Three-phase transformerless series-connected current source inverter with capacitor voltage balancing control method

Abstract

In medium-voltage and high-power applications, the series-connected current source converter (SC-CSC) is a good candidate. However, most existing series-connected CSCs require transformers. Recently, a single-phase transformerless series-connected current source converter has been proposed. It eliminates the bulky and costly transformer, achieving lower cost and smaller system size. In this work, the three-phase version of this inverter is proposed and investigated. Since the original single-phase topology cannot be directly extended to the three-phase system, the original topology is modified to eliminate circulating currents. In practical implementations, mismatches in capacitors can destroy the inherent voltage balance of the inverter. To address this issue, a voltage balancing control strategy is introduced to regulate the capacitor voltages under parameter mismatch conditions. The proposed control method restores the capacitor voltage balance without modifying the topology or affecting its current balancing characteristics. The operation principles of the proposed three-phase inverter and the effectiveness of its capacitor voltage balancing strategy are validated through MATLAB/Simulink simulation results.