**Shuo Chen 1, Xiao Zhang 1,\*, Xiang Wu 1, Guojun Tan <sup>1</sup> and Xianchao Chen <sup>2</sup>**


Received: 6 March 2019; Accepted: 26 March 2019; Published: 29 March 2019

**Abstract:** In traditional sensorless control of the interior permanent magnet synchronous motors (IPMSMs) for medium and high speed domains, a control strategy based on a sliding-mode observer (SMO) and phase-locked loop (PLL) is widely applied. A new strategy for IPMSM sensorless control based on an adaptive super-twisting sliding-mode observer and improved phase-locked loop is proposed in this paper. A super-twisting sliding-mode observer (STO) can eliminate the chattering problem without low-pass filters (LPFs), which is an effective method to obtain the estimated back electromotive forces (EMFs). However, the constant sliding-mode gains in STO may cause instability in the high speed domain and chattering in the low speed domain. The speed-related adaptive gains are proposed to achieve the accurate estimation of the observer in wide speed range and the corresponding stability is proved. When the speed of IPMSM is reversed, the traditional PLL will lose its accuracy, resulting in a position estimation error of 180◦. The improved PLL based on a simple strategy for signal reconstruction of back EMF is proposed to ensure that the motor can realize the direction switching of speed stably. The proposed strategy is verified by experimental testing with a 60-kW IPMSM sensorless drive.

**Keywords:** interior permanent magnet synchronous motor (IPMSM); sensorless control; adaptive algorithm; super-twisting sliding mode observer (STO); phase-locked loop (PLL)
