A Low Frequency Ripple Current Suppression Strategy for Single-Phase Photovoltaic Grid-Connected Inverter

Due to the absence of the insulated transformer, the non-insulated photovoltaic (PV) inverter possesses excellent properties such as small size, light weight, etc. However, the inherent parasitic capacitance between the PV panels and the ground brings serious leakage current problem, which has been the focus of researchers. Since the instantaneous power of the single-phase inverter results in a ripple current at a double-frequency ripple(100Hz), according to the theorem of conservation of power, the fluctuation of PV panels output voltage leads to a double frequency ripple of input current, which will have a negative influence on the maximum power point tracking in terms of PV panels and reduce the utilization efficiency of solar energy. This paper aims to investigate the suppression of the leakage current of PV single-phase inverters and the double-frequency ripple, the circuit proposed in this paper substitutes a bridge arm of the conventional PV grid-connected inverter with a Boost converter, which can eliminate the leakage current directly. The suppression strategy of double-frequency ripple for the proposed topology is provided as well. By transferring the double-frequency ripple in the DC-link capacitor of the inverter to another capacitor that has no connection to loads, it can suppress the low-frequency ripple current of the input side effectively. The paper verifies the feasibility of the proposed topology and the corresponding control strategy through simulation and experimental results.