System Voltage Stability Research Articles

Solving Reactive Power Scheduling Problem using Multi-objective Crow Search Algorithm

This paper presents the solution of multi-objective based optimal reactive power dispatch (MO-ORPD) problem by optimizing the system power losses and voltage stability enhancement index (VSEI)/L-index objectives. ORPD problem is considered as an important issue from system security and operational point of view for optimal steady-state operation of power system. Here, single-objective based ORPD problem is solved using Crow Search Algorithm (CSA) and multi-objective based ORPD problem is solved using multi-objective CSA (MO-CSA). The CSA is considered as an efficient and robust algorithm which determines the global optimal solution for solving the non-linear and discontinuous objective functions. Two standard test systems, i.e., IEEE 30 and 57 bus systems are considered to show the effectiveness, suitability and robustness of CSA and MO-CSA for solving the ORPD problem.

Coordinated Recovery Strategy for Multi-infeed HVDC Systems Based on MIESCR

A coordinated recovery strategy, based on MIESCR, is proposed for the converters Excessive dynamic reactive power demand and the low speed of power transmission recovery in multi-infeed HVDC system in this paper. Firstly, the article deduces the consistency of two type definition of MIESCR, and uses the respective advantages of the definition to improve the physical meaning of MIESCR; and then it elaborates the role of MIESCR played in in MIDC system voltage and power-angle stability Third, this pages put forward MIESCR as the fundamental to distinguish the strength of AC system, and use the size of MIESCR to arrange the recovery order of DC systems. Furthermore, the parameter of PI controller is used to realize the control of each DC system current. There is a great method to ensure coordinate control of PI controller. The last, a double infeed HVDC system simulation model, based on two actual DC system of China Southern Power Grid, is built on Electromagnetic transient simulation software of PSCAD/EMTDC to confirm the validity of this method proposed in this paper.

Application of SMES Technology in Improving the Performance of a DFIG-WECS Connected to a Weak Grid

Wind Turbine Generator (WTG) has become one of the most popular renewable-based power generation that is broadly connected to electricity grids worldwide. Till the year 2019, the total WTGs installed worldwide reached about 650.8GW. The WTG is interfaced to the electricity grid through power electronic converters with a proper control algorithm to facilitate a smooth power delivery as well as maintaining the system voltage and frequency stability during wind intermittency. However, power grids are usually subjected to load expansion which affects the stiffness of the grid and hence its stability. A weak electricity grid exhibits voltage instability that may affect the performance of WTGs and in some cases may lead to serious damages to the wind turbines and the entire system. In this paper, superconducting magnetic energy storage (SMES) technology based on fuzzy logic controller is implemented to effectively resolve this issue and improve the overall performance of WTGs. Hysteresis current and fuzzy logic-based control system is proposed to control the energy exchange between the SMES coil and the investigated system. Results show the effectiveness of the SMES to improve the overall system performance and along with the fault ride-through capability of the doubly-fed induction generator (DFIG).

Maiden Voltage Control Analysis of Hybrid Power System With Dynamic Voltage Restorer

This work is a maiden attempt towards the voltage stability enhancement of a hybrid power system (HPS) comprising of Parabolic Trough solar power (PSP), Dish-Stirling Solar Power (DSP) and diesel generator (DG). DSP coupled with induction generator requires reactive power for its field winding to be magnetized whereas PSP employing permanent magnet synchronous generator (PMSG) doesn’t require reactive power for excitation. So, it’s worthwhile to infer that PSP reduces the reactive power requirement for its own functionality and may meet the same load demand at low voltage compensation. Lower voltage compensation requirement results in higher voltage stability. Besides, dynamic responses of the system are also improved as the HPS has been incorporated with Voltage Compensating Devices (VCDs) like Static Var Compensator (SVC), Static Synchronous Compensator (STATCOM) and Dynamic Voltage Restorer (DVR). Inclusion of FACTS devices reduces the probability of the transient voltage instability. HPS with FACTS devices under PSP has been subjected to the critical change in load with positive and negative infinite slope at regular interval of time to see the system practicality and its feasibility. The graphical and numerical analysis of the proposed system explicitly shows that the proposed HPS with PSP retains the system voltage stability with great margin under DVR. The efficient hybrid power system as a whole has been achieved to maintain the system reliability in terms of voltage because of the presence of PSP and DVR.

