Research On Fault Equivalent Method For Distributed Generation With High Penetration Rate In Distribution Network

Due to the cleanliness and renewable characteristics of renewable energy,renewable energy such as wind power and photovoltaic power generation has gained worldwide attention.In most cases,the renewable energy power generation connect to the power grid as distributed generation(DG).As the DG penetration rate increases,the influence from the DG on the fault characteristics of the power grid will increase gradually.Therefore,it is necessary to study the fault characteristics of DG.In particular,it is necessary to study the equivalent fault characteristics of DGs with high penetration rate.DG can be divided into inverter type,asynchronous type and synchronous type according to interface.Among them,the fault characteristics of inverter type and doubly fed asynchronous type differ greatly from traditional power generation.In this paper,inverter-interfaced distributed generation(IIDG)based on PQ control and doubly fed induction generator(DFIG)is taken as the research object to study the fault equivalent method for DGs with high penetration rate in distribution network.First of all,the domestic and international research on IIDG and DFIG are investigated comprehensively,including the control strategies and fault characteristics of IIDG and the fault characteristics of DFIG and their related equivalent method.Taking into account the principle of PQ control and the low voltage ride through(LVRT)and current limiting characteristics of the IIDG,PSCAD simulation model of the IIDG is builded.At the same time,considering the fault characteristics of DFIG and its characteristics of LVRT,the PSCAD simulation model of DFIG is completed.Secondly,the fault characteristics of the IIDG based on the PQ control strategy are analyzed in detail.Based on the analysis,the fault equivalent method of multiple IIDGs connected to the same bus is analyzed,including the fault equivalent method for multiple IIDGs with same capacity and multiple IIDGs with different capacity.At the same time,based on the relationship between the adjacent buses,the iterative calculation method is used for the equivalence for multiple IIDGs at different location.Then the fault equivalent method for multiple IIDGs in distribution network is proposed.The method divides the distribution network by the fault location and AC power supply location,and then equates the IIDGs in the same area to achieve the equivalent fault characteristics of the IIDGs.Simulation in PSCAD verifies the validity and accuracy of the fault equivalent method for IIDG with high penetration rate.In addition,based on the electromagnetic characteristics of DFIG,the fault current expression of DFIG considering the impact of crowbar is deduced.By analyzing the fault characteristics of multiple DFIG connected to the same bus,an accurate equivalent method by accumulate the fault current for DFIGs connected to the same bus is obtained.By using the relationship between the electrical quantities of adjacent buses and the fault current expression of a single DFIG,the fault equivalent method of multiple DFIG connected to different bus is obtained.The simulation based on PSCAD shows that this method has a high degree of accuracy.This paper completes the research on the fault equivalent method of distributed generation with high penetration rate in distribution network,including fault equivalent method for IIDGs and DFIGs with high penetration rate,which is innovative and has high practical value.