One Improved Sliding Mode DTC for Linear Induction Machines Based on Linear Metro

In order to achieve faster speed tracking ability with lower thrust ripple for the linear induction machine (LIM), one robust speed control strategy using sliding mode direct thrust control (SM-DTC) is first proposed based on the space vector modulation (SVM) technique with the secondary flux-linkage orientation. Then, one improved maximum thrust per ampere technique is presented to further minimize the primary current and copper loss under the constant output thrust. Full comparison has been made among the proposed SM-DTC, the conventional DTC and field orientation control methods in different typical working states. Comprehensive simulation and experiments have been done on the basis of two 3 kW arc induction machines (as one demonstration prototype for the real LIM), which adequately confirm that the proposed method can successfully get faster dynamic response with lower thrust ripple.