Flexible AC Transmission Research Articles

Utilization of adaptive swarm intelligent metaheuristic in designing an efficient photovoltaic interfaced Static Synchronous Series Compensator

To cope with the growing load demand of power system due to world’s rapid socio-economic growth, the system compels to run with increased load. Hence, the system must sustain at maximum loading level, termed as the Maximum Loadability Limit (MLL) of the system, without violating its security limits. To increase the system-MLL further the Static Synchronous Series Compensator (SSSC) among existing Flexible AC Transmission Systems (FACTS) devices has been preferred here for its capability of compensating the real and reactive power losses simultaneously. Initially, the SSSC parameters are optimized which are further validated through the dynamic model of the Photovoltaic (PV) interfaced SSSC (PV-SSSC) in MATLAB/SIMULINK. To make the PV-SSSC more efficient, firstly, the maximum feasible power can be acquired from PV system using a robust Maximum Power Point Tracking (MPPT) technique. Secondly, Firing Angle Optimization (FAO) can improve the output power quality of the inverter in SSSC. Thus, this research handles three optimization problems separately i.e., the SSSC parameter optimization, the FAO (minimization), and the MPPT (maximization) problems. For solving such complex, nonlinear, and nonconvex engineering optimization problems, a recently developed swarm-based metaheuristic namely Levy Flight motivated Adaptive Particle Swarm Optimization (APSOLF) technique is employed. Moreover, the superiority of APSOLF is justified over contemporary state-of-the-art techniques using statistical analyses. The APSOLF-based-MPPT can achieve tracking-efficiency above 99.8% and the lowest settling-time. The APSOLF-based-FAO attains 6.7148% THD satisfying the IEEE-519 standard without any filter circuit The MLL point enhancement and bus voltage profile improvement are also the notable observations.

Contingency constrained TCSC and DG coordination in an integrated transmission and distribution network: A multi-objective approach

Transmission System Operators (TSO) deploy Flexible AC Transmission Systems (FACTS) for congestion management in order to meet technical and multilateral power supply transactions. These power commitments are however constrained by thermal, voltage and stability limitations. On the other hand, the campaign to de-carbonize the power supply framework as seen Distribution System Operators (DSO) accommodate an increased penetration of Distributed Generation (DG) within their distribution networks. However, prerogative of system operators for separate planning of FACTS and DG systems can worsen power system’s key performance indicators especially under huge load growth and severe contingencies. Therefore, this paper developed an approach for contingency constrained coordination of Thyristor Controlled Series Compensator (TCSC) and DG through a multi-level optimization, comprising of a hybrid real power flow index and particle swarm in the first level and a multi-objective variant of particle swarm optimization in the second level. The contingency constrained coordination aimed to improve Available Transfer Capability (ATC), power loss and voltage deviation. Two models of DG were coordinated with TCSC under normal and contingency cases. Results indicate that while ATC improvement for various transactions were achieved with TCSC, additional power losses incurred was further reduced with DG deployment in coordination with TCSC. Furthermore, the Pareto front, which establishes the correlation between objectives shows a diving parabola that is partly nonlinear. Also, the TCSC−DGPQ provide superior ATC and power losses compared with TCSC−DGPV. Again, under (N−1) contingencies, the TCSC−DGPQ provides improved ATC compared with other contingency cases under TCSC only.

A reactive power planning model for power transmission systems using meta-heuristics algorithms

The load patterns in electricity markets are changing rapidly worldwide. The power engineers are becoming more vigilant in providing an uninterrupted power supply at different loading conditions. This study proposes a unique planning strategy of reactive power (VAr) considering a static load model in the power transmission system. The active/ reactive power-oriented exponential load model for static load is considered during the study of load flow solution. The load flow solution’s power losses are measured and minimized by properly placing compensation devices. A flexible ac transmission system (FACTS) technology has been applied in this proposed planning strategy to compensate for reactive power. The separate and collective effect of active and reactive power modeling on load flow is also observed during the calculation of the total operating cost (TOC) of the system. The TOC is formulated empirically by adding different cost components such as cost owing to real power loss, VAr generation cost component, and compensation device cost component. A real-world power transmission system is considered in the study to validate the impetus of the proposed planning strategy.

