Research On Dual Inverter Control System Of Double Fed Induction Motor

With the development of power electronics and electric drive technology, DC speed regulation system has been replaced by AC speed regulation system which has become the main driving mode of industrial production and social life. As a kind of special induction motor, doubly fed induction motor has the advantages of simple control, wide speed regulation range, convenience of energy feedback, which has great potential in the future motor control system.This thesis presented a kind of dual inverter control system for doubly fed motor based on large amounts of reference material. The proposed motor control system has the advantages of wide speed regulation range, more safety and stability. Besides, the power distribution between two inverters can be adjusted. If one inverter broken, the other one can work alone. The proposed strategy is suitable for application in electric cars and other occasions which needs a wide speed range and high safety and stability.AC motor is an higher-order, multivariable, nonlinear system. Before the study of dual inverter control system, the mathematical models of doubly fed induction motor(DFIM) were detailed analyzed, and then gives mathematical models of doubly fed induction motor in the two-phase stationary and synchronous rotating coordinate system. Besides this thesis also analyzed the principle of rotor initial position angle observation based on stator oriented flux. Then the expression of rotor initial position angle is derived.Besides of in-depth analysis of the principle of dual inverter motor control system for doubly fed motor, this thesis proposed the double current loop control strategy in order to realize stator and rotor current independent control and inverters power adjustable. To further improve the system speed range, the excitation regulator is designed. When constant torque control, it makes the system run at maximum torque current ratio conditions. When constant power control, it makes the system run at weak magnetic conditions. In order to improve the security and reliability of the system, the operation strategy of the single inverter is presented. The system can be operated stably in the case of a single inverter fault. A rotor initial position angle observation method is applied to the control system of dual inverter, which can effectively reduce the impact current in the starting process. The model of dual inverter speed regulation system is built in Matlab/Simulink, and the characteristics of wide speed range, adjustable power between two inverters, operation strategy of the single inverter are verified.The stator and rotor side voltage and current of doubly fed induction generator is convenient to observe, which provides convenience for the design of speed sensorless control system. After the comparison between open loop observation scheme, the closed-loop control scheme based on stator currents and model reference adaptive system(MRAS) strategy based on the stator flux, this thesis presents dual inverter control’s observation scheme based on MRAS and the derivation of the adaptive law is also carried out. The MRAS scheme can eliminate the speed error in the observation, which can enable good observation effects to obtain accurate velocity information, improve the robustness and reliability of the control system.In the end, the experimental platform of double fed motor control system is built, and the control system is verified.