Adaptive Quasi-Three-Level PWM Control Method for Suppressing Overvoltage at Load Coil Terminal of Switching Power Amplifier

Active magnetic bearing (AMB) is a crucial technology for high-speed rotational machines. The switching power amplifier is the vital actuator that drives the AMB to generate electromagnetic levitation force. With the use of new generation wide-band SiC power devices, there are opportunities to enhance the dynamic performance of the switching power amplifiers by significantly increasing the switching frequency compared to conventional Si-based ones. However, the high voltage slew rate
dv/dt
during the switching transients poses new challenges to the reliability of AMB. These challenges include overvoltage and voltage oscillation at the terminal of load coils, which are widely concerning. This article explains the mechanism of overvoltage phenomenon using the wave reflection theory. A novel quasi-three-level pulsewidth modulation control method is then proposed to suppress overvoltage and voltage oscillation at the load coil terminal without additional circuits for the drive or snubber. The method involves inserting a short intermediate voltage platform into the switching transients, and the dwell time of the inserted voltage plateau is determined by factors such as the length of the power cable. An online adaptive adjustment algorithm is used to optimize circuit impedance matching for better overvoltage suppression. Finally, the proposed method was tested on a SiC half-bridge switching power amplifier with a switching frequency of 50 kHz. The results showed a reduction in overvoltage at the load terminal from 3 to 1.2 times the dc bus voltage, validating the effectiveness of the method.