Transient Voltage Instability Identification Based on Positive-Feedback Unstable Region Mapped by Power Factor during Load Dynamics
Wang Xiaohui, Dang Chongyang, Liu Junyu, Ding Zewen
Key Laboratory of Power System Intelligent Dispatch and Control of Ministry of Education School of Electrical Engineering Shandong University Jinan 250061 China
Abstract：New-type modern power systems require the emergency control responding to system transients more than event-records. Hence the identification of voltage instability using the measurable electrical quantities and the positive-feedback mechanism is more adapted to such requirement. However, the conventional and typical criteria of such a kind are derived from Thevenin equivalent circuit. They are possibly difficult to capture the exactly-same measurement consistent to ideal Thevenin equivalence, when they are applied on practical power grids. If the system voltage drops rapidly, these criteria are also prone to invalidity for some intermittent short-periods, causing time-delay of judgement. This paper aimed to promote the performance of the response-driven identification on the transient voltage instability by deriving the criteria from the deduction on essential dynamics. The mechanism of such instability due to load dynamics was found out to be associated with the intrinsic feature of power-recovery in loads. Then the unstable region in mathematics could be formulated by the state variables of loads' equivalent resistance in the differential equations modeling such a power-recovery feature. The positive-feedback characteristics in the unstable region were depicted on the basis of these state variables. The consistency in the changing trend between power factor and these state variables during voltage transients was discussed. The criteria mapping the positive-feedback unstable region with power factor and equivalent power quantities were proposed. The adaptability of the proposed criteria was explored, emphasizing the analysis on why the conventional positive-feedback criteria tend to be invalid in the scenario of rapid voltage-drop. The proposed criteria were validated by the benchmark system, namely China Electric Power Research Institute's Voltage Collapse (CEPRI-VC) system, as well as the ten-thousand-node testing system with 10575 buses in specific. The results confirmed the effectiveness of the proposed positive-feedback criteria mapping the unstable region by power factor. The proposed criteria resulted in the missing alarm rate (MAR) of 0% in both systems. They also resulted in the false alarm rate (FAR) of 8.50% in CEPRI-VC system and 2.38% in the ten-thousand-node testing system, respectively. The performance of the proposed criteria could be promoted furtherly by increasing the parameter of criteria-holding duration threshold and/or decreasing the parameter of voltage-safety threshold. Fig.9 and Fig.15 demonstrated the variation of relevant electrical quantities during transients in case of voltage instability. They indicated the judgement process of the proposed criteria, which were always satisfied even if voltage dropped rapidly. The figures also showed the intermittent failures in the conventional criteria, explaining why they retarded the discrimination speed. This paper reached the following conclusions. The unstable region depicted by the dynamics of equivalent resistance in load model of power recovery can reflect the essential mechanism of transient voltage instability. There exists the consistent variation between power factor and the equivalent load resistance in unstable region of voltage transient instability. Mapping the unstable region with the positive-feedback variation of power factor can facilitate the construction of measurable criteria. The proposed criteria get rid of the constraint of voltage variation speed on the judgement accuracy, demonstrating robustness in case that the voltage drops rapidly.
王晓辉, 党崇阳, 刘峻宇, 丁则文. 功率因数映射负荷正反馈不稳定域的暂态电压失稳判别[J]. 电工技术学报, 2025, 40(17): 5476-5486.
Wang Xiaohui, Dang Chongyang, Liu Junyu, Ding Zewen. Transient Voltage Instability Identification Based on Positive-Feedback Unstable Region Mapped by Power Factor during Load Dynamics. Transactions of China Electrotechnical Society, 2025, 40(17): 5476-5486.
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