Failure Mechanism of Improved Three-Level Power Amplifier for Active Magnetic Bearings

In switching power amplifiers used in active magnetic bearings, three-level modulation technique is commonly used to reduce the current ripple of switching power amplifiers, so as to improve the performance of active magnetic bearing system. In our research, it is found that when a modified three-level PWM modulation technique was used in the switching power amplifiers, the output current waveform of the three-level PWM power amplifier was inconsistent with the theoretical waveform sometimes. At the same switching frequency, the current ripple of the modified three-level PWM power amplifier was much bigger than the theoretical value. The failure phenomenon is introduced and the failure mechanism of the modified three-level PWM power amplifier is theoretically analyzed for different carrier waves based on the analysis of the modified three-level PWM modulation technology in this paper. It is found that the deviation of bias voltage setting in the modified three-level PWM circuit results in its failure, and the failure mechanism is different for different carrier waves. Simulation and experimental results are in good agreement with the theoretical analyses. Finally, some suggestions about avoiding the failure of the modified three-level PWM power amplifier are proposed.