Real-time Voltage Stability Monitoring Research Articles

WAMS Based Real-Time Voltage Stability Monitoring for Various Load Models in the Presence of a DFIG Integrated Wind Farm

With rising global energy demand, transmission lines are operated at their limits, causing electrical grids to operate under extreme voltage instability conditions. To meet the increased load-demand and the forced tendency across the globe of tilting towards even more renewable generation, solar and wind farms are integrated with increased size and capacity. These uncontrolled natural power injection again may affect the system’s voltage stability. To avoid blackouts and to achieve the maximum voltage stability of power systems, operators need to do effective real-time grid monitoring and control at load terminals. Load models are important in the analysis of voltage stability, and accurate load models are useful in analysing the voltage stability conditions. Phasor-measurement-unit (PMU) based wide-area monitoring and smart-automation is an innovative technology for measuring load voltage magnitude, phase angle, and frequency variations in a DFIG integrated large wind power system. This research paper focuses on estimating the real-time voltage stability through the use of linear, nonlinear, and dynamic load models in presence of a DFIG based wind-farm in WSCC three-machine nine-bus power network using PMU data. This study is carried out using MATLAB-Simulink software.

Real-time voltage stability monitoring model of wind power plant penetration in electrical power system networks

The intermittent output power of wind power plants can affect the stability of the power grid, so a real-time monitoring model is needed. This study uses data from the southern Sulawesi network which is interconnected with wind power plants in real-time, and the IEEE 30 bus data is used as method validation. The method used is the New Voltage Stability Index (NVSI) based on Matlab. The results of the stability index on the IEEE 30 bus data are < 1 or are at the standard of stable criteria, namely 0.95 p.u. The result of the stability index of the South Sulawesi network is line number 49 from Latuppa to Poso has the highest value of 0.0473, the second is line number 18 from Bosowa to Tello is 0.0390, and the third is line number 24 from Tello 30kV to Barawaja is 0.0221, the other bus voltages have lower values. So it can be concluded that the network of South Sulawesi is stable, and intermittent wind power has no effect on voltage stability.

Real-time voltage stability monitoring using weighted least square support vector machine considering overcurrent protection

In this paper, a comprehensive scheme is proposed for online monitoring of voltage stability using the Weighted Least Square Support Vector Machine (WLS-SVM) that the effect of overcurrent protection for transmission lines is factored in. The operation of protection systems, due to their nonlinear effect on the system graph, changes the linear and nonlinear equations of the system which cannot be solved by conventional methods. To prevent the maloperation of the overcurrent protection system, coordination between Directional Overcurrent Relays (DOCRs) has been done by linear programming to reach the globally optimum values for DOCR settings. As a result, WLS-SVM is used by implementing collected data from Phasor Measurement Units (PMUs). In addition to solving linear equations instead of quadratic equations, WLS-SVM solves the problems of noise sensitivity and lack of sparseness of the solutions. Also, Principal Component Analysis (PCA) has been used for the dimensionality reduction of the input vector applied to WLS-SVM in this work to make it suitable for real-time applications. Moreover, the measurement errors between measurements obtained from PMUs and the reference values have been taken into account. Then, real-time power system stability monitoring is performed by predicting a voltage stability assessment index using WLS-SVM to evaluate the voltage stability status in a real-time manner. Results of the proposed method regarding efficiency demonstrate high accuracy and better performance in comparison with other approaches. The simulation of the presented approach is carried out on the IEEE 39-bus and IEEE 118-bus systems.

RTDS 기반의 시각동기 위상측정데이터를 이용한 실시간 전압안정도 감시 및 선로정수 추정

RTDS 기반의 시각동기 위상측정데이터를 이용한 실시간 전압안정도 감시 및 선로정수 추정

PMU-Based Distributed Non-Iterative Algorithm for Real-Time Voltage Stability Monitoring

The Phasor measurement unit (PMU) measurements are mandatory to monitor the power system's voltage stability margin in an online manner. Monitoring is key to the secure operation of the grid. Traditionally, online monitoring of voltage stability using synchrophasors required a centralized communication architecture, which leads to high investment cost and cyber-security concerns. The increasing importance of cyber-security and low investment cost have recently led to the development of distributed algorithms for online monitoring of the grid that are inherently less prone to malicious attacks. In this work, a novel distributed non-iterative voltage stability index (VSI) is proposed by recasting the power flow equations as circles. The online computations of VSI are simultaneously performed by the processors embedded at each bus in the smart grid with the help of PMUs and communication of voltage phasors between neighboring buses. The distributed nature of the index enables the real-time identification of the critical bus of the system with minimal communication infrastructure. The effectiveness of the proposed distributed index is demonstrated on IEEE test systems and contrasted with existing methods to show the benefits of the proposed method in speed, interpretability, identification of outage location, and low sensitivity to noisy measurements.

