Research On Frequency Control Of Variable-Speed Pumped Storage Units Participating In Wind Power-Containing Grids

In the context of China’s ecological civilization construction,with the "dual-carbon" goal being incorporated into the overall layout,China is accelerating the transformation towards a new energy-dominated power system,represented by wind power.However,the issue of reduced power system inertia and weakened grid frequency regulation capacity due to large-scale wind power grid connection is becoming increasingly apparent.Pumped storage power stations can operate as both power generation and energy storage facilities,and by configuring technologically mature and operationally flexible pumped storage power stations,a high proportion of renewable energy can be integrated into the power system to facilitate new energy consumption and maintain power system security and stability.The new type of variable-speed pumped storage unit adopts a Doubly Fed Induction Generator as the power generation motor,which can achieve variable-speed constant-frequency operation compared to conventional pumped storage units.By adjusting the current and voltage in the machine-side and grid-side converters,the decoupled control of active and reactive power of the unit can be achieved,and the unit’s operating efficiency can be improved by adjusting the rotor speed.In order to better play the important role of the DFIG pumped storage unit in grid frequency regulation,this paper studies the control strategy of the DFIG pumped storage unit participating in system frequency regulation,with the following main work:Firstly,a power grid simulation model with a variable-speed pumped storage unit is constructed,and the modeling of the variable-speed pumped storage unit is studied in detail.The variable-speed pumped storage unit is composed of a DFIG,a converter,a pump-turbine,and a governor.Considering the slow response of the pump-turbine power,based on the operating characteristics of the DFIG and the pump-turbine under the power generation and motor conditions,two different control strategies,namely power priority and speed priority,are proposed.The control strategy for the rapid power response of the variable-speed pumped storage unit suitable for grid frequency regulation is determined through simulation comparison of the unit under different operating conditions.Secondly,in the process of the variable-speed pumped storage unit participating in the primary frequency regulation of the power grid,considering the issues of new energy consumption and economic cost of grid frequency regulation,an optimized control strategy is proposed for the variable-speed pumped storage unit and wind power unit to participate in the primary frequency regulation of the power grid.This strategy improves the frequency regulation capacity of the power grid and completes the optimal allocation of active power required for primary frequency regulation from the perspective of frequency regulation economy.A prediction model is established based on the system’s state space equations,considering the operating restrictions of the variable-speed pumped storage unit and wind power unit,and introducing the power balance constraint of primary frequency regulation of the power grid.The optimization control of the variable-speed pumped storage unit power change and wind turbine pitch angle change is carried out with the aim of minimizing the frequency regulation cost of the variable-speed pumped storage unit and wind power unit.The effectiveness of the proposed strategy is verified based on the MATLAB/Simulink simulation platform,and the results show that compared with the traditional PI control,this strategy not only has better frequency regulation effect but also achieves the optimal power allocation of the variable-speed pumped storage unit and wind power unit based on economic efficiency during the frequency regulation process.Finally,during the process of variable-speed pumped storage units participating in grid secondary frequency regulation,the water hammer effect of the unit itself will have a negative impact on the grid secondary frequency regulation when there is a large change in active power of traditional hydropower units.In this paper,an additional control loop is added to the variable-speed pumped storage unit when the active power of the unit is given.The opening of the guide vane of the traditional hydropower unit is fed back to the variable-speed pumped storage unit as a control input in advance.When the traditional hydropower unit experiences power rejection,the variable-speed pumped storage unit can supplement the power shortfall in a timely manner,improving the quality of grid secondary frequency regulation.In addition,due to the longer time scale of grid secondary frequency regulation,the fluctuation of active power of wind power units is considered as a system power disturbance,and model predictive control is used to minimize the grid frequency deviation as the control objective,taking into account the operational constraints of each unit,and achieving optimal allocation of active power among various frequency regulation units.The effectiveness of the above control strategies is verified on the MATLAB/Simulink simulation platform.By comparing the frequency regulation without pumped storage units and with traditional PI control participating in grid frequency regulation,the strategy has a significant improvement effect in reducing the maximum frequency deviation of the grid and shortening the frequency recovery time.