Control strategy for a three phase series-connected hybrid inverter system

A hybrid inverter system aiming at a higher voltage higher capacity higher efficiency inverter system having fewer harmonics in its output is proposed. The system consists of a GTO inverter operating in a square-wave switching mode and a neutral-point-clamped IGBT inverter operating in a PWM switching mode. The former produces a basic part of the resultant output. The latter not only produces an additional part of that to control the resultant output, but also offsets the harmonic components generated by the GTO inverter. A basic control strategy for the hybrid inverter system is proposed, and its validity is verified by experimental investigations.