Research On Control Strategy Of Distributed Energy Storage For Frequency Regulation In New-type Power System

With the proposal of the national dual carbon goal,the scale of grid connection for renewable energy source(RES)such as wind power and photovoltaic is rapidly increasing,leading to new challenges for grid frequency security.The high proportion of RES connected to the power grid based on power electronic equipment reduces the equivalent inertia of the power grid.At the same time,due to the random fluctuation of the output of RES,it is more prone to system frequency instability caused by power imbalance in the power grid.Distributed energy storage systems(ESS)based on grid connected power electronic converters have advantages such as fast response speed and flexible operation mode,which can alleviate the frequency regulation pressure brought by the "high renewable energy and power electronics" power system to traditional units.This thesis mainly studies the control strategy of distributed ESS when participating in primary and secondary frequency regulation of the power grid.This thesis first derives the frequency regulation equivalent model of a new-type power system containing RES,and discusses the impact of RES on the frequency response characteristics of the power grid.An equivalent model of power grid frequency regulation with ESS is established and simplified,and the equivalent models of primary and secondary frequency regulation of regional power grids with ESS is determined.The control strategy of distributed ESS participating in the primary frequency regulation of the power grid have studied and improved,and adaptive adjustment of frequency regulation control methods and parameters is achieved.A strategy for ESS is proposde which combines the virtual inertia control method and the virtual droop control method with real-time fuzzy adaptive adjustment of the weight coefficients based on frequency changes.Meanwhile,the SOC change and its upper and lower limit constraints are considered by a nonlinear adjustment method.Through numerical analysis,it is verified that this strategy can balance the frequency regulation effect of the power grid and the SOC of ESS,and has good adaptability to different distributed ESS.To deal with the problem of large-scale solution for distributed ESS participating in the optimization of power grid secondary frequency regulation,an intermediate aggregation unit is introduced in the distributed ESS scheduling process to reduce the number of variables in the optimization of power grid frequency regulation.Based on this,a two-layer control strategy for distributed ESS participating in power grid secondary frequency regulation is proposed.The first layer takes the frequency regulation consumption function of the energy storage aggregation control unit as the objective,and performs power instructions issued by the dispatch center to the energy storage aggregation control unit.The second layer aims to balance the SOC of each distributed ESS in the energy storage aggregation control unit,and ultimately determine the frequency regulation output power of each distributed ESS.A simulation calculation model based on MATLAB/Simulink is established and Cplex is called for solution.The results show that the use of aggregation method can reduce the computational workload of the dispatch center,and the economic assignment of ESS power can be achieved through a two-layer control strategy,taking into account the differences in charge states of distributed ESS.