Simplified variable frequency multilevel inverter topology

Multilevel inverters offer high power capability, associated with lower output harmonics and lower commutation losses. The important disadvantages are their complexity, requiring a great number of switches, and a rather complex control circuitry. This paper reports a new multilevel inverter topology using an H-bridge output stage with a bidirectional auxiliary switch with variable frequency. The topology produces a significant reduction in the number of switches and capacitors required to implement a multilevel output. The new topology is used in the design of a five-level inverter. It uses only five controlled switches, eight diodes, and two capacitors. The new topology achieves a 37.5% reduction in the number of main power switches required (five in the new against eight in any of the other three configurations) and uses no more diodes or capacitors that the other configurations require. Additionally, the circuit required for multilevel inverter operation is implemented using a microcontroller circuit, reducing overall system cost and complexity. Theoretical predictions are validated using simulation in Matlab, and satisfactory circuit operation is proved with experimental tests performed on a laboratory prototype.