An Improved Indirect Field-Oriented Control Scheme for Linear Induction Motor Traction Drives

The traction characteristics of a linear induction motor (LIM) are quite different from those of a rotary induction motor (RIM) due to the parameters variations caused by longitudinal end effect, transversal edge effect, and so on. The conventional indirect field-oriented control (IFOC) scheme of the LIM based on flux attenuation compensation is not suitable for high-power traction drives due to the deviation of current and thrust characteristics. In this paper, the traction characteristics of the LIM and RIM are compared from different perspectives. The performance of different control schemes of the LIM is discussed with consideration of the output limitations of the inverter. The IFOC scheme based on optimized slip frequency for the LIM is proposed. By dynamically adjusting the d- and q-axis reference currents and corresponding closed-loop control, the output thrust of the LIM is shifted close to the peak operation point. The average output thrust of the LIM can be increased without increasing the primary current, which can reduce the influence of end and edge effects on thrust performance. The effectiveness of the proposed scheme is verified by both simulation and experiments on an LIM metro vehicle.