Variable structure direct torque control of encoderless synchronous reluctance motor drives with maximized efficiency

In this paper, a flexible DTC based on variable structure approach and space vector modulation is presented for encoderless Synchronous Reluctance Motor (SynRM) Drives. According to this method, a sliding mode-plus-PI controller is designed for torque and flux control in stator flux reference frame, respectively. The proposed controller is able to reduce the torque, flux, current and speed pulsations during steady-state behavior while the fast response and robustness merits of the classic DTC are preserved. In addition, an on-line adaptive loss minimization controller (ALMC) for SynRM drives is introduced. The ALMC provides a novel pattern of change in stator flux magnitude to achieve a minimum motor input power at any operating condition. The operating of the ALMC results in a smooth and fast loss minimization. Very low speed estimation (5 r/min) is satisfied by the elimination of the voltage sensors' dc offset. The simulation and experimental results obtained verify that the encoderless efficiency-optimized VS-DTC proposed for SynRM drives presents a good performance with minimized number of dependent parameters.