**Junlei Chen, Shuo Chen, Xiang Wu, Guojun Tan \* and Jianqi Hao**

School of Electrical and Power Engineering, China University of Mining and Technology, Xuzhou 221116, China **\*** Correspondence: gjtan@cumt.edu.cn; Tel.: +86-138-0521-9335

Received: 10 June 2019; Accepted: 1 July 2019; Published: 3 July 2019

**Abstract:** The scheme based on direct torque and flux control (DTFC) as well as active flux is a good choice for the interior permanent magnet synchronous motor (IPMSM) sensorless control. The precision of the stator flux observation is essential for this scheme. However, the performance of traditional observers like pure integrator and the low-pass filter (LPF) is severely deteriorated by disturbances, especially dc offset. Recently, a sliding-mode stator flux observer (SMFO) was proposed to reduce the dc offset in the estimated stator flux. However, it cannot eliminate the dc offset totally and will cause the chattering problem. To solve these problems, a novel super-twisting sliding-mode stator flux observer (STSMFO) is proposed in this paper. Compared with SMFO, STSMFO can reduce the chattering and fully eliminate the dc offset without any amplitude and phase compensation. Then, the precision of the stator flux and rotor position can be greatly improved over a wide speed region. The detailed mathematical analysis has been given for comparing it with another three traditional observers. The numerical simulations and experimental testing with an IPMSM drive platform have been implemented to verify the capability of the proposed sensorless scheme.

**Keywords:** interior permanent magnet synchronous motor (IPMSM); active flux; sensorless control; stator flux observation; super-twisting sliding-mode stator flux observer (STSMFO)
