The Transient Characteristics And Solutions Of Double-system Electric Locomotives During The Process Of Switching Its Supply Systems

At present, both of the trunk rail and the inter-city rail in China adopt the 25 kV AC power supply system at industrial frequency, while urban rail employ the 1.5 kV DC power supply system. With the rapid development of rail transit in China, the interconnection problems of three kinds of rail transit have emerged, the development of double-system locomotives is an effective way to realize the train transport across three kinds of the rail. However, the process of switching the power supply of double-system electric locomotives is different from neutral-section passing of traditional electric locomotives. Therefore, the study of transient characteristics of double-system locomotive during the process of switching the power supply, and puts forward corresponding suppression measures have important significance. For this aim, the main researchs have done in this paper is as follows:(1) The topologies of both traditional and new type of traction drive system about double-system locomotive are described. Furthermore, the working principle and the control method of four quadrant converter and traction inverter are studied, and the simulation model of double-system locomotive is built on the Matlab/simulink platform. The waveforms of voltages and currents of the locomotive under steady state obtained from the simulations are analysised, and the validity of the simulation model is verified.(2) Under the dc supply system, the stability of DC link voltage of locomotive is analysised when the power of the motor is changing. The processes of switching the power supply of double-system locomotive are studied. While the electric locomotive switching from AC mode to DC mode, the equivalent circuit model in DC side of its traction drive system is built. The expressions of voltage and current in DC bus in the process of disconnecting the AC power, coasting through the middle of the non-electrified areas by inertia, and closing the DC breaker are obtained by mathematical deduction, and the correctness is verified by some simulations. On the other hand, when the electric locomotive switching from DC mode to AC mode, the the mechanism of magnetizing rush current in transformer with residual flux is analysed, then the relationship between the magnetizing rush current and closing time is studied by some simulations on the model. Most of all, the harmonic characteristics of grid current are analysed.(3) The existing electric locomotive harmonic suppression method-multi-converter based on carrier phase-shifting technique is introduced, and its validity is verified by simulation. For the characteristics of current harmonics in the process of DCtoAC, the paper put forward three new measures to suppress the harmonics:1. Changing switching-angle to suppress the magnetizing inrush current.2. An oscillating demagnetization approach is presented, which is based on LC Plus four quadrant converter circuits.3. Employing an isolation transformer based on inductive filter to protect the traction network from the harmonic currents, and the effect of the approach is verified by simulations.