Study On The Reactive Power Coordinated Control In Hybrid DC Asynchronous Interconnection System

The Hybrid DC asynchronous interconnection system combines the advantages of Line Commutated Converter HVDC(LCC-HVDC)and Voltage Source Converter HVDC(VSC-HVDC),which provides a more flexible way of transmission to get the greatest economic and technological benefits.However,because the end system is weak switching reactive power compensation devices easily leads to commutation voltage fluctuations.Besides,AC side faults easily cause LCC-HVDC commutation failure and DC block fault.Then the DC transmission power is greatly reduced,seriously affecting the safe and stable operation of the power grid.Therefore,it is of great significance to adopt a suitable reactive power coordinated control strategy to improve the stable operation level of AC and DC transmission systems.Firstly the main circuit of hybrid DC asynchronous interconnection system and its control system are analyzed.And VSC-HVDC unit control system mathematical model is derived.Based on the actual parameters of Luxi BTB HVDC,hybrid DC asynchronous interconnection system is built on the PSCAD/EMTDC simulation platform and its operating characteristics are deeply research.Then,the reactive power control of hybrid DC asynchronous interconnection is analyzed comprehensively.The station slow reactive power control,conventional DC unit reactive power auxiliary control,flexible DC unit fast reactive power control and dual unit reactive power coordinated control are studied respectively.At the same time,the problem of low reactive power capacity and poor DC fault recovery characteristics caused by conventional DC transmission drop point weak AC transmission system is deeply analyzed and verified,which lays a theoretical foundation for the reactive power coordinated control strategy.Finally,the reactive power control of multi mode coordinated reactive power control strategy for HVDC reactive power compensation equipment and flexible DC unit is put forward.What's more,the effectiveness of the proposed strategy of DC power control system of wave steady-state control mode and transient mode is verified by PSCAD/EMTDC simulation.The results show that the steady-state and transient voltage stability of Hybrid DC asynchronous network is improved,and the probability of commutation failure is significantly reduced by using the proposed reactive power coordinated control strategy,which demonstrates the rationality and effectiveness of the strategy.