Study On Control Method Of Parallel-connected Induction Motors In Diesel Locomotive

For the advantage of lower cost, lightness, and compact structure, the control method of two or three induction motors connected in parallel fed by a single inverter has been generally applied in diesel locomotive’s traction system. However, differences in motor parameters, mismatch between wheel diameters and different adhesion conditions of each wheel can affect the performance of the locomotive control. So it is very necessary to study the control method of parallel connected induction motors.This dissertation is based on the research of diesel locomotive, and mainly studies the control method of parallel-connected induction motors including motor vector control and adhesion control. First, the steady-state model of parallel connected motors is built on the basis of steady-state model single motor. The influence of wheel diameters and parameters differences to torques imbalance is analyzed.Second, vector control method of parallel-connected induction motors is studied including traditional control method and means flux linkage oriented control method. However, the dynamic control performance of traditional method is not satisfactory and the torque utilization is not high. With a heavy unbalanced load, the mean rotor flux oriented method cannot start successfully, and the stator current’s imbalance degree is still high. For the shortcomings of these two methods, the weighted vector control method is proposed based on vector control method based on the average rotor field oriented method. The flux linkage of dual induction motors is reoriented, and then the control expressions of weighted rotor flux linkage and weighted torque of dual motors are derived, the q-axis component of stator current is used to control the weighted torque of two motors, and the d-axis component of stator current is used to control the weighted rotor flux. Weighted value is achieved by real-time calculation of q-axis component of stator currents.。The presented method can overcome the shortcoming of mean rotor flux oriented method which may not start at heavy unbalanced load and reduce the degree of stator current imbalance.Third, speed-sensorless control is applied on the basis of parallel control. The parameters of each motor, namely rotor flux, and speed were estimated using q-axis flux observers. And the stability is analyzed.Fourth, the dynamics model of dual axles is built based on the analysis of force interaction between traction motor and transmission gear, and the wheel-rail contact theory. An adhesion control method suit for locomotive is described in detail. At last, the parallel control method is verified on5.5kW experimental platform.