An active line conditioner to balance voltages in a three-phase system

In this paper a new configuration for an active line conditioner is proposed to correct dynamically voltage unbalances in a three-phase AC system. In the proposed system it is shown that the injection of a correction voltage V/sub inj/ in one phase is sufficient to nullify the negative sequence voltage component in the incoming three phase supply. The resulting three phase voltages at the load terminals are essentially positive sequence voltages and hence are balanced. It is further shown that the kVA requirement of the proposed active line conditioner is small, typically 3% for a ten percentage unbalance in the input supply. The dynamic cancellation of the negative sequence voltage component by the proposed scheme drastically improves the performance of induction motor loads connected to a weak AC system. A thorough analysis of the scheme along with the suitable design guides are presented. Finally selected experimental results on a laboratory prototype active line conditioner are detailed.