Research On Active Frequency Response Coordinated Control Of AC And DC Interconnected Grid

The frequency response capability determines the frequency stability of the power system,and the current high proportion of renewable energy,high proportion of power electronics(double high)power system shows low fast frequency response(low inertia,low primary frequency regulation capability)characteristics,the pressure to maintain frequency stability under large disturbances has increased suddenly.In view of the characteristics of the spatial and temporal distribution of frequency under large disturbances,which limits the fast frequency response of back-to-back DC systems and the difficulty of existing frequency control measures to effectively coordinate the control different frequency regulation resources,the research related to active frequency response coordinated control of AC and DC interconnected grid is presented in this paper.The scope of application and theoretical depth of active frequency response control are extended: based on the core idea of active frequency response and its framework,for the backto-back DC interconnection scenario,the active frequency response control principle considering frequency safety is proposed;furthermore,from the perspective of the cost of emergency control,the active frequency response control principle that coordinates safety and economy is proposed.A regional grid frequency response model is built: frequency response models for thermal,hydro and gas units with dynamic characteristics;a general frequency regulation model for energy storage and a generator-load model.In addition,in order to accurately abstract and describe the network structure of the actual grid,a dynamically revisable back-to-back DC system network structure model and its contact line frequency response model are established.In order to balance the grid frequency regulation demand and the energy storage device’s own SOC state limitation,a refined energy storage frequency response model with adaptive SOC feedback constraints is established.An active frequency response control strategy for back-to-back DC systems is proposed: based on the analysis of the DC modulation function and scheduling rules of the back-to-back DC interconnection system,a three-stage active frequency response control strategy of the back-to-back DC system considering frequency safety is established based on the model predictive control algorithm,taking into account the transient characteristics of different frequency station after the disturbance.On this basis,an active frequency response control strategy is proposed for the optimal coordination of frequency safety and operation economy,taking into account the virtual control characteristics of energy storage devices and the difference of control costs under different control methods of frequency regulation resources.Simulation examples and result analysis show the good feasibility and applicability of the proposed two strategies.The proposed active frequency response control strategy for back-toback DC interconnection system can improve the frequency response and power support capability of the back-to-back DC system and achieves the optimal allocation of power shortage.The proposed safety and economic coordinated active frequency response control strategy further can realize the reduction of active regulation cost through the optimization of performance-cost economic coordination among frequency regulation resources.Based on the idea of active frequency response,for the back-to-back DC asynchronous interconnection scenarios,the method proposed in this paper can give full play to the overall frequency response of the back-to-back DC system;for the optimal control of safety and economic coordination,the method proposed in this paper can effectively coordinate the economic cost on the basis of ensuring the safety and stability of the system frequency,which provides effective solutions to the severe situation of frequency stability in power systems after large disturbances.