Research On Security Region Characterization And Power Flow Problem Using A Dynamic System Based Method

Power flow calculation and security region characterization are the core tools for the stable and safe operation of power systems,providing support for power system planning,safety analysis,optimal power flow,transmission capacity analysis,and other applications.However,with the advancement of the construction of the power system with renewable energy as the main body,energy services such as storage and integrated energy systems have emerged to help achieve the goals of carbon neutrality and peak carbon dioxide emission.Since a large number of renewable energy,storage,and multi-energy entities are connected to the power grid,the resource allocation,safe operation,and reliable power supply are facing huge challenges.Based on the dynamic system theory,this research develops corresponding theories and solving algorithms for the power flow calculation,the optimal allocation of storage using a region-based method,and characterization of the integrated energy system security region.The main research contents are as follows:(1)A power flow calculation method based on the trajectory of the dynamic system is proposed.The method can robustly give a high-voltage power flow solution when the power flow solution exists,and maintain stable computing performance under heavy loading conditions;when the power flow solution does not exist,the degree of unsolvable power flow is quantified by the degenerated stable equilibrium point.Based on its mismatch information,a robust power flow restoration method is proposed to quickly restore power flow.The algorithm overcomes the shortcomings of traditional power flow methods,such as frequent divergence,sensitivity to initial values,and inability to provide power flow recovery information.(2)A complete characterization of multi-period security region based on the parametric dynamic system is proposed.Based on the uncertainty model of renewable energy,the energy storage model,and the AC power flow model,the definition of the multi-period security region is given.A three-stage characterization technique based on the decoupling idea is developed.The introduction of two decoupling parameters reduces the problem dimension and computational complexity.By proving the relationship between the multi-period security region and the regular stable equilibrium manifolds of corresponding parametric dynamical systems,the complete and rapid characterization of the multi-period security region is realized.(3)A multi-objective energy storage optimal allocation model that considers the nonlinear energy storage model and integrates the users’ preference for each objective is proposed.An improved three-stage method based on a dynamic system is used to quickly locate the preferred feasible solution and the preferred Pareto optimal solution.The optimization goal of storage allocation considers the optimization of system flexibility in addition to traditional operating costs and environmental costs.The maximization of the flexibility will be reflected in the expansion of the multi-period wind power feasible injection region.This optimization goal will maximize the role of energy storage to support a high proportion of renewable energy consumption.(4)A complete characterization method of the integrated energy system security region based on the quotient gradient dynamic system is proposed.Based on the AC power flow model,the nonlinear natural gas model,the nonlinear heat system model,and the renewable energy uncertainty model,the analytical expression of the integrated energy system security region is realized.By proving the relationship between the regular stable equilibrium manifold of the quotient gradient dynamics system and the integrated energy system security region,the complete characterization of the integrated energy system security region is achieved for the first time.The proposed method is robust and accurate.(5)In order to further improve the computational efficiency of the security region,a fast characterization technology of the integrated energy system security region based on the fast and slow dynamic system is proposed.By exploring the two time-scale properties of the dynamical system,the decomposition of the dynamical system into the fast and slow dynamical system is realized.Based on the relationship between the fast-slow dynamic system and the dynamic system in the trajectory and the stable equilibrium manifold,the equivalent relationship between the fast-slow manifold and the integrated energy system security region is established.The non-convex and disconnected features of the integrated energy system security region are also fully explored.