Design of angular position and velocity observer for servo motors with reslovers

Resolvers are extensively used to measure absolute angular position and velocity of servo systems; the analog outputs of the resolver are amplitude modulated signals that contain the angular position information. In order to obtain the rotor angular position and velocity information, a state-observer-based resolver-to-digital conversion (RDC) method is presented in this paper. Theoretical analysis shows that both the second-order state observer and the third-order one can drive the tracking error converge to zero when the velocity is constant. But once the velocity varies, the tracking error of the former method exist bias in principle while another still can converge to zero. Compared with the arctangent method, the proposed method can obtain angular velocity without a differential operator, and has the ability to suppress disturbances. Compared with angular tracking observer, the proposed method can obtain angular position and velocity in higher precision since the changes of the motor speed is considered. Experimental results demonstrate effectiveness of the proposed method.