Research On AC Motor Control By Changin Winding Turns

In typical AC motor control applications such as electric vehicles, electric traction, machine tool spindle drive and servo, drive systems are required not only to provide high torque at low speed operation, but also have a wide speed range. A good speed control method can both meet the speed, torque requirement and play a role in energy conservation. Conventional motor is difficult to meet these requirements directly. Generally it needs mechanical transmission systems, motor weakening control and other ways to expand the speed and torque range. But this will increase the weight of the system and reducing efficiency. Aiming to expanding the speed range of AC motor, this thesis analyzes some common methods, focusing on changing the number of turns to reduce the counter electromotive force value to extend the speed range. This thesis proposes the concept of equivalent number of turns and verify the feasibility of making the equivalent number of turns continuously adjustable in a specific range.Firstly, this thesis discussed the principles of AC motor speed range extension, analyzes several common ways to extend AC motor speed range:pole-changing control, field-weakening control and changing the winding structure, introduces some research directions and results in this field currently, and indicating their respective applications and shortcomings.Secondly, this thesis elaborates the principle of extending the speed range by changing the number of winding turns, demonstrates the impact of changes of winding turns on the motor performance, introduces a method of changing the number of winding turns. From the application of electric vehicles, the concept of stator equivalent number of winding turns can be proposed. Controlling on and off of the semiconductor switch by pulse can change the equivalent number of winding turns.Finally, this method is simulated and through the comparison of stator current before and after the switching time, it can be verified that the equivalent number of winding turns can be changed continuously by adjusting the duty cycle of the pulse.