Study On Operation Characteristics And Recovery Strategy Of HVDC System Under AC Fault

As HVDC transmission plays an increasingly important role in modern power systems,research on the operation and control technology of HVDC systems is becoming more and more important.However,the failure of the inverter side commutation failure of the HVDC transmission system seriously threatens the safe and stable operation of the complex AC/DC grid,especially the AC/DC system with the weak AC system or multiple DC feeds.Reactive power control,as an important control function in HVDC transmission system,is not only related to the stable operation of the HVDC system,but also has a great correlation with the stability of the AC system voltage.Making full use of the HVDC system's own reactive power adjustment capability is beneficial to meet the different operational needs of the AC and DC systems.This paper first introduces the research status of HVDC,and explains the necessity of researching the control characteristics of HVDC.The paper analyzes the basic principles of VDCOL control and its deficiencies.Based on two optimization directions,namely,inflection point parameter optimization and curve line type optimization,the current optimal control strategies of VDCOL control of HVDC are analyzed,and the direction of VDCOL optimization control is prospected.Next,this paper systematically explores and accurately calculates the components of the instantaneous power components.Under asymmetric conditions,the instantaneous power calculation method under the condition of not considering and considering the zero-sequence component is given based on the ?? and the dq rotating coordinate system.The difference between the three-phase instantaneous power calculation method and the single-phase power calculation method is analyzed,which lays a foundation for the subsequent research on the reactive power characteristics of the converter station.Finally,by quantitative analysis of the characteristics of AC bus voltage,reactive power and DC current under AC fault,this paper proposes an AC fault recovery strategy that is conducive to suppress continuous commutation failure of HVDC.At the same time,considering the variation characteristics of electrical angles and their interactions during the duration of the fault,the constraint relationship between DC current and AC bus voltage under different fault types is obtained according to the HVDC quasi-steady-state calculation formula and the operating range of the converter's firing angle..Finally,the proposed control strategy is applied to the CIGRE HVDC standard test model.The simulation proves the effectiveness and robustness of the proposed recovery strategy in suppressing subsequent commutation failure and improving system recovery performance.