Fractional order PI speed control for permanent magnet synchronous motor drives

In this paper, a fractional order proportional and integral (FOPI or PI^α) speed control method for permanent magnet synchronous motor (PMSM) is presented. Based on the modeling of current loop in PMSM vector control, the speed PI^α controller is designed which fulfills specifications of the given phase margin and open loop gain crossover frequency. Numerical solution of phase crossover frequency is executed for each integral order by using Newton iteration method. The corresponding gain margin is achieved afterwards. Furthermore, the parameters of PI^α controller are tuned by selecting the maximum gain margin of speed loop. The simulation results show that the speed step has small overshoot and fast response, which can verify the effectiveness of the proposed control strategy.