Multi-Terminal HVDC System With Offshore Wind Farms Under Anomalous Conditions: Stability Assessment

Droop control is widely adopted to control Multi-Terminal high-voltage Direct Current (MTDC) systems with offshore wind farms. During permanent faults, the faulty line should be isolated promptly to preserve a high reliability of the MTDC system. This paper examines the MTDC system performance following a faulty line outage. This study aims to identify the outage types that may lead to a complete loss of system voltage stability and the outages that may have a secondary effect on the system. Moreover, strategies for dealing with outages that may lead to a complete shutdown of the system are also presented. Furthermore, the ranges of droop gains’ values that can be employed following fault occurrence to preserve system transient stability are studied. Different scenarios are explored during faulty conditions such as surplus and sparsity of wind power, line overcurrent, outage of lines connected to wind farms, and outage of lines connected to AC grids to validate this study. MATLAB/Simulink platform has been employed to elucidate the presented concept.

A super-resolution perception-based incremental learning approach for power system voltage stability assessment with missing PMU measurements

This paper develops a fully data-driven, missing-data tolerant method for post-fault short-term voltage stability (STVS) assessment of power system against the incomplete PMU measurements. The super-resolution perception (SRP), based on deep residual learning convolutional neural network, is employed to cope with the missing PMU measurements. The incremental broad learning (BL) is used to rapidly update the model to maintain and enhance the online application performance. Different from state-of-the-art methods, the proposed method is fully data-driven and can fill up missing data under any PMU placement information loss and network topology change scenario. Simulation results demonstrate that the proposed method has the best performance in terms of STVS assessment accuracy and missing-data tolerance among the existing methods on the benchmark testing system.

OPTIMIZED MAXIMUM LOADABILITY OF POWER SYSTEMS USING AN ENHANCED DYNAMIC JAYA ALGORITHM

The problem of Maximum Loadability of power systems is addressed in this paper using a proposed dynamic JAYA algorithm. The maximum loadability problem is a typical optimization problem in which the maximum loadability point is to be determined optimally. Voltage stability of power systems is maintained by determining the estimated margin between the system operating point and the maximum loadability limit. The basic JAYA algorithm has been introduced to solve foremost optimization problems with small-scaled nature. However, when applied to large-scale, nonlinear and non-convex constrained problems, it showed a poor convergence characteristic. In order to deal with these weaknesses, the original algorithm has been improved by adding some dynamic features to its convergence behavior. The modified algorithm has been presented and validated when applied to well-known typical power systems. The obtained results were compared to the results achieved by other equivalent optimization techniques.

A Scheme for Position and Capacity Determination of Distributed Generation Considering Load Distribution and System Voltage Stability

The purpose of this study was to investigate a simplified distributed generation (DG) Position and Capacity Determination model (DG-PCD model) based on the coupling relationship between load distribution and voltage stability in the distribution network. First, based on the relationship between voltage stability and system equivalent impedance and the relationship between system equivalent impedance and load distribution, the relationship between voltage stability and load distribution is deduced, and the concept of influencing impedance mode is proposed and used in DG site selection. Then, build a DG-PCD model considering voltage stability, active power loss and line thermal stability margin, and use genetic algorithm (GA) to solve the model. Finally, an improved IEEE33-node system calculation example is analyzed. The results show that compared with the existing methods, the proposed method can get better results faster. This Proposed method not only simplifies the DG-PCD model, but also quantifies the relationship between voltage stability and load distribution. This provides a new reference index for the voltage control of the power grid.

Research on power system static voltage stability considering geomagnetic disturbances effect

AbstractThe reactive power losses caused by the power grid Geomagnetically Induced Current (GIC) severely disturb the static voltage stability of power systems, and may even trigger voltage collapses. In this paper, the 1 V/km uniform induced geoelectric field is adopted to analyze how greatly geomagnetic disturbance (GMD) can influence the static voltage stability of power systems, given the features of GMD disasters hitting the power grids of China. Considering the GIC reactive power losses, a method that combines second‐order sensitivity adaptive variable step size and local curve fitting is put forth to calculate the critical point of the active power and voltage nodes (PV) curve. With the increment ratio of the curve slope set at discretion, the method enables the curve to approach its critical point with great strides, a design managing to reduce the quantity of power flow calculations remarkably. By taking into account the reactive power violation of PV nodes in the acquisition of load increment step size, the method calculates the critical point of the PV curve in a much more accurate way. The method applied to the Northwest 750 kV power grid, the calculation results suggest that the 1 V/km induced geoelectric field markedly undermines the static voltage stability, thus posing grave threats to the above grid.

Impact of Wind Farms on Power System Voltage Stability (Dept.E)

Steady state analysis of wind turbine generating units (WTGUs) interconnected with the grid is needed as the use of WTGU are getting more popular and many new systems are being planted. In this paper, probabilistic voltage stability algorithm of WTGUs interconnected with the utility grid is developed via power Moy analysis where these units are modeled as P-Q bus(es) by detecting the collapse p oint on the Q-V curves. The developed algorithm also facilitates the computation of both the real and reactive power output of the fixed speed pitch regulated wind turbine at a specific site, wind turbine characteristics, wind speed and terminal voltage. The probabilistic nature of wind is considered by introducing the expected voltage stability margin is an index that combines both of the voltage stability and the wind distribution in one index. The proposed algorithm is implemented and applied on the IEEE 26-bus, voltage stability margin (VSM), and expected voltage stability margin (EYSM) are calculated at each wind speed. The accumulation of the EVSM over a specific period, can be considered as the system voltage stability margin which is a single value that can be compared with the voltage stability margin of the all-conventional power system.

Selection the optimum place of FACTS devices using fuzzy control system

In this paper, the voltage stability of the power system is studied during fault conditions. Enhancement of the system’s stability will be achieved by utilizing Flexible AC transmission systems (FACTS) controllers at the best place in the system. The optimum placement of (FACTS) controllers occurred on the most affected bus by the fault in the system (weakest bus). Two approaches have been used in this study to effectively obtain the best location of the (FACTS) controllers in the system. The first method is based on computing the deviation which occurs in the active power and reactive power due to the fault at each load bus at a time. Whereas the second method is performed through exploiting a MATLAB fuzzy set technique utilizing two indices: Line Flow Index (LFI) and Voltage Profile Index (VPI) during fault and steady-state conditions. The results show that both of these indices resulted in the same bus as the best location. Remedial actions in the attempt at improving in the stability of the power system are discussed taking the advantage of using (FACTS) compensation (SVC) and (STATCOM) at the most vulnerable system buses. In this work, MATLAB program with an IEEE 24 bus system is examined.

Effect of ambient temperature variations on estimation of proximity of the voltage collapse point

Due to deforestation, greenhouse gases and increasing air conditioner systems, the temperatures are changing drastically and the effects are prominent in summer and winter seasons. These ambient temperature variations are affecting the transmission system parameters and also the voltages at various buses. Changes in the transmission line parameters have non-negligible impact on system performance and present Energy Management applications are not considering these temperature variations in the power system state estimation. In this paper, impact of temperature variations on the power system Voltage Stability assessment is considered. Voltage stability assessment methods make use of the load flow results. Load flow results without considering the temperature variations are inaccurate in the real-time and leading to the erroneous results in the voltage stability assessment. In view of this, studies have been carried out on IEEE 30-bus, 118-bus and 300-bus systems, incorporating the seasonal temperature variations on various types of conductors, and also demonstrated the impact with conventional and ZIP type load models. In this paper, four voltage stability indices NLVSI, L m n , FVSI and VCPI(power) are used for identifying the proximity of voltage collapse point, critical line, critical bus voltage, critical bus angle, total system active power loss, total system reactive power loss etc.

Optimal reactive power planning in power transmission system considering FACTS devices and implementing hybrid optimisation approach

This study introduces a techno-economic planning strategy of reactive power (VAr) in power transmission systems. This planning strategy primarily has been focused on reactive power planning (RPP) through operating cost minimisation ensuring cost-oriented system security. The objective function (operating cost) is blended with four different components viz. cost due to real power loss, VAr generation cost, additional VAr compensation devices cost and line charging cost. FACTS (flexible AC transmission system) devices are installed at weak positions through different echelons to improve the system voltage stability. The authors also implemented the probabilistic hybridisation of crow search algorithm and JAYA to find out the optimal set of controlling parameters related to VAr. Finally, a sharp and minute analysis of the results has been done to validate the proposed strategy under multi-loading conditions. To understand the efficiency and efficacy the code profiling and simulation has been rendered on IEEE 30 bus and UPSEB 75 bus test system.

Distributed real-time power management for virtual energy storage systems using dynamic price

Energy storage systems (ESS) are widely used in active distribution networks (ADN) to smoothen the drastic fluctuation of renewable energy sources (RES). In order to enhance the scalability and flexibility of ESS, a virtual energy storage system (VESS), which is composed of battery energy storage system (BESS), RES as well as flexible loads (FL), is developed in this paper to realize the functionalities of ESS in more cost-effective way in ADN. Aiming at achieving voltage regulation, dynamic pricing strategies based on system voltage condition are designed for VESS. A distributed real-time power management model containing dynamic pricing strategies is proposed to accomplish the voltage regulation and economic power sharing in VESS. Moreover, a set of distributed algorithms, over time-varying unbalanced directed networks, are designed for dynamic pricing strategies and optimal power management model. Furthermore, the convergence property, optimality and system voltage stability are explained by detailed mathematical analysis. Three various case studies which were ran on a real time digital simulator (OPAL-RT OP5600) were designed to validate the effectiveness of the strategy. Finally, simulation results show that the economic power dispatch and voltage regulation are achieved among VESS simultaneously, even in the presence of time-varying directed and unbalanced communication networks.

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.

Deeply Hidden Moving-Target-Defense for Cybersecure Unbalanced Distribution Systems Considering Voltage Stability

A recent proactive defense mechanism, named as moving-target-defense (MTD), has been proposed as a prevailing topic that is capable of actively changing transmission line reactance to preclude cyberattacks. However, the MTD strategy has seldom been studied for the unbalanced AC distribution system in the existing literature. Towards the end, this paper proposes a deeply-hidden MTD (DH-MTD) to elaborately hide both the self and mutual reactance of each phase at the transmission line installed with D-FACTS devices. Both the branch and injection power phasor measurement functions are integrated into DH-MTD in the cyberattack scenario and under the normal operating condition, while the system voltage stability is ensured. The proposed DH-MTD model is solved using a nonlinear least square (NLS) method based on the trust-region algorithm due to the non-Gaussian noise assumption. Also, we cope with the MTD allocation (MTDA) problem using a data-driven normalized PDF peak residual (NPPR) index. The effectiveness of the proposed DH-MTD method is demonstrated in the unbalanced IEEE 123-bus distribution system against both branch and node cyberattacks.

Optimal network reconfiguration and DG allocation using adaptive modified whale optimization algorithm considering probabilistic load flow

The optimal DG allocation (ODGA) and network reconfiguration (NR) are significant tools to improve voltage stability and minimize power losses in a distribution network. In a real power distribution network loads are random variables, thus ODGA and NR processes are incorporated using a probabilistic load flow (PLF). The reactive power capability of DGs has a significant impact on the network parameters which can be studied using PLF. In the present work, an ODGA and NR processes have been incorporated to improve the voltage stability and loss profile of the distribution system considering probabilistic loads and DGs which are operated at varying pfs. The optimization problem has been solved using an adaptive modified whale optimization algorithm (A-MWOA). A novel technique based on depth first search algorithm has been employed to check radiality constraints. The effectiveness of proposed technique has been tested on two standard distribution networks.

Co-ordinated and real time voltage control of DSTS-biomass based isolated hybrid power system using Grey Wolf optimization

This paper proposes a co-ordinated reactive power control strategy analysis in Line Side Converter (LSC) of Doubly Fed induction generator (DFIG) and in the Automatic voltage regulator (AVR) of synchronous generator (SG) in isolated Dish Stirling solar Thermal(DSTS) – Biomass hybrid power system. This co-ordinated control strategy greatly maintains the autonomous hybrid power system voltage deviation by adjusting the reactive power imbalance caused due to the impulsive reactive power nature of DFIG coupled with the DSTS and load. Gain values of Integral Order Proportional Integral (IO-PI) controller in LSC and AVR are optimized to maintain the system voltage stability. Modern and simple Grey wolf optimization algorithm has been used to extract the superior PI gain values to maintain system stability with less reaction time. The proposed co-ordinated control strategy has been tested with various load disturbance and with dynamic input power feed from DSTS to validate the system robustness. Also, the optimized gain value based voltage deviation values are validated in real time with dSPACE.

Voltage Stability Analysis of Front-End Speed Controlled Wind Turbine Integrated into Regional Power Grid Based on Bifurcation Theory

Since wind power has characteristics such as intermittent and fluctuation, the integration of large-scale wind turbines into the power grid will bring a great impact on the voltage stability of the system. In this paper, the influence of the front-end speed controlled wind turbine (FSCWT) on the system voltage stability is studied. An actual model of the wind turbines, including the FSCWTs, connected to a regional power grid in Zhangye, Gansu Province, is established. Firstly, differential-algebraic equations (DAEs) describing the dynamic characteristics of the wind turbine are given and the mathematical model of the system includes FSCWT is established. The continuation method is used to track the balance solution of the DEAs within given parameter intervals. Based on that, the influence of the reactive power variation and wind speed fluctuation on the stability of system voltage is analyzed through both the bifurcation theory and the time-domain simulation. Results show that the Hopf bifurcation (HB) and the saddle-node bifurcation (SNB) are inherited for the system, indicating that such bifurcations are the essence of nonlinear dynamics that lead to voltage instability. The greater the disturbance of the bifurcation parameter Q1, the shorter the time of voltage collapse and the smaller the stable operation area of the system. With the increase of wind speed, the amplitude of system voltage will increase slightly, but the HB point will appear in advance, which is more likely to lead to voltage instability and further reduce the stable operation area of system voltage.

DAĞITILMIŞ SERİ REAKTÖRLERİN(DSR) GÜÇ SİSTEMLERİNE ETKİLERİ

Distributed Flexible Alternating Current Transmission System (DFACTS) devices are devices that are connected in series to the transmission line and even adding reactance. Devices, also referred to as Distributed Serial Reactors (DSR), have the ability correct impedance imbalance by interfering with line parameters in the power system. In addition, voltage balancing as a result of balanced load flow enables more power transmission or more efficient use of the power system's transmission capability. For this reason, the use of the system to control its loadability without expanding its dimensions is becoming more and more widespread. In this study, the effects of DSR devices on system loadability and voltage stability and their applicability are analyzed. The analysis was carried out on the Institute of Electrical and Electronics Engineers (IEEE) 6-bus Standard system using the Power World Simulator Program. The effects of DSR on the system were investigated by performing load flow.