An improved sliding mode observer for position sensorless vector control drive of PMSM

This paper proposes a position sensorless control scheme for permanent magnet synchronous motor (PMSM) drive using an improved sliding mode observer (SMO). It is more precise than the conventional SMO and also the structure is simple. Compared with traditional SMO, the sign function is replaced by a saturation function, as well as directly differential speed calculation method is replaced by phase-locked loop (PLL). To achieve better filtering effect and simplify the hardware structure, a variable cut-off frequency low-pass filter is designed. The stability condition of EMF based SMO is studied to make sure that the observer is stable in converging to the sliding mode plane. The paper analyzes the structure and performance of the improved SMO strategy with DSP based experiments. Results show that the proposed SMO of PMSM can satisfactorily estimate the position and speed of PMSM.