Multilevel DC link inverter

This paper presents a new class of multilevel inverters based on a multilevel DC link (MLDCL) and a bridge inverter to reduce the number of switches, clamping diodes or capacitors. An MLDCL can be a diode-clamped phase leg, a flying capacitor phase leg, or cascaded half-bridge cells with each cell having its own DC source. Connecting one of the MLDCLs with a single-phase bridge inverter can form a multilevel voltage source inverter. The MLDCL provides a DC voltage with the shape of a staircase approximating the rectified shape of a commanded sinusoidal wave, with or without pulse width modulation, to the bridge inverter, which in turn alternates the polarity to produce an ac voltage. Compared with the cascaded H-bridge, diode-clamped and flying-capacitor multilevel inverters, the MLDCL inverters can significantly reduce the switch count as the number of voltage levels increases. For a given number of voltage levels, m, the required number of active switches is 2×(m-1) for the existing multilevel inverters but is m+3 for the MLDCL inverters. Simulation and experimental results are included to verify the operating principles of the MLDCL inverters.