Multiple modularity topology for smart transformers based on matrix converters

Abstract

A novel matrix converter-based topology to be applied in smart transformers (STs) is proposed, based on the concept of multiple modularity. To replace the conventional ST topology obtained by H-bridge modules including DC electrolytic capacitors, the proposed ST topology uses two kinds of matrix modules to provide flexibility in the AC–AC structures to build complex ST. Fewer power semiconductor devices are used in each module to reduce the costs. The AC–AC matrix converters and the high-frequency transformers eliminate electrolytic capacitors, enhancing ST reliability and power density. The modulation method for the proposed ST structure needs suited carrier waves and switching processes. The half-Venturini modulation method shows several switching sequences leading to voltage imbalances in the input film capacitor divider. Therefore, the paper investigates and analyses the influence of switching sequences on the capacitor voltages in detail. The results show that the different switching sequences will cause different currents flowing into capacitors, leading to different results in capacitor voltages. Based on the analysis, proper modulations are recommended for the proposed topology. In order to verify the feasibility of the proposed topology as well as the correctness of the analysis on modulations, simulations and hardware-in-loop experiments are carried out. It is found that the modularity concept is feasible, and a suitable modulation sequence was developed to balance the input capacitors voltages.