Decentralized Suppression Strategy of Common Ground Circulating Current Caused by Grounding Fault in PV Modules in Single-Phase PV Grid-Connected Systems

The complicated series-parallel wiring and aged insulation of photovoltaic (PV) power plants leave the system prone to PV grounding faults. The resultant common ground circulating current will increase the operation stress of the switching devices and jeopardize system stability. To address these problems, a comprehensive decentralized control strategy is proposed in this paper to suppress the circulating currents. The influence of the PV grounding fault on the system stability is firstly analyzed. Based on the equivalent form of the circulating currents, a control strategy is designed to suppress the common ground circulating current. Furthermore, to ensure the stable currents and DC-link voltages during grounding fault transients, another control strategy is designed to operate the three-level PV interfacing converter for suppressing the overshoots of the currents and DC-link voltages. With the two controllers and the three-level converter, the generated circulating currents can be effectively eliminated in both steady and transient states. It is worthy of mentioning that the proposed methods are a decentralized control scheme, which can improve the stability and scalability of the system. The effectiveness of the proposed solution is validated by performing the real-time hardware-in-loop tests.