| In recent years, Chinese Railway has been developing rapidly. Employing electric traction AC drive control technology is the most appropriate option for locomotives with heavy rolling stock or high speed passenger train in the modern railway sytems. The control technique of traction motor for locomotives is one of the key technologies in controlling for AC drive system. The research direction of the modern control strate-gy of the traction motor are mainly vector control scheme and direct torque control scheme. Currently, Beijing Jiaotong University and China CNR Corporation Limited have developed jointly the vector control scheme for controlling traction motor and has been putting into the applications for the locomotives and high speed trains, and it has been undertaking further improvement. Compared with the vector control scheme, the direct torque control scheme has its own outstanding characteristics and suitable for the applications both in China railway systems and Vietnan underconsructing urban transit systems. Base on research and development about AC drive electric locomotive of Chi-na CNR Corporation Limited, the direct torque control algorithm of induction traction motors in electric locomotive traction AC drive system is investigated and probed in this dissertation. Main achievement results of outcome of my research are obtained as fol-lows:A direct torque control (DTC) algorithm of induction traction motors is proposed to optimize the torque performance in the base speed region with continuous stator-flux linkage locus. During medium motor speed range, based on the continuous stator flux-linkage track control in the DTC algorithm, stator flux-linkage track can be smoothly switched from roundness to polygon, and hexagon at last, with the advantage of steady torque response and small torque ripple. Furthermore, during high motor speed range, a modulation strategy with advanced non-zero voltage vector inject is pro-posed to achieve smaller minus value of torque ripple; hence average torque value is higher and stability of torque response is improved. The control performance of the proposed control strategy is both fast system response and easy algorithm realization; it also retains advantages of traditional DTC algorithm. Theory analysis and experimental results both verify the effectiveness and feasibility of the proposed DTC method with optimized the stator flux-linkage locus and improved the torque performance.A direct torque control (DTC) algorithm based on symmetrical polygon stator-flux locus is proposed in this article with asynchronous traction motors as the research object. By analyzing the excitation current changes, a control algorithm characterized by mul-tiple symmetrical stator-flux trajectories in shape of circle, hexagon or other polygons between them is designed. Smoother stator-flux trajectories are obtained and are favor-able to improving the harmonic elimination capability and the switching frequency util-ity. This DTC algorithm is simple in structure and is easy to implement as it only re-quires adding stator flux regulation to the traditional DTC algorithms. Its effectiveness and feasibility are demonstrated by both theoretical analysis and experimental results.In view of speed control characteristics of induction traction motors and the prob-lems of direct torque control (DTC) algorithm in current applications, this paper presents a DTC algorithm characterized by closed loop power control respectively in constant-power field-weakening region of the induction traction motors. This algorithm only requires to add a stator flux control algorithm to the traditional DTC structures, which shows simplicity, maintains features of traditional algorithms such as uncompli-cated control circuit, less dependence on motor parameters, etc., moreover obtains im-provement of torque and power performance. The effectiveness and feasibility of this DTC algorithm are demonstrated by both theoretical analysis and experimental results. |
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