Stability Margin Enhancement Research Articles

Assessment of Linear Quadratic Regulator Based Optimal Stabilization of Weak-Grid-Following Inverter Interface

An optimal state- feedback based decentralized stabilizing control scheme for weak-grid connected inverter interfaces is proposed here. Linear Quadratic Regulator (LQR) based feedback control options viz. small-signal perturbations in the reference signals, and in the control gains are explored for the same. It is shown that, with full-state feedback of local control variables, the stability enhancement is not much effective with gain perturbations. Rather, the reference set-point change is shown to stabilize the inverter to weak-grid interconnection. Eliminating the need of communication assisted auxiliary inputs or the need for their estimation, the proposed approach is effective in achieving stability margin enhancement for wider range of X/R ratios and grid impedances. The cost of achieving stabilization using totally device-level information is the compromise made in set-point adjustment. However, this can be adopted for emergency weak-grid scenarios in a generic power system. The proposed control augmentation is analysed for different operating scenarios in which one or the other control loops are enabled, and corresponding modifications in the controller are discussed. The proposed claims are validated using small-signal models, simulation studies in MATLAB/Simulink as well as with a power-hardware-in-the-loop (PHIL) experimental setup.

CNN‐LSTM based power grid voltage stability emergency control coordination strategy

AbstractThe occurrence of cascading failure and small probability contingency in hybrid AC/DC power grid aggravates the mismatch risk of traditional emergency control with offline‐predetermination–online‐practice (ODOP) mode. To ensure the voltage stability of power grid under large disturbances, this paper proposes a voltage stability emergency control coordination strategy based on convolutional neural network (CNN) and long short‐term memory (LSTM) network. First, the mismatch mechanism of traditional emergency control is revealed under the variation of operating conditions. Second, the start criterion of complementary emergency control with ODOP mode is proposed, and the CNN‐LSTM network is established to quantitatively evaluate the voltage stability margin. Finally, the emergency control sensitivity index is proposed to predict the stability margin enhancement under alternative emergency control measures, and the optimal ODOP‐based emergency control strategy is determined to coordinate multiple voltage stability emergency control measures. Case studies are performed in the actual Northwest China local region hybrid AC/DC power grid with voltage instability problems, and the simulation results verify the effectiveness of the proposed method.

Investigation of the impact of PSO, ABC, BFO and Cuckoo search optimization techniques on UPFC device for sustainable voltage stability margin improvement

This paper investigates the enhancement of voltage stability margin using Unified Power Flow Control (UPFC) device tuned with Particle Swarm Optimization (PSO), Artificial Bee Colony (ABC), Bacterial Foraging Optimization (BFO) and Cuckoo Search techniques (CS) on Nigerian 330 kV 56-bus practical network. In order to have a voltage stable power system, it is good to keep voltages within the acceptable limits. This is achieved using continuation power flow embedded in Power System Analysis Toolbox (PSAT). The optimal location and tuning of the UPFC device is determined using line stability index and the met-heuristics techniques. The effects of UPFC and the proposed optimizing techniques on voltage stability margin are examined. The results so obtained for tuning PSO, ABC, BFO and Cuckoo Search with UPFC device are compared to know the technique that yields the best loading parameter for Nigerian 56- bus power system for voltage stability margin enhancement. It is found that UPFC tuned with Cuckoo Search outperforms the other techniques in terms of the increased loading parameter of the Nigerian power system with margin improvement of 86.6%, 90% and 88.6% for Adiabor (Bus 45), Jalingo (Bus 34) and Jos (Bus 13). The tuned UPFC device has proved beyond reasonable doubt that it can improve voltage stability margin of the entire Nigerian 330 kV Network as envisaged from results before and after optimization.

