Maximization of Sensorless Capabilities of Hybrid Excited Permanent Magnet Motors

This paper proposes an improved control strategy for hybrid excited permanent magnet (HEPM) motors in low-speed sensorless operating condition. In low speed region, the rotor position is retrieved by exploiting the rotor anisotropy via high frequency (HF) voltage signals. Non-zero cross-differential inductances induce an estimation error which could lead lower performance and instability issues. The proposed method exploits the excitation current of HEPM motor to reduce or even nullify the estimation error. The operating trajectory for stator and excitation currents is obtained via a two-step optimization procedure. The algorithm aim is the minimization of the position estimation error and the maximization of motor efficiency, by respecting the motor constraints. Simulation results validate the effectiveness in the position error reduction. Moreover, the efficiency of the drive under the proposed control strategy is compared to the benchmark maximum-torque-per-ampere policy.