The Short-Circuit Fault Detection And Protection Techniques For An Offshore DC Microgrid

Nowadays,offshore platforms have become a meaningful way to develop and utilize marine resources and obtain marine information.Due to the long distance to the coast and the finite energy of single new energy,the multiple ocean energies generations for the offshore platform power system is the best way for electrical energy obtaining.The offshore platform has the characteristics of the area limitation,the power types of equipment concentration,and the cables in the smoke and damp environment chronically.Hence,it is easy to have the weak insulation dots leading to short-circuit fault.Meanwhile,the finite area makes the line impedance smaller,and the fault current rises faster when the short-circuit fault is happening,and the offshore platforms are unattended.Therefore,the reliability requirements of the short-circuit fleet location and cutoff are restricted,and the research is of great significance for practical engineering application prospects.Based on the current principle of DC fault detection,a kind of ring DC microgrid system running independently on the offshore platform is the research object.Aiming at the requirement of higher reliability and faster detection speed of DC microgrid in the offshore platform,this paper puts forward a kind of compound short circuit fault protection scheme that combines differential current protection with directional current protection.This scheme uses the differential current method based on Kirchhoff s current law to realize the rapid detection and location of bus short circuit fault.Aiming at the characteristics of many branch circuits and short lines in the offshore platform,the short circuit fault of each branch is accurately located by the direction characteristic of branch current and the current threshold size,which improves the economy of short circuit fault detection.Given the problem of synchronous acquisition and processing of bus fault signals,an analog signal operation method is proposed,which can meet the different needs of practical engineering.An offshore platform DC microgrid ring bus system and detection protection unit are established in MATLAB/Simulink.The effectiveness of the fault protection scheme is verified by simulation.According to the designed hardware circuit,the experimental platform of an offshore DC microgrid is built,and the effectiveness of the proposed composite short circuit fault detection and protection scheme is further verified by setting short circuit fault in bus and branch circuits.The results show that the proposed scheme can isolate the fault circuit quickly and accurately and can ensure the regular operation of the non-fault circuit.DSP control is used to process the fault signal.The fault detection time of the bus is about 90 microseconds,and the fault detection time of the branch is about 220 microseconds.The operational amplifier circuit is used to deal with the fault signal.The detection time of the bus fault is only 55 microseconds,and the detection time of the branch fault is only 40 microseconds.The proposed short-circuit fault detection and protection scheme can provide a guarantee for the long-term safe operation of an offshore DC microgrid.