Enhanced Buck–Boost Neutral-Point-Clamped Inverters With Simple Capacitive-Voltage Balancing

In traditional neutral-point-clamped (NPC) inverters, two major operating issues encountered are their relatively limited voltage-buck variation range and capacitive-voltage imbalance, which can cause low-order harmonics to appear at the inverter output. Various methodologies have so far been introduced for extending the inverters' variation range to include voltage-boost operation, but they generally require the inclusion of large passive components or have not yet been optimized in terms of waveform quality. The balancing of their capacitive voltages using a simple technique has also not yet been investigated in the context of buck-boost energy conversion, even though relevant techniques for traditional NPC inverters do exist but are generally overburdened by the accompanied switching loss increase and more complex control and hardware circuitries. To address these two topological concerns simultaneously, two new buck-boost NPC inverters with simple capacitive-voltage-balancing capability are proposed. Both inverters are demonstrated to exhibit a doubling of voltage gain, with one of them also shown to produce a better output waveform quality. Simulation and experimental results are provided for verifying the viability and practicality of the proposed inverters.