The Study Of VSC-HVDC Connection Of Wind Farms To The Transmission System

In recent years, with the development of power electronics, VSC (voltage source converter) has became an active player in electricity transmission and distribution. This paper is mainly concerned about a VSC-HVDC(Voltage source converter high voltage direct current) converters to connect a wind farm and also to improve the fault ride-through capability of the wind farm at the expense of the AC fault.Because of a high degree of flexibility and controllable characteristics,VSC-HVDC primarily finds its application in the field of renewable energy distributed generation,supplying of isolated load, asynchronous network interconnection and other fields. In renewable energy,Wind power is one of the fastest growing sustainable energy resources over the past decade. But the integration of wind generation to power grid can bring many power quality problems because of the randomicity and intermittence of wind energy, the relevant influences on the host grids need to be carefully investigated.In this paper, First, this paper presents the possible improvements of voltage quality in connection of a wind farm to transmission network using VSC-HVDC link. The important influence of voltage fluctuation caused by the wind farm integration is analyzed. The dynamic behavior of the system is verified by simulation analyses using laboratory standard power system software package, PSCAD/EMTDC.Secondly, this paper presents a nonlinear control scheme for VSC-HVDC transmission system. The design of the proposed nonlinear controller has been performed in a rotating reference frame fixed to the grid voltage vectors. The controller is designed to provide high dynamic performance and complete decouple control of active and reactive power. Steady state and transient performance under various operating conditions have been examined. The nonlinear controller has provided complete decouple control of active and reactive power.At last, ANN (an artificial neural network) based current controller for a HVDC transmission link is described in this paper. a controller model which based on RBFNN Theory and PID control technology is designed by using S function. Based on this, A HVDC control system is built and simulated in PSCAD and Matlab. Radial basis function neural network is optimized based on gradient descent algorithm, and its model is constructed, then the M language program is written. By adjusting parameters of PID controller, the output approximately tracks the input.It is proved that the VSC-HVDC has great impact on the wind power system to improve system transient stability and provide the reactive voltage supporting effect in order to improve system voltage stability. The results prove validities of the operation principle and control strategy, which gives very good reference value for the VSC-HVDC used in the wind system in the future. and show the system posses fault tolerance capability and strong stability.