Research On Fault Current Analysis And Suppression Of Distribution System With High-Density Inverter-Interfaced Distributed Generations

As power electronic technology develops rapidly in the world,more and more distributed generations(DG)are connected to the distribution network through high-power electronic device,which leads to the essential change of the fault current characteristics of the distribution network.The characteristic of the fault current is the basis of the research on the relay protection and automatic fault processing technology of the distribution network.The fault current provided by inverter interface distributed generation(IIDG)to the distribution network is related to its inverter control strategy,especially under the low voltage ride through(LVRT)control strategy.According to the different voltage drop degree of the points of common coupling,IIDG has different output modes such as constant power,fault ride-through and off-grid,which will affect the calculation of short-circuit current.At the same time,due to the contribution of IIDG to short circuit current,the relay protection device meets new challenges in setting calculation.To this end,this paper studies the calculation and suppression methods of fault current in distribution networks with high-density inverter distributed power.The main tasks of this paper are as follows:(1)The distribution network model with IIDG is established,and PQ and LVRT control models are established.The three-phase short-circuit current under different rated capacity of system(S),different short-circuit impedance of network(Z)and different output of IIDG(P)was obtained by simulation,and the fault current characteristic under each condition was analyzed.(2)The method of voltage estimation of the point of common connection based on deep learning is studied.A large amount of simulation data is trained through deep learning algorithm,it sums up the relationship between the different rated capacity of system(S),different short-circuit impedance of network(Z),different output of IIDG(P)and the voltage of the points of common coupling.According to the data under different short circuit conditions,the voltage prediction method is applied to the selection of the LVRT output mode.And the validity and correctness of the proposed method are verified by fault calculation and simulation comparison.(3)Based on the controllability of the IIDG current phase,a fault current suppression method is proposed to solve the problem of the protection setting after IIDG is connected to the distribution network.According to the superposition theorem,the fault current flowing into the protection device is analyzed,and the corresponding mathematical model is established.According to the different ways of solving the IIDG current phase,two different control modes are given,so as to achieve the suppression purpose of fault current.The correctness and effectiveness of the two fault current suppression methods proposed in this paper are verified by DIgSILENT/PowerFactroy simulation software.