A unified power compensation system for the large-scale grid-tied renewable energy generation system

This paper proposed a unified power compensation (UPC) system by using a cascaded inverter plus DC/DC boost converters as the interfacing circuit between the high voltage level power grid and the battery storage systems in order to both compensate the real power fluctuation produced from the renewable energy generation systems and provide the reactive power compensation capability without shortening the battery life cycle when needed. The proposed system can manage the state-of-charges (SOCs) of batteries to be equal to avoid the overcharge or overdischarge of single battery stack. Meanwhile, the dc-link voltages of all H-bridge modules assumed in the cascaded inverter can be easily controlled to be equal also under the condition of producing/absorbing real or reactive power. The multifold operation will assist the renewable energy generation systems to be the grid friendly power sources.