Nonlinear modeling and design of initial position estimation and polarity detection of IPM drives

This paper proposes a novel initial rotor position estimation algorithm for Interior Permanent Magnet Synchronous Machine (IPMSM) drives. First, the rotor position is determined based on the machine saliency using the flux equations in the stationary reference frame. Since the machine saliency performs two periods in one electrical cycle, there exists an ambiguity of 180° in the estimation result. The location of the magnetic north pole is detected using a generalized polarity detection method. This method injects voltage pulses and compares the current response with the expected response using the d-axis differential inductance profile. An accurate nonlinear machine model is introduced for analysis and simulation of sensorless control in IPMSM drives. The model uses the machine flux as dynamic equation and the flux current relationship as output function avoiding approximations due to saturation. The initial position detection procedure is validated with this model using experimental current-flux data.