Operation And Characteristics Of Multi-Infeed LCC HVDC

The use of High Voltage Direct Current(HVDC)power transmission technology has become common in modern power system.During past two decades,HVDC technology has been extensively used for long distance bulk power transmission to remote areas.The matured high power electronics technology has made HVDC possible to overcome the concerns of recent power market i.e.security,reliability,power flow and power regulation problem of conventional HVAC system.In China,the demand of power is drastically increased in recent years due to industrialization;such situations make HVDC an economic candidate because the distance between power generation plants and load areas is significantly very high.The conventional HVDC uses Line-Commutated Converters(LCC).The LCC technology is well matured than other available conversion schemes(i.e.voltage source converters)and it is widely used in high power projects.China will have approximately 50 HVDC links by 2020 and a single LCC based link with highest capacity is 12GW between ChangJi-GuQuan.Despite of new HVDC technologies,conventional LCC based HVDC is anticipated to play an integral role in future power system transmission.On other hand,the increasing penetration of HVDC transmission in existing power network have led to a situation where numerous HVDC links terminate to electric vicinity of each other's ac network or even on same ac busbar.Such scenarios are termed as multi-infeed HVDC system.The HVDC studies,during early years,focused on stability,AC/DC interaction,connection with weak ac system,harmonics,power control,reactive power support and allied problems i.e.commutation failure,transient over-voltage,maximum achievable power,fault recovery time and etc.But,nowadays,due to increasing multi-infeed HVDC scenarios,the phenomena such as transient over voltage,commutation failure,fault recovery time,harmonics interaction and voltage/power stability for multi-infeed configuration have grabbed much attentions.The concomitant problems i.e.local/concurrent commutation failure,power flow,inter-converter voltage interaction,dc-dc interaction,ac-dc interaction and hierarchical connections have also been studied during recent years.However,these phenomena have lack of true data.Hence,the main objective of this study is to probe the true behavior of local/concurrent commutation failure,discrete tap position problem in power flow and dc-dc interaction for multi-infeed HVDC systems.The voltage stability is also investigated with the help of Jacobian matrix.A new mathematical relation is developed which estimates the increase in local commutation failure immunity index.The multi-infeed LCC HVDC model is developed in PSCAD/EMTDC for commutation failure and ac-dc/dc-dc interactions.The discrete tap position problem and voltage stability analysis are addressed using MATLAB.The CIGRE first benchmark model is taken as reference to develop multi-infeed test system.