阅读说明：本技术 一种抑制无刷直流电机转矩脉动的pwm控制方法 (PWM control method for inhibiting torque ripple of brushless direct current motor ) 是由 朱义潜 于 2021-03-16 设计创作，主要内容包括：本发明公开了一种抑制无刷直流电机转矩脉动的PWM控制方法,当无刷直流电机工作在120度二相导通方式时,通过对无刷直流电机控制系统中非导通相逆变桥开关管与导通相逆变桥开关管进行互补的PWM控制,使非导通相续流的平均电流大幅度变小；优点是在开关损耗小、电流波动小、不需要检测反电势过零点、成本较低以及控制简单的同时,能够显著降低非导通相续流的平均电流,大幅度改善由于非导通相续流引起的无刷直流电机转矩脉动,较大程度提高无刷直流电机的控制性能。(The invention discloses a PWM control method for inhibiting torque pulsation of a brushless direct current motor, which is characterized in that when the brushless direct current motor works in a 120-degree two-phase conduction mode, the average current of non-conduction phase follow current is greatly reduced by performing complementary PWM control on a non-conduction phase inverter bridge switching tube and a conduction phase inverter bridge switching tube in a brushless direct current motor control system; the method has the advantages that the average current of non-conducting phase follow current can be obviously reduced, the torque pulsation of the brushless direct current motor caused by the non-conducting phase follow current is greatly improved, and the control performance of the brushless direct current motor is greatly improved while the switching loss is small, the current fluctuation is small, the back emf zero crossing point does not need to be detected, the cost is low, the control is simple.)

1. A PWM control method for inhibiting torque ripple of a brushless DC motor is characterized in that when the brushless DC motor works in a 120-degree two-phase conduction mode, the average current of non-conduction phase follow current is greatly reduced by performing complementary PWM control on a non-conduction phase inverter bridge switching tube and a conduction phase inverter bridge switching tube in a brushless DC motor control system.

2. The PWM control method for suppressing the torque ripple of the brushless DC motor according to claim 1, wherein during the conduction period of two phases in the brushless DC motor control system, under the condition that the switching tube of the upper bridge arm of the current inflow phase inverter bridge is turned on and the switching tube of the lower bridge arm of the current outflow phase inverter bridge is PWM controlled, the PWM control complementary to the switching tube of the lower bridge arm of the current outflow phase inverter bridge is performed on the switching tube of the upper bridge arm of the non-conduction phase inverter bridge, and the dead time is set;

and in the conduction period of two phases in the brushless direct current motor control system, PWM control is carried out on a switching tube of an upper bridge arm of a current inflow phase inversion bridge, and PWM control complementary to the switching tube of the upper bridge arm of the current inflow phase inversion bridge is carried out on a switching tube of a lower bridge arm of the current outflow phase inversion bridge under the condition that the switching tube of the lower bridge arm of the current outflow phase inversion bridge is switched on, and dead time is set.

Technical Field

The present invention relates to a PWM control method, and more particularly, to a PWM control method for suppressing torque ripple of a brushless dc motor.

Background

The brushless direct current motor and the control system thereof are widely applied to various fields due to the advantages of good speed regulation performance, high efficiency, simple control, low cost and the like. The brushless direct current motor control system is usually realized by adopting a three-phase full-bridge inverter structure, the brushless direct current motor control performance is greatly influenced by the existence of torque ripple, and particularly, when the brushless direct current motor control system runs at a low speed, the torque ripple suppression technology is a hot problem of the research of the brushless direct current motor all the time because the torque ripple causes equipment noise and vibration.