Hybrid voltage stability and security assessment using synchrophasors with consideration of generator Q‐limits

Increased power demands, push for economics and limited investment in grid infrastructure have led utilities to operate power systems closer to their stability limits. Voltage instability may trigger cascade tripping, wide-area voltage collapse, and power blackouts. Real-time voltage stability monitoring possible with deployment of phasor measurement units (PMUs) is essential to take proactive control actions and minimise the impact on the system. This study presents a novel online algorithm for (a) hybrid perturbation analysis based voltage stability monitoring (HPVSM), (b) including Q-limit in voltage stability index, and (c) real-time security analysis using voltage stability index. HPVSM-based voltage stability index is computed using the data obtained from linear state estimator and PMU measurements. Typically measurement-based schemes ignore the impact of generator Q-limits and security analysis is not feasible. The proposed HPVSM-based index considers the impact of generator Q-limits violations by anticipating the critical generators using real-time PMU measurements. Contingencies are ranked using the proposed voltage stability index for security analysis. Results simulated for the 9-bus WECC, IEEE 14, 57, and 118 bus systems highlight the superiority of the proposed method in real-time voltage stability and security analysis.

Voltage Stability Online Monitoring and Analysis Method Based on the Fixed-Point Principle

ABSTRACT Continuous assessment of voltage stability is vital to ensure the secure operation of the power system. Based on this concern, a number of online voltage stability analysis methods have been proposed. Among these indices, the impedance match concept based on Thévenin equivalent has attracted a lot of interest. However, the traditional impedance match is reported not to perform as expected under multi-load power systems. This paper proposes a new approach for voltage stability assessment based on the Banach fixed-point theorem. This leads to a real-time voltage stability monitoring scheme without the need to estimate Thévenin parameters. The derived method was tested on a 5-generators and 18-bus system by time-domain dynamic simulations and simulated on an actual power system using real phasor measurement unit.

Information-Energy Flow Computation and Cyber-Physical Sensitivity Analysis for Power Systems

Power systems are the typical cyber-physical systems in which the closed-loop hierarchical control systems (HCSs) are widely used to ensure their stable and safe operation. To describe the coupling operation mechanism of an HCS and power grid by expanding current steady-state power flow analysis theory, we propose an information-energy flow model and develop a matrix-based computational approach. With the help of the methods, we can directly calculate the mutual influence of the cyber and physical parts. Since the mechanism of power flow computation is mature, we focus on the cyber side, proposing an information-flow-oriented network model as well as a matrix-based computation method for its information flow. In particular, we develop a minimum-cut-set-based partition and equivalence method to address a complex cyber network with non-linearity issues associated with data processing. Subsequently, we discuss cyber-physical sensitivity and vulnerability issues. In the case study, we calculate the information-energy flow of an IEEE 14-node system with real time-voltage stability monitoring and control application and compare the results with simulation results. The similarity of the results between the two methods verifies the effectiveness of our approach.

A Distributed Voltage Stability Monitoring Method Based on Local Measurements and Line Parameters

This paper proposes a distributed real-time voltage stability monitoring method based on local measurements and line parameters. Local PV sensitivity (PVS) is adopted as the indicator of voltage stability. Compared with traditional methods, the proposed method only requires local voltage magnitude, active power flow measurements and the parameters of transmission lines connected to local node. The proposed method will check the operation status of each transmission line first and thus formulate the calculation expression of the voltage stability index. Then we will calculate the PVS accordingly. And we have analyzed the uncertainty of PVS led by the measurement errors. Simulation studies using IEEE 39 nodes system will be introduced and used to demonstrate the effectiveness of the proposed method.

