Novel unity power factor circuits using zero-vector control for single-phase input systems

This paper proposes two novel circuits which realize a unity input power factor single-phase to three-phase converter with a motor load. The power supply is connected to the neutral point of the motor, and the three-phase inverter is controlled to act also as a virtual ac/dc converter leg. This virtual leg is controlled by zero vectors of the three-phase inverter. The main features of these circuits are as follows. No inductive components are required. A reduction in the number of switching devices compared with conventional topologies. Motor current increases because converter input current also flows through the motor windings. A full-bridge converter can be built using the same number of switching devices as the conventional half bridge and with no need for a capacitive leg with an accessible neutral point. In this paper, the proposed full-bridge-type circuit is experimentally tested using a 750-W induction motor as load.