Short-circuit Current Calculation For Distribution Networks With Distributed Power Sources Connected

The large-scale integration of distributed power sources has introduced more energy conversion and control links to the distribution network,resulting in an increase in the nonlinearity of the system and a fundamental change in its fault characteristics.Moreover,the parameters in the distributed power source fault equivalent model are influenced by the uncertainty factors at the moment of fault occurrence,so there is uncertainty in the calculated value of short-circuit current at a certain time in the future.Therefore,the traditional short-circuit current calculation methods for distribution networks cannot meet the increasing penetration rate of distributed power sources.Therefore,it is particularly important to study short-circuit current calculation methods suitable for distribution networks with distributed power sources.To solve the nonlinear equations of distribution network short-circuit current calculation with distributed power sources,this paper proposes a method based on Newton iterative algorithm to solve the short-circuit current:This method separates the real part and imaginary part of the current in the node equation,derives the voltage amplitude and phase angle correction equations,and corrects the node voltage amplitude and phase angle by solving the voltage amplitude and phase angle correction values obtained from the correction equations.The calculation is iterated continuously until the correction values reach convergence accuracy.The proposed algorithm was tested on an improved IEEE 15 node system,using PSCAD simulation results as the standard,and compared with traditional short-circuit current calculation methods for distribution networks with distributed power sources.The results indicate that the proposed method has high accuracy.In addition,compared with the Gaussian Iterative method,the proposed algorithm requires fewer iterations and is more efficient.To address the issue of uncertainty in the calculation results of short-circuit current after faults caused by the instantaneous power uncertainty of distributed power sources,an affine arithmetic based short-circuit current interval algorithm for distribution networks with distributed power sources is proposed,considering the power fluctuation of distributed power sources:The proposed algorithm is divided into two stages:the first stage is the moment of fault occurrence,and a conservative interval affine optimization model for the injection current of distributed power sources is established.The fluctuation range of the power of distributed power sources at the moment of fault occurrence is used as a constraint to solve the fluctuation range of the injection current amplitude of distributed power sources;The second stage is to establish an affine optimization model for the short-circuit current range of the transmission line after a fault occurs.The fluctuation range of the injected current amplitude of the distributed power source at the moment of the fault occurrence is used as a constraint to solve the range of the short-circuit current amplitude of the distribution network transmission line.Comparing the proposed algorithm with Monte Carlo method,the interval of the line short-circuit current amplitude obtained by the proposed algorithm is slightly larger than that calculated by Monte Carlo method,so the proposed method has good conservatism.Moreover,the proposed algorithm does not need iterative calculation,and the calculation speed is significantly improved compared with the Monte Carlo method.