Reduced-Switch-Count Six-Leg Converters for Three-Phase-to-Three-Phase/Four-Wire Applications

Two reduced-switch-count ac/ac dc-link six-leg converters are investigated in this paper. The proposed topologies allow for three-phase-to-three-phase power conversion to supply a three-phase four-wire load without any capacitor dc-link-midpoint connection. The converters provide bidirectional power flow and power-factor control. Pulsewidth modulation techniques are derived by using the concept of local and general apportioning factors. The overall control strategy for providing dc-link voltage and power-factor control is presented. A control strategy to obtain the maximum utilization of the dc-link voltage is also proposed. In addition, several relevant characteristics of the converter are addressed, such as voltage analysis, distorted and unbalanced voltages operation, shared-leg currents, power rating, and total harmonic distortion. The proposed converters are compared to six-leg converters that use the capacitor dc-link-midpoint connection and also to the full-bridge seven-leg converter. Experimental and simulated results are presented.