Research Of Technology On Operation And Control Of Doubly-Fed Wind Generator

As an effective solution to environment pollution and energy lack, wind energy generation has received great attention. Due to its advantages such as flexible connection of mechanical-electric system, high efficiency and small capacity due to deal with slip power, Doubly Fed Induction Generator(DFIG) has became the main stream engine. This paper discusses the control technology of wind energy generation system with DFIG, and the control strategy under unbalance voltage is mainly discussed. The contents and contributions of this dissertation are as follows:This dissertation analyzes the operation theory of DFIG, and establishes the steady state mathematical modle of DFIG, and discusses the interrelations of key physical parameters such as rotor current, power and slip. The simulation models of DFIG are established on MATLAB/Simulink environments.By studying the stator-flux oriented vector control and the grid-voltage vector control, a vector controller of DFIG suitable for symmetrical grid voltage is designed. The inner-loop is used to control the rotor current, and the outer-loop is used to realize of the largest wind energy capturing and reactive power control. In the grid voltage oriented vector control, the function of grid-side converter is to maintain the stability of DC-link bus voltage. Based on the introduction of wind turbine operation characteristics, this paper makes a simulation on the maxim power capture scheme, which does not need wind speed measure. The reactive power limit of DFIG is calculated, and reactive power control schemes of DFIG is discussed. The simulation results on MATLAB/Simulink environments verifies the control strategy, which can realize good static and dynamic performance and the decoupling control of active power and reactive power.As voltage imbalance is the most common grid fault, the symmetrical component method is adopted to study the behavior of DFIG under unbalanced grid voltage. In the positive-and negative-synchronously rotating frames, the mathematical modle of DFIG under unbalanced grid voltage is deduced. Based the proposed model, the stator output instantaneous active power and reactive power are deduced and analyzed. This paper puts forward four kinds of unbanlanced control strategy suitable for the condition of unbalanced grid voltage, which can minimize oscillations in either active power, or electromagnetic torque, or stator currents, or rotor currents with the proposed control strategy.