Centralized power control strategy for AC-DC hybrid micro-grid system using multi-converter scheme

In this paper, an ac-dc hybrid micro-grid system including a centralized power control scheme is proposed. Multiple ac-dc bidirectional converters connected in parallel are considered in the system instead of a single converter that connects ac and dc buses. The proposed control scheme is basically coordination of two modes-control of power through the converters and selection of converter units. The power through the converter is controlled because the load unbalance between ac and dc buses should be mitigated. Selection of converter units is also important because each small unit can deal partial amounts of power of the entire micro-grid system and therefore control of parallel operation of multiple converter units should be considered. If any converter fails to operate in the system then the alternate converters come into operation, so that the micro-grid system will not be totally disconnected and thus reliability of the system is ensured. This will also increase the efficiency of the system during low power transmission condition. The system operation is investigated under three different conditions to show the effectiveness of the proposed control scheme.