Abstract: When medium and small power convertors of power transistors are used to drive AC and DC motors,it is possible to have good control performance.In order to savemore energy and increase torque output,the control strategy of sine-wave currentsource should be used for the AC motors.In this paper,the principle for generating sine-wave current by power transistorswith inductive load such as motor windings is described in detail.The main components of this system are described too.