Researsh On Voltage Stability Of AC/DC Hybrid Power System With FACTS Devices

With the development of China’s electrical industry, the load and installed generation capacities are expanding. It’s significant to study the voltage stability of power system. Meanwhile, the power electronic technology is promoting the progress of flexible AC transmission systems (FACTS) and high-voltage DC (HVDC) transmission. The power grid is becoming an AC/DC hybrid power system, which will bring the new contents of voltage stability research.In this thesis, the study on voltage stability of AC/DC hybrid power system includes three aspects:the accuracy of voltage stability evaluation index based on phasor measurement, the impact on voltage stability of multi-infeed HVDC system with ultra high-voltage DC (UHVDC) hierarchical connection mode, the dynamic voltage stability criterion and its quantitative application.With the information of phasor measurement, the voltage stability evaluation indices are built. According to the information of bus phasor measurement, indices are built based on ratio of impedance module, feasible solution of quadratic equation of bus voltage and power transfer limit. According to the information of branch phasor measurement, indices are built based on feasible solution of quadratic equation of branch voltage and perturbation of complex power. Three factors, which are DC control modes, load location and load change characteristics, are put forward to analyze their influence on the accuracy of these indices, based on the wertern system coordinating council (WSCC) three-machine nine-bus AC-DC hybrid system.The impact of UHVDC hierarchical connection mode is analyzed based on multi-port thevenin equivalent method. The multi-infeed short circuit ratio (SCR) is taken to describe voltage stability of multi-infeed HVDC system. The change, hierarchical connection mode will bring to the SCR, is investigated. The calculation of multi-infeed interaction factor (MIIF) is a central part of the multi-infeed SCR calculating. So the deviation of MIIF between the conventional method and the menthod considering the power characteristics of DC system is analyzed.Finally, a dynamic voltage stability criterion is proposed based on the Thevein equivalent method with deviation correction. The reliability of criterion is verified concerning the computing time, the time of switching devices and the real power system. To use the criterion quantitatively, the participating factor of unstable modal and voltage amplitude is introduced. Based on this, a control strategy, combining the static voltage stability information and dynamic voltage stability information, is proposed. The accuracy and efficiency of strategy is verified by time domain simulation of AC/DC hybrid power system.