Failure mechanism of three-level power amplifier for active magnetic bearings

The switching power amplifiers with high efficiency are often required in active magnetic bearings, but they have some problems due to the switching process. In fact, the control current in the switching power amplifiers is superimposed with a considerable number of higher harmonics. The three-level PWM modulation was proposed to obtain smaller current ripples or lower harmonics. However, three-level PWM modulation was found to be failure under some conditions and the failure had seriously affected its application. The failure mode and failure mechanism are in detail studied in this paper. Meanwhile, the methods for reducing such failure in the three-level switching power amplifiers are suggested.