Bidirectional buck–boost converter-based active power decoupling method for single-phase photovoltaic grid-connected inverters

Abstract

In a single phase, two-stage photovoltaic (PV) grid-connected system, the transient power mismatch between the dc input and ac output generates second-order ripple power (SRP). To filter out SRP, bulky electrolytic capacitors are commonly employed. However, these capacitors diminish the power density and reliability of the system. To address this issue, this paper introduces a power decoupling method. This method utilizes a bidirectional buck–boost converter, connected in parallel to the DC link, to divert SRP to a small capacitor within the single-phase grid-connected PV inverter, eliminating the need for electrolytic capacitors. The proposed topology consists of a dc–dc stage, a decoupling stage and an inverter stage, where each stage is controlled independently. In consideration of the instantaneous power fluctuations on the filtering elements, the optimal voltage reference of the decoupling capacitor is derived and implemented in the proposed decoupling control strategy. Thus, the capacitance for decoupling is minimized and the volume of the inverter is reduced. Discontinuous current control is adopted to charge and discharge the decoupling capacitor, which simplifies the decoupling control design. Finally, the steady-stage and dynamic responses of the proposed inverter are validated by simulation and experimental results in a 1-kW PV prototype.