An Analysis on the VSC-HVDC Contribution for the Static Voltage Stability Margin and Effective Short Circuit Ratio Enhancement in Hybrid Multi-Infeed HVDC Systems

Over the years, high voltage transmission of large energy blocks over long distances has widely developed from the Line Commutated Converter (LCC) technology. However, the continuous expansion of the AC network and the increase in renewable energy penetration leads to the weakening of Electric Power Systems (EPS), causing operational problems for the LCC-HVDC. This paper evaluates the degree of contribution of the VSC-HVDC on the LCC-HVDC dynamic performance when the infeed is in a hybrid multi-infeed HVDC system. Through a steady-state mathematical framework, the new concept of Hybrid Power Voltage Interaction Factor (hPVIF) is proposed to assess the transient stability improvement of LCC. Additionally, this article introduces two key contributions from hPVIF: the complementary Improved Commutation Failure Immunity Index (iCFII), as a measure of the effective short circuit enhancement, as well as the apparent line length, which emulates the line lengths adjusting the power dispatch in the VSC-HVDC. PSCAD/EMTDCTM time-domain dynamic simulations are performed to assess the indexes, and the Matlab® software will be used to assist in mathematical operations.

Assessment and Enhancement of Hopf Bifurcation Stability Margin in Uncertain Power Systems

Uncertainties in the forecasted load and generation can have a catastrophic impact on power system stability. For a reliable power supply, a sufficient dynamic stability margin is always desired. This paper introduces a novel boundary eigenvalue-based approach for the determination of Hopf Bifurcation Stability Margin (HBSM), which, explicitly, accounts for the impact of uncertainties in specified renewable generation and loads. Since the Hopf bifurcation stability problem is nondeterministic, it requires large computational efforts to determine the HBSM. Most of the available methods are based on statistical data, which are computationally less efficient for such applications. In this paper, a non-statistical uncertainty based control rescheduling strategy is proposed to enhance the stability margin of the system. To balance the trade-off between solution quality and computation time, the proposed approach is composed of two stages: i) determination of boundaries of critical eigenvalues; and ii) optimal setting of the controllers by minimization of a boundary active power loss based objective function under the given range of uncertainties. The proposed approach is demonstrated on standard IEEE test systems with promising results to show the importance and its reliability.

Optimal Planning of Multiple Renewable Energy-Integrated Distribution System With Uncertainties Using Artificial Hummingbird Algorithm

Appropriate installation of renewable energy-based distributed generation units (RDGs) is one of the most important challenges and current topics of interest in the optimal functioning of modern power networks. Due to the intermittent nature of renewable energy sources, optimal allocation and sizing of RDGs, particularly photovoltaic (PV) and wind turbine (WT), remains a critical task. Based on a new metaheuristic known as the Artificial hummingbird algorithm (AHA), this paper provides a novel approach for addressing the problem of RDG planning optimization. Considering various operational constraints, the optimization problem is developed with multiple objectives including power loss reduction, voltage stability margin (VSM) enhancement, voltage deviation minimization, and yearly economic savings. Furthermore, using relevant probability distribution functions, the ambiguities related with the stochastic nature of PV and WT output powers are evaluated. The proposed algorithm was compared to two of the recent metaheuristics applied in this domain known as improved harris hawks and particle swarm optimization algorithm (HHO-PSO) and hybrid of phasor particle swarm and gravitational search algorithm (PPSOGSA). The IEEE 33-bus and 69-bus systems are assessed as the test systems in this study. According to the findings, AHA delivers superior solutions and enhances the techno-economic benefits of distribution systems in all the scenarios evaluated.

Optimal Design and Control of SSSCs for TLs Considering Technical and Economic Indices Using GA and SAMPE-JAYA Algorithms

Improving transmission lines (TL) steady-state stability limit can be achieved by Static Synchronous Series Compensators (SSSC) that work as a converter-based compensator. The modification of the SSSC function to inject both active and reactive power into the TL improves its performance according to different indices. The TL improvement indices include the reduction of TL losses, the enhancement of dynamic stability margin and the improvement of voltage profile along the TL. The economic index is considered a vital factor in the design of SSSC devices installed in TLs. This paper proposes an objective function to design and control SSSC devices by considering various technical and economical indices. The formulation of the objective function requires power flow analysis in the compensated transmission line under different loading conditions and compensation levels. The proposed multi-objective function includes the transmission line losses, the dynamic stability span, and the cost of SSSC device. The Genetic Algorithm (GA) and Self-adaptive Multi-population Elitist Jaya Algorithm (SAMPE-JAYA) are proposed as optimization techniques to obtain the minimized value of the multi-objective function. This paper proposes the installation of two SSSC devices in TL that leads to the improvement of the design and control indexes. The proposed objective function and the optimization techniques are applied for tie-line (400kV, 400km) that connects between two networks.

