Frequency Regulation Strategies of BESS and Doubly-fed Variable Speed Pumped Storage Unit Under Multiple Operating Conditions

Renewable energy generations have limited frequency capability, and their increasing penetration brings severer challenges to the frequency regulation of power grids. Meanwhile, emerging electrical devices such as doubly-fed variable speed pumped storage unit (DFVSPSU) or battery energy storage system (BESS) provide an opportunity for advanced frequency regulation. As opposed to fixed-speed pumped storage units, DFVSPSU can respond to grid frequency changes in both generating and pumping conditions with large capacity. With the rapid discharge/charge characteristics, BESS can participate in the power grid frequency regulation quickly. Therefore, combining different frequency regulation advantages of DFVSPSU and BESS, a frequency regulation strategy considering different operating conditions to ensure frequency safety is put forward in this paper. Firstly, the advanced strategy adopts power priority and speed priority control methods for the control of DFVSPSU. Furthermore, a coordinated control method of virtual inertia and virtual droop is developed for the control of BESS. Finally, using MATLAB/Simulink platform, dynamic simulations are carried out in a modified IEEE-9 bus system integrated with DFVSPSU and BESS to verify the feasibility and effectiveness of the proposed strategy.