The Study Of Winding Rotor Motor's Doubly Fed Speed Adjusting System Used By Shaft Hoist

Wound-rotor induction motors that adjust speed by connecting resistors in series to rotor circuit have been easily found in the electrically controlled systems of shaft hoist. This method regulates speed by changing the number of steps of the additional resistor in the rotor circuit, so it's hard to realize smooth speed-regulation. Also its performance is poor. During the speed-regulating process, a great amount of slip power transforms to heat through rotor circuit resistor. And when the load is down, the potential energy has been wasted. To solve this problem, a doubly fed speed adjusting vector control system has been design which can realize speed adjusting and energy feedback when the load is down.Firstly, this paper introduce the development and theory of doubly fed speed adjusting. Then based on the theory and the characteristic of shaft hoist, the feasibility of doubly fed speed adjust system has been analyzed. Combining the characteristic of doubly fed speed adjusting with vector control theory, we get the mathematical model based on synchronism rotate coordinate system. In order that the machine carries out completely speed control, it must use the vector decoupling of the MT voltage. The paper gives the vector control speed system of the doubly fed machine on the stator magnetic field orientation. After the process of the stator magnetic field orientation, used the special mathematical model when the load is down, the control model of doubly fed speed adjusting is gotten. By using MATLAB/Simulink, the whole system has been built. The double closed loop of the rotate speed and stator current has been used to improve the system performance.The test shows that the vector control speed adjusting system has low inverter power, high power factor, perfect dynamic performance, etc. It has good prospect on industry application.