Enhancement of stability margin based on dynamic brake strategy

The Rate of Change Kinetic Energy (RACKE) method achieves considerable reduction in computing time by virtue of the way that it does not need the solution of system equation beyond fault clearing time. In RACKE method the machine which tends to lose synchronism can be defined as that which has the largest negation RACKE value. The injection of the brake ought to be achieved when RACKE of the machine liable to be unstable reaches its maximum negative value. Elimination happens when RACKE of the machine is zero and disturbance angular velocity passes through zero changing sign from positive to negative. To defining the instant of injection and elimination of brake, RACKE method can be used to investigate the transient stability margin of a power system through evaluation of RACKE value at the instant of fault clearance. The simulation demonstrates that the applying of a braking resistor at the terminal of each of the machines, pulling of synchronism, simultaneously brings the system into stable trajectory. It is clear from the results obtained that dynamic braking depending on the RACKE criterion for insertion and removal of the brake gives excellent results in an enhancement of transient stability margin.

Research on stability margin enhancement for low‐voltage multi‐terminal DC system based on additional damping control

The low-voltage multi-terminal DC system is becoming an important form of the distribution network in the future. However, the system stability margin will be weakened by the negative impedance characteristics of the DC network. The additional control method by using Lyapunov theory has become a feasible solution to improve system stability. However, the traditional way of using empirical values to design parameters of the weighted matrix cannot ensure that the solved feedback law is optimal, resulting in the limitation of control performance. In order to solve this problem, the dominant mode which determines the system stability margin is studied. Then an additional damping control method is further proposed, and its feedback law is designed and further improved by optimising the parameters of weighted matrix Q, based on the improved particle swarm optimisation algorithm, meanwhile, the optimal configuration of the dominant mode is used as the target for the parameter design. Finally, the proposed method is tested and verified, and the results show that the proposed method can significantly improve the system stability margin and dynamic performance with small control costs, and ensure the constant voltage of the DC network and safe system operation under disturbances.

Optimal coordinated voltage control of AC/DC power systems for voltage stability enhancement

With the increasing use of LCC-HVDC links as bridges for bulk-power delivery, voltage stability control has become a crucial issue in hybrid AC/DC power systems. This paper proposes an optimal coordinated voltage control (CVC) of AC/DC systems to enhance steady-state voltage stability. Notably, the CVC incorporates the controls of HVDC rectifier and inverter converters. First, the voltage stability indicator, L-index, in AC systems is extended to AC/DC systems. Then, based on the voltage stability sensitivities, the CVC is modeled as a linearly constrained quadratic programming (LCQP) problem to coordinate the controllable resources of AC/DC systems, which can result in fast and effective solutions. Further based on the CVC, a control strategy is designed to simultaneously meet the requirements of voltage stability margin enhancement and voltage deviation correction. In addition, the potential of HVDC systems participating in voltage stability control is illustrated. The results of simulations performed for two AC/DC power systems show that the proposed method can effectively coordinate control variables to enhance voltage stability.

Robust H∞ control for stability assessment in grid‐connected offshore wind and marine current hybrid system

The geographic suitability brings the offshore wind farm (OWF) and marine current farm (MCF) together with their aggregated power fed to grid simultaneously in most relevant energy harnessing infrastructures. However, stability assessment of the integrated system is a major concern due to the integration of stochastic and intermittent sources with parametric uncertainty. Bridge-type fault current limiter (BFCL) has consolidated their application for a suitable enhancement of stability margin for most modern supply systems. In this article, a detailed modelling of the integrated system is carried out in the presence of BFCL along with consideration of uncertainty as well. A robust H∞ controller design strategy for stability assessment of grid-connected OWF and MCF in the presence of parametric uncertainties is presented in this article. Linear matrix inequality (LMI) conditions are derived in the context of evaluating the robust controller gain with respect to desired robust stability margin. The efficacy of the controller design is compared with that of H∞ loop shaping and conventional P-I control through different case studies with simulation followed by real-time digital simulator (RTDS) validation.

