Power Flow Calculation And Reactive Power Control Strategy For Wind Farms & AC-DC Power System Simulation Algorithm

Wind energy occupies a larger proportion of power energy with the rapid development of wind power. It would severely affect the power grid. Power flow calculation is a basic method to analyze the power grid after the wind farm accessed. Based on the model of induction generator and doubly-fed induction generator(DFIG), an alternating algorithm between main grid and wind farm is proposed. The wind farm is added to the main grid as a PQ node when the main grid is calculatting. The voltage of export bus from main grid calculation is a input variable of wind farm calculation, and the P and Q of export bus from wind farm calculation are input variables of main grid calculation. The simulation is carried out on IEEE9 system, replacing the generator3 with an actual wind farm in Inner Mongolia. Induction generator and DFIG are both simulated. The result proves that the method is feasible.When the wind farm connected to grid , the active power will fluctuation with the change of wind speed, and then cause the fluctuation of reactive power and voltage. A reactive power control strategy is proposed in this paper for reactive power balance and voltage stability of wind farms. The control objective is to maintain reactive power exchange between wind farm and the grid at a specific value. To achieve the control target, both SVC and Doubly Fed Induction Generator (DFIG) are used. In addition, a method is proposed to determine the adjusting order of DFIGs according the sensitivity their reactive power output to the reactive power export of wind farms, so the total reactive power of DFIGs could be at least. Finally the effectives of the control strategy is verified in an operation condition of a wind farm in Inner Mongolia.The modern power system has become a AC-DC hybrid system with the development of HVDC. A DC transmission system transient simulation method is proposed in addition to the traditional AC power system transient simulation. The algorithm carry out the AC system and DC system simulation alternately. The DC system is seen as a load in the process of AC system simulation, in the DC system simulation, the voltage of connect bus comes form AC system simulation is an input variable. The simulation algorithm is verified in east china power grid.