Research On Low-frequency Magnetic Field Emission Characteristics Of Vehicle Power Supply System Of High-speed Maglev Train

In recent years,with the rapid development of economy and social progress,people's travel needs have become higher.The high-speed maglev train has the advantages of fast speed,low energy consumption and comfort.Its maximum speed is600km/h,which complements the speed gap of wheel-rail traffic and air traffic,and is of great significance to the development of Chinese transportation system.The high-speed maglev train is a non-contact rail transit system,which causes the return current of the onboard power supply system can not be grounded directly through the track.Therefore,the onboard power supply system will cause serious low frequency magnetic field emission problems.First,the topology structure of the vehicle power supply system is analyzed,this thesis focuses on the main circuit structure of boost chopper,inverter,DC-DC converter,suspension chopper,pilot chopper and eddy current brake chopper,and analyzes the performance of the above converter equipment.The principle of energy current conversion of converter equipment of vehicle power supply system is analyzed,and the circuit diagram of equivalent principle circuit is obtained.Next,the theoretical model of each converter device is established,and simulation models of multi-phase boost chopper circuit based on BOOST circuit,three-phase voltage bridge inverter circuit,phase-shifted full-bridge ZVS circuit and H-bridge four-quadrant chopper circuit are obtained.Then,the control strategy of the converter equipment in the vehicle power supply system is introduced in detail.The double closed-loop control circuits of the linear generator and the power supply rail of the boost chopper using PID control principles,the control circuit of the inverter using the SPWM principle,the control circuit of the DC-DC converter combining the principles of PID control and phase shift control,and the control circuit of three power choppers using the two-level control method are established.Next,the co-simulation model of the main circuit of the converter equipment is established,and the results comply with the actual output fluctuation,which proves that the converter equipment simulation model meets the actual requirements.Finally,this thesis establishes a low-frequency magnetic field emission model of N4 main grid by field-circuit combined simulation method.And,the correctness of themodel is verified through comparison with the experimental data.The low-frequency magnetic field emission of the N4 main power grid is analyzed on four operation conditions of train including low speed,medium speed,high speed and eddy current braking.Through the analysis of the simulation results,it is found that the frequency of the disturbance current on the power cable of the vehicle power supply system is mainly distributed at the switching frequency and harmonics of the vehicle-mounted converter and transformer equipment.Moreover,the bandwidth and amplitude of the disturbance spectrum increase with the train speed increases.The disturbance frequency of the magnetic field is consistent with the harmonic disturbance frequency of the power cable,and the intensity of the magnetic field under the eddy current braking state is the largest.