A Hybrid Binary Multilevel Cascaded Inverter for Medium-Voltage Applications

This paper introduces a hybrid binary cascaded multilevel inverter (BCMLI) that allows the supply voltage of the lowest level to be a floating capacitor and thus reducing the need of multiple separated sources. Multiple such BCMLIs can be cascaded to increase the number of levels. This paper extends the configuration with two of 3-cell hybrid BCMLI modules cascading to achieve 29 voltage levels. A utility-scale hybrid BCMLI was designed and built using a single-source as the input and LLC converters to produce the 2-kV, 11.2-kW step-like output with 15 voltage levels. Two of such units were further cascaded to produce the 4-kV, 22.4-kW step-like output with 29 voltage levels. The circuit and control have been designed and simulated, and the hardware prototype has been built and tested. The total harmonic distortion was measured at 3.5% under the full-load condition. The LLC stage is a gallium nitride based converter operating at 1 MHz for an ultra-compact design. As the only loss is on the LLC stage, and high-voltage side is nearly lossless, the overall system efficiency exceeds 98.8%.