A Study on Wheel Creep Characteristic for Electric Railway Vehicles

초록

Invertor application is broadening with vector control characterized by its strong control over torque and the development of devices with magnetic blow-out [1][2][3], and followings can be acquired when vector control is introduced into electric railway vehicle control.[5] (1) Improvement of torque accuracy transferred from axes to rails. (2) Improvement of re-adhesion control when axes are revolving and gliding by fast torque response. (3) Regenerative brake application until a car stops Since the accuracy of torque decides car's acceleration/deceleration, slip, and re-adhesion, the effect of vector control is huge for railway vehicles. The re-adhesion of railway vehicles is important to evaluate car performance. Re-adhesion is known to be acquired by reducing motor torque with the 1st delay filter which is proportional to slip velocity[6][7]. Re-adhesion is the technology to improve performance by detecting accurately slip and controlling torque according to slip. There are two method: (1) Separate re-adhesion after detecting slip (2) Continuous velocity detection in the creep area and torque control according to it. There are many studies under way, and it is to reduce motor torque when slip is detected.[8][9][10][11] In this paper, vector control was introduced to the control of induction motors which have a wide range of velocity control like traction motors, and equivalent test equipment was used to test adhesion control. PWM modulation which is used by power semiconductor from low modulation rate to 180° was used for inverters. Low switching frequency was used for compensation for a dead time which has an influence on torque pulsation and current waveform in the low velocity area. And good results were acquired with a loop to control instantaneous current. In the motor operation tests, we found out regenerative braking is possible before a stop and checked the effective results of vector control. As for re-adhesion control, a generally used torque reduction method by 1st delay of slip velocity was applied with a velocity control loop which reduce torque in proportion to slip velocity. Compared to the torque reduction method, when the velocity control loop was added, slip velocity dropped, and acceleration rose under the same condition. And test results confirmed that adhesion characteristics could be improved by this method.