Motor Flux Estimator Based on Phase-Locked Loop and PI Regulator at Low Speed

Voltage model has been widely used in the field of motor control due to the advantages of the simple structure and less parameters required. A novel motor flux estimator based on phase-locked loop and proportional-integral (PI) regulator is proposed in this paper. This estimator calculates the set point of the torque component of electromotive force (EMF) through synchronous frequency and flux. Then, errors between the set point and the actual value of the EMF torque component are corrected by PI regulator to estimate the flux. This method avoids the problem of the saturation brought by the traditional integrator and the problem of the initial phase error. It also solves the magnitude and phase error problems at low speed in the flux estimator based on the low-pass filter. Finally, the simulation and the experiments are implemented on a cycloconverter-fed motor drive system to verify the effectiveness of this method. Simulation results show that this algorithm works very well at 0.2 Hz, and experimental results show that this algorithm can work well at 0.5 Hz. Meanwhile, this algorithm could detect the initial position of the rotor of separately excited synchronous motor.