations. The first situation is that the current flows from the B-phase into the C-phase and flows out, and the B-phase is the current inflow. Phase, C-phase is the current outflow phase, B-phase inverter bridge is the current inflow-phase inverter bridge, C-phase inverter bridge is the current outflow-phase inverter bridge, and switch tube VT3 is the current inflow-phase inverter bridge upper arm switch tube , the switch tube VT6 is the switch tube of the lower bridge arm of the current inflow phase inverter bridge, the switch tube VT5 is the switch tube of the upper bridge arm of the current outflow phase inverter bridge, and the switch tube VT2 is the switch tube of the lower bridge arm of the current outflow phase inverter bridge. The two cases are that the current flows from the C phase into the B phase, the B phase is the current outflow phase, the C phase is the current inflow phase, the B phase inverter bridge is the current outflow phase inverter bridge, and the C phase inverter bridge is the current inflow phase reverse. Switching bridge, switch tube VT3 is the switch tube of the upper bridge arm of the current outflow phase inverter bridge, switch tube VT6 is the switch tube of the lower arm arm of the current outflow phase inverter bridge, switch tube VT5 is the switch tube of the upper bridge arm of the current inflow phase inverter bridge , the switch tube VT2 is the switch tube of the lower bridge arm of the current inflow phase inverter bridge. In the first case, if the switch tube VT3 is turned on, the switch tube VT2 performs PWM control with a set duty ratio. In this PWM control mode, the method of the present invention controls the non-conductive phase inverter bridge lower bridge The arm switch VT4 is turned off, and the upper arm switch VT1 of the non-conducting phase inverter bridge is controlled for PWM control, and a complementary PWM output control mode is formed with the switch VT2 (set the appropriate dead time according to the actual use needs) If the switch tube VT3 performs PWM control with the set duty ratio, the switch tube VT2 is turned on, and under this PWM control mode, the method of the present invention controls the non-conduction phase inverter bridge upper bridge arm switch tube VT1 to be turned off , control the switch tube VT4 of the lower arm of the non-conducting phase inverter bridge to perform PWM control, and form a complementary PWM output control mode with the switch tube VT3 (set appropriate dead time according to the actual use situation). In the second case, if the switch tube VT5 is turned on, the switch tube VT6 performs PWM control with a set duty ratio. In this PWM control mode, the method of the present invention controls the non-conductive phase inverter bridge lower bridge The arm switch VT4 is turned off, and the upper arm switch VT1 of the non-conducting phase inverter bridge is controlled for PWM control, and a complementary PWM output control mode is formed with the switch VT6 (the appropriate dead time needs to be set according to the actual use situation) If the switch tube VT5 performs PWM control with the set duty ratio, the switch tube VT6 is turned on, and under this PWM control mode, the method of the present invention controls the non-conduction phase inverter bridge upper bridge arm switch tube VT1 to be turned off , control the switch tube VT4 of the lower arm of the non-conducting phase inverter bridge to perform PWM control, and form a complementary PWM output control mode with the switch tube VT5 (set appropriate dead time according to the actual use situation).

Taking the most widely used H_PWM_L_ON modulation mode as an example, the phase currents of the brushless DC motor using the PWM control method of the present invention and the brushless DC motor not using the control method of the present invention (existing method) are tested respectively. The PWM waveform of the existing method of the H_PWM_L_ON modulation method is shown in FIG. 4 , the PWM waveform of the H_PWM_L_ON modulation method combined with the PWM control method of the present invention is shown in FIG. 5 , and the phase current waveform of the brushless DC motor of the existing method of the H_PWM_L_ON modulation method is used. As shown in Figure 6, the phase current waveform of the brushless DC motor using the H_PWM_L_ON modulation method combined with the PWM control method of the present invention is shown in Figure 7. In Figures 6 and 7, the abscissa represents time, the unit is s, and the ordinate represents time Current, in A. Analysis of Fig. 6 and Fig. 7 shows that without adopting the PWM control method of the present invention (existing method), when the non-conducting opposite electromotive force voltage is less than 0, the freewheeling diode is realized through the lower arm diode of the non-conducting phase inverter bridge. When the conducting reverse electromotive force voltage is greater than 0, there is no freewheeling. Using the PWM control method of the present invention, when the non-conducting reverse electromotive force voltage is greater than 0, since the switch tube of the lower bridge arm of the non-conducting phase inverter bridge is also performing PWM control, so Freewheeling is realized through the switch tube of the lower bridge arm of the non-conducting phase inverter bridge, so that when the non-conducting opposite electromotive force voltage is greater than 0 and less than 0, there is freewheeling, and the direction is opposite, so that the average freewheeling current is greatly reduced. When the other three modulation modes of PWM_ON, ON_PWM and H_ON_L_PWM are adopted, the phase current of the brushless DC motor can also produce the same effect in combination with the PWM control method of the present invention.

To sum up, compared with the existing method, the PWM control method of the present invention can greatly reduce the average current of the non-conducting phase freewheeling current and greatly improve the torque of the brushless DC motor caused by the non-conducting phase freewheeling current. pulsation, greatly improving the control performance of the brushless DC motor.

Claims (1)

1. a PWM control method for suppressing the torque ripple of the brushless DC motor, it is characterized in that when the brushless DC motor works in a 120-degree two-phase conduction mode, the non-conduction phase in the brushless DC motor control system is reversed. The bridge switch tube and the conduction phase inverter bridge switch tube perform complementary PWM control, so that the average current of the non-conduction phase freewheeling current is greatly reduced; During the conduction period of two phases in the brushless DC motor control system, under the condition that the switch tube of the upper bridge arm of the inverter bridge of the current inflow phase is turned on, and the switch tube of the lower bridge arm of the inverter bridge of the current outflow phase is PWM controlled, the non-conduction phase is controlled by PWM. The switch tube of the upper arm of the inverter bridge performs PWM control complementary to the switch tube of the lower arm of the inverter bridge of the current outflow phase, and sets the dead time; During the conduction period of two phases in the brushless DC motor control system, PWM control is performed on the switch tube of the upper arm of the inverter bridge for the current inflow phase, and the switch tube of the lower arm of the inverter bridge for the current outflow phase is turned on. The switch tube of the lower arm of the inverter bridge performs PWM control complementary to the switch tube of the upper arm of the inverter bridge of the current inflow phase, and sets the dead time.

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