Control of a hybrid seven-level PWM inverter

A control strategy to operate a hybrid multilevel inverter is described in this paper. The inverter produces seven-level PWM voltage waveforms using twelve transistors and a three-phase transformer for harmonic elimination offering the following advantages: flying capacitors with neutral clamped circuits are not required, a small number of switching devices is used and the PWM switching losses are minimal. The proposed control technique is implemented on an 8 - bit microcontroller, and was designed to operate all the transistors of the converter using only one carrier and modulating signals, offering a simple control solution. The circuit operation and the design of the control principle are discussed in this paper together with experimental results obtained with a 1 kW prototype.