An Improved Sliding Mode Observer for Speed Sensorless Vector Control Drive of PMSM

This paper proposes a speed sensorless control scheme for permanent magnet synchronous motor (PMSM) drive using an improved sliding mode observer (SMO). A variable frequency or cutoff frequency in low pass filter is not essential to use in the improved SMO. Since the product of the improved SMO gain and the control action of sigmoid function, which replaces the Bang-Bang control or discontinuous control, commonly found in the conventional SMO, can determine the equivalent back emfs. The estimated rotor position and speed are obtained directly from them. Therefore, the low pass filter can be eliminated and the improved SMO could simplify the conventional SMO. Also, the cutoff frequency tuning is not necessary. A DSP based digital controller using the TMS320F2812 from the Texas Instruments has been employed to realize the proposed sensorless control scheme. Experimental results show that the proposed control scheme can achieve robust sensorless requirement