Study On Voltage Stability On-line Monitoring Of Load Center Based On PMU Parameter Identification

Recently, power system has changed from integration with generation, transmission and distribution into an open and competitive environment. The using intensity of existing transmission equipment is growing with the increasing in demand for transmission capacity, and voltage instability becomes more and more prominent. So the unsafe voltage has becomes one of the major factors of limiting voltage power transmission. Voltage instability may occur in the main network or regional network, and most of them occur quite suddenly, which requires the power system operating state dynamic analysis, continuous monitoring, and fast and accurate data processing of system voltage stability determination. PMU can implement the data of entire network synchronous collecting, real-time recording, remote real-time transmission and synchronous analysis and process, and on this basis to obtain voltage and current etc electrical quantities which reacts the running state of system, and achieve dynamic monitoring of system’s operation under the space-time coordinates, which makes the research foundation of on-line voltage monitoring and control.Firstly, the paper introduces the background, purpose and research status of the subject, and explains the mechanism of voltage instability and corresponding voltage stability methods are summarized, describes the research status and working principle of PMU.Secondly, considering the effect of different load models on voltage stability, the paper elaborates respectively static load model and dynamic load model and their respective impacts on system voltage stability, obtains conclusion that the constant power load model of ZIP load model and the induction motor of dynamic load model is harmful to voltage stability, which is verified by EPRI36 buses system.Then, the paper makes the static security analysis for actual grid, and the N-1 fault scanner for entire network to obtain the corresponding P-V curves and calculates the corresponding power reserve coefficient Kp.On the basis of above work, the V-Qsensitivity analysis and modal analysis for the limit point of the P-Vcurve under the small perturbations are made to obtain the system voltage weak areas with the result of bus participation factors, branch participation factors and generator participation factors.Finally, regarding the voltage weak area of load center as an integral object of study, the paper converts voltage weak areas into fictitious bus with an aggregated load in application of REI based on system’s bus voltage, current and power phase collected by PMU. Thevenin equivalent to represent an external system is developed and Kalman Filter is applied to track constantly Thevenin equivalent parameters, which can get the Thevenin equivalent model of the system. Considering voltage constraints, this paper derives the expression of critical voltage stability on the flow section space and proposes voltage stability margin index VSMI.Case studies in voltage weak area B1 (CJQ) of actual grid validate the feasibility of the proposed method, and achieve the on-line voltage stability monitoring of load center.