Short-term Power Supply Capacity Evaluation In Active Distribution System Considering Uncertainties

The power supply capacity(PSC)of distribution network(DN)refers to the maximum load that DN can supply under the branch power and node voltage constraints,which is one of the important indexes of reliability and security.With the transition from traditional DN to active distribution system(ADS),the randomness and uncertainties of high-proportioned distributed energy resources(DER)have rising impacts on DN.The flexible load(FL)and energy storage(ES)have given users more initiative.Furthermore,complex fault conditions and variable topologies have effects on the PSC.Thus the PSC is affected by various uncertainties,and it is vital to consider them during the evaluation,which is of great guiding meaning on the planning,dispatching and operation of ADS.Define DER,load and ES as the "unit" s of ADS.In order to describe the impacts of uncertainties,the outputs of fixed load and DER were forecast based on error correction,and the probability models were built with related probability distributions.Considering the impacts of electric price on FL and ES,the probability models of interruptible load,transfer load and ES were established.Finally,the multi-senario of "unit" s outputs was generated based upon the scenario generation and reduction technique.The fault ranking method,which was used to sort the possible faults in DN,was combined with the multi-senario of “unit”s outputs,to establish the multi-senario of PSC evaluation.In order to evaluate the PSC quantitatively,a series of probability evaluation indexes were defined in value,fluctuation,contribution etc.to evaluate the PSC with the repeated power flow method based on the relative growth rate.At last,an IEEE case study was employed to verify the correctness and effectiveness of the method.The results of the probability evaluation to quantify the power supply capacity are analyzed from the numerical size,fluctuation level,contribution degree the PSC of ADS is evaluated by the repetitive power flow method based on the relative growth rate,and the correctness and validity of the algorithm are verified by an IEEE example.In the operation of ADS,the access of DER will effectively increase the PSC.In order to obtain the PSC changes quickly when inserted DER switched,the sensitivity analysis(SA)was carried out.Based on generalized sensitivity formula,the SA of PSC evaluation indexes were conducted and the sensitivity formulas were deduced.Within a certain capacity of DER,the sensitivity indexes could apply to projecting the PSC values and its evaluation indexes accurately,improving the evaluation efficiency of PSC.