The torque ripple of the 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 a current loop control mode, and the torque ripple caused by non-conducting phase free flow is related to a PWM modulation mode. When the brushless dc motor works in a 120-degree two-phase conduction mode, the following 6 common PWM modulation modes are available: making a first PWM _ ON; secondly, ON _ PWM; h _ PWM _ L _ ON; h _ ON _ L _ PWM; fifthly _ PWM _ L _ PWM; sixthly, PWM _ ON _ PWM. The 6 PWM modulation modes are all unipolar control (only one switch tube is used for PWM control on the upper switch tube and the lower switch tube of the same bridge arm, and the other switch tube is normally closed), the 6 PWM modulation modes have corresponding bipolar PWM modulation modes (namely the upper switch tube and the lower switch tube of the same bridge arm are simultaneously used for PWM complementary control), and the torque pulsation caused by non-conducting phase follow current of each bipolar PWM modulation mode is similar to that of the corresponding unipolar PWM modulation mode. In the 6 PWM modulation modes, H _ PWM _ L _ PWM and PWM _ ON _ PWM do not have non-conducting phase follow current, but H _ PWM _ L _ PWM has the disadvantages of large switching loss and large current fluctuation, and PWM _ ON _ PWM needs to detect back electromotive force zero crossing points, so that the cost is relatively high and the control is complex, so that the two modulation modes are rarely adopted and are not suitable for popularization and application. The PWM _ ON, ON _ PWM, H _ PWM _ L _ ON and H _ ON _ L _ PWM have the advantages of small switching loss, small current fluctuation, no need of detecting counter potential zero crossing points, relatively low cost and simple control, and are several PWM modulation modes mainly used at present. However, as shown in table 1, there is a non-conducting phase continuous flow in all of the four modulation modes of PWM _ ON, ON _ PWM, H _ PWM _ L _ ON, and H _ ON _ L _ PWM, and the control performance of the brushless dc motor has a larger space for improvement.

TABLE 1 interval of non-conducting phase current under four PWM modulation modes

In table 1, (+) indicates that a forward freewheeling current flows in the non-conductive phase winding, (-) indicates that a negative freewheeling current flows in the non-conductive phase winding, and x indicates that no freewheeling current flows.

Disclosure of Invention

The invention aims to solve the technical problem of providing a PWM control method for inhibiting torque pulsation of a brushless direct current motor, which can remarkably reduce the average current of non-conducting phase follow current, greatly improve the torque pulsation of the brushless direct current motor caused by the non-conducting phase follow current and greatly improve the control performance of the brushless direct current motor while having small switching loss, small current fluctuation, no need of detecting counter potential zero crossing points, lower cost and simple control.

The technical scheme adopted by the invention for solving the technical problems is as follows: when the brushless DC motor works in a 120-degree two-phase conduction mode, the average current of non-conduction phase follow current is greatly reduced by performing complementary PWM control on a non-conduction phase inverter bridge switching tube and a conduction phase inverter bridge switching tube in a brushless DC motor control system.

During the conduction period of two phases in the brushless direct current motor control system, under the condition that a switching tube of an upper bridge arm of a current inflow phase inversion bridge is switched on and a switching tube of a lower bridge arm of the current outflow phase inversion bridge is subjected to PWM control, PWM control complementary to the switching tube of the lower bridge arm of the current outflow phase inversion bridge is carried out on the switching tube of the upper bridge arm of the non-conduction phase inversion bridge, and dead time is set; and in the conduction period of two phases in the brushless direct current motor control system, PWM control is carried out on a switching tube of an upper bridge arm of a current inflow phase inversion bridge, and PWM control complementary to the switching tube of the upper bridge arm of the current inflow phase inversion bridge is carried out on a switching tube of a lower bridge arm of the current outflow phase inversion bridge under the condition that the switching tube of the lower bridge arm of the current outflow phase inversion bridge is switched on, and dead time is set.

Compared with the prior art, the invention has the advantages that when the brushless direct current motor works in a 120-degree two-phase conduction mode, the non-conduction phase inverter bridge switching tube and the conduction phase inverter bridge switching tube in the brushless direct current motor control system are subjected to complementary PWM control, so that the average current of non-conduction phase follow current is greatly reduced, and the torque pulsation of the brushless direct current motor caused by the non-conduction phase follow current is improved.

