An Optimized Asymmetric Pulsewidth Modulation for Sensorless Control of Permanent Magnet Synchronous Machines

This article proposes an optimized asymmetric pulsewidth modulation (OAPWM) for saliency-based sensorless control of permanent magnet synchronous machines (PMSMs). Compared with the conventional symmetric space vector PWM, OAPWM has merits of longer active vectors and more accurate current slope measurements, which are beneficial to the low-speed sensorless drives. In OAPWM, a distributed zero vector is inserted between two adjacent active vectors. Thus, the current ripple and the power loss can be reduced. Moreover, the length of zero vector is optimized considering the current ripple and modulation index. Then, a current oversampling method and the least square algorithm are adopted to improve the calculation accuracy of the current slope. And the average phase current in one PWM period is calculated using six sampling points. The effectiveness of OAPWM for sensorless control is verified on both 500- and 1500-W PMSMs based on a single field programmable gate array. In comparison with the conventional methods, more accurate position estimation can be achieved during both the transient and steady-state processes.