Automatic calibration of output signals from resolvers

The outputs of resolvers are amplitude modulated signals, one with the sine and the other with the cosine of angular position. In order to obtain the rotor angular position and velocity information, detection and demodulation are required. However, detection results often contain dc offsets, amplitude deviation and non-orthogonal phase shift. To enhance demodulation accuracy, a calibration procedure is necessary before demodulation. An offline automatic calibration method was introduced to meet this need. A state observer was introduced to estimate the amplitude and dc offsets of the detected signals. To estimate the phase shift, a two variable quadratic goal function was constructed, which can be resolved by gradient estimator. Compared with the method that using only gradient estimator, the multiple-roots problem was resolved. The validity of the calibration method was proved by experiments. The proposed method doesn't need complicated parameter selection, and converges to single root with high accuracy.