Research On Transient Voltage Stability Of AC/DC Hybrid Receiving-end Power Grid

Voltage stability is the foundation of power system security and stability. Alongwith the rapid development of HVDC and the need for energy distribution, AC/DChybrid system emerged in multiple regional power grid. HVDC will increase theflexibility of the system operation and the transmission capacity is expanded, butthe system structure becomes more complicated. The receiving-end power gridoften runs in heavy-load mode, an increasing proportion of these factors lead togrowth trend of voltage instability or voltage collapse or partial loss of load causedby large-scale blackout.In this paper, on the basis of reviewing the existing power system transientvoltage stability methods, the author points out that there is not yet a rigorousevaluation method and transient voltage instability criterion, we can only use someempirical methods to judge the transient voltage stability of the power system forengineering application. Firstly, through the analyzation and summarization of theprocess and characteristics of the actual power transient voltage instability incidents,in allusion to whether there is a short-circuit fault or not, whether it causedlarge-scale of power flow transferring or not, whether it has AD and DC couplingrelationship or not, this paper proposed a new classification of AC/DC hybridsystem voltage instability incidents. Then it laid the foundation for transient voltageinstability recognition and the application of stability control measures. Through thecalculation contrast of static and transient voltage stability limit for simple AC/DChybrid system, we can see that, for DC blocking fault which may cause voltageinstability, only consider the effect of large-scale trend transferring regardless ofimpact of the short circuit fault, using a reasonable method for the static voltagestability limit can approximately calculate the transient voltage stability limit. Secondly, an on-line voltage stability evaluation index LPQbased on PMUmeasurement considering the influence of active and reactive power transmission isproposed. We can quickly and efficiently determine the level of static voltagestability system, LPQindicators can also be used in the transient voltage stabilitycriterion using practical engineering situations in calculating the impact of transientvoltage stability without short-circuit failure; Voltage stability margin index APMand RPMis put forward, based on the active and reactive power flow of ACtransmission line and bus voltage, we can determine the receiving end systemstability margin; On the basis of the above-mentioned study, an online voltagestability assessment system is proposed. Adopt different assessment methodaccording to the characteristic difference of the fault, it can significantly simplifythe online calculation scale and largely enhance the calculation speed. Furtherdeepen the understanding of voltage stability problems and provides reference forsecurity and stability control measures. Through the AC/DC actual hybrid systemsimulation examples analysis, the proposed indicator LPQis checked, the resultshows that the comprehensive consideration of active and reactive power flowtransmission LPQvoltage stability index can be better achieved under the firstcategory of unstable fault transient voltage stability judgment. It will be importantfor system voltage instability prevention and the implementation of stability controlmeasures.