A Power-Decoupled Current-Source Inverter for PV Energy Harvest and Grid Voltage Regulation

The single-phase microinverter (SMI) is becoming one of the most cost-efficient interfaces for bridging photovoltaics (PV) and power systems. However, in the maximum power point tracking operation, the SMI injects an intermittent active power to the grid, which leads to voltage variations at the point of common coupling (PCC). This certainly dampens the power quality of grids. Besides, the power mismatch between the dc and ac terminals of SMIs will render a double-line-frequency pulsating power at the dc terminal, which inevitably increases the power ratings of the circuit components of the SMIs. To address these issues simultaneously, a power-decoupled current-source inverter (PD-CSI) is proposed in this article. The PD-CSI can provide the required reactive power compensation for regulating the PCC voltage. Meanwhile, it is imbedded with an active power decoupling circuit, which can actively store the double-line-frequency pulsating power in a film capacitor so that the PV can be operated at a constant dc current. The state-space model and steady-state operation of the PD-CSI are elaborated. The controllers are designed for achieving the active power decoupling operation and the PCC voltage stabilization. Experimental and simulation results in an 110-V ac microgrid have been provided to validate the simultaneous functionalities of the active power decoupling and grid voltage regulation for the proposed PD-CSI.