Drawings

Fig. 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 first waveform diagram of a PWM control method for suppressing torque ripple of a brushless DC motor according to the present invention;

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

FIG. 4 is a PWM waveform of a conventional method using H _ PWM _ L _ ON modulation;

FIG. 5 is a PWM waveform using H _ PWM _ L _ ON modulation in combination with the PWM control method of the present invention;

FIG. 6 is a diagram of phase current waveforms for a brushless DC motor using a conventional method of H _ PWM _ L _ ON modulation;

fig. 7 is a phase current waveform diagram of a brushless dc motor using H _ PWM _ L _ ON modulation in combination with the PWM control method of the present invention.

Detailed Description

The invention is described in further detail below with reference to the accompanying examples.

Example (b): when the brushless DC motor works in a 120-degree two-phase conduction mode, the average current of non-conduction phase follow current is greatly reduced by performing complementary PWM control on a non-conduction phase inverter bridge switching tube and a conduction phase inverter bridge switching tube in a brushless DC motor control system, so that the torque pulsation of the brushless DC motor caused by the non-conduction phase follow current is improved, and the control performance of the brushless DC motor is greatly improved.

In the embodiment, during the conduction period of two phases in the brushless direct current motor control system, under the condition that the switching tube of the upper bridge arm of the current inflow phase inversion bridge is switched on and the switching tube of the lower bridge arm of the current outflow phase inversion bridge is subjected to PWM control, the switching tube of the upper bridge arm of the non-conduction phase inversion bridge is subjected to PWM control complementary to the switching tube of the lower bridge arm of the current outflow phase inversion bridge, and dead time is set; and in the conduction period of two phases in the brushless direct current motor control system, PWM control is carried out on a switching tube of an upper bridge arm of a current inflow phase inversion bridge, and PWM control complementary to the switching tube of the upper bridge arm of the current inflow phase inversion bridge is carried out on a switching tube of a lower bridge arm of the current outflow phase inversion bridge under the condition that the switching tube of the lower bridge arm of the current outflow phase inversion bridge is switched on, and dead time is set.

The brushless dc motor is a three-phase brushless dc motor having a phase a, a phase B, and a phase C, and the brushless dc motor control system is configured as a three-phase full-bridge inverter, and its circuit diagram is shown in fig. 1. In fig. 1, a switching tube VT1, a switching tube VT4, a diode VD1 and a diode VD4 form an a-phase inverter bridge of a three-phase full-bridge inverter, a switching tube VT3, a switching tube VT6, a diode VD3 and a diode VD6 form a B-phase inverter bridge of a three-phase full-bridge inverter, a switching tube VT5, a switching tube VT2, a diode VD5 and a diode VD2 form a C-phase inverter bridge of a three-phase full-bridge inverter, and a V2 forms a C-phase inverter bridge of a three-phase full-bridge inverter_aIs a relative ground voltage of A, V_bIs B voltage relative to ground, V_cIs C voltage to ground, i_aIs a phase current of A phase, i_bIs a B-phase current, i_cIs a C-phase current e_aIs A counter electromotive force, e_bIs B counter electromotive force, e_cC is the reverse electromotive force, R is the stator winding resistance, L is the equivalent inductance of the stator winding, V_nFor the voltage of the central node of the armature winding of a brushless DC motor, U_dcIs the dc bus voltage. The implementation method applied to the brushless direct current motor control system is explained as follows:

