Abstract: As an important part in the active magnetic bearing, its performance has great impact on the active magnetic bearing system. Most of the active magnetic bearing systems use current-mode switching power amplifiers. Besides the parameters of current controller, modulation techniques play an important role in the performance of current-mode switching power amplifiers. A comparative study is made among three most widely used modulation techniques, i.e. triangle wave comparison method, hysteresis comparison method and sample-and-hold method. Based on introducing the operating principle of three modulation techniques, their static performance, dynamic performance and harmonic content are analyzed. Simulation models are built by using Simulink and prototypes of the three power amplifiers. The results of simulations and experiments show that the triangle wave comparison method has the best performance due to constant switching frequency, less harmonic content and high reliability. The conclusions have some guiding significance to the design of current-mode switching power amplifiers for active magnetic bearings.

Key words: Active magnetic bearings, Current-mode power amplifier, Hysteresis comparison method, Sample-and-hold method, Triangle wave comparison method