GRID INTEGRATION USING STATCOM

Commonly Static Synchronous Compensator (STATCOM) are employed extensively as voltage regulator and reactive power compensators in transmission power system. This research paper deals with the integration of PV system with wind power generating system using STATCOM. Static synchronous compensator is a power electronic device which uses force commutated device like IGBT, GTO etc. to control the reactive power flow in a power system network and stability of power network is increased. STATCOM is a member of Flexible AC Transmission Systems (FACTS) family of devices which is connected in shunt with the line hence it is a shunt device. Index Terms—STATCOM, PV System, Wind energy system,

Development of optimal placement and sizing of FACTS devices in power system integrated with wind power using modified krill herd algorithm

PurposeThis study aims to intend and implement the optimal power flow, where tuning the production cost is done with the inclusion of stochastic wind power and different kinds of flexible AC transmission systems (FACTS) devices. Here, the speed with fitness-based krill herd algorithm (SF-KHA) is adopted for deciding the FACTS devices’ optimal sizing and placement integrated with wind power. Here, the modified SF-KHA optimizes the sizing and location of FACTS devices for attaining the minimum average production cost and real power depletions of the system. Especially, the objective includes reserve cost for overestimation, cost of thermal generation of the wind power, direct cost of scheduled wind power and penalty cost for underestimation. The efficiency of the offered method over several popular optimization algorithms has been done, and the comparison over different algorithms establishes proposed KHA algorithm attains the accurate optimal efficiency for all other algorithms.Design/methodology/approachThe proposed FACTS devices-based power system with the integration of wind generators is based on the accurate placement and sizing of FACTS devices for decreasing the actual power loss and total production cost of the power system.FindingsThrough the cost function evaluation of the offered SF-KHA, it was noted that the proposed SF-KHA-based power system had secured 13.04% superior to success history-based adaptive differential evolution, 9.09% enhanced than differential evolution, 11.5% better than artificial bee colony algorithm, 15.2% superior to particle swarm optimization and 9.09% improved than flower pollination algorithm.Originality/valueThe proposed power system with the accurate placement and sizing of FACTS devices and wind generator using the suggested SF-KHA was effective when compared with the conventional algorithm-based power systems.

The Impact of Serial Controllable FACTS Devices on Voltage Stability

As the world's population continues to grow, the demand for electricity is also increasing rapidly. Ensuring the quality of power supply, voltage stability, unity power factor, and minimizing power losses is essential for delivering power to every user end. In order to achieve this, compensation techniques are needed. This project focuses on Serial controllable Flexible AC Transmission Systems (FACTS) devices, such as Controllable Series Compensator (CSC) and Static Synchronous Series Compensator (SSSC), which have a significant impact on the voltage and power stability of an electric power system (EPS). The mathematical derivation of the voltage dependency of CSC and SSSC is extracted for the single-load infinitive-bus model (SLIB). New analytical equations are developed to compare the impact of CSC and SSSC on voltage stability in a five-bus system. The results of the analysis are expected to reveal that CSC has a crucial role to play in enhancing voltage stability, and its impact is greater than that of SSSC when considering equal CSC and SSSC MVA ratings. When it comes to voltage controllability, SSSC (Static synchronous series compensator) is superior to CSC (Controllable Series Compensator), especially in situations where there are having low voltages or having low loads.

Insights Into Dissipating Energy-Based Source/Sink Characterization of TCSC and STATCOM for Low-Frequency Oscillations

Determination of the sources of oscillations in the power system helps operators take appropriate preventive actions. In recent years, the dissipating energy flow (DEF) method has emerged as a promising tool for the online localization of low-frequency oscillation sources. In literature, the mathematical foundation of the DEF method is well-studied for networks with synchronous generators. In this paper, we extend the analysis to flexible AC transmission systems (FACTS). We derive the DEF-expressions for a thyristor controlled series capacitor (TCSC) and a static synchronous compensator (STATCOM) operating with conventional control strategies. Specifically, TCSC with both fixed and variable compensation, and STATCOM in grid-following mode with dc-link voltage and ac voltage-reactive power droop control are considered. Analyzing their respective DEFs, we obtain the conditions for which these FACTS devices could appear as the sources of low-frequency oscillations. Our findings are structured into propositions and are supported through numerical case studies on IEEE test systems.

