A secure system integrated with DC-side energy storage for renewable generation applications

Massive energy storage capability is tending to be included into bulk power systems especially in renewable generation applications, in order to balance active power and maintain system security. This paper proposes a secure system configuration integrated with the battery energy storage system (BESS) in the dc side to minimize output power fluctuation, gain high operation efficiency, and facilitate fault ride through, which is suitable for unidirectional renewable power generation systems (power transfer from renewable sources to the grid). The system utilizes robust diode units (DUs) to protect receiving-end devices against dc faults. Also, the BESS and half-bridge modular multilevel converter (MMC) at the receiving end can operate safely and flexibly to achieve stable and high-quality power transfer, in both source power intermittency and dc-link fault cases. Depending on BESS sizing, the source system power fluctuation can be reduced (absorbed by the receiving-end BESS) when a receiving-end grid fault occurs. Topological configuration and control design of the proposed system are pre-sented. Simulation results show the effectiveness of the proposed system in both dc and ac fault cases, with power fluctuation elimination functionality highlighted. The receiving-end operation losses are investigated, showing a high-efficiency system. In addition, key system implementation considerations regarding the proposed system are elaborated.