A compact state observer on PMSM for velocity estimation and rejection of torque ripple is proposed in this paper. By means of the field orientation principle of PMSM, a linear model is used in this state observer. A PID regulator is tuned in it to reject parameter variation. Since the instantaneous velocity can't be estimated truly when speed is very low because too little position pulses from optical encoder can be gotten in one time interval, a sliding compensation scheme is merged in this state observer to compensate the low estimated velocity error. Simulation and experimental results verify the validity of this scheme. The servo performance can be improved dramatically and this hybrid observer can be easily used in the PMSM servo system.
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