Electromagnetic Computation And Design Study Of High-power Linear Induction Motors

Linear induction motor (LIM) can convert electrical energy into linear motion mechanical energy directly without any intermediate conversion or gears. As a result of the "zero transmission" it has several advantages over the traditional way of transmission, such as simple structure, no contact, no wear, low noise, high speed and high precision. In recent years, along with the improved requirements of higher processing quality and precise positioning in industrial applications, the LIMs have been widely concerned. With the research and application of electrification driven train in the high-speed rail transport system and with the research trial of electromagnetic catapults in military use, the manufacturing research of high-speed, high-power linear induction motor enters a period of rapid development.Generally speaking, the LIM has larger air gap than ordinary rotating motors, its efficiency and power factor are relatively lower than the rotating motor with same capacity. Moreover, since the discontinuity in the primary and secondary structure of LIM, there exists unique end effect. It will cause the distortion of air-gap magnetic field which affects the motor performance. All these features require electromagnetic field analysis and they should be considered in the electromagnetic design.Firstly, the electrical equivalent circuit based on the structure characteristic of the double-sided LIM has been established, using the quasi-two-dimensional electromagnetic theory. And based on that theory, a set of formulas for calculating the equivalent circuit parameters of double-sided LIM with short secondary has been derived under certain assumptions, considering with the end effect. The equivalent circuit has taken full account of the end effect, secondary leakage reactance and skin effects of the linear induction motor. And these effects have been reflected on the computation formulas of corresponding parameters.Secondly, the electromagnetic design method for the LIM has been studied and a set of electromagnetic design procedure has been developed. Two machines have been designed through this procedure, which have all achieved the anticipated design requirements.Finally, modeling and calculation of a LIM have been implemented using two-dimensional (2D) time-harmonic FEM, and operation performances of no-load starting has been analyzed, especially the magnetic force and the magnetic field distortion near the ends of the secondary. The correctness of the theoretical derivation and the equivalent circuit has been verified too.