Single-Phase Hybrid Cascaded H-Bridge and Diode-Clamped Multilevel Inverter: RL Load Case

Each of the three multilevel inverter topological families - diode-clamped, cascaded H-bridge and flying capacitor - has its particular advantages and disadvantages. Hybrid multilevel inverters, combining two topologies, can yield more advantages than each possesses and even result in novel behavior, as in the case of connecting together a single-phase diode-clamped inverter and a single-phase cascaded H-bridge inverter in series. This paper considers such a hybrid inverter supplying moderately-lagging power factor loads, which results in a different number of waveform levels than for unity power factor loads. A novel modulation scheme optimized for this load type is proposed, which yields lower harmonic distortion for both lagging power factor and unity power factor loads than when using the existing modulation scheme. Simulation and test results are shown as corroboration of the reduced distortion.