I-f Control Method of IPMSM to Reduce Oscillation Speed with High Torque

An initial start-up with I-f control is used to increase the rotor speed to enable a model based sensorless control. However, the insufficient damping ratio of I-f control can cause speed oscillations, which lead to a startup failure or an inaccurate transition to sensor-less control. In this paper, the insufficient damping ratio of the open I-f control system is derived using small signal analysis. Perturbation mechanical power is analyzed by perturbation theory, it is expressed as a function of the oscillation speed and angle and used to analyze the active damping control system. The effectiveness of active damping control is analyzed based on the derived equations by pole trajectory according to motor speed and damping gain. The effectiveness of the proposed method is verified by simulations and experiments results under various load and starting conditions.