Impact of D-STATCOM in distribution systems with load growth on stability margin enhancement and energy savings using PSO and GAMS

Impact of D-STATCOM in distribution systems with load growth on stability margin enhancement and energy savings using PSO and GAMS

Comparison of Optimum Wind–Solar DG, Statcom and Capacitor Placement and Sizing Based on Voltage Stability Margin Enhancement in Microgrid with Three Different Evolutionary Algorithms

This study evaluates the most effective method to maximize the voltage stability margin in two simulated microgrids under seven different scenarios, 33 and 69 IEEE RTS models. Three different evolution algorithms are used to improve the voltage stability margin. Moreover, other power system indices such as voltage profile improvement and reducing the power losses are considered in the presented simulations. Power system limitations such as power flow restriction, line heat capacity, power transmission capacity through the line as well as voltage variation constraint are viewed to make the simulation more realistic. This paper presents solar–wind DGs, Dstatcom and capacitor placement and sizing separately as well as simultaneously. The main objective of this study is to achieve the maximum voltage stability margin in microgrids and its comparison by three different evolutionary algorithms, particle swarm optimization (PSO), genetic algorithm (GA) and honey bees mating optimization (HBMO). In the first stage, GA is applied on all seven scenarios. After selecting the best combination of the devices which creates the maximum voltage stability margin, the combination is also studied using two other evolutionary algorithms, PSO and HBMO.

Enhancement Voltage Stability of the Iraqi Power Grid Using Shunt FACTs Devices

Due to raise in demand, the transmission system becomes more exhausted, which in turn, forces the system to be more susceptible to voltage instability. The aim of this research is to study the enhancement in voltage stability margin by installation the SVC which is represented as Static of VAR Compensator or STATCOM that is represented as Static of Synchronous Compensator. Voltage stabilization dilemma considers an essential issue in the electric networks which may lead to a voltage collapse in electric power networks. L-index has been used to predict and identify points of breakdown voltages in the power system with sufficient accuracy. L -index has been employed due to its accuracy and effectiveness in the computing voltage collapse points for different load buses with sufficient precision at a short circuit and also at various loads situations. Voltage stability index has been tested on the 9-wscc test system and 14-IEEE test system .Then it has been applied to the Iraqi national grid 400 kV. A shunt facts(SVC or STATCOM) devices are installed individually at the weak bus bar based on Voltage Stability Index(L indicator) detection, The simulation results are first obtained for an uncompensated system, and the voltage profiles are studied. The results so obtained are compared with the results obtained after compensating the system with SVC and STATCOM to show the voltage stability margin enhancement. The outcomes acquired after simulation demonstrate the performances of shunt fact devices (SVC and STATCOM) when connected to a system Subjected to 3-phase short circuit fault at different locations. All the simulation results have been carried out using MATLAB version 7.10 and Power System Analysis Toolbox (PSAT) package.

Optimal placement of D-STATCOM using sensitivity approaches in mesh distribution system with time variant load models under load growth

Abstract In this paper, an approach for optimal placement of D-STATCOM in mesh distribution systems using sensitivity approaches is proposed. The main contributions of the paper are as follows: (i) Optimal D-STATCOM placement based on the new voltage sensitivity index in mesh distribution system, (ii) optimal D-STATCOM size determination for seasonal loads with load growth scenario, (iii) comparison of D-STATCOM placement and size determination with the existing sensitivity methods, and (iv) impact of optimal D-STATCOM placement on voltage stability margin enhancement, energy loss reduction and cost of energy savings. The results of voltage profile improvement, reduction in power losses, reduction in cost of energy loss, improved voltage stability margin, cost of energy loss savings, installation cost of D-STATCOM and annual savings are obtained for UK 38 bus practical mesh distribution system.

