Sensorless control for IPMSM using PWM excitation: Analytical developments and implementation issues

Persistent, transient and, very recently, pulse width modulated voltage excitation are employed to track saliency of IPM machines, aiming at estimating rotor position. In this paper current transient response introduced by standard (or slightly modified) PWM excitation is considered and analytical relationship between phase current derivatives, inductance and rotor position is derived. A complete mathematical model is developed in the case of IPM machine, by taking also into account the dependence of the rotor position estimation error on the mutual inductance, which is neglected in the past literature adopting the same sensorless approach. Estimation is performed within a single PWM period, differently from previous approaches. Measurement of current derivatives is obtained from dedicated Rogowski coils, oversampling and real-time processing of the measured values. Acquisition issues due to short application times of voltage vector (e.g. during zero and low speed operations) have been overcome by means of a proper edge-shifting technique on the PWM signals. A motor drive system for fractional power high speed IPM motor is considered as a test bench to prove the effectiveness of the proposal.