Fractional-order phase lead compensation for multi-rate repetitive control on three-phase PWM DC/AC inverter

For constant voltage constant frequency pulse-width modulation (PWM) inverter system, repetitive control (RC) can achieve zero steady-state tracking error for any periodic signal. Multi-rate repetitive control (MRC), which is featured by a fast system sampling rate and a reduced RC rate, is able to lower CPU computation load while achieving low tracking error and fast convergence speed. To accurately compensate the phase lag of MRC, this paper proposes a fractional-order phase lead compensation solution to further improve the tracking performance. Implemented with a Lagrange polynomial, the fractional-order phase lead compensator has more accurate and flexible phase lead compensation than traditional phase lead compensator. Experimental results are provided to show the effectiveness of the proposed fractional-order phase lead compensation.