Benefits of cascaded inverters for electrical vehicles' drive-trains

Currently small electric vehicles use low voltage batteries around 48V with high current levels in order to reach a power of several kW for the traction chain. One of the objectives of future converters is to increase the AC amplitude to higher levels (up to 300V) in order to decrease current level, while keeping the same transferred power. As a consequence of higher voltage levels, the global conduction losses will be reduced in the traction chain. Voltage source inverters are generally used in order to drive electric motors. Multilevel voltage source inverters, namely cascaded H-bridge, are under investigation in this paper, in their application to electrical vehicles. This paper presents a numerical and experimental analysis of cascaded H-bridge inverters. The expected benefits of cascaded inverters for electric vehicle are a better management of battery cells, improved output voltage waveforms and spread thermal losses sources. Several parameters and experimental results are investigated in this paper such as converter losses, efficiency, volumes (heat sink, passive components) and spectral analysis of output voltage.