Analysis of output precision characteristics of digital switching power amplifier in the active magnetic bearings system.

Power amplifier is the key component of the magnetic bearing systems, and its precision characteristics have decisive influence on the overall performance. We analyze the factors in the formation of precision characteristics of typical digital switching power amplifier under two-level modulation, and reveal that the inherent ripple characteristic and precision of current detection are the main limits. The relationships between inherent ripple characteristic and its main influencing factors, such as bus voltage, modulation frequency and constants of electromagnetic coil have been derived in this paper. By suppressing the analog noises and drifts in current detection circuit, and calibrating the analog to digital converter, the precision performances of the current detection circuit had been improved efficiently to avoid becoming the dominant factor of the formation of the precision characteristics, which make that the precision of output current is nearly determined by the inherent ripple characteristic. The experimental results show that the output current ripple is very close to the inherent ripple characteristic if the precision of current detection circuit is high enough. Furthermore, the approaches discussed can describe the formation of precision characteristics by theoretical calculation of inherent ripple characteristic under the conditions of different implementations. [ABSTRACT FROM AUTHOR]