The slip and skid readhesion control used in recent inverter motor cars judges a slip/skid by the rotational speed and acceleration of the axle calculated from speed sensor pulses, and determines directive value to reduce motor torque.
      However, frequent failures in the traction motor speed sensor have led to maintenance problems with the main power circuit. Improvement of reliability can therefore be expected by performing vector control without using a speed sensor. The Railway Technical Research Institute (RTRI) has proposed a new slip/skid detection method using information from the traction motor current rather than from the speed sensor (Fig. 1).
      In the vector control, the inverter output current is normally controlled to a constant level. In this state, if an axle starts to slip or skid, the traction motor current of the slipping axle decreases rapidly, while that of the non-slipping axle increases rapidly (Fig. 2). By focusing on the difference in current of each traction motor, a slip or skid can be detected with a level of performance equivalent to that of the speed sensor (Fig. 3). A running test showed this proposed system to be effective, opening up the prospect of its use as a new slip/skid detection method.
      This research was conducted with a subsidy from the Promotion System of Basic Research in the Transportation Field of the Corporation for Advanced Transport & Technology (CATT).