Study On The Fault Analysis Method And Adaptive Current Protection Of The Distribution Nerwork With IIDG And DFIG

The development and application of the new energy sources such as wind power and solar energy power has entered a rapid stage.With the continuously increasing capacity of grid-connected new energy sources,the regulations of low voltage ride through capability have brought challenges to the safe and stable operation of the distribution network,especially the fault current characteristics and relay protection configuration of the traditional distribution network.The fault current characteristics are different from that of traditional synchronous generators.They have an important impact on the relay protection and reliability of the distribution network.This dissertation carried out systematic research work on the fault current characteristics of the new energy sources,equivalent model of multi-type new energy sources under faults,calculation method of fault components and relay protection principle of the distribution network with new energy sources.The fault current characteristics are the basis of fault analysis and relay protection.According to the characteristics of the new energy sources,the new energy sources can be divided into two types: inverter-based generators(such as inverter interfaced distributed generator,IIDG)and generators of doubly-fed type(such as doubly-fed induction generator,DFIG).Firstly,the low-voltage ride through(LVRT)operation strategies for different types of new energy sources are studied.Based on it,the fault current characteristics of IIDG are studied.Double loop cascade control system is simplified and the fault current analytical expressions of the IIDG are obtained.Besides,Considering the rotor current inner loop controller designed for typical I and II systems and the effects of continuous excitation,the fault current analytical expressions of the DFIG are obtained.The calculation method of fault components is a foundation for relay protection settings.The complex fault current characteristics make the conventional calculation method difficult to be applied for the distribution network with new energy sources.Hence,the mathematical model of the IIDG is established.Then,under the asymmetric fault conditions,the mathematical model of the DFIG under balanced stator current control strategy is established.Finally,the unified equivalent model for new energy sources is proposed.Based on it,a novel calculation method of fault components is studied.Nonlinear equations for each sequence node voltage equation,fault boundary conditions and mathematical models are established.The above equations are solved iteratively with the improved PSO algorithm.The correctness of the proposed calculation method is verified by simulation results.With the large-scale new energy sources connected to the distribution network,traditional single-terminal radial network topology becomes a two-terminals or multiterminals network.The selectivity and reliability of traditional relay protection have been greatly affected.In order to address this issue,the method of using the local information and mathematical model of IIDG to obtain the status of the IIDG is studied,which can obtain the reference of the active power without communication.Based on it,the adaptive current protection scheme is proposed considering the fault current of the IIDG.Finally,the simulation results show the validity of the proposed protection straegies.At the end of this dissertation,the research work and results are summarized and the prospects of further research are pointed out.