Research On Voltage Stability In AC-DC Hybrid Transmission System

In order to make use of resources better, enhance the economic efficiency and protect the environment, development direction of power grid domestic and international is large power grid, high pressure, and long-distance transmission. However, the traditional AC transmission has problems of large loss and poor stability in the large capacity, long-distance transmission, it's not suitable as transmission mode when transmission distance is more than 1000 km. DC transmission, which has advantages of fast adjustment power, no stable limit problem in synchronization operation, reliable operation, and the line low cost, is especially suitable for application in high power, long-distance transmission occasion; However, It will absorb large reative power when AC-DC hybrid transmission works,which leads to voltage instabilityBecause the tradition analysis methods used by AC-DC hybrid transmission are too simple and lack of analysis of voltage instability mechanism, taking the AC-DC hybrid transmission as the research object, Voltage Stability in AC-DC Hybrid Transmission System is studies from three aspects:the static voltage stability, dynamic voltage stability and transient voltage stability. During the analysis of Static voltage stability, the method of continuous flow is used to study the PV curve of the common AC system and AC-DC Hybrid Transmission System. The continuous changes about the load parameters are recorded for studying the maximum load and voltage collapse point; the continuous changes about the transmission power are recorded for studying the maximum transmission power of DC line. The bifurcation theory is used during the analysis of dynamic voltage stability. The dynamic mode of generator and HVDC is established, and dynamic flow equation is got. Using the bifurcation theory singularity tracking method, the dynamic bifurcation point will be got before the system meets the static bifurcation point. At last, time domain simulation method is used to study the transient voltage stability, the results show that, in the three-phase short-circuit fault, the power angle of generators, power transmitted by DC line, the extinction angle at the inverter tend to be stability. Constant extinction angle at inverter side can make inverter converter AC bus voltage restore to the steady-state level.