Short Circuit Calculation Of Distribution Network With Distributed Generation

Under the dual pressure of energy demand and environmental protection,distributed generation,as an effective supplement to centralized power generation,has been vigorously developed.However,at present,there are many types of distributed generation,and its structure and access mode are quite different from the traditional AC synchronous motor.Its transient output characteristics are greatly affected by the control strategy,which leads to great changes in the short-circuit current output characteristics of distributed generation.With the increasing penetration of distributed generation,its impact on the safe and stable operation of distribution network is becoming more and more significant,resulting in the power flow of distribution network from one-way to two-way,short-circuit current and short-circuit capacity increase.In addition,when the short-circuit fault occurs in the distribution network,it may cause large-scale disconnection of distributed generation.Therefore,it is particularly important to carry out the research on the transient output characteristics of distributed generation and explore the shortcircuit calculation method suitable for the distribution network with distributed generation.Firstly,based on the analysis and summary of the control method of grid side inverter and the low voltage ride through strategy based on reactive current support,this paper builds a simulation model through PSCAD to simulate the transient output characteristics of the inverter distributed generation,and analyzes the influence of the control strategy on the transient output characteristics of the inverter distributed generation.Then,according to the grid connection mode,DG is divided into the grid connected distributed generation of motor type units and the grid connected distributed generation of inverter type.Considering the control strategy,the voltage control current source fault calculation model of the inverter type distributed generation is given,and the motor type grid connected distributed generation is equivalent to the fault calculation model of impedance and voltage source in series.Based on the fault calculation models of these two types of distributed generation,the fault calculation model of distribution network is established.The motor type distributed generation and the inverter type distributed generation are used as two kinds of excitation sources to act on the distribution network with short circuit fault.The distribution network is regarded as a linear distribution network.By using the superposition theorem,a short circuit calculation algorithm of distribution network with distributed generation is given.The forward and backward method is used to calculate the power flow of distribution network,and the node voltage before fault is obtained.The fault components of each node and branch are obtained by superposition theorem.In order to decouple,the iterative method is used to calculate the fault current generated by inverter grid connected distributed generation.Finally,Matlab is used to program the proposed algorithm,and IEEE 14 bus distribution network is selected as an example to verify the correctness and effectiveness of the short circuit calculation method for distribution network with distributed generation.