Sensorless IPMSM drive with rotor position estimator based on analysis of phase current derivatives

This paper describes a sensorless Interior Permanent Magnet Synchronous Motor (IPMSM) drive designed for traction applications. Wide-speed sensorless operation is provided with the use of three methods of rotor position estimation designed for: a standstill, low- and high-speed range. The paper focuses on the high-speed estimation algorithm. The estimator uses the derivatives of motor phase currents resulting from PWM modulation to obtain the rotor position. The algorithm is characterized by very simple formulae. The calculation of the rotor position is performed in every PWM cycle. However, the determination of phase current derivatives requires a special current measurement algorithm in which sampling is coordinated with inverter transistors switching. The basis of the algorithm is presented, accompanied by an error analysis. The current sampling issues are reviewed and the laboratory test results are given and discussed.