Research On Short-Circuit Fault Early Detection And Breaking Technology For LVDC Distribution System

With the continuous expansion of the scale of urban power grid and the continuous improvement of the power quality requirements from the users,traditional AC power distribution system is facing new challenges,and the low voltage DC power distribution system has received more and more attention with many advantages at the same time.However,the lack of stable and reliable short-circuit protection technology is one of the main bottlenecks which limit its development.DC short circuit current has high rising rate and without natural zero point,which make the DC arc difficult to be extinguished;besides,the short-circuit withstand ability of power electronic device is much weaker than power cable,for these reasons,DC short circuit protection technology put forward a high requirements to the speed.In view of this,the DC short circuit fault early detection and breaking technology are carried out in this dissertation,which mainly contains the following aspects:(1)The short circuit transient process and transient characteristics of internal converter in low voltage DC power distribution system are analyzed,and the DC short circuit fault simulation model is established by MATLAB/Simulink,based on the theoretical analysis and simulation results,the basic characteristics of DC short circuit are summarized.(2)The experimental circuit and control loop of DC short circuit fault is designed,and the DC short circuit experiment system with short circuit control,signal measurement and conditioning,data acquisition and processing,and upper monitor is developed,which can provide the experimental condition to the research of DC short circuit fault early detection and breaking technology.(3)The DC short circuit fault early detection technology based on MALL AT fast wavelet algorithm and the voltage and current dual wavelet decomposition is presented in this dissertation,and the FPGA module from NI Compact-RIO is used to realize the presented technology.Finally,the experimental results show the early detection technology can effectively remove impulse noise interference,distinguish between DC transient process and short circuit fault,which has good reliability and rapidity.(4)The DC short circuit fault fast breaking technology based on early detection and eddy current repulsion mechanism is presented,and the DC short circuit breaking equipment is designed.Furthermore,the designed equipment is testing in the DC short circuit experiment system,and the test result shows the effectiveness of low voltage DC short circuit breaking based on early detection and eddy current repulsion mechanism.This dissertation presents a short circuit fault early detection technology for low voltage DC power distribution system,which realizes the early identification of DC short circuit fault for the mechanism of fault signal singularity detection.On this basis,the DC short circuit fault breaking technology based on early detection and eddy current repulsion mechanism is presented,which can provide some novel ideas and methods for the research of DC short circuit fault protection technology.