Research On Control Strategy Of Wind Turbine Converter For Brushless Excitation Synchronous Generator

This dissertation deals with the control strategy of converters for brushless electric excitation synchronous generator (BEESG)in wind power, which can make wind turbine achieve maximum power point tracking and power generation variable speed constant frequency(VSCF) mode.The structure characteristic of BEESG wind turbine is introduced by compared with other kinds of wind turbines which are widely used, and the operation control principle of EESG is analyzed. The stator side output power of BEESG can be controlled by adjusting the rotor side filed voltage. Furthermore, the theory of VSCF and converter system is investigated.The physical model of EESG is introduced, and mathematical model of three phases and six phrases EESG are established, at the same time their respective characteristics are analyzed. According to the equation expressions build by theoretical analysis, the simulation model based on state space of EESG is established by Matlab/Simulink software. The model mentioned above has built the theoretic and simulation platform for the further study excitation control and load-bearing of EESG.The excitation power plays an important role in controlling active power output of wind turbine. Excitation control algorithm of current inner loop and power outer loop is designed based on the analysis of structure and model of excitation system. Based on the analysis of mathematical model of grid side converter grid voltage feed-forward control of direct current control is pulled in. Control algorithm of line side converter is established by direct current inner loop and DC voltage outer loop. In order to lock phase accurately in grid voltage imbalance, decoupled double synchronous reference frame PLL is introduced. After that a850kW BEESG wind turbine system is established by Matlab/Simulink software, which simulates the operation of the normal boot process and grid voltage dropped to20%of rated voltage. The simulation indicated that wind turbine field voltage tracking speeds—active power curve rapidly and stably, continuous operate625ms at the20%rated voltage, which shows the effectiveness of the control scheme.In this dissertation, control sequence is established. The generator no-load results, load results and low voltage ride through results are verified that the proposed method has satisfied requirements.