Study On Reactive Power Optimal Control For Offshore Wind Turbine Based On Multi-objective Control

In this thesis, a large-scale offshore wind farm is studied, taking into account the long-distance submarine power cable charging power larger which is easy to cause bus voltage fluctuations problems. The converter of wind turbine is made full use to reactive power compensation, while relying on wind farm equipment to achieve reactive offshore wind farm reactive power compensation. The research work is as followed.Firstly, a novel offshore wind farm modeling scheme is used to analyze the reactive power compensation which greatly improves the traditional methods of simple superposition of the unit, so that the proposed modeling method of large-scale offshore wind farm is closer to the actual operation. The transformer modeling analysis on multi-machine system is taken into account the method, while the equivalent circuit and high-voltage AC submarine cable is also studied deeply.Secondly, based on the offshore wind farm transmission model parameters and submarine cable systems, the control scheme and calculation method of reactive power compensation for offshore wind farms are analyzed, and reactive power loss calculated in different sizes, different transmission distance offshore wind farm which includes land single-ended and two ends compensation. The conductor loss of submarine cable compensation is calculated, which is namely wind farm output curve.Finally, the selection of objective function, power and variables constraints of the wind power system reactive power optimization program are analyzed, while the location, grouping schemes and compensation effects of the economy of submarine offshore wind farm reactive power compensation is also studied, the objective function of minimized test point loss and voltage fluctuations based on goal programming are proposed, while the optimal value of the multi-objective function is calculated. The reactive power control method is analyzed by simulation software PSCAD with an offshore wind farm connecting grid project. The multi-objective optimization algorithm were compared the proportion optimization which is widespread use in reactive power field. Simulation results show that:when the grid voltage drops, the proposed optimization method can rapid uplift the voltage of PCC, greatly improving the ability of reactive power compensation system, which verify the validity of the proposed reactive power optimization scheme.