Research On Configuration Of Reactive Power Equipment For Long-Distance Offshore Wind Power Clusters Via Flexible HVDC Transmission

In recent years,the vigorous development of clean energy has become the mainstream of research,and offshore wind power has become an important strategic direction for energy development in various countries due to the advantages of stable resources,high annual utilization hours,not taking up no land resources,and suitable for large-scale development.With the further development of offshore resources,global wind power is gradually showing the trend of scale,clustering and distant sea.With the increasing offshore distance of wind power development,flexible DC transmission has become the first choice for long-distance wind power grid connection because of its certain reactive power voltage control capability instead of high-voltage AC transmission.However,due to the expanding scale of offshore wind power and the random and variable operating conditions of wind farms,a single offshore converter station as reactive power compensation cannot meet the requirements.Therefore,there is an urgent need to study the reactive power voltage characteristics and steady-state operation range of converter stations for flexible and straight outgoing deep-sea wind power cluster systems,as well as the reactive power configuration design scheme for offshore wind power flexible and straight systems applicable to engineering reality.The main contents are as follows.(1)Research on offshore wind farm network organization,grid connection scheme and system reactive power voltage characteristics.Firstly,a comparative analysis of the main wiring,transmission system and reactive power compensation devices of offshore wind farms is conducted,and a more widely used scheme of offshore wind farm network organization and grid connection is given;secondly,an equivalent model of the AC submarine cable is established,and the influence of charging power on the system voltage is analyzed in combination with the specific reactive power control strategy of the converter station;finally,by changing the active power output of the wind turbine,the key nodes in the offshore wind farm are Finally,by varying the active power output of the wind turbine,the voltage fluctuations at key nodes in the offshore wind farm are analyzed,including the wind turbine end,the pooling system bus,the AC side bus of the converter station,and the high voltage side of the offshore booster station.(2)The steady-state operating range and dynamic reactive power margin of the offshore converter station are studied.Firstly,an equivalent model of single-end converter station is established,the constraints to be satisfied by the steady-state operating range of the converter station at the sending end are analyzed,and the steady-state operating range of MMC in the PQ plane is solved by the tracing point method;secondly,the influence of the reference value of the flexible AC voltage and the length of the high-voltage AC submarine cable on the steady-state operating range is analyzed,which provides a feasible method to obtain the steady-state operating range of the converter station of the wind power cluster via the flexible direct transmission system.Finally,the dynamic reactive power margin of the converter station is defined,and the corresponding compensation scheme of the system is proposed for the case that the converter station is left with different reactive power reserve.(3)Study the reactive power configuration optimization scheme of the wind power cluster system in the deep sea via flexible direct transmission.Firstly,based on the currently available reactive power compensation configuration principles and combined with the absorption reactive power capacity of the converter station,a variety of optional reactive power compensation schemes are obtained based on the aforementioned model characteristics analysis of offshore wind farms sent out via soft and direct transmission system;secondly,quantitative analysis is conducted for the reactive power compensation and transmission capacity of multi-scene submarine cables under different operating conditions to determine whether the minimum high resistance compensation capacity of the frequency overvoltage analysis,the requirements of minimum high resistance compensation capacity for line current analysis,minimum high resistance compensation capacity at the first end of the line and maximum compensation capacity are determined,and then the compensation scheme is revised;finally,the reactive power compensation configuration scheme applicable to the actual project is derived by comparing the alternative schemes in terms of active power loss.