A Practical Method For Calculating The Critical Wind Power Ratio In Wind-thermal-bundled DC Sending System

At present,as the world's coal,oil and natural gas and other non-renewable energy reserves are shrinking and drying up increasingly,it is urgent to accelerate the develop-ment of alternative renewable energy and explore sustainable development strategy.Among them,wind power generation is the most mature,most developed and commer-cialized generation mode of renewable energy development and utilization.In view of the inverse distribution of energy resources and energy demand in China,the wind power base and coal base are mainly distributed in the West and North,and there are both ob-jective needs for large and long distance transportation to the eastern and central load centers.Using the way of wind-thermal-bundled power transmitted by HVDC system,can not only meet the needs of large-scale energy outgoing,but also greatly improve the utilization of DC system.Nowadays,because of the increasing trend of the permeability of new energy and electricity in the northwest region,the northwest power grid is re-stricted by the lack of hydropower,and the new energy base adopting the original net-worked DC delivery method is facing diflficulties,so there is a technical need for wind-thermal-bundled DC islanding operations.From the perspective of voltage stability,this paper analyzes the allocation of criti-cal wind power ratio in the wind-thermal-bundled DC sending system.The short-circuit ratio is defined as the evaluation index of voltage stability.The minimum short-circuit ratio of direct current system of wind-fire bundled islanding system is determined ac-cording to the technical requirements of DC island system access,the calculation formula of effective short circuit ratio is derived from the corresponding equivalent simplification and the short circuit calculation of the wind-thermal-bundled DC island sending system,the relationship between the short-circuit ratio and the load ratio of the delivery end sys-tem and the wind power penetration rate is obtained.The electromagnetic transient model is built in the simulation software based on the practical basis of Hazheng DC transmission system.Taking the constructed electromag-netic transient model as an actual example,the three-phase short-circuit fault at the con-verter busbar and the derivation and the calculated value of the short-circuit ratio are re-spectively set up under different local load ratios for different wind power permeabilities.The relative validity of the two methods is compared to verify the correctness of the the-oretical derivation of the short-circuit ratio.The critical wind power ratio is determined by considering the different fault types and different fault locations in the electromagnet-ic transient models with different local load ratios.And through the simulation,the criti-cal short-circuit ratio that can determine the voltage stability of the DC island sending system under various conditions was determined,and it was substituted into the short-circuit ratio calculation formula to obtain the calculation formula of the critical wind power ratio.The calculation method of the critical wind power ratio under different local load ratios for wind-thermal-bundled DC island sending system is given,and it is of guiding significance to the configuration of windfire proportion in energy base.