A PLL-based filter for speed noise reduction in drives using a resolver transducer

In many industrial drives the motor rotation speed measurement is obtained by means of an electromagnetic resolver that furnishes a shaft position measure. To obtain the speed measure, a derivative operation is needed; as a consequence, especially at the lowest speeds, the measured signal results are rather noisy and a suitable filter becomes necessary. The paper presents a solution to such problem based on the employment of a phase locked loop architecture based on a stationary Kalman filter that predicts the values of the mechanical variables at each sampling period. The proposed filter can be easily implemented on a digital microcontroller and it also provides an acceptable estimation of the acceleration.