Evaluation for Voltage Stability Indices in Power System Using Artificial Neural Network

At present, the evaluation of voltage stability assessment experiences sizeable anxiety in the safe operation of power systems. This is due to the complications of a strain power system. With the snowballing of power demand by the consumers and also the restricted amount of power sources, therefore, the system has to perform at its maximum proficiency. Consequently, the noteworthy to discover the maximum ability boundary prior to voltage collapse should be undertaken. A preliminary warning can be perceived to evade the interruption of power system's capacity. This paper considered the implementation of real-time system monitoring methods that able to provide a timely warning in the power system before the voltage collapse occurred. Numerous types of line voltage stability indices (LVSI) are differentiated in this paper to resolve their effectuality to determine the weakest lines for the power system. The line voltage stability indices are assessed using the IEEE 9-Bus and IEEE 14-Bus Systems to validate their practicability. Besides that, this paper also introduced the implementation of real-time voltage stability monitoring by using Artificial Neural Network (ANN). Results demonstrated that the calculated indices and the estimated indices by using ANN are practically relevant in predicting the manifestation of voltage collapse in the system. Therefore, essential actions can be taken by the operators in order to dodge voltage collapse incident from arising.

Spoofing GPS Receiver Clock Offset of Phasor Measurement Units

We demonstrate the feasibility of a spoofing attack on the GPS receiver of a phasor measurement unit (PMU). We formulate the attack as an optimization problem where the objective is to maximize the difference between the PMU's receiver clock offset (with respect to the GPS time measured by the onboard satellite clocks) before and after the attack. Since the PMU uses this clock offset to compute a synchronized time stamp for its measurements, an error in the receiver clock offset introduces a proportional phase error in the voltage or current phase measurements provided by the PMU. For the most general case, the decision variables in the optimization problem are the satellites' ephemerides, pseudoranges, and the receiver's Earth-Centered Earth-Fixed (ECEF) coordinates. The constraints are cast such that the decision variables and the satellite positions computed from the solution of the optimization problem are close to their pre-attack values, so as to avoid possible detection schemes that check for large jumps in the values of these variables. We show that the spoofing attack is feasible for any number of visible satellites. As an illustration of the impact of such spoofing attacks, we present simulation results in which the attack induces errors in a real-time voltage stability monitoring algorithm that relies on the phase information from measurements provided by PMUs.

Improved Algorithm for Identification of Thévenin Equivalent Parameters for Voltage Stability Analysis

This paper proposes an improved algorithm for tracking the Thévenin equivalent parameters with local phasor measurements for voltage stability analysis. Estimation errors between the Thévenin equivalent voltage and impedance are mathematically formulated, and then used to correct the equivalent parameters with two subsequent measurements. This algorithm does not introduce any parameters drift problems and does not need a large data window to converge. A 2-bus test system, the IEEE 14-buses system and an actual 500kV grid system from China are used to test the proposed algorithm. Test results indicate that this algorithm is accurate, robust and fast for real time voltage stability monitoring and control.

A New Method for Monitoring Local Voltage Stability using the Saddle Node Bifurcation Set in Two Dimensional Power Parameter Space

This paper proposes a new method for monitoring local voltage stability using the saddle node bifurcation set or loadability boundary in two dimensional power parameter space. The method includes three main steps. First step is to determine the critical buses and the second step is building the static voltage stability boundary or the saddle node bifurcation set. Final step is monitoring the voltage stability through the distance from current operating point to the boundary. Critical buses are defined through the right eigenvector by direct method. The boundary of the static voltage stability region is a quadratic curve that can be obtained by the proposed method that is combining a variation of standard direct method and Thevenin equivalent model of electric power system. And finally the distance is computed through the Euclid norm of normal vector of the boundary at the closest saddle node bifurcation point. The advantage of the proposed method is that it gets the advantages of both methods, the accuracy of the direct method and simple of Thevenin Equivalent model. Thus, the proposed method holds some promises in terms of performing the real-time voltage stability monitoring of power system. Test results of New England 39 bus system are presented to show the effectiveness of the proposed method.

Voltage Stability Monitoring Based on the Concept of Coupled Single-Port Circuit

This paper reveals that the impedance match (or the Thevenin circuit) based voltage stability monitoring techniques have problems to predict voltage stability limits when applied to multi-load power systems. Power system loads are nonlinear and dynamic. They cannot be simply represented as Thevenin circuit parameters for impedance match analysis. To overcome these difficulties, a new concept called “coupled single-port circuit” is proposed in this paper. The concept decouples a meshed network into individual single generator versus single bus network and, as a result, a modified version of the impedance match theorem can be used. This leads to a real-time voltage stability monitoring scheme without the need to estimate Thevenin parameters. The scheme can estimate voltage stability margin and identify weak areas in a system based on the SCADA and PMU data. Case studies conducted on several test systems have verified the validity of the proposed method.