HF Pulsating Carrier Voltage Injection Method Based on Improved Position Error Signal Extraction Strategy for PMSM Position Sensorless Control

High-frequency (HF) pulsating carrier voltage injection method is widely used in position sensorless control of permanent magnet synchronous motor. In this method, the position error signal (i.e., amplitude of $q$-axis HF carrier current) is extracted by band-pass filter (BPF) and low-pass filter (LPF). However, with the BPF+LPF-based position error signal extraction strategy, position estimation loop may face the problem of conflict between filtering accuracy and dynamic performance. The conflict is reflected as estimated speed harmonic or position estimation error cannot be balanced at the same time, especially in speed step and load change condition. In this article, an improved position error signal extraction strategy based on amplitude observer (AO) is proposed. First, the AO-based strategy demodulates $q$-axis current directly, which gets rid of the BPF. Second, the AO has the capability of automatic secondary HF harmonic filtering, so the LPF is eliminated as well. Third, the AO extracts the position error signal by closed-loop, which helps to improve the extraction performance under dynamic condition. With the AO-based position error signal extraction strategy, the position estimation loop features both high filtering capability and wide bandwidth. Experimental results demonstrate that compared with BPF+LPF-based strategy, the secondary HF harmonic components of estimated speed are eliminated and the position estimation error is decreased at the same time.