Individual DC Voltage Balance Control for Cascaded H-Bridge Electronic Power Transformer With Separated DC-Link Topology

For the electronic power transformer, the dc voltage balance is an important issue. Unbalanced dc voltages will degrade the performance of the device and may trigger the dc voltage protection. In this paper, an overall individual dc voltage (including high-voltage and low-voltage dc-link voltages) balance strategy is proposed for the electronic power transformer with separated dc-link topology. The strategy adjusts active powers flowing through the isolation and output stages in different power modules to enhance the dc voltage balance capability. Through the strategy, the high-voltage and low-voltage dc-links can be well balanced when unbalance occurs among different power modules (e.g., component parameter mismatches or some of the high-voltage or/and low-voltage dc-links are connected with renewable energy sources or/and dc loads). The proposed strategy is analyzed and supported by experimental validation.