| In recent years,with the continuous development of distributed generation,DC energy storage device and the wide application of DC load,DC distribution system has become a hot topic of research,application and development direction in China and abroad.This research based on National High-tech Research and Development Program(863 Program)in sub-research "Key technology of guarantee the reliability of flexible Multi-DC distribution system in DC control strategy and protection",built a four-terminal DC distribution system simulation model,analyzed DC distribution topology structure,voltage level and control strategy.Then this research took all kinds of possible fault occurred in DC distribution system and its influencing factors in theoretical analysis and simulation verification.Based on fault analysis,this research studied DC distribution network protecting configuration.Firstly,based on analysis of topology in existing DC field,comparation of advantages and disadvatages of three DC distribution system topology in future,and discussion of DC voltage level formulation principle,this research chose two-terminal powered topology structure as basic topology in DC distribution system simulation model,the DC voltage is ±10kV.In design of converters,this research chose constant DC voltage-reactive power and constant active-reactive power control strategies to control two-level voltage source converter of AC/DC converter;adopt constant current control strategy to control bidirection BUCK-BOOST converter,and built DC distribution system electromagnetic transient simulation model in MATLAB/Simulink.Secondly,based on DC distribution system simulation model in this research,the DC distribution system fault characteristics have been analyzed.Through the theoretical derivation to analysis the DC side pole-to-pole short circuit fault and positive cable grouding fault characteristics of AC/DC converter in DC distribution system,and consider the influences of converter grounding modes,fault resistance,fault distance and current-limiters in DC fault.Analyzed the fault characteristics of AC side fault,also consider the impacts of AC side fault to DC side.Analyzed the DC/DC converter high voltage and low voltage fault characteristics and their influences to DC side.Simulated all conditions above in MATLAB/Simulink,and extracted related fault characteristics for protection configuration.Finally,based on DC distribution system fault analysis,this research presented protection zones,combining the characteristic of DC distribution system,illustrated the basic requirement and configuration principle of DC distribution system.In order to satisfied the demand of protection requirement in DC distribution system,this research proposed a fast DC protection method based on local information according to existing DC system protection method and theory.Through the analysis of fault power flow,protection theory and configuration setting,this research took a large amount of simulation and obtained this protection method could action in 2ms when fault occurred in protection zone,verified its validity and feasibility. |
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