Inverter control of linear induction motors with different reaction plates

In recent years, attempts to develop new means of high speed efficient transportation have led to considerable world wide interest in high speed trains. This in turn has generated interest in the linear induction motor, which is considered to be one of the most suitable propulsion systems for super-high-speed trains. The operation of linear induction motors is based upon the same natural principles as the cylindrical rotor form of the machine, and this implies that the same methods of speed control by static frequency changer can be used. Linear motor speed control using·a variable frequency invertor, which has been used for some years with rotary induction motors, is investigated in this work. The steady-state performance of a motor fitted, in turn, with an aluminium reaction plate and aluminium cl added steel reaction plate, is described. A 3-phase variable frequency d.c. link-fed invertor has been constructed to provide speed control for the motor. The d.c. link is supplied from a voltage source. The invertor has a single a.c. side commutation and operates with threethyristor triggering, that is with 180° thyristor conduction, giving a quasi-square wave output voltage. The logic control and thyristor switching circuits have 'been designed and built and are described in detail. From no-load and locked rotor tests, the equivalent circuit parameter for the linear induction motor with the two types of reaction plates have been measured for different frequencies with a sinusoidal supply. These are used to predict the motor steady-state performance. The measured performance of the motor with each type of rotor with a sinusoidal supply is compared with the results predicted for various frequencies (50, 40, 30, 20 and 10 Hz), allowing for the effect of the variation of the equivalent circuit rotor resistance parameter with slip frequency. A comparison of the motor performance is made when fitted with both types of reaction plate, when excited both sinusoidally and from the invertor.