Development of a Robust Random Switching Hysteresis PWM Inverter for Linear Positioning Control

Robust random switching control for a three-phase hysteresis current-controlled PWM inverter to promote its ability in servo driving control is studied in this paper. After observing the effect of varying band on the output harmonic distribution characteristic of a hysteresis current-controlled PWM inverter, a random switching hysteresis PWM scheme is developed. A robust spectrum shaping technique is devised such that the randomized inverter output harmonic spectrum is further shaped to the desired pattern. In the resulted frequency spectrum, the magnitudes of lower-frequency harmonics are reduced significantly. This makes the hysteresis PWM inverter suitable to serve as a driving source for position servo motor drives. The effect of AC motor neutral point isolation on the random switching performance is observed. The developed random switching inverter is used to power a linear permanent magnet synchronous motor-driven magnetic suspended positioning stage, and the resulted position control performance is demonstrated by some simulated and measured results.