Research On Control And Protection Strategy Of Large-scale Energy Storage System

The energy storage technology can smooth the power fluctuation of the intermittent power plant via its PQ-control strategy and make it possible and stable for the synchronization of the intermittent power plant and the grid. Therefore, it’s important and necessary to study on the large-scale energy storage system (ESS) comprehensively.First of all, this paper makes the deduction of the mathemetical model of the power conducting system (PCS), most of which are voltage source converters (VSC). Using the convertion among three-phase symmetric coordinate system, a-β coordinate system and d-q coordinate system, the mathemetical model of the PCS is deducted under two-phase rotating coordinate system, as well as its models under positive d-q coordinate and negative d-q coordinate. These models lay a solid fundation on the deduction of the ESS’s control strategy in the following part.According to the two different operation modes of the ESS, the deduction processes of corresponding control strategies are given in this paper under grid-connected situation and islanding situation. After the simulation verification in the electromagnetic simulation software, the PQ-control and Vf-control are proved to be accurate and reliable as the cotrol strategies of the ESS under different modes.The most important part of this paper is the design and proposing of the fault diagnosis and protection strategy, according to the structure of the ESS which is made up of several energy storage units in parallel. On the basis of the study of the main structure and operation modes of the ESS, as well as its control strategies, the theoretical analyses of the ESS with different fault locations are made and the simulation verifications are proceeded, considering the distinctive fault features of the ESS. Using the analyses and summaries of the simulation results, a novel protection strategy, which is suitable for the large-scale ESS, is proposed and proved to be effective after the test and simulation verification. This protection strategy and simulation results of the grid-connected ESS can be useful and with reference value when designing and configurating the protection of the MW-level ESS.