when A-B phase is electrified, the C phase is a non-conducting phase, the C phase inverter bridge is a non-conducting phase inverter bridge, the switching tube VT5 is an upper bridge arm switching tube of the non-conducting phase inverter bridge, the VT2 is a lower bridge arm switching tube of the non-conducting phase inverter bridge, the A phase and the B phase are two conducting phases, at the moment, two conditions exist, the first condition is that current flows out from the A phase to the B phase, the A phase is a current inflow phase, the B phase is a current outflow phase inverter bridge, the B phase inverter bridge is a current outflow phase inverter bridge, the switching tube VT1 is an upper bridge arm switching tube for current inflow phase inverter bridge, the switching tube VT4 is a lower bridge arm switching tube for current inflow phase inverter bridge, the switching tube VT3 is an upper bridge arm switching tube for current outflow phase inverter bridge, the switching tube VT6 is a lower bridge arm switching tube for current outflow phase inverter bridge, the second condition is that current flows out from the B phase to the A phase and flows out from the A phase, the phase B is a current inflow phase, the phase A inverter bridge is a current outflow phase inverter bridge, the phase B inverter bridge is a current inflow phase inverter bridge, the switching tube VT1 is a current outflow phase inverter bridge upper bridge arm switching tube, the switching tube VT4 is a current outflow phase inverter bridge lower bridge arm switching tube, the switching tube VT3 is a current inflow phase inverter bridge upper bridge arm switching tube, and the switching tube VT6 is a current inflow phase inverter bridge lower bridge arm switching tube. In the first situation, if the switching tube VT1 is conducted, the switching tube VT6 performs PWM control with a set duty ratio, and in this PWM control mode, the method of the present invention controls the switching tube VT2 of the lower arm of the non-conducting phase inverter bridge to turn off, and controls the switching tube VT5 of the upper arm of the non-conducting phase inverter bridge to perform PWM control, and forms a complementary PWM output control mode with the switching tube VT6 (a proper dead time is set according to the actual use situation), and the waveform diagrams of the PWM control of the switching tube VT5 and the switching tube VT6 are shown in fig. 2; if the switching tube VT1 is PWM controlled by a set duty ratio, the switching tube VT6 is conducted, under the PWM control mode, the method of the invention controls the switching tube VT5 of the upper bridge arm of the non-conducting phase inverter bridge to be turned off, controls the switching tube VT2 of the lower bridge arm of the non-conducting phase inverter bridge to be PWM controlled, forms a complementary PWM output control mode with the switching tube VT1 (sets a proper dead time according to the actual use condition), and carries out PWM control on the switching tube VT1 and the switching tube VT2, and the waveform diagram is shown in FIG. 3. In the second situation, if the switching tube VT3 is conducted, the switching tube VT4 performs PWM control at a set duty ratio, and in this PWM control mode, the method of the present invention controls the switching tube VT2 of the lower arm of the non-conducting phase inverter bridge to turn off, and controls the switching tube VT5 of the upper arm of the non-conducting phase inverter bridge to perform PWM control, and forms a complementary PWM output control mode with the switching tube VT4 (a proper dead time is set according to actual use requirements); if the switching tube VT3 is PWM controlled by a set duty ratio, the switching tube VT4 is conducted, under the PWM control mode, the method of the invention controls the switching tube VT5 of the upper bridge arm of the non-conducting phase inverter bridge to be switched off, controls the switching tube VT2 of the lower bridge arm of the non-conducting phase inverter bridge to be PWM controlled, and forms a complementary PWM output control mode with the switching tube VT3 (sets a proper dead time according to the actual use requirement).

