Improved Repetitive Control with Enhanced Active Damping Method for 400Hz Inverter

Since the harmonic frequency of 400Hz inverter is relatively high, it is difficult to eliminate the low-order harmonics with the traditional dual-loop control. Aiming at achieving zero steady-state error and enhancing the ability to suppress harmonics, the plugged-in repetitive control (RC) with the damping-based notch filter (DNF) is proposed. The DNF not only ensures the high open-loop gain at harmonic frequencies, but also facilitates the stability identification by ‘the two unit circles’. As the magnitude/phase-frequency behavior of the RC control plant is anticipated to be characterized by OdB and 0 degree, the internal current loop is regulated by the elaborated active damping loop with phase compensation. As the minimal-phase behavior is guaranteed, the harmonics around the resonance frequency $\boldsymbol{f}_{\mathbf{r}}$ is well suppressed without threatening the stability of the RC-based system. Experimental results finally validate that the total harmonic distortion (THD<1%) is reduced by the elaborated repetitive control strategy.