**Shuang Wang, Jianfei Zhao \* and Kang Yang**

School of Mechatronic Engineering and Automation, Shanghai University, Baoshan District, Shanghai 200444, China; wang-shuang@shu.edu.cn (S.W.); yangk@shu.edu.cn (K.Y.)

**\*** Correspondence: jfzhao@shu.edu.cn; Tel.: +86-021-6613-0935

Received: 5 November 2019; Accepted: 12 December 2019; Published: 14 December 2019

**Abstract:** In this paper, a new sensorless control scheme with the injection of a high-frequency square-wave voltage of an interior permanent-magnet synchronous motor (IPMSM) at low- and zero-speed operation is proposed. Conventional schemes may face the problems of obvious current sampling noise and slow identification in the process of magnetic polarity detection at zero speed operation, and the effects of inverter voltage error on the rotor position estimation accuracy at low speed operation. Based on the principle analysis of d-axis magnetic circuit characteristics, a method for determining the direction of magnetic polarity of d-axis two-opposite DC voltage offset by uninterruptible square-wave injection is proposed, which is fast in convergence rate of magnetic polarity detection and more distinct. In addition, the strategy injects a two-opposite high-frequency square-wave voltage vectors other than the one voltage vector into the estimated synchronous reference frame (SRF), which can reduce the effects of inverter voltage error on the rotor position estimation accuracy. With this approach, low-pass filter (LPF) and band-pass filter (BPF), which are used to obtain the fundamental current component and high-frequency current response with rotor position information respectively in the conventional sensorless control, are removed to simplify the signal process for estimating the rotor position and further improve control bandwidth. Finally, the experimental results on an IPMSM drive platform indicate that the rotor position with good steady state and dynamic performance can be obtained accurately at low-and zero-speed operation with the sensorless control strategy.

**Keywords:** sensorless control; high frequency square-wave voltage; interior permanent-magnet synchronous motor (IPMSM); magnetic polarity detection; rotor position estimation
