Active compensation of unbalanced supply voltages for two-stage direct power converters using the clamp capacitor

Unbalanced supply voltages can be fully compensated in boost type power converters with active front end if sufficient energy storage is provided by the DC-link capacitor. In converters that have no energy storage, for example in a matrix converter, the maximum voltage transfer ratio will be reduced if one or more input lines is at a reduced voltage. Control techniques to compensate the effect of unbalanced voltage supply for matrix converters allow for a limited output voltage and power capabilities, which depends on the level of unbalance. This paper proposes the utilization of the clamp capacitor, which is normally needed only to protect a Direct Power Converter (DPC), to extend the operating range of a Two-Stage DPC during unbalanced supply conditions preserving its theoretic maximum voltage transfer ratio capability. This solution is validated through simulations.