A Cost Effective Sensorless Control Method for Permanent Magnet Synchronous Motors Based on Average Terminal Voltage

This paper presents the design, analysis, and implementation of a high performance and cost effective sensorless control scheme for the extensively used brushless DC motors (BLDCM), permanent magnet synchronous motors (PMSM), and interior permanent magnet synchronous motors (IPMSM). In the proposed approach, instead of sensing the non-excited back emf or injecting the additional high frequency switching signals, the commutation signals are extracted directly from the specific average line to line voltages with simple RC circuits and comparators. As a result, the proposed approach is particularly suitable for rectangular current commutation. For the case of sinusoidal commutation, which is desired for PMSMs and IPMSMs, the required continuous position can be obtained from the speed information which is calculated and updated every 60 electric degrees. Moreover, the speed-dependent commutation error caused by the low pass filter and inherent armature inductance is analyzed. An optimal commutation strategy is proposed to keep the armature current as small as possible. Compared with the conventional methods, complex calculation and sensitive machine parameters are not required in the proposed approach. Because of the inherent low cost property, the proposed control algorithm is particularly suitable for air purifiers, air blowers, cooling fans, air conditioners, and related home appliances, etc. Theoretical analysis and various experiments have been conducted to evaluate the effectiveness of the proposed method