Parallel Structure Fractional Repetitive Control for PWM Inverters

In this paper, a parallel structure fractional repetitive control (RC) scheme is proposed to improve the performance of pulsewidth-modulation (PWM) inverters in fractional cases where the sampling rate of the digital control system is not an integral multiple of the fundamental frequency. By introducing a correction factor, the new control scheme increases the control gains for all harmonics and locates poles accurately at targeted harmonic frequencies. As a result, the proposed control scheme achieves better tracking and rejection performance than conventional RC. Moreover, the parallel structure fractional repetitive controller requires less data memory. Dynamic response is also improved. The stability and convergence of this method are proved. Experimental results on a single-phase PWM inverter illustrate the advantages of this control scheme.