AC characteristics in AC/DC/DC conversion

The use of line commutated static converters can cause significant problems in power-supply networks, owing to the reactive power and the harmonic components generated. Technological improvements in power transistors suggest that DC/DC convertors supplied by diode rectifiers could be applied more profitably than phase-controlled AC/DC convertors. This especially holds true for applications where inversion of the power flow is not required. The paper considers the AC characteristics of a double conversion system composed of a 3-phase bridge diode rectifier loaded by a PWM chopper. The relationships between the AC currents, chopper modulator parameters and pulse number of the AC/DC rectifier are investigated. The chopper operating conditions, which provide a balanced system of alternating currents are determined: consequently, an improvement in the overall power factor is obtained.