Analysis of High Speed Characteristics for Linear Induction Machines

Linear induction machines (LIM) can be used as continuous duty machines for high speed propulsion and provide a low cost solution for very long stroke in comparison to linear synchronous machines (LSM). However, electromagnetic analysis of the LIM indicates that at high speeds, thrust force generated for propulsion and normal force as a by-product which can increase friction tend to reduce. This indicates that for high speeds, the system would require larger Iq and Id currents to generate the required amount of force. Using finite element analysis, it has also been found that there exists a trailing eddy current density which at high speeds causes a significant depreciation of the forces. Also, the variation of average thrust and normal forces with respect to frequency at one particular linear speed (5 m/sec) is presented, and asymmetry effect and the definition of 'negative frequency' have been explored