Study On Control Strategies For AC/DC Coordination Control To Improve Grid Transmission Capacity

As multi-infeed HVDC system in the transmission of power in West to East operated, AC/DC hybrid transmission system is forming in China gradually. The complexity of the grid characteristics makes network security risks greatly increased,The AC/DC interactions can’t be ignorable. How to use AC-DC coordination technology to improve power system safety and stability in China becomes one of the focusin the scientific research and production departments.HVDC Power Transmission System had significant advantage in power regulation.When system disturbances, regulating DC power byappropriatecontrol laws can improve the dynamic performance and the transmission capability of the system. Compared by otherstability control measures,HVDC modulation is fast and flexible,so coordinated control of AC and DCplay an important role in maintaining the security and stability of the AC/DC powersystem.If AC powersystemgoes wrong in the AC/DC powersystem,additional control of the DC powersystem can be used to provide power support for ACpowersystem,and it canimprovesystem’s security and stability.If DC powersystemgoes wrong,the redudant power can be transferred to other AC/DC powersystem by the emergency power support and overload capacity of DC powersystem,this can reduce negative influence to the power systemFirst of all,this article analyzes the theory of mathematical model and control of HVDC system,and describe hierarchical structure and control of HVDC system.the article proposed control strategy of AC-DC coordination in based of DC emergency support. The policy applied to the regional networking of AC-DC hybrid system solves the synchronization of the regional grids, whenmonopolar locking and bipolar lockingoccurs in DC systemsbetween regional grids.The transmission capability security and stability of AC/DC hybrid transmission system is improved.The policy can also be used in islanded system, AC fault and monopolar locking of DC system occurs in theislanded system can cause frequency oscillation,when AC-DC coordinating control measures is taken, frequency stability and transmission capability of the islanded system can both be ipmproved.