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Automatic calibration of resolver signals via state observers

Resolver sensors are utilized as absolute position transducers in many industrial applications. To get position information from resolvers, envelope detection and angle demodulation are required. Ideally, the signals after envelope detection are two sinusoidal orthogonal envelope signals. However, these sinusoidal envelope signals are often disturbed by unexpected actions such as DC offsets, amplitude deviation, and non-orthogonal phase shift. To overcome the influences of these factors and improve demodulation accuracy, an offline automatic calibration method for the two sinusoidal envelope signals is proposed. A state observer is introduced to estimate the amplitude and DC offsets of the envelope signals. To estimate the phase shift, a sinusoidal signal whose DC offset is a function of the phase shift of the envelope signals is constructed based on properties of triangle functions. Its offset could also be estimated by an observer. The simulation results revealed that the proposed method can converge to a single root accurately without complicated parameter selection. The validity and performance of the calibration method are verified in an experimental prototype.