Systematic error cancellations and fault detection of resolver angular sensors using a DSP based system

Resolver sensor based angular position and speed sensing are extensively used in safety critical servo applications that demands accurate as well as high-resolution position and speed information for feedback control. In this paper, a novel scheme for position and speed sensing along with fault detection and identifications of a resolver sensor with systematic errors like magnitude imbalance, imperfect quadrature, and inductive harmonics is presented. The proposed scheme of resolver-to-digital (R/D) conversion mitigates the errors in position and speed estimate due to these common resolver imperfections and provides fault indicators such as good resolver signal, degradation of signal, and loss of signal for fault tolerant operation and diagnosis of malfunctions in the sensor system for safety critical systems. The proposed method incorporates software generation of the resolver carrier using a digital filter for synchronous demodulation without unintended time delay of the processed outputs, in such a way that there is substantial saving in hardware, for instance, carrier oscillator and associated digital and analog circuits for amplitude demodulators. The R/D converter incorporates an adaptive phase-locked loop (APLL) that accurately estimates the angular position and speed for a large range of operation along with superior tracking performance under dynamic conditions. Also, it provides the estimate of the magnitudes of the resolver outputs, estimate of the imperfect quadrature, and indication of harmonic distortion in the sensing angle, which can be used to directly access the quality of the resolver sensor system. Computer simulations and experimental results demonstrate an accurate R/D converter with adaptive capabilities to mitigate all the major systematic disturbances with reduced hardware complexity.