Efficiency Investigation of a Battery Modular Multilevel Management Converter System

Abstract:
This paper presents a performance analysis of the battery modular multilevel management (BM3) topology. For this purpose, its performance is compared for different configurations, varying by the number of battery cells connected in series in each submodule of the inverter system. Calculations are made by simulating an electric vehicle model in the worldwide harmonised light-duty vehicles test procedure (WLTP), differentiating in terms of inverter, battery and system efficiency, as well as semiconductor and battery losses. Results show, that increasing the voltage level of each submodule leads to an improvement in the total system efficiency. Additionally, an analysis of the junction temperatures of the MOSFETs confirms the advantages of using a higher number of battery cells in each submodule due to a decrease in the temperature of the semiconductors. Another aspect of this analysis of the BM3 topology is the effect of increasing the number of MOSFETs connected in parallel at each switch position on the performance of the inverter system. Parallelizing MOSFETs improves the performance by reducing the conduction losses of the semiconductors. However, the use of more than three semiconductor switches adds practically no benefit in either efficiency increasing or in temperature reduction, but significantly rises the cost of the system.