An Improved Active Flux Observer based on Specified Centre Frequency Estimator for PMSM Encoderless Drives

In recent years, the active flux concept has been widely adopted by industrial encoderless control thanks to its wide operation range, low parameter dependence, and multi-motor type universality. Although integrations are essential to estimate the active flux from the voltages and currents in the stationary reference frame, the pure integrator is a critically stable system and the observed flux can deviate from the actual flux due to saturation effects caused by the unknown initial value of the integral and the DC offset. In this work, we proposed one improved active flux observer based on specified centre frequency estimator to overcome the drawbacks of the pure integrator and further enhance the accuracy of the rotor position estimation. Simulation results confirm that the proposal achieves good control performances at both low and high speed ranges.