Harmonic Analysis Of Urban Rail Transit Power Supply System And Study Of The Impacts To The City Distribution Network

Urban rail transit power supply system is an important part of the urbandistribution network．It is the power source of rail transportation system，and its dutyis to provide safe and reliable power for the metro vehicles and power lightingequipment. The urban rail transit systems generally adopt DC traction power supplynetwork and use a lot of nonlinear power electronic equipment，such as rectifier andinverter. These equipment can produce harmonics and may do harm to the citypower grid．So it is very important to study the influences of urban rail transit powersupply system and its harmonics on urban distribution network.Firstly，this paper makes a detailed analysis of the structure and characteristicsof urban rail power supply system and the metro vehicle and simply introduces theconcepts of Zhengzhou rail transit (subway) power system and harmonics．Takingthe example of Zhengzhou metro transit line1，this paper builds the dynamic modelof metro traction power system by MATLAB/Simulink tool．Secondly，according tothe electrical parameters of metro transit line1，it builds the dynamic model of themetro vehicle．Thirdly，this paper implements a simulation of the process of onemetro vehicle from start，traction and coasting to braking and analyzes the harmonicsdistribution in the whole operating process．Finally，it makes some simulations ofmany vehicles working under different operating conditions according to differentrates of traffic flow and analyzes the harmonics distribution and its influence onurban distribution network.The paper introduces the calculation methods of fundamental power flow andharmonics power flow and predicts their distribution in Zhengzhou rail transit powersystem by combining simulation and program．According to the electrical parametersof Zhengzhou metro transit line1，this paper estimates the maximum traction powerwhich is acquired from the traction networks when the subway train is towed withfour kinds of load conditions．Then mathematical models of traction load are built onthe basis of the results．Taking advantage of Simulink tool in MATLAB，the AC simulation models of the metro power system are built when the train is towed inearly，short，long term and typical kinds of load conditions and the AC-DC powerflow calculations are completed through the interactive operation with computerprograms．Besides，this paper builds an equivalent model of24-pulse rectifier andmakes up computer programs to calculate the harmonics power flow by forming theharmonic equivalent circuit with each harmonic mathematical model. Finally，itproves that the results of harmonic power flow calculation in this paper is correctand reasonable compared with the measured data．With the results，we can analyzethe harmonic characteristics of Zhengzhou Metro and the influences of harmonics onurban distribution network．The analysis shows that Zhengzhou rail transit powersystem injects little harmonics into the urban distribution network in the initial stageand near future of its operation and its impact on urban distribution network is verysmall，but the content of harmonics injected by Zhengzhou rail transit power systemmay exceed the national standard requirements in the forward of its operation．Soharmonics produced by Zhengzhou rail transit power system in the forward maybring great harm to the urban distribution network and some harmonic suppressionmeasures should be taken when necessary.