Double line frequency ripple cancelling for single-phase quasi-Z-source inverter

Double line frequency ripple (2ω ripple) power inherently exists in single phase dc-ac or ac-dc pulse width modulation converters because of instantaneous power unbalance between the dc and ac side. In order to achieve stable operation and maintain a high maximum power point tracking (MPPT) efficiency, traditional single-phase quasi-Z-source inverter (QZSI) for photovoltaic application uses large electrolytic dc capacitors in the impedance network to suppress this 2ω ripple. This paper proposed an active power decoupling method to cancel the 2ω ripple in both the input and impedance network. By adding another phase leg, an ac capacitor and a high frequency inductor in series, the second ac power path is developed to absorb the power pulsating at twice the line frequency. With selected capacitance and closed-loop control for the voltage on the added ac capacitor, the 2ω ripple would be eliminated with the minimum costs. The other ac output of the QZSI would not be influenced because the original two phase legs (the original H-bridge) maintains the same operation. The merits of the presented method includes 1) reduced device size by replacing bulky dc capacitor to small ac capacitor; 2) ripple free input to achieve high MPPT efficiency. Theoretical analysis, control strategy, simulation and experimental results are provided to demonstrate and verify the method.