Unbalance Compensation for PV-Dominated 3P-4W Distribution Networks

Three-phase four-wire low-voltage distribution networks exhibit unbalance issues due to arbitrarily connected devices. Owing to current limiting in three phases and neutral line, as well as limited measurement and communication links, unbalance compensation is challenging. This paper presents a hierarchical unbalance compensation control strategy using PV inverters for 3P-4W low-voltage distribution networks, which consists of two tactics based on the variation of communication conditions, namely decentralized and distributed control. The decentralized control is the optimal unbalanced current compensation for local or downstream load, which is designed decentralized and appropriate for PV inverters with only local measurement. The distributed control is the unbalanced current compensation at substation transformer, which can be implemented by means of executing compensation instructions by PV inverters with a low bandwidth one-way communication to the transformer. By accurately calculating the injected negative and zero sequence currents of PV inverters, unbalance compensation can be achieved considering the complex current and power constrains of PV arrays. The effectiveness of the proposed control method is valid by hardware-in-loop tests.