| With the development of power electronics technology,the previous technical problems of DC distribution network have been solved,and its technical and economic advantages gradually emerged.Compared with the AC distribution network,the DC distribution network has obvious advantages,such as low line loss,high power quality,large power supply capacity,and easy access to distributed power of convenient distributed energy.It will become an important part of the future distribution network.DC distribution lines are a significant part of the DC distribution network,and DC line protection is the key to ensuring the safe and stable operation of the DC distribution network.This paper focuses on the research of DC line protection methods in DC distribution network.First of all,based on several topologies of existing DC distribution networks,this paper builds a fault simulation model of ± 10 k V DC distribution network on the PSCAD simulation platform.The control principle of the main components in the model is analyzed,including voltage source converter,DC transformer,DC/DC converter and photovoltaic power generation device.The characteristics of two faults in the DC line of the DC distribution network is analyzed.The simulation results of the main components during steady-state operation verify the effectiveness of the model.The simulation results of two faults in the DC distribution network line verify the correctness of the fault theoretical analysis.Secondly,aiming at the topology of the multi-branch DC distribution network,a DC distribution line protection method based on the product of current variation is proposed.Through analysis,it is found that under internal faults,the polarity of the current variation is positive;under external faults,the current at both ends of the line changes in the opposite direction.Taking advantage of this difference,multiply the change of current at both ends of the line and then integrat e the product result.The fault is identified with the positive and negative of the integration result.The fault pole is judged according to the magnitude ratio of the positive and negative short-circuit current mutations.The protection plan is proposed.Simulation results show that the method has strong anti-transition resistance,noise resistance and anti-synchronization error capability,and is not affected by distributed capacitance.Finally,a DC distribution line protection method based on waveform similarity is proposed.Introduce the Fréchet distance algorithm and DTW distance algorithm to measure the similarity of the current at both ends of the line,construct fault recognition criteria,and use normalization to eliminate the effect of current amplitude.By simulation,the correctness of the protection principle and the effectiveness of the protection method are verified,and the action performance of the protection is tested.Through simulation comparison,the anti-synchronization errors of several similarity algorithms are analyzed.It is found that DTW distance algorithm is better than Fréchet distance algorithm,correlation coefficient algorithm and cosine similarity algorithm in anti-synchronization error performance. |
