| In the context of coping with global climate change and achieving the goal of "carbon neutrality",vigorously developing renewable energy such as photovoltaic and wind energy,and realizing the clean transformation of energy production is an inevitable choice to alleviate the energy crisis and climate warming.However,the fluctuation and uncertainty of wind and solar bring severe challenges to the safe and reliable operation of distribution networks(DN).To address these challenges,this thesis focuses on the utilization and safety problems caused by the high proportion of distributed generations(DGs)connected to the distribution network,and carries out research on the dispatchable region of distributed generations(DRDGs),starting from the level of "model-theory-algorithm-application".The main content and contributions of this thesis are as follows:(1)With the maturity of distributed generations technology,the DRDG based on the simplified linear model can no longer meet the requirements of complex control schemes.Therefore,the theory of the nonlinear dispatchable region of distributed generations and a complete characterization method are proposed in this thesis.The model of DRDG includes nonlinear AC power flow equations,thermal limit constraints,various distributed generation models and other security constraints,etc.To characterize the DRDG,a nonlinear dynamic system—quotient gradient system(QGS)is developed,and it has been proved theoretically that the DRDG equals the union of regular stable equilibrium manifolds of the QGS.Based on this theory,a method for fast characterization of the dispatchable region is proposed.It is verified by calculation examples that the method can accurately characterize the dispatchable region of distributed generations with various control modes,and possesses efficient calculation speed and robust numerical convergence characteristics.(2)A large number of discrete control actions are used in the DN,such as capacitor banks and on-load tap changer,etc.Aiming at the DRDG with discrete variables,a two-stage discrete dispatchable region characterization algorithm based on QGS is developed.The first stage solves the relaxed solution after the discrete variables are relaxed,and in the second stage,the branch pruning operation is used to solve the discrete operating points.The numerical results show that the proposed method can accurately characterize discrete dispatchable region of distributed generations,and the effect of discrete tap positions on the DG hosting capacity in distribution networks is directly demonstrated.(3)In the distribution network,the proportion of energy storage and electric vehicles is increasing.Among them,the energy storage has multi-period coupling charge-discharge characteristics,while electric vehicles are flexible loads with significant timing characteristics,so the single-period DRDG can no longer meet the operation requirements.In this thesis,the multi-period DRDG is proposed,and the coupling model of energy storage and a variety of electric vehicle timing sequence models are added.The multi-period DRDG is characterized by QGS.Furthermore,the supporting effect of energy storage on the hosting capacity of renewable energy in the distribution network and the influence of electric vehicle volatility on the DRDG are analyzed through the simulation example.(4)This thesis conducts preliminary exploration of three application scenarios in the DRDG from the application level.Firstly,the DRDG is used to evaluate and improve the safety of distribution network,which can directly identify the dangerous scenarios and shore up the weak spots to improve the safety of operation.Secondly,a generalized dispatchable region of distributed generations with objective function constraints is proposed to provide a reference tool for operators with both safety and economy.Finally,the evaluation index of distribution network operation and planning based on DRDG is developed,which provides a new dimension reference for planning and operation optimization. |
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