| With wind power penetration increasing, the effects on power system become more significant due to the uncertain nature of wind power, and the serious challenges at power system security operation and control are encountered whether wind power is integrated into grid as large-scale centralized mode or small-scale decentralized mode. At present, since the reative power and voltage issues emerged at the regional grid with wind power, it is necessary for increasing the capbility of accepting wind power and ensuring power system operation security. For utilizing the reactive power control of DFIG and optimizing the reactive power of the regional grid with multi wind farms, the reacitve power and voltage optimal coordinated control strategy is studied, and a digital/physical hybrid simulation system for wind power control is constructed to verify the proposed contro strategy. The main contents and contributions are as follows:(1) The mathematical models of DFIG and PWM converter under three-phase stationary coordinate and the synchronous coordinate are constructed, and the relationship is derived in detail which is between the rotor voltage, current and output power of DFIG stator in steady state conditions. The general control strategy for DFIG wind turbine is introduced, and the control model for dual PWM converters were built up.(2) Based on the theoretical analysis above, it was analyzed in particular that the impact on DFIG reactive power limit caused by design of rotor converter, stator winding, the grid side converter and terminal voltage factors, etc. For the optimal operation control of the DFIG, it were studied deeply that the characteristics of four control strategy including the full compensation control, the minimum rotor current control, the minimum power loss control, and the constant rotor current control. The algorithm for calculating the rotor current reference values were given. According to control of reactive power compensation, three coordinated control strategies are proposed which are based on RSC priority, GSC priority, and proportional dispatching, so as to achieve fully use of converter capacity.(3) A coordinated control strategy of reactive power optimization for multi wind farms integrated into regional grid is proposed, which considered the voltage quality and power loss synthetically, and optimal solution is solved via genetic algorithm. An improved genetic algorithm is proposed which utilized the reactive power sensitivity to voltage and to power loss. As results, the optimal computing speed of genetic algorithm and the real-time performance of the coordinated control are improved significantly. Supported by above studies, a design scheme of online pre-alarm and reactive power optimal control system for wind power grid integration is proposed that based on the ultra-short-term wind power prediction and reactive power optimization. Secondary development is performed which utilized the engine mode supported by PowerFactory software and DGS interface, and the data interface is developed which used for exchanging data with EMS. Finally, the pre-alarm and reactive power optimal control system is realized which takes PowerFactory engine as the computing core.(4) According the requirement of study on wind power control, a design scheme for DPHS is proposed which is based on the NI-PXI platform. The stability of the proposed scheme is analyzed via using the simplified model of the DPHS, and the base demands for the interface algorithm and parameters are discussed. A control strategy for synchronizing grid voltage signal between digital simulation and physic simulation is proposed. Based on the above study, a real DPHS system is established, on which wind power control and coordinated control for multiple wind farm are performed, and the validity of the proposed scheme and the feasibility of the control strategy are verified.
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