Selected harmonic reduction in static D-C — A-C inverters

An a-c voltage control technique is described that eliminates the third and fifth harmonic voltage present in the a-c load-voltage waveform of a 2-controlled-rectifier or transistor d-c to a-c single-phase inverter. The addition of two more controlled rectifiers or transistors to the basic circuit makes it possible to control the fundamental frequency component of the a-c load voltage from maximum to zero without reintroducing the third and fifth harmonics. The same technique can be used in a 12-controlled-rectifier or transistor d-c to 3-phase a-c inverter. In the case of the 3-phase inverter, the lowest harmonic of the fundamental frequency present in the line-to-line a-c voltage is the eleventh.