PURPOSE:To prevent the end effect that the characteristic is deteriorated when a slip is small by increasing the slip frequency in response to the frequency of a motor current when the frequency obtained from the speed command and a speed detected value exceeds the rated value. CONSTITUTION:A current from a trolley wire 2 is inputted to an inverter 6 to drive a linear induction motor 80, and the inverter 6 is controlled by applying signals from a voltage/current detector 10 and speed detecting means 12 and a speed command 100 to a controller 140. At this time, a slip frequency setter 24 is added into the controller 140, and when the frequency command 104 is the rated frequency of lower, the constant slip frequency command is applied. When exceeding the rated frequency, a frequency instruction unit 16 is controlled to increase the slip frequency. Accordingly, the phenomenon of the linear induction motor that the smaller the slip frequency become, the more the characteristic is deteriorated is compensated to improve the operation.
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