Research On Fault Analysis And Protection Scheme Of DC Distribution Network

In recent years,with the continuous development of science and technology,the power consumption in load-intensive areas is getting larger and larger,and the requirements for power quality are becoming more and more strict.The existing AC power distribution system can not meet the user's power demand..In the DC distribution network,the control of active power and reactive power on the AC side is independent,and there is no problem of frequency offset and three-phase asymmetry in the DC network,the power quality is better,and the DC power distribution system gradually Going into people's field of vision.However,the current research on DC distribution networks at home and abroad is still in its infancy,and there are still many challenges in DC distribution networks.One of the main challenges is the lack of effective protection against DC grid faults.Therefore,this paper focuses on the protection strategy of DC distribution network.A DC-side fault protection scheme based on the voltage ratio and voltage change rate of DC reactor is proposed for DC line fault characteristics.This paper first introduces the development status and research background of DC distribution network.Based on the voltage criterion and topology of DC distribution network,the construction standards of DC distribution network are studied.Based on this,a four-port ring DC distribution network is built on the real-time digital simulator(RTDS),and the master-slave control principle of constant voltage and constant power is constructed.Then,this paper divides the DC distribution line fault into regional faults and out-of-zone faults.Defining faults other than DC lines is an out-of-zone fault.This paper analyzes in detail the fault characteristics of positive and negative pole ground faults and bipolar short faults in and out of the zone and the influence on DC line voltage and current.The fault voltage characteristics of the positive-side grounding short-circuit fault,the negative grounding short-circuit fault and the bipolar short-circuit on the DC-side line are mainly studied.Finally,a DC-side fault protection scheme based on the voltage ratio and voltage change rate of the DC reactor is proposed for the fault characteristics analysis of the DC line fault.The protection scheme mainly includes three parts: the initiation protection criterion,the main protection criterion and the backup protection criterion.In this paper,the change rate of line voltage and the continuous detection time at fault are used as the starting protection criterion to judge whether the line is faulty.The main protection criterion is divided into fault identification criterion and fault selection criterion.In this paper,the bus voltage on both sides of the line is The ratio of the line voltage is used as the fault identification criterion to judge whether the fault occurs in the zone or outside the zone;the positive and negative of the positive and negative voltage change rates are used as the fault selection criteria to determine whether the fault occurs between the positive pole,the negative pole or the poles.In this paper,the concept of predictive voltage is quoted,and the difference between the predicted voltage and the measured voltage at the time of failure is used as the backup protection criterion.The scheme was verified by simulation in RTDS,which proved its effectiveness.