Research On Torque Ripple Of Traction Motors In Electric Multiple Units

ABSTRACT:When a high-speed train is moving, the motors convert electrical energy into mechanical energy to produce tractive force by which the train is driven. Therefore, the performance of traction motors affects the dynamic characteristic of the train. With the inverter power supply, the input voltage of traction motors contains many harmonics. The harmonic voltage produces harmonic current and harmonic flux, and then the harmonic torque is produced, which can cause the electromagnetic torque ripple. So how to calculate the harmonic torque accurately and undermine harmonic effectively are the problems when people analyze and design motors. The problems mentioned above are researched based on the electromagnetic theory in this thesis.With the principle of SPWM control technology, a deep analysis of the single-phase and three-phase SPWM inverter circuit are made, and the double Fourier series expression of the output harmonic voltage is obtained. Then the inverter circuit is simulated by MATLAB/Simulink software, the distribution of harmonic spectrum of output voltage is obtained. The various adverse impacts of harmonics on asynchronous motors are discussed.On the basis of electromagnetic theory of motor operation, the harmonic magnetic potential of asynchronous traction motors is discussed, and the generating mechanism of harmonic torque is analyzed in detail. Based on the study of fundamental and harmonic equivalent circuit, the calculation formula of harmonic ripple torque is derived with the principle of virtual displacement. Next, the system models of asynchronous traction motors under the ideal power supply and inverter power supply are established respectively. The latter adopts the control method according to the rotor field oriented vector control. Then the model is simulated, and the simulation results are compared with the test ones. Finally, an example of asynchronous traction motor harmonic torque is given and analyzed. All the work may be the basic for a further study on harmonic torque impact on traction motors.In the CRH380XL Electric Multiple Units, a field test of traction motors is conducted, the test data are analyzed, and the relevant conclusions are verified. Then a software is compiled to analyze the harmonic spectrum and torque ripple quickly according to the test data.From the aspects of SPWM inverter harmonic suppression and traction motors parameter optimization, the measures are suggested to reduce torque ripple, especially the method of harmonic injection and specific harmonic elimination. In addition, a low-pass filter circuit is designed to eliminate the harmonic effect on traction motors.