| At present,a large number of renewable energies are integrated into the power grid which has a great impact on the quality of power system frequency for the uncertainty and volatility of its output.Energy storage system has the advantages of fast response,high accuracy and bidirectional transmission of energy which has been widely used in power system,and the auxiliary power grid frequency regulation with energy storage system has become one of the hot research fields.The energy storage system of auxiliary power grid for frequency regulation is generally distributed in the grid side and power generation side,and it is of great significance to design a reasonable control strategy.The energy storage converter is a power electronic device and it lacks inertia and damping characteristics.Therefore,the VSG technology is applied in energy system in the grid side,but most studies ignore the influence of the physical constraints of the energy storage system in the VSG control strategy,which leads to the control strategy is not suitable enough for energy system.The research focus of auxiliary frequency regulation control strategy for energy storage system on the generation side is to coordinate the output distribution control of energy storage system and traditional generation.Actually,due to the large demand for energy storage capacity on the generation side,multiple energy storage systems are generally required for frequency regulation.Different energy storage systems have different characteristic parameters and different output priorities in different grid environments.In the process of frequency modulation,it is necessary to comprehensively improve the effect and benefit of frequency modulation,which has not been fully considered,and the comprehensive control strategy is ought to be studied.Firstly,the equivalent model of grid side energy storage system and generation side energy storage system participating in power grid frequency regulation is established.According to the characteristics of multiple energy storage systems participating in frequency regulation,a system equivalent model considering the technical characteristics of energy storage system is proposed.Different system parameters are configured according to the characteristics of different energy storage systems,which can effectively reflect the participation of different energy storage systems in frequency regulation.Secondly,the application of VSG in energy storage converter is mainly studied for the control strategy of auxiliary frequency modulation of energy storage system at grid side.The equivalent model of VSG is established,and its grid operation characteristics are analyzed.According to the constraints of the energy storage system,the key control parameters of the virtual synchronous machine are designed.An optimal VSG control strategy based on grid frequency variation is proposed.In the process of auxiliary frequency regulation of grid side energy storage system,this strategy can adaptively change the key control parameters,optimize the dynamic process while maintaining certain inertia and damping of the system,and meet the requirements of physical constraints of energy storage system.Finally,the process of energy storage system participating in automatic generation control(AGC)is mainly studied for the control strategy of auxiliary frequency modulation of energy storage system at the generation side.Several typical control methods of AGC frequency regulation by energy storage system at generation side are described.At the same time,the technical characteristics of different energy storage systems and the influence of different grid conditions on AGC frequency regulation effect are analyzed.On the one hand,the multiobjective programming algorithm is applied to improve the control effect of the system in economy,frequency quality and state of charge of the energy storage system.On the other hand,the optimal solution selection method based on adaptive weight factor is proposed to bring different factors into the decision-making process in the selection of strategies,the effect and benefit of frequency modulation are effectively improved.The effectiveness of the two optimal control strategies is verified by Matlab / Simulink platform.The results of simulations prove the superiority of the proposed control strategies by comparing with other strategies. |
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