Optimal UPFC Placement for Voltage Stability Enhancement

The Unified Power Flow Controller is a versatile and important device for improving the operational efficiency of power systems in the flexible AC transmission systems family. It finds applications in improving voltage stability in addition to provide a better voltage profile and reducing transmission loss. This paper presents a Chemical Reaction Inspired Optimization based method for placement of unified power flow controllers with the objective of raising the voltage stability. Most of the existing methods place all the given unified power flow controllers without analysing whether each of the given unified power flow controllers is actually needed to improve voltage stability or other selected performances. The proposed method tries to place only the essential unified power flow controllers from the allocated number of devices, besides providing optimal line locations and unified power flow controller parameters. It also includes the results of the proposed method for three standard test systems and compares them with existing methods to depict the dominance of the proposed method.

DE-Based Design of an Intelligent and Conventional Hybrid Control System with IPFC for AGC of Interconnected Power System

In this study, a fuzzy proportional integral derivative controller (FPID) was adjusted using the differential evolution (DE) method to enhance the automated generation control (AGC) of a three-zone reheat-type power system. The objective function used in this study was an integral of the time-weighted absolute error (ITAE). In the optimization, the gain control parameters of the proportional integral (PI), the integral (I), and FPID were optimized and compared to improve the limitations drawn by the controller over a few parameters. To demonstrate that FPID controllers with IPFC produce better and more accurate optimization results than integral and PI controllers optimized by DE, the interline power flow control (IPFC) of a flexible AC transmission system (FACTS) device with suitable connections and control parameter optimization was used. Also, the particle swarm optimization (PSO) PID with IPFC was compared with the proposed DEFPID + IPFC, and better results were achieved by using the DE technique. Similarly, to demonstrate the suggested technology’s strong control capacity, random load changes were applied to the system in various conditions, and it was demonstrated that the suggested control unit easily tolerated random load perturbations and returned the system to a stable functioning state.

Power Quality Improvement in Multifeeder Using MC-UPQC

Power Quality (PQ) issues have been a major concern as there is increased load demand and usage of variety of nonlinear loads. The innovation of Flexible AC Transmission System (FACTS) devices is a great way of solving PQ issues. Many devices like UPFC, D-STATCOM, and TCPST are emerging and are widely used for PQ improvement. In this paper, the Multi Converter Unified Power Quality Conditioning (MC-UPQC) System will be used for improving PQ in multi-bus systems. The system of MC-UPQC contains one shunt and two series Voltage Source Converter (VSCs). The conventional methodology contains one shunt and one series static devices. In the proposed methodology, two series VSCs will be used for further reduction of overall THD value. The simulation results of a reduction in THD and an improvement in PQ are compared with and without the proposed using MATLAB. Keywords—PQ, MC-UPQC, series VSC, shunt VSC, MATLAB.

A CVaR-constrained optimal power flow model for wind integrated power systems considering Transmission-side flexibility

The integration of renewable power can pose uncertainty to power system operation, causing operational risk like power imbalance or line congestion. To improve the operational security and economy of the system under uncertainties, this paper considers two potential directions. The first is to enhance the system capability for safely accommodating uncertainties using various network resources. Such capability is often termed as the operational flexibility. The second direction is to employ appropriate risk management methods. With these two directions, a conditional value-at-risk (CVaR)-constrained optimal power flow (OPF) model is developed in this paper for wind-integrated power systems. In this model, dynamic line rating (DLR) and flexible AC transmission system (FACTS) technologies are exploited to unlock transfer capacities of transmission lines and enable line reactance control. As a result, power system has capability to allow more flexible and cost-efficient power flow distributions. That is, additional operational flexibility is provided by the transmission-side DLR and FACTS technologies. Such flexibility is termed as the transmission-side flexibility. Meanwhile, CVaR is employed as the risk management tool to control the security level of each operational constraint. To address the non-linearity of CVaR and solve the proposed model, a novel solution method is developed by combining Gaussian mixture model for uncertainty modelling with cutting-planes for CVaR reformulation. Numerical experiments in MATLAB reveal the economic benefit of the proposed model: the inclusion of transmission-side flexibility in formula can reduce the operational cost by 6.10% on a 14-bus system. The simulation results also show that the proposed solution method overcomes the poor system security associated with the traditional Gaussian method and is more economical than the previous robust method (3.79% reduction in operational cost on a 14-bus system).

