Research On Current Controller Of Vector Control System For Asynchronous Motor

Current controller plays an important role in achieving rapid and accurate torque or speed control of vector-controlled AC motors. However, cross-coupling caused by the reference frame transformation, which increases with the synchronous frequency, impairs the characteristics of torque response. Meanwhile, the signal delay increases undesired cross coupling, which has a significant impact on high power and low switching frequency AC drive system. Based on thses issues, this paper makes some researches on current controllers of vector control system.In order to achieve good decoupling performance and to improve the dynamic property of the asynchronous machine, induction machine complex vector models are established based on complex vector notation. Time delay model is studied and the strategy to expand bandwidth is proposed due to delay issues. The property of classical controller is analyzed, which introduces the regarding problems of cross-coupling and lags in response.To solve the problems, this paper thoroughly researches and analyzes different decoupling strategies of current controllers, including the controllers of synchronous PI control, feedforward decoupling, backforward decoupling, internal model control, dynamic decoupling, complex control and two others based on complete machine model. The zero-ploe map, the diagram of frequency response and the coupling response, are used to analyze all kinds of controllers under different conditions. Simulation is also performed to compare the performances of the controllers.Based on the above studies, to get more accurate results, this paper makes some researches on the discretization methods of current controllers. The characteristics of discrete control system are discussed, z-domain machine and delay models are established, and the controllers are designed in the discrete zone. Four common discretization methods, including Forward Euler, Backward Euler, Tustin/Trapezoid, Direct Digital Design, are also detailedly discussed and compared via simulation.In the end, this paper makes an introduction of the7.5kw AC drive platform, and performs the simulation and experiment over typical current controllers. Results show the functions of vector control system and current controller arithmetics can implement perfectly, and the effectiveness of proposed controllers is also proved.