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. A multilevel voltage-source inverter can be formed by connecting one of the MLDCLs with a single-phase bridge 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 pulsewidth 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 well as the number of gate drivers 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.