| In order to cope with environmental pollution,energy crisis and climate warming,large-scale integration of renewable energy generations(REGs)will become the main feature of the future distribution systems.The impacts of large-scale REG integration on distribution systems are as follows.On the one hand,REGs can meet local load demand,which supports the reliability and power supply capacity of distribution systems.On the other hand,the power flow characteristics of the distribution systems will be largely changed,which may cause problems such as reverse power flow and overvoltage.Moreover,the output power of REGs brings about strong uncertainty,which further increases the difficulty of distribution system analysis and decision.Therefore,it is necessary to carry out the research on the evaluation and promotion methods of key technical indicators of distribution systems under the large-scale integration of REGs.The main contributions of this dissertation are as follows.1)In order to evaluate the reliability index more comprehensively and to support the coordinated power supply capacity analysis,a novel REG-integrated distribution system reliability evaluation method is proposed.The target distribution system includes substations and medium voltage networks,and this method considers the substation transformer faults and REG integration.Based on the feeder partition,a fault impact analysis method for distribution systems with substation transformer is proposed.And the reliability evaluation process based on quasi sequential Monte Carlo simulation is proposed.2)The existing studies fail to take into account the various reliability requirements of users,resulting in a large margin of power supply capacity results.In order to deal with this problem,an analysis method of power supply capacity and planning economy for two-level distribution systems is proposed.The differential reliability constraints and REG integration are considered.In order to analyze the coupling relationship between power supply capability and reliability under the condition of REG integration,the overall and differential reliability constraints are added to the power supply capability evaluation model.Considering the power supply capacity and total cost of distribution system,the power supply cost is analyzed.3)In order to solve the problem of overvoltage in distribution system with largescale REGs,the active-reactive voltage control and optimized operation method is proposed.The influencing factors of voltage deviation are analyzed by theoretical derivation.Besides capacitor banks,REGs and energy storage devices are introduced and the voltage deviation index is improved.The solution is realized by hybrid coding scheme and adaptive particle swarm optimization algorithm based on distributed entropy.4)In view of the strong uncertainty brought by REGs,an active distribution system flexibility evaluation method considering the prediction error of REGs and load is proposed.The direction matrix is extended to sequential direction matrix,which is used to describe the specific direction of the uncertain space in the operation of distribution systems.Based on the sequential direction matrix,the uncertain variables are described.On this basis,the mathematical model of active distribution system flexibility evaluation is established,which is a main problem nested with a sub problem.It is used to quantify the adaptability of distribution systems under the disturbance of multiple uncertain variables.5)An active distribution system flexibility evaluation method considering the probability characteristics of REGs and load is presented.Based on the concept of probability sequence,REG probability modeling and load probability modeling are carried out.Then the uncertainty region with probability characteristics is constructed.The weight coefficient is introduced into the objective function of the main problem to reflect the influence of probability characteristics on flexibility evaluation. |
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