For Locomotive Traction Induction Motor Drive Technology Research

The safe operation of rail transit is directly related to people's life, work and social development. Safe, quick, comfortable travel is always the tenet of railway transportation. In locomotive traction AC drive systems, traction converter as the key power component, its safe operation is directly related to the reliable operation of the whole system. The research on the fault tolerance of traction converter therefore has important practical significance. With the wide application of vector control and direct torque control in locomotive traction, motor parameter identification will no doubt improve the dynamic property of the traction system. In order to realize the full utilization of power converter switching frequency and reduce the influence of harmonics on the system performance, the synchronous modulation seems to be an inevitable choice with the rise of the modulating frequency. As a consequence, for the reliable operation and better control performance, the inverter fault tolerance, motor parameter identification and synchronous modulation in locomotive traction are studied in detail in this dissertation.The single phase fault tolerance operation, in which the fault bridge is disconnected from the motor terminal, is studied under the fault of traction converter. Based on the double revolving field theory and method of symmetrical component, the corresponding equivalent circuit is derived, and it is pointed out that the motor can still working under traditional open loop control method, but with low loading capacity and no self-starting ability. The dynamic mathematical model of motor under this single phase operation is derived and the corresponding double closed loop control method is also presented. For the existence of torque pulsation, whether to set the low pass filter in the speed loop or not is dependent on the system inertia.The three phase fault tolerance scheme is discussed in detail, in which the motor terminal corresponding to the fault bridge is connected to the middle point of dc-link and the motor line-to-line voltages can be modulated as a result. In order to synthesize the zero voltage space vector which does not exist in this topology, two switching sequences are proposed and the resulting almost three times difference in harmonic copper losses is presented using double Fourier integral analysis. Because of the middle point connection with the motor terminal, the upper and lower capacitor voltage will fluctuate, even drift in opposite direction. The fluctuation is formulated providing that three phase currents are symmetrical. The effect of the fluctuation can be neutralized by compensation to modulating waveform. The drifting can be solved by modulation strategy and certain switching state two different perspectives, the reliable operation is therefore improved.In the procedure of rotor time constant identification with d axis voltage and reactive power two models, any parameter difference between the one used in the models and that in the motor will cause the wrong identification result. The detailed parameter sensitivity formulations of the two models are derived, pointing out that two models have opposite sensitivity to stator resistance and mutual inductance. Therefore, two models are combined as one mixed model to fully utilize their own advantage by adjusting weight factor at different conditions.Based on the FFT analysis, two synchronous modulation models with different symmetric form are presented. On the basis of transcendental equation solved for switching angles, the formulation is converted to one single objective optimization problem with certain constraints. The problem is solved using sequential quadratic programming. The piecewise polynomial fitting is adopted to the solved results for more easily practical implementation.The low power physical experiment platform is set up with TMS320LF2407A as the main controller. The single phase and three phase fault tolerance schemes are tested respectively. The results validate the correctness and feasibility of two schemes.