Dc and pulse-current traction motors to solve the "steering" problem, some countries have used thyristors without commutators and three-phase ac asynchronous traction motors with variable frequency traction motors, and high-speed maglev vehicles driven by linear induction motors.The thyristor has no commutator and the traction motor consists of a synchronous motor and a set of thyristor inverters.
Thyristor and rotor position detector instead of dc traction motor commutator and carbon brush structure.This motor has the advantage of a dc motor without the "reversal" of the problem.However, the thyristor and its control system are very complex, so the electronic components directly affect the reliability of the motor.Three-phase ac asynchronous frequency traction motor is an ideal traction motor with simple structure, reliable operation and low cost.But because of the need of frequency conversion, its development and application are limited.In the 1960s, the development of high power thyristor frequency conversion device made the induction motor frequency conversion speed adjustment can be realized successfully.Many countries have adopted three-phase ac asynchronous traction motor frequencies for locomotives and automobiles.Experiments on high-speed maglev vehicles in the federal republic of Germany and Japan use linear induction motors.Its primary winding lies on the ground guide rail, and the ground of the inverter power supply generates a traveling wave magnetic field. Adjusting the frequency of the power supply can change the speed of the high-speed maglev vehicle.Secondary winding reaction plate, mounted on the frame of the vehicle.The primary traveling wave magnetic field and induced current interact to not only generate thrust, but also to generate magnetic levitation vehicles that pull through and brake conditions play a role in dynamic braking.
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