The medium voltage direct hanging energy storage system has been widely used in high capacity applications, which gets rid of power frequency transformer and is of high conversion efficiency. This paper introduces the medium voltage direct hanging energy storage system topology scheme. In order to improve the battery life and capacity utilization, the in-phase and inter-phase battery equalization control strategies are studied. Finally, the simulation results on medium voltage direct hanging energy storage system prove the correctness and effectiveness of the equalization control strategy.
Constant speed pumped storage unit is widely used, however it cannot adjust the input power when working in the electric mode, and cannot work in the best efficiency when the head of the reservoir changes greatly. Therefore, it is necessary to study and develop the variable speed pumped storage systems. This paper has studied on variable speed operation of static frequency converter for pumped storage units. Besides, development status of variable speed pumped storage system at home and abroad is investigated. Furthermore, classification and advantages and disadvantages of variable speed pumped storage system are also introduced, mainly including two typical variable speed pumped storage systems, i.e., doubly-fed variable speed system and full power variable speed system.
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