When the A-C phase is electrified, the phase B is a non-conducting phase, the phase B inverter bridge is a non-conducting phase inverter bridge, the switching tube VT3 is an upper bridge arm switching tube of the non-conducting phase inverter bridge, the switching tube VT6 is a lower bridge arm switching tube of the non-conducting phase inverter bridge, the phase A and the phase C are two conducting phases, at the moment, the first condition is that current flows out from the phase A into the phase C, the phase A is a current inflow phase, the phase C is a current outflow phase, the phase A inverter bridge is a current inflow phase inverter bridge, the phase C is a current outflow phase inverter bridge, the switching tube VT1 is an upper bridge arm switching tube of the current inflow phase inverter bridge, the switching tube VT4 is a lower bridge arm switching tube of the current inflow phase inverter bridge, the switching tube VT5 is an upper bridge arm switching tube of the current outflow phase inverter bridge, the switching tube VT2 is a lower bridge arm switching tube of the current outflow phase inverter bridge, and the second condition is that current flows out from the phase C into the phase A and the phase A, the phase C is a current inflow phase, the phase A inverter bridge is a current outflow phase inverter bridge, the phase C inverter bridge is a current inflow phase inverter bridge, the switching tube VT1 is a switching tube of an upper bridge arm of the current outflow phase inverter bridge, the switching tube VT4 is a switching tube of a lower bridge arm inverter bridge of the current outflow phase, the switching tube VT5 is a switching tube of an upper bridge arm of the current inflow phase inverter bridge, and the switching tube VT2 is a switching tube of a lower bridge arm of the current inflow phase inverter bridge. In the first situation, if the switching tube VT1 is conducted, the switching tube VT2 performs PWM control at a set duty ratio, and in this PWM control mode, the method of the present invention controls the switching tube VT6 of the lower arm of the non-conducting phase inverter bridge to turn off, and controls the switching tube VT3 of the upper arm of the non-conducting phase inverter bridge to perform PWM control, and forms a complementary PWM output control mode with the switching tube VT2 (a proper dead time is set according to actual use requirements); if the switching tube VT1 is PWM controlled by a set duty ratio, the switching tube VT2 is conducted, under the PWM control mode, the method of the invention controls the switching tube VT3 of the upper bridge arm of the non-conducting phase inverter bridge to be switched off, controls the switching tube VT6 of the lower bridge arm of the non-conducting phase inverter bridge to be PWM controlled, and forms a complementary PWM output control mode with the switching tube VT1 (a proper dead time is required to be set according to the actual use condition). In the second situation, if the switching tube VT5 is conducted, the switching tube VT4 performs PWM control at a set duty ratio, and in this PWM control mode, the method of the present invention controls the switching tube VT6 of the lower arm of the non-conducting phase inverter bridge to turn off, and controls the switching tube VT3 of the upper arm of the non-conducting phase inverter bridge to perform PWM control, and forms a complementary PWM output control mode with the switching tube VT4 (a proper dead time is set according to actual use requirements); if the switching tube VT5 is PWM controlled by a set duty ratio, the switching tube VT4 is conducted, under the PWM control mode, the method of the invention controls the switching tube VT3 of the upper bridge arm of the non-conducting phase inverter bridge to be switched off, controls the switching tube VT6 of the lower bridge arm of the non-conducting phase inverter bridge to be PWM controlled, and forms a complementary PWM output control mode with the switching tube VT5 (a proper dead time is required to be set according to the actual use condition).

