Cascaded converters for EVs with single power source and increased power quality

Purpose – The aim of this paper is to improve and adapt cascaded multilevel converters for electric vehicles (EVs) to have all the advantages of these converters and to eliminate its limitations in the use of EVs applications. Specifically, the purpose is to use only a single power source (battery pack, fuel cell, etc.) and generate a higher power-quality than regular multilevel converters. Design/methodology/approach – This paper is based on a cascaded multilevel converter conformed by two 3-level inverters connected in series. The voltage sources of the auxiliary inverter were replaced by floating capacitors which work as active filters, reducing the power sources to one. The floating capacitor voltages were controlled by a PI controller that adjusts the modulation index (m) to obtain a zero average power in the auxiliary inverters, and a predictive control selects the optimal redundant state to reduce the error and balance in all the capacitor voltages. As the modulation index is determined by the PI controller, the output voltage magnitude must be controlled by a variable voltage source (e.g. buck-boost chopper). Additionally, the converter works with new optimal voltage asymmetries to obtain higher power quality and capacitor control stability. Findings – The proposed converter uses a topology that conventionally generates 9-levels of voltage, but with the proposed asymmetry it can generate 11-levels. Also, the auxiliary power sources were eliminated. Research limitations/implications – The proposed solution has a limited dynamic response due to the variation rate of the capacitor voltage, which is limited by the load current and the capacitance. However, the dynamic response and control stability is satisfactory for EVs applications. Originality/value – The paper presents a new control to manage the floating capacitor voltages and uses new voltage asymmetries in cascaded multilevel converters.