Improvement of EMI behavior of NPC multilevel inverter without balancing the voltage boundaries of DC bank capacitors

摘要

For multilevel inverters, the balancing of the voltage boundaries of DC bank capacitor permits to attenuate the low frequency ripples of the output voltage. In addition, this operating gives outstanding results with high switching frequency, especially for differential conducted mode. In contrary, the common conducted and radiated modes can be deteriorated, and so necessitate input and output performing EMI filters. The originality of this work is to analyze a NPC multilevel inverter with low switching frequency, without balancing the voltage boundaries of DC bank capacitors, and without using EMI filters. To ensure a satisfying differential conducted mode, a Modulated Hysteresis Current Control (MHCC) is used. This principle uses a low switching frequency mono carrier signal. So, the common conducted mode is highly strengthened, and the radiated emission is attenuated especially if the technique of laminar bus bar connection is used. The values of the THD voltage and current, of the output power factor, of the test bench efficiency validate the proposed technique.