When the B-C phase is electrified, the phase A is a non-conducting phase, the phase A inverter bridge is a non-conducting phase inverter bridge, the switching tube VT1 is an upper bridge arm switching tube of the non-conducting phase inverter bridge, the switching tube VT4 is a lower bridge arm switching tube of the non-conducting phase inverter bridge, the phase B and the phase C are two conducting phases, at the moment, the first condition is that current flows into and flows out of the phase C from the phase B, the phase B is a current inflow phase, the phase C is a current outflow phase inverter bridge, the phase B is a current inflow phase inverter bridge, the phase C is a current outflow phase inverter bridge, the switching tube VT3 is a current inflow upper bridge arm switching tube, the switching tube VT6 is a current inflow phase inverter bridge lower bridge arm switching tube, the switching tube VT5 is a current outflow phase inverter bridge upper bridge arm switching tube, the switching tube VT2 is a current outflow phase inverter bridge lower arm switching tube, and the second condition is that current flows into and flows out from the phase C, the phase C is a current inflow phase, the phase B is a current outflow phase inverse bridge, the phase C is a current inflow phase inverse bridge, the switching tube VT3 is a current outflow phase inverse bridge upper bridge arm switching tube, the switching tube VT6 is a current outflow phase inverse bridge lower bridge arm switching tube, the switching tube VT5 is a current inflow phase inverse bridge upper bridge arm switching tube, and the switching tube VT2 is a current inflow phase inverse bridge lower bridge arm switching tube. In the first situation, if the switching tube VT3 is conducted, the switching tube VT2 carries out PWM control with a set duty ratio, under the PWM control mode, the method controls the switching tube VT4 of the lower bridge arm of the non-conducting phase inverter bridge to be turned off, controls the switching tube VT1 of the upper bridge arm of the non-conducting phase inverter bridge to carry out PWM control, and forms a complementary PWM output control mode with the switching tube VT2 (sets a proper dead time according to the actual use requirement); if the switching tube VT3 is PWM controlled by a set duty ratio, the switching tube VT2 is conducted, under the PWM control mode, the method of the invention controls the switching tube VT1 of the upper bridge arm of the non-conducting phase inverter bridge to be switched off, controls the switching tube VT4 of the lower bridge arm of the non-conducting phase inverter bridge to be PWM controlled, and forms a complementary PWM output control mode with the switching tube VT3 (a proper dead time is required to be set according to the actual use condition). In the second situation, if the switching tube VT5 is conducted, the switching tube VT6 performs PWM control at a set duty ratio, and in this PWM control mode, the method of the present invention controls the switching tube VT4 of the lower arm of the non-conducting phase inverter bridge to turn off, and controls the switching tube VT1 of the upper arm of the non-conducting phase inverter bridge to perform PWM control, and forms a complementary PWM output control mode with the switching tube VT6 (a proper dead time is set according to actual use requirements); if the switching tube VT5 is PWM controlled by a set duty ratio, the switching tube VT6 is conducted, under the PWM control mode, the method of the invention controls the switching tube VT1 of the upper bridge arm of the non-conducting phase inverter bridge to be switched off, controls the switching tube VT4 of the lower bridge arm of the non-conducting phase inverter bridge to be PWM controlled, and forms a complementary PWM output control mode with the switching tube VT5 (a proper dead time is required to be set according to the actual use condition).

Taking the most widely applied H _ PWM _ L _ ON modulation method as an example, phase currents of a brushless dc motor adopting the PWM control method of the present invention and a brushless dc motor not adopting the control method of the present invention (conventional method) are respectively tested, where the PWM waveform of the conventional method adopting the H _ PWM _ L _ ON modulation method is shown in fig. 4, the PWM waveform of the conventional method adopting the H _ PWM _ L _ ON modulation method in combination with the PWM control method of the present invention is shown in fig. 5, the phase current waveform of the conventional brushless dc motor adopting the H _ PWM _ L _ ON modulation method in combination with the PWM control method of the present invention is shown in fig. 6, the phase current waveform of the brushless dc motor adopting the H _ PWM _ L _ ON modulation method in combination with the PWM control method of the present invention is shown in fig. 7, and in fig. 6 and 7, the abscissa represents time, and the ordinate represents current, and the unit is a. As can be seen from fig. 6 and 7, without using the PWM control method (existing method) of the present invention, when the non-conducting opposite electromotive force voltage is less than 0, freewheeling is realized by the diode of the lower arm of the non-conducting inverter bridge, and when the non-conducting opposite electromotive force voltage is greater than 0, no freewheeling is present, and with the PWM control method of the present invention, when the non-conducting opposite electromotive force voltage is greater than 0, because the PWM control is also performed on the switching tube of the lower arm of the non-conducting inverter bridge, freewheeling is realized by the switching tube of the lower arm of the non-conducting inverter bridge, and thus, when the non-conducting opposite electromotive force voltage is greater than 0 and less than 0, and the direction is opposite, the average current of the freewheeling is greatly. When the other three PWM _ ON, ON _ PWM and H _ ON _ L _ PWM modulation modes are adopted, the phase current of the brushless direct current motor can also generate the same effect by combining the PWM control method.

In summary, compared with the conventional method, the PWM control method according to the present invention can greatly reduce the average current of the non-conducting-phase follow current, greatly improve the torque ripple of the brushless dc motor caused by the non-conducting-phase follow current, and greatly improve the control performance of the brushless dc motor.