Research On The Impact Of Large-scale Wind Turbines Ntegration On The Grid

As the increased penetration of wind power generations in power system, modern grid codes concerning grid-connected wind turbines are developed. As a result, the wind turbine under normal grid conditions is well understood and applied, the fault ride-through operation and control of the wind power system when grid fault condition has been the main subject of much recent research and development worldwide. Because of the uncontrolled wind power and the grid system fault, countries have advantage over wind power generation have already come up with different standards of fault ride-through. This dissertation intends to study the control of DFIG and PMSG wind turbine in low voltage ride through technology. Verify the correctness of the study by theoretical analysis and the simulation model.1. Introduce the construction of two mainstream VSCF wind turbine, build up the aerodynamic model of the wind power system and the driveline components.2. The precise mathematical model of DFIG’s grid-side converter and rotor-side converter are created. Based on the model, the dissertation presents an integrated system model with network, DFIG, grid-side converter and rotor-side converter included in the two-phase synchronous reference frame. Thereafter, a classical vector control scheme based on grid/stator voltage orientation and composed of dual closed-loops, viz., DC-link voltage control and AC current control loops, for DFIG’s grid-side converter is introduced. While for rotor-side converter a precise control model taking the stator voltage variation transients into account is constructed in the synchronous reference frame, and improved vector control scheme is suggested based on stator voltage orientation. Simulated analysis verifies the correctness and effectiveness of the proposed DFIG’s control model and the system’s new vector control scheme under relatively grid voltage sag.3. The mathematical model of PWM converter is studied, and the part of the DC of Dual-PWM is described through analyzing the power transformation theory. The simulation models of the controller of grid-side converter which uses voltage-oreinted vector control strategy and the controller of motor-side converter which uses the rotor flux-oriented vector control strategy are built, and the simulation results show that the model and the control strategy are correct, which provides simulation platform support for the low voltage ride through.4. The dissertation studies control strategies and protection schemes for DFIG wind generation systems under serious grid voltage dip conditions. The timing of rotor crowbar’s switching on and off is optimized. The impact of value of resistor series-connected to rotor crowbar on faulted network recovery is analyzed. On the basis, a fault ride-through operation scheme composed of a series-connected resistor rotor crowbar and an improved grid-side converter control strategy is proposed. In PMSG, the study puts forward a set of control logic for the based low voltage ride through. In the directly-driven permanent magnet wind power system simulation platform, the low voltage ride through of directly-driven PM wind generation system is achieved by using the power storage crowbar and reactive power control strategy during the breakdown time.