Investigation of flux-weakening performance and current oscillation of permanent magnet brushless ac drives

The flux-weakening performance of permanent magnet brushless ac drives is investigated based on both floating-point and fixed-point DSPs. The current oscillation is observed when the drive operates at high-speeds under the flux-weakening control with the fixed-point DSP. It is due to the on-line compensation of the resistance voltage drop and quantisation errors of the fixed-point architecture of the DSP, as confirmed both theoretically and experimentally. A simple look-up table scheme is proposed to eliminate the oscillation and to achieve the high flux-weakening capability.