Extrapolation technique for improving the effective resolution of position encoders in permanent-magnet motor drives

This paper describes an extrapolation scheme for high-resolution rotor-position prediction using data from a low-resolution encoder. The predictor approximates the previous rotor movement profile by a polynomial equation, which is then used to predict the subsequent rotor motion. The low- and transient-speed characteristics are examined, and it is shown experimentally that the technique can produce effective resolution improvements by a factor of 9. When the rotor velocity reverses, large errors can arise, but it is demonstrated that this problem can be overcome by including motor current data in the position predictor.