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

Abstract

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.