An active filter method to eliminate dc-side low-frequency power for single-phase quasi-Z source inverter

Second harmonic pulsating power flows through the dc side of the single-phase quasi-Z-source inverter (qZSI). This requires bulky capacitor banks and inductors to suppress the second harmonic ripple of dc-link voltage and inductor currents. However, the resultant qZS network seriously deteriorates the system reliability, efficiency, volume, weight, and cost. This paper proposes an active filter integrated single-phase qZSI topology to transfer the low-frequency (second harmonic) power ripple directly from the ac load to the active filter ac capacitor. Thus low-frequency power ripple will not be present at the dc side, and constant inductor current and constant capacitor voltage are ensured. The qZS impedance is small because only high frequency switching ripple is present and the active filter supports ac voltage (large ripple) enabling small values of capacitance - both of these characteristics result in low size and low weight. This paper investigates the analysis, modeling, parameter design method of qZS network and active filter, as well as control strategy of the proposed topology. Comparative evaluation and experimental results verify the proposed new topology system.