| At present,the proportion of renewable energy such as solar energy and wind energy in power grid energy supply is increasing.However,renewable energy power generation is affected by natural conditions and often shows unstable characteristics.Therefore,the high penetration of intermittent renewable energy power generation will bring a series of technical challenges to power grid interconnection,power quality,reliability protection,scheduling control and other aspects.Hybrid Energy Storage(HES)combines various storage units to form an energy storage system with higher overall value,which can improve the flexibility of the power grid,increase the integration of renewable energy,and make up for the imbalance between power consumption and power generation.Therefore,the hybrid energy storage system including flywheel energy storage with fast response speed and long cycle life and lithium battery is taken as the basis of this study.In view of the problems arising from the first frequency regulation of new energy power generation stations,the study takes wind power plant as the research object,and uses flywheel energy storage to meet the instantaneous power fluctuation demand.The flywheel combined with lithium battery is used to meet the time and power fluctuation demand of new energy power station,and the positive significance of"flywheel+lithium"hybrid energy storage system in enhancing the power grid’s absorption capacity of wind power and improving the power quality of the power grid is explored.Firstly,the basic units of the hybrid energy storage system of"Flywheel+lithium" are studied.In terms of flywheel energy storage,based on the basic structure and working principle of the flywheel device,a double-closed-loop charge and discharge control strategy of the flywheel energy storage system was proposed.In this strategy,permanent magnet synchronous motor was selected as the flywheel drive,and the motor control mode was controlled by constant torque Angle in vector control,so as to improve the output response ability of the energy storage unit.In the aspect of lithium battery energy storage,the polarization characteristics of batteries are considered in the design of control strategy,and the influencing factors of battery terminal voltage change are modeled and analyzed to ensure the safe operation of the energy storage unit.Then,simulation models of flywheel energy storage and lithium battery energy storage were built by MATLAB,and the chargingdischarge output characteristics of the two energy storage modes were analyzed,which laid a foundation for studying the primary frequency modulation control of wind farms assisted by hybrid energy storage system.Secondly,the capacity configuration scheme of "flywheel+lithium" hybrid energy storage system is optimized.For wind power generation system,an economic evaluation model of hybrid energy storage system based on wavelet packet decomposition was established.The wind power signals were decomposed into wave signals in different frequency bands,and then frequency modulation tasks of lithium battery energy storage and flywheel energy storage were assigned.In order to maximize Net Present Value(NPV),the minimum annual energy storage cost is taken as the objective function,and the pattern search method is used to solve the problem,so as to compare the economy of different configuration schemes.Based on MATLAB platform simulation,it is verified that this research can not only ensure the frequency modulation performance of wind farm-energy storage hybrid system,but also determine the energy storage capacity of wind farm based on economic optimization,as well as the configuration ratio of flywheel energy storage and lithium battery in the hybrid energy storage system,so as to improve the overall economic benefits of the system.Finally,in order to improve the effect of primary frequency modulation in the gridconnecting process of new energy power stations,a combined wind-storage control system is designed,and a control strategy of primary frequency modulation assisted by "flywheel+lithium" hybrid energy storage system is proposed.Based on the analysis of the operating data and frequency modulation performance of wind farm power generation equipment,the dynamic model of wind power generation system is constructed.Combined with the output characteristics of "flywheel+lithium" hybrid energy storage system,the energy management architecture of the system is designed to suppress random fluctuations of grid-connected power and ensure the safe operation of energy storage equipment.The combination method of sliding average filtering and fuzzy control is adopted to rationally distribute energy storage compensation power.While improving the primary frequency modulation performance of the system,the recovery time of hybrid energy storage system is shortened,and the State of Charge(SOC)of energy storage unit is improved,so as to realize the complementary advantages between flywheel and lithium battery.The simulation analysis based on the MATLAB platform shows that:when the system frequency is disturbed,the scheme can effectively improve the primary frequency modulation effect of the new energy power station by adjusting the output power of the hybrid energy storage system,and enhance the power grid’s absorption capacity of renewable energy.In the frequency modulation process,the hybrid energy storage system can maintain good adaptability to the change of compensation power,realize the reasonable distribution of frequency modulation power,and extend the service life of each energy storage unit. |
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