The Optimal Allocation Of Energy Storage Considering Uncertainty And Inertia Support In T&D System

With the issue of environmental pollution becoming increasingly serious,reducing carbon emissions has become a widely recognized consensus in human society.Vigorously develop-ing renewable energies to replace traditional fossil fuels is one of the key measures to address this problem.With the penetration of high-proportion renewable energies and the widespread application of power electronic devices in power systems,there have been significant changes in the planning,design,and operation mode of power systems.During the energy substitution process,there are two major challenges that the power system is facing.Firstly,the volatility of distributed renewable energies and increasing diversity in user loads present uncertainty prob-lems in the system.To achieve safe and efficient operation of power systems,it is necessary to balance risks and benefits and make full use of available resources.Secondly,as renewable en-ergies based on power electronic equipments replace traditional fossil fuel-based synchronous generators,the original rotational inertia in power systems is reduced,which is significantly af-fecting the system frequency stability.This thesis focuses on the role played by energy storage systems（ESSs）in addressing these two major challenges,including planning,design,optimiza-tion,operation,etc.,the highlights and main contributions of which are elaborated below.（1）The thesis proposes the optimal operating strategies of a flexible interconnected power system considering with ESSs.Faced with the trends of increasing renewable energy pene-tration and diversified user loads,a new type of honeycomb flexible interconnected network（HFIN）topology is introduced first,which takes the power electronic-based smart power/in-formation exchange station（SPIES）as the core device.Through flexible interconnection,mu-tual power support,and other means,it overcomes the shortcomings of traditional topology of power systems and plays multiple roles of ESSs.Subsequently,a two-stage dispatching model of HFIN consisting of day-ahead scheduling and real-time operation is established.The former determines the day-ahead scheduling plan based on forecast data,while the latter contains multi-ple uncertainties caused by the implementation of operational scenarios,which may bring about dispatching cost risks.Inspired by risk management methods in the financial sector,this thesis uses conditional value-at-risk（CVa R）to model multiple uncertainties and risks in the two-stage dispatching of HFIN.Monte Carlo simulation and K-means clustering algorithms are applied to obtain multiple uncertainty scenarios.Therefore,a two-stage stochastic optimization dis-patching model for HFIN considering CVa R is established,and numerical simulation is used to verify the proposed method.Based on the proposed optimization method,the risk dispatching results verify the feasibility of the two-stage dispatching method for HFIN considering multi-ple uncertain risks,and reveal the economic dispatch role of network-integrated ESSs and the backup mutual power support from the shared ESSs in SPIES.By analyzing the multi-time scale operating characteristics of flexible interconnected power systems with ESS under steady-state conditions,the foundation is laid for the further studies about the configuration problems of siting and sizing of ESSs.（2）The thesis proposes the a siting and sizing method of ESS considering the robust op-eration of interconnected power systems.Considering the shortcomings of using stochastic optimization methods to handle extreme operating scenarios,and based on the multi-time scale operating characteristics of ESSs,further exploration is conducted on the optimal siting and sizing of multi-role ESSs.For the proposed HFIN system,considering the uncertainty of re-newable energies and extreme operating scenarios,and combining the backup mutual power support from the shared ESSs in SPIES,a robust optimization method for ESS siting and sizing that satisfies system emergency backup constraints is proposed.Combined with the column and constraint generation algorithm and the big-M method,the proposed optimization model can be decomposed into a mixed-integer second-order cone programming（MISOCP）master problem and sub-problems for iterative solution.Based on the optimization results of the test-ing case,the feasibility of the proposed robust optimization method for ESS siting and sizing is verified.In addition,compared to existing interconnected power systems,the proposed HFIN system utilizes the multi-role characteristics and operation flexibility of ESS.This leads to a decrease in the configuration and operational costs associated with ESS,while still satisfying the emergency reserve requirements of the system.Besides,the operational lifespan of ESS is also relatively longer.（3）The thesis proposes an optimal configuration method for grid-forming ESS consid-ering inertia support under transient-state conditions.To address the issue of the insufficient rotational inertia caused by the transition from traditional fossil fuels to renewable energies,a feasible solution is to install ESSs with virtual inertia（VI）at appropriate locations for improving the system frequency stability.Building on the previous work,the further research investigates the optimal configuration of ESSs under transient-state conditions.For the grid-forming con-trolled ESS with virtual synchronous generator（VSG）control,the state-space model of the system dynamic is first established.In order to more accurately evaluate the characteristics and transition mechanism of transient disturbances in the system,an appropriate method for equivalenting the disturbance strength of nodes is proposed based on Kron reduction.Then the guidance of allocating ESSs optimally for improving system transient performance is provided via H₂-norm calculation and projected gradient derivation.Through the time-domain simula-tion verification,the proposed method can significantly improve the system’s post-disturbance transient performance.Meanwhile,the proposed node disturbance equivalenting method en-hances the efficiency of VI configuration.（4）The thesis proposes an optimal configuration method for grid-following ESS consid-ering inertia support under transient-state conditions.Unlike grid-forming controlled ESSs,traditional grid-following controlled ESSs usually do not have the ability of inertia response.Therefore,additional VI control should be added to grid-following control and the correspond-ing configuration strategy needs to be explored.Based on the proposed optimization method for improving system transient performance targeting H₂-norm and the node disturbance equiv-alenting method inspired by Kron reduction,a VI optimal configuration method for a grid-following/grid-forming hybrid system is thus proposed.Based on the time-domain simulations,the effectiveness of the proposed method is verified.Through the comparative analysis of op-timization results,the respective characteristics and differences of the two different ESS VI implementation methods are revealed from the perspective of transient inertia support,which will provides a guidance for the optimal configuration of ESSs.