Torque Ripple Suppression in Wide Speed Range of Brushless DC Motor Based on Regenerative Boost Inverter

Brushless DC motors are favored in aerospace, industrial automation, and household appliances because of their high power density, high efficiency, simple structure, and small size. However, the torque ripple inherent in the brushless DC motor limits its use in high-stability, high-precision applications. The torque ripple caused by commutation is the largest and can be up to 50% of the average torque. Therefore, many scholars have researched commutation torque ripple suppression from various perspectives, such as modulation, direct torque control, and control circuit topology. Among them, changing modulation methods and direct torque control often prolong the commutation time during high-speed motor operation. In order to achieve fast phase commutation while effectively suppressing commutation torque ripple, this paper proposes a regenerative boost inverter topology and control strategy for torque ripple suppression of wide-speed range. Firstly, the causes of commutation torque ripple are analyzed in terms of the PWM_ON modulation method generally used for two-phase conduction. Commutation torque ripple can be suppressed by increasing the average value of the bus voltage during commutation to twice that of the previous non-commutation period. Secondly, the relation curve between commutation torque ripple and angular speed shows that the bus voltage cannot be increased further due to the limitation of the power supply voltage. Thus, it cannot effectively suppress the commutation torque ripple when the motor runs at high speed. Therefore, the paper proposes a regenerative boost inverter topology consisting of a switching tube, a diode, an electrolytic capacitor, and a three-phase bridge inverter circuit. When the motor runs in the low-speed range, a smooth motor commutation through pulse width modulation is sufficient. As the bus voltage required for commutation is less than the power supply voltage on the DC side, no electrolytic capacitor is needed to assist in the boost. In this case, the expected value of the electrolytic capacitor voltage should be zero. However, to prevent negative charging of the electrolytic capacitor, the expected voltage value is set to a positive value, smaller than the DC bus voltage. Hysteresis band track control is used for this electrolytic capacitor voltage. When the deviation between the desired and actual value of the electrolytic capacitor exceeds a given positive threshold, consider discharging the electrolytic capacitor. When it is below a given negative threshold, consider charging the electrolytic capacitor. Under higher speeds, the DC power supply needs to be connected in series with the electrolytic capacitor to raise the bus voltage during commutation when the desired value of the electrolytic capacitor is the difference between the four times back-EMF amplitude and the power supply voltage. All the energy of the electrolytic capacitor comes from the regenerative feedback of the motor during non-commutation periods. Finally, the variation of the electrolytic capacitor voltage during a single switching cycle is quantified, and a capacitor selection method is given. The feasibility and effectiveness of the proposed control strategy are verified by Matlab simulations and DSP drive experiments. According to the experimental results, the commutation torque ripple is 8.6% at 500 r/min and 10.3% when the speed is increased to 2 000 r/min. The results show that the proposed control scheme can provide the higher bus voltage required for the commutation of the motor and thus achieve a fast and smooth commutation over a wide speed range. © 2024 China Machine Press. All rights reserved.