Gyuláné Vincze, Gergely György Balázs
Budapest University of Technology and Economics Department of Electric Power Engineering
Some of the modern high-speed vehicles are driven by linear induction motor (LIM). The principles of the linear and the rotating induction motors are the same, and the field oriented control can be applied as well. The rotating magnet field is equivalent to the moving (running) field at the linear version. The construction differences between the rotating and linear motors:
at the linear motor, the squirrel cage rotor is replaced by a more or less well conductive solid rail or a tape,
instead of the circular stator coil, there are plane unfolded phase coils at the linear motor and the coils have beginnings and ends,
the linear induction motors are produced with much larger air gap than the rotation motors.
Some of the listed construction differences only modify the regular parameters of the induction motors. Nevertheless the phenomenon of the so called end effect causes starker differences. The generation of the secondary current in the solid rail – that replaces the squirrel cage rotor - is delaying at the entrance therefore the effective length is reduced, and at the exits it ends with a delay, that causes additional loss.
At linear motor the primary part with active coil is equivalent to the stator of the conventional motor, while the squirrel cage rotor is equivalent to the solid rail or tape shape passive secondary part. Basically there are two possible solutions of the linear induction motor driven vehicles:
short primary part linear motor drive, when the active coil of the motor is on the vehicle with the inverter supply and the control, and the secondary part is a solid rail or tape installed along the whole track,
long primary part linear motor drive, when the active coil of the motor is installed on the track with the inverter supply, and the secondary part is on the vehicle.
Generally the A./ solution is designed for vehicles running on conventional rail track on wheels. The secondary part can be the rail (rail head motor that has an additional function beside the conventional locomotive drive) and it can be horizontally or vertically placed solid rail or tape. Fig.5.16. presents the schematic diagram of the construction.
The resultant current excitation vector of the three phase coil is in a hurry to the inducted „rotor flux” of the track-rail with d=ϑ(τp/180°) displacement distance that is equivalent to the ϑ torque angle.
The B./ solution is applied at high-speed magnetic levitated vehicles, where the installation of the track is expensive. This solution has a great advantage: the inverter supply is performed outside the vehicle, the high power electric energy transmission would cause difficulties. The levitation distance of the electro-dynamically levitated vehicles can reach 10-20 cm, the linear induction motor must operate with such long air gap.
(The literature used for this chapter: …)