Unified AC Transmission Expansion Planning Formulation incorporating VSC-MTDC, FACTS devices, and Reactive Power compensation

The main aim of the static Transmission Network Expansion Planning (TNEP) is to determine which and where new transmission equipment must be installed. The complexity added by the non-linearities leads to simplifications, which include the DC model. However, most non-linearities are solvable nowadays. Thus, the new scenario of large non-dispatchable power sources penetration and the several developments in technologies, e.g, Flexible AC Transmission Systems (FACTS) devices and High Voltage Direct Current (HVDC) interconnections, motivate the use of the AC model with its non-linearities. Some research works address the use of some of those technologies for TNEP in an independent fashion, which can lead to sub-optimal solutions. In this work, Voltage Source Controlled-Multiterminal HVDC (VSC-MTDC) systems, FACTS devices, and Reactive Power Planning (RPP) are integrated into the same planning optimization process, so that a unified AC TNEP formulation is proposed. A non-linear mathematical programming technique and a differential evolution based metaheuristics are chosen to achieve an optimal transmission configuration. To evaluate the benefits of the proposed approach, two IEEE modified test systems (9 and 118 buses) are used. Results suggest that more economical solutions can be obtained if different types of reinforcement strategies are taken into account in a unified approach.

Optimization of location and rating of unified power flow controllers for congestion management

Large number of contracted power exchanges among sellers and purchasers, in a deregulated power market causes transmission line congestion. Congestion of lines undermines the security and economy of power networks. Flexible AC transmission system (FACTS) devices are introduced at appropriate spots to change the power flow in order to keep the flow of the lines within their capability. In this work, the most commonly used unified power flow controller (UPFC) is proposed for achievement of changing the line flow and for easing congestion from the over loaded lines. The size and site of UPFC controllers significantly impact their performance in congestion management task. The location and size of the UPFC devices are to be optimized by using an optimization algorithm. Whale optimization algorithm (WOA) is exploited in this effort for realizing the aim of determination of site and size of the FACTS converters. The present method has lesser quantity of variables which are tuned to get best outcomes. The suggested WOA based technique is executed on the IEEE 57 bus system. The outcomes comparison is made with particle swarm optimization algorithm (PSO) and firefly algorithm (FFA) and the better improved outcomes are found.

WAMS-based Hierarchical Active Power Differential Signal Algorithm for Backup Protection of a FACTS Compensated Transmission Network

This paper proposes a hierarchical active power differential signal-based generalized backup protection algorithm using Wide Area Measurement System (WAMS) data for Flexible AC Transmission System (FACTS)-compensated transmission networks. The proposed algorithm can be used for backup protection of transmission systems with any shunt and series-type FACTS devices. The increased number of FACT compensators affects the reliable operation of primary and backup protection of the transmission lines. Both shunt and series compensated lines cause malfunctioning of existing backup protection schemes. The proposed algorithm utilizes the sequence components of bus voltages and active power differential signals of lines to identify the faulty line. The algorithm is validated on a modified 9-bus system under MATLAB/SIMULINK platform. It is observed that the algorithm is suitable for identifying a faulty line in transmission systems containing both uncompensated and compensated lines with series or shunt-type FACTS controllers. This algorithm has the advantage that it uses a generalized backup protection logic and can be used for the accurate identification of a faulty line irrespective of the type of compensation devices.

Enhanced Control Designs to Abate Frequency Oscillations in Compensated Power System

The interconnection of transmission, distribution, and generation lines has established a structure for the power system that is intricate. Uncertainties in the active power flow are caused by changes in load and a growing dependence on renewable energy sources. The study presented in this paper employs several controlling strategies to reduce frequency variations in series-compensated two-area power systems. Future power systems will require the incorporation of flexible AC transmission system (FACTS) devices, since the necessity for compensation in the power system is unavoidable. Therefore, a static synchronous series compensator (SSSC) is installed in both areas of our study to make it realistic and futuristic. This makes it easier to comprehend how series compensation works in a load–frequency model. With the integration of electrical vehicles (EVs) and solar photovoltaic (PV) systems, several control strategies are presented to reduce the frequency oscillations in this power system. Particle swarm optimization (PSO) is used to obtain the best PI control. To improve results, this work also covers the design of fuzzy logic control. In addition, the adoption of neural network control architecture is proposed for even better outcomes. The outcomes clearly show how well the proposed control techniