Study On Matching Method Of DC Traction Voltage Of Multi-current System Electric Locomotive

At present,the mainstream traction network of power supply system has the following types: AC25kV/50 Hz and AC15kV/16.7Hz,mainly used for the long distance,fast speed and high power of the main line railway and intercity railway;DC 3kV and DC1.5kV are mainly used for urban rail transit with short transmission distance,slow operation speed and small operation power.With the development of urban agglomeration and the implementation of "the Belt and Road Initiative" national strategy,the urgent requirements for the cross-border and multi-power supply system operation of electric locomotives in China have been put forward.Under the DC power supply system of multi-current electric locomotive,the DC traction network is directly connected to the traction inverter after passing the flat-wave reactor.Different DC voltage levels will cause the mismatch between the traction network voltage and the DC link voltage.In this context,the specific research contents of this paper are as follows:(1)This paper introduces the circuit structure of traction drive system of multi-current electric locomotive,and further analyses the main circuit of the system when AC power supply system and DC power supply system are used.In AC mode,the working principle and control strategy of grid-side converter are analyzed.In view of the low working frequency of converters in electric locomotives,the multiple harmonic suppression technology is introduced into the control.The simulation results show that the technology can greatly reduce the total harmonic distortion rate of the high voltage side current of traction transformer.In DC mode,the direct connection between traction network and inverters,whi ch is widely used at present,is introduced.The adverse effects of this connection mode on motor design and system operation are analyzed when various DC power supply modes need to be dealt with.(2)In order to solve the above problems,a method of using net side converter multiplexing as front-stage chopper is proposed to realize the matching of dc traction voltage and dc link voltage of the system.In order to suppress the ripple and improve the equivalent switching frequency,the chopper adopts the four-phase staggered parallel structure,establishes the small signal model of the circuit in different modes,designs the corresponding control strategy on this basis,and verifies the feasibility of the method through the simulation model built on Matlab/Simulink.(3)The real-time simulation platform based on HIL is built,the specific steps and methods of the experiment are introduced,the overall scheme of the experiment is designed,and the experimental model of the front-stage lifting chopper proposed in this paper based on equipment reuse is established.The experimental results show that both Boost mode and Buck mode can stabilize the dc link voltage at the appropriate size and effectively suppress the current ripple.The system has good stability and dynamic response ability in the face of voltage fluctuation of dc traction network and load variation of traction motor.