Fault Analysis And Location Methods For DC Distribution Network With Power Electronic Transformer

The development of distributed renewable energy is crucial to accelerate the energy structure transformation and has great potential to replace fossil fuels.With the rapid development of renewable energy,DC distribution network is the suitable structure for balancing the local power supply and the local DC load.Meanwhile,DC distribution network have merits in efficiency,reliability and flexibility compared with traditional AC distribution network.However,DC distribution network confronts with great challenge in terms of DC fault.Short-circuit current in DC network have short duration but escalates rapidly until it reaches the current peak,which is in large magnitude and poses great threat to power devices in converters.This means fault detection and location methods should have greater accuracy with limited time window to protect other devices in the DC network.By establishing and solving the circuit equations and state-space equations,this paper analyses the fault characteristics of typical DC faults,including pole-to-pole fault and pole-to-ground fault,in the DC distribution network with power electronic transformer.Typical parameters are extracted from the fault components to reflect the relationship with the fault distance,which is fundamental to fault location methods.This paper proposes two fault locations methods: single-terminal fault location method based on the auxiliary injection unit and two-terminal fault location method based on the ratio of transient voltage(ROTV).The first method measures the fault distance by injecting the probe current into the fault segment with the auxiliary injection unit and recognizing the dynamic response of probe current.The concept of ROTV was introduced to realize the fault location in the second method,which uses two-terminal information to eliminate the impact of fault resistance.Numerous simulation results verify the proposed methods in PSCAD/EMTDC.It proves that two proposed methods are not sensitive to sampling frequency and have great tolerance to fault resistance.In different fault conditions with fault distance and fault resistance varying in a wide range,proposed methods prove to have accuracy and robustness.