Maximum Force Control of a Linear Induction Motor Drive

Linear induction machines (LIM) have shown their advantages in high speed propulsion in a variety of applications, such as military, and transportation. Implementation of vector control to achieve position, speed, and force control in linear induction machines has been a focal area of research for the past decade. However, due to the trailing eddy current effects and magnetic asymmetry effects, vector control can not provide the perfect functionality for LIM as it does for rotary induction machines (RIM). Furthermore, the vector control schemes are relatively complicated. Therefore, searching for an adequate control scheme with ease in implementation and low cost is the motivation of this paper. Using finite element analysis (FEA) the relationship between traction force and different ranges of linear speed and excitation frequencies in motoring, generating, and electromagnetic braking regions has been found. By storing these characteristics in the form of lookup tables which provides excitation frequencies resulting in maximum accelerating and decelerating forces, a closed-loop control scheme incorporating position, speed, and force controls with fast response has been proposed.