Studies On Spatio-temporal Coordination Of Load Restoration Considering Renewable Energy Participation

In recent years,renewable energy sources(RESs)are widely integrated in power grids all over the world,and they become the indisputable part of power systems.The risk of bulk system blackouts as well as the difficulty of power system restoration is increased because of the penetration of intermittent and fluctuant RESs.The uncontrolled re-integration of RESs makes the restoration process more complex.However,with improved control ability,RESs can be flexiable sources that provide power support to benefit restoration system restoration(PSR).Therefore,it is necessary to itegrate RESs into PSR optimizations.Since large-scale load shedding is a common phenomenon in a partial or complete collapse of a power system,the load restoration is critical for restoring power service and completing the whole PSR process.In order to ensure the efficiency and security of the restoration process,the study of RES penetrated load restoration is significant.Aiming at the highly efficient load restoration using RESs,the dissertation establishes the framework of spatio-temporal coordination of load restoration considering RES penetration.Series of studies handle several problems including the decision-making in the uncertain load restoration process,the spatial coordination of load restoration in the coupled transmission and distribution(TS-DS)system,and the temporal coordination of multi-step load restoration decisions.The main contents and contributions are summarized as follows:1)The framework of spatio-temporal coordination of load restoration considering RES penetration is established.First,in order to handle the uncertainty problem in the load restoration process,the utility-oritend decision-making method is proposed.It traces the risk of uncertainties,accelerates the restoration process by applying RESs and avoids security violations.Furthermore,in order to realize the spatial coordination,the decentralized load restoration scheme for the TS-DS system is proposed.Accordingly,the effeicncy and security of restoration are ensured by the independent decision-making as well as coordination of regional grids in the TS-DS system.Finally,the two-stage receding horizon control(RHC)scheme is proposed to realize the temporal coordination.The two-stage RHC coordinates the multi-step load restoration under load-source uncertainties and provides better arrangements of RESs in the dynamic decision-making process.2)A new utility-based load restoration optimization method is proposed to deal with decision-making problem under uncertain conditions.The method combines the risk and return of load restoration strategy and provides the utility function to present the preference of strategy.Furthermore,the utility-oriented optimization model is constructed to select the strategy with the largest utility value with a certain confidence level.To achieve efficient utilization of on-line data and ensure highly computational efficiency,the utility-oriented optimization is transformed as a scenario-based linear program(LP)problem.The utility-oriented method fills the gap between on-line data and the optimal load restoration strategy under uncertain conditions,and it has flexible robustness regarding security requirements and data exactness.Therefore,it is particularly applicable for on-line load restoration with wind power penetration.The effectiveness of the proposed method is validated using IEEE-30 bus test system and a practical power system from the northeast of Shandong province,China.3)A new decentralized load restoration scheme is proposed in order to realize efficient restoration coordination in the TS-DS system.First,to maintain independent operations of the TS operator(TSO)and DS operators(DSOs)and avoid the centralized data processing burden the TS-DS system is divided into several subsystems according to their physical connection.Then,in order to implement the independent but coordinated decision-making of subsystems,a decentralized decision-making framework is established by model decoupling and iterative interaction between TS and DSs.Furthermore,for the sake of the convergence of the non-convex models integrated iterative calculation process,the original decentralized optimization method is further improved to obtain the optimal decentralized load restoration strategy.The proposed decentralized restoration scheme considers detailed operation of bulk system load blocks so that RESs in multi-voltage level grids are utilized.Besides,it solves the non-convergence problem of the decentralized optimization method and allows independent decision-making of the TSO and DSOs.The effectiveness of the proposed method is validated using two IEEE standard test systems and a real-world power system.4)A conditional value-at-risk(CVaR)based two-stage RHC method is proposed for the efficient dynamic load restoration decision-making in the RES penetrated TS-DS system.First,the framework of RHC load restoration decision-making is established.Accordingly,the multi-step coupled load restoration process is completed by coordinating multi-scale time-horizon and correcting corresponding parameters.Therein,the CVaR value is employed to describe uncertainties of the load and source sides.It benefits uncertain on-line load restoration by tracing the threshold of load source uncertainties with fast calculation.Further,in order to improve the computation of the multi-step load restoration optimization in the TS-DS system,two-stage load restoration models are constructed with the first stage relaxed multi-step optimization and the second stage single-step tracing optimization.By solving LP,mixed integer linear program(MILP)and mixed integer quadratic program(MIQP)problems,the proposed CVaR based two-stage RHC method achieves on-line receding horizon load restoration of the coupled TS-DS system facing with load-source uncertainties.The effectiveness of the proposed method is validated using the IEEE standard test systems and a real-world TS-DS system.