A Three-Phase Smart Inverter for Frequency and Voltage Regulation in an Unbalanced Distribution System

In recent years, the use of renewable energy (RE) in distributed power generation has been increasing. However, a key drawback of RE is unstable power output that causes systemic effects. Moreover, with the increasing penetration of RE in three-phase distribution systems, the problem of unbalanced three-phase systems becomes increasingly challenging. This paper proposes a novel control strategy for a grid-connected three-phase four-wire smart inverter. By using the proposed power control strategy and the positive- and negative-sequence decoupling controls, the smart inverter can provide not only frequency but also voltage regulation to maintain a balanced and stable system. To verify the feasibility of the proposed method, a 2 kW grid-connected three-phase four-wire prototype inverter was implemented, which was connected to a three-phase AC source for analysis. The experimental results indicate that the proposed control strategy is a feasible scheme. System frequency regulation and phase voltage compensation can be achieved to support the system under an unbalanced or unstable condition.