Voltage stability boundary and margin enhancement with FACTS and HVDC

Voltage stability is a major concern of today’s power system, especially under heavily loaded conditions because of reactive power limits. FACTs devices are very effective solution to prevent voltage instability and voltage collapse due to fast and very flexible control. In this paper, the impacts of SVC, STATCOM, TCSC and HVDC on voltage stability boundary (VSB) in P–Q plane have been studied. The bus impedance matrix and load flow results are used to find the voltage stability boundary. The Zbus is modified to take into account the effect of FACTS on VSB. The variable susceptance model for SVC and variable series impedance power flow model for TCSC are used in Newton Raphson’s method. The STATCOM is modelled as variable voltage source connected in series with an equivalent impedance of the shunt connected transformer. Similarly HVDC is also modelled as two STATCOMs connected at each end of the line one as rectifier and another as inverter. Some important bus and line stability indices are evaluated to determine the most effective location for SVC/STATCOM and TCSC/HVDC respectively in order to achieve the maximum enhancement of voltage stability margin. The study has been carried out on IEEE-14 bus and IEEE-30 bus test systems using MATLAB programming. A comprehensive study is done to compare the effectiveness of FACTS devices and HVDC on voltage stability margins.

Static Voltage Stability Margin Enhancement Using Shunt Capacitor, SVC and STATCOM

This paper presents the study of static voltage stability margin enhancement using shunt capacitor, SVC and STATCOM. AC and DC representations of shunt compensation devices are used in the continuation power flow process in static voltage stability study. Various performance measures including PV curves, voltage profiles, and power losses are compared. Placement and sizing techniques of shunt compensation devices are proposed for loading margin enhancement. The study has been carried out on the IEEE 14 bus test system.

Active Power Rescheduling for Avoiding Voltage Collapse Using Modified Bare Bones Particle Swarm Optimization

MW-generation rescheduling is being considered for voltage stability improvement under stressed operating condition. At times it can avoid voltage collapse. This paper describes an algorithm for determination of optimum MW-generation participation pattern for static voltage stability margin enhancement. The optimum search direction has been obtained by employing modified bare born particle swarm optimization technique. Optimum search direction is based on maximization of distance to point of collapse in generation space. Developed algorithm has been implemented on a standard 25 bus test system. Results obtained have been compared with those obtained using standard particle swarm optimization.

A New Meta-heuristic Technique Based on Robust Power System Stabilizer with Wind Power Penetrations

In this paper a robust Power System Stabilizer (PSS) is proposed based on inverse additive perturbation in a power system with wind farms. The proposed controller designed by new Improve Bacteria Foraging Algorithm (IBFA) to achieve robustness of this strategy where the optimization process is formulated based on an enhancement of system robust stability margin. The designed optimal PSS is based on Fuzzy Logic Controller (FLC). The effectiveness of the proposed technique is tested over ten macine 39 buses New England power system. Obtained results demonstrate the superiority of proposed technique over conventional PSS.

Transient Stability Study of a Reality 500kV Power System Using Statcom

Many of papers refers to study of application for Flexible Alternative Current transmission Systems (FACTS). Especially for using reactive compensators for 500kV power system in order to increase the static voltage stability margin and transient stability enhancement have considered. This paper presents a simulation model of the Static Synchronous Compensator (STATCOM) is developed to study its dynamic characteristics. The developed STATCOM is connected at the Point of Common Coupling (PCC) of the Doubly Fed Induction Generator (DFIG) wind turbine system connected to the weak distribution grid for steady state and dynamic voltage regulation purpose. The purpose of this paper is to solve the above problems in order to suggest a solution of the appropriate shunt compensator for a reality 500KV power system. Simulation results have shown that STATCOM helps to keep the steady state terminal voltage of the DFIG system to its rated voltage during the entire operation region of the DFIG. STATCOM maintains the fast voltage regulation (or voltage restoration) at the PCC during step change in reactive load causing voltage swelling or sagging. STATCOM does this by dynamically exchanging the reactive power with the power grid. The results of this work are of certain practical significance and applicable value.