Research On Direct Torque Control For Traction Motor And Hardware In Loop Simulation Based On RT-LAB

Along with the large-scale construction of high speed and heavy haul railway network project, as the important trunk railway motive power, electric locomotive and EMU has a very broad application prospects, and that electric traction drive control is the key technique whose control performance will directly influence the operational performance of locomotive and EMU and it is the core of the locomotive and EMU. When direct torque control is adopted to the AC drive system, torque ripple causes idling and slide and unfixed switching frequency cannot make full use of switch resources in low speed control; stator current has a large number of low-order-harmonics which provokes a pollution of traction power supply network in medium speed control. Therefore, analyzing the reasons of motor torque ripple in low speed control and raising improvement actions, studing stator current harmonic characterisyics in medium speed control and presenting measures to restrain the harmonics, improving the operational performance of the direct torque control system in all speed zone have great theoretical and engineering significance.Firstly, the basic mathematic model on the induction motor and the two-level inverter is briefly introduced, and the relationship between switch condition and space voltage vector is also studied in this paper. Then the structure of two typical direct torque control scheme is compared and expounds the basic principle and implementation method, qualitative analysis of torque ripple and flux distortion are presented in low direct torque control, and the stator current containing harmonics is analyzed by FFT in medium direct self control.Secondly, aiming at the defects of DTC in low speed zone, SVM-DTC based on space vector modulation strategy is introduced to replace the look-up switch table DTC, which fixs switching frequency and reduces the torque ripple at the same time. In order to eliminate the stator current harmonics in medium speed zone, two angular corner folding modulation strategies are presented, and about that lots of theoretical analysis and derivation are completed, the double angular corner folding modulation is better than the single angular corner folding modulation on harmonic suppression.To achieve the goal that traction motor operates by direct torque control in all speed zone, two flux observers widely applied are introduced in this paper. According to the operation characteristics of traction motor, a full variable speed scheme of traction drive system is designed which consists of direct torque control of circular flux trajectory, direct self control of polygon flux trajectory and squsre wave control.Finally, the hardware-in-loop experiment platform based on RT-LAB real-time simulator and TMS320F2812DSP controller is established, and based on it controlled object modeling and programming are completed, and the related experiment of direct torque control algorithm is finished based on the experiment platform. The simulation and experimental results demonstrate that the direct torque control algorithm designed in this paper correctness and effectiveness.