Research On Coordinated Control Strategy Of Thermal Power And Hybrid Energy Storage System For Secondary Srequency Modulation

With the incorporation of a large number of renewable energy into the power grid,thermal power units are more and more frequently involved in the frequency modulation of the power grid.However,thermal power units have problems such as slow response speed and difficulty in tracking the frequency modulation command in the process of participating in the secondary frequency modulation.To solve this problem,a hybrid energy storage system composed of energy-type lithium ion battery energy storage unit and power-type flywheel energy storage unit can be used to assist the secondary frequency regulation of thermal power units.Therefore,there is an urgent need to study the capacity allocation method of hybrid energy storage system and the coordination control strategy of thermal power unit-hybrid energy storage system.In this paper,a 250 kW/50 kWh flywheel energy storage unit and a 250 kW/500 kWh lithium-ion battery energy storage unit are used to assist the secondary frequency regulation of the thermal power unit.The main work is as follows:(1)In this paper,the control system characteristics of thermal power units are firstly studied in depth,and the physical process of secondary frequency regulation of thermal power units is investigated.Then a simulation model of a thermal power unit with an installed capacity of 250 MW is established and its dynamic characteristics are verified by building a simulation model of the turbine,boiler and turbine digital electro-hydraulic regulation system in Matlab/Simulink.(2)A simulation model of a 250 kW/50 kWh flywheel energy storage unit and a 250kW/500kWh lithium-ion battery energy storage unit was developed in Matlab/Simulink.Finally,the dynamic characteristics of the flywheel energy storage unit and the lithium-ion battery energy storage unit are verified.(3)The structure of the hybrid energy storage system connected to a thermal power unit is analysed to obtain the charge and discharge commands of the hybrid energy storage system,and then the wavelet packet decomposition method is used to decompose the obtained charge and discharge commands.The number of layers of wavelet packet decomposition and the nodes allocated to different energy storage arrays are determined according to the signal band bandwidth of each layer after wavelet packet decomposition and the response time of different energy storage units,so as to obtain the reference power of the energy storage arrays.finally,according to the calculation method of the secondary frequency regulation integrated index of thermal power units,a hybrid energy storage system capacity allocation method is proposed to ensure the secondary frequency regulation integrated index is increased by two times,while the capacity of the storage system is reduced to the greatest extent.(4)By establishing a joint simulation model of thermal power unit-hybrid energy storage system,the effect of secondary frequency modulation of two different coordinated control strategies of power frequency division and real-time compensation is compared,the principle of turbine rotor life loss is analyzed,and then a coordinated control strategy of thermal power unit-hybrid energy storage system based on real-time compensation and state of charge(SOC)of hybrid energy storage system is proposed,The service life loss of steam turbine caused by responding to AGC instructions is reduced.Finally,according to the actual output power data of a thermal power unit with a rated installed capacity of 250 MW,the proposed coordinated control strategy is verified through the simulation experiment of the thermal power unit-hybrid energy storage system model.