Single‐stage high‐frequency‐isolated three‐phase four‐leg buck–boost inverter with unbalanced load

Abstract

A three-phase four-leg inverter shows its preponderance on providing energy to unbalanced load and high DC-link utilisation. To increase the power density of the traditional three-phase four-leg inverter with power frequency isolation, this study proposes a single-stage isolated three-phase four-leg inverter. To ensure the symmetry of three-phase output voltages, the proposed converter provides the path for neutral current resulted by the unbalanced load. It achieves buck-boost DC/AC conversion by introducing the transformer whose turns ratio provides additional voltage gain. The working frequency of the transformer is in accord with the switching frequency, so high-frequency electrical isolation is realised with a single-stage structure as well. The specific mode analysis and the relationship between the switching states and the voltage vectors are presented. A modified three-dimensional space vector pulse width modulation algorithm with a simplified section partition method is proposed, which guarantees the voltage-second balance of the transformer within one switching cycle as well. In order to explore the feasibility of the topology and control strategy, the simulation is done by MATLAB/Simulink. Then a prototype was built in the lab and the experimental results verify that the inverter can produce balanced voltages under both balanced and unbalanced load.

Leakage Current Reduction in Single-Phase Grid-Connected Inverters—A Review

“…Recent research focuses on designing a single-stage buck-boost inverter topology [84][85][86], basically to reduce the number of components such as switches; also, the two-stage power conversion results in the complex circuit structure and control algorithm [87]. Generally, single-stage buck-boost inverters consist of distinct circuits operating individually in buck/boost or positive/negative modes, the latter leading to crossover distortion in the output current [88].…”