Research On Control Strategy Of VSC-HVDC For Wind Farm Interconnection

With the continuous development of the wind power generation technology and the increasing expansion of the capacity of the wind farm, the wind power transmission is becoming gradually important. Among many grid connection technologies of wind farms, HVDC-Flexible transmission (VSC-HVDC) provides reactive support for the wind farms and AC systems. It is very suitable for interconnection between the wind farms and grid. This paper focuses on the vector control of doubly-fed wind power generator and passive-based control strategy of VSC-HVDC.The transmission methods of Grid Connection technology of Wind Farms are analyzed in this paper. And the advantages of VSC-HVDC used in grid-connected wind farms are elaborated. To analyze the characteristics of the wind farm, the performance and vector control of doubly-fed generator are studied. The simulation results in Matlab/Simlink show that the vector control strategy of doubly-fed wind generator can realize the independent control for active power and reactive power and the maximal power capture.The mathematical model of VSC-HVDC system is built and VSC system is proved to be a passive system in this paper. Two passive controllers of inner loop are designed according to the requirements of the control system. One is passive controller based on Lagrange (EL) model, the outer ring of the PI controller is eliminated by using the given active power and constant reactive power control on the side of the wind farm rectifier to simplify the controller, it can achieve the DC constant voltage and the reactive power transmission by using the constant DC voltage and reactive power control on the side of the grid inverter under the control strategies; the other is passive controller based on port controlled Hamiltonian model (PCHD). By selecting the desired interconnection and damping configuration, the control method is to track reference value using Hamiltonian function. Finally, Matlab/Simulink simulation results show that the VSC-HVDC system can realize grid fault isolation. And it provides a certain amount of reactive power for wind farms. The designed two controllers can achieve independent control for active power and reactive power with good transient performance.