A new motor speed extraction method based on the combination of smoothing and polynomial fitting filter

In this paper, based on the combination of the design method of the polynomial fitting filter and that of the smooth filter, from the aspect of difference filter, a new method of extracting the rotational speed according to the discrete position signal is proposed. Compared to the traditional method such as the direct difference method, the smoothing difference method, the new one can greatly reduce the speed ripple caused by the position discretion. And besides, the order of the differentiator can be selected according to the system bandwidth demand. In addition, the coefficients of the differentiator are all integers, so the calculation cost is low. The simulation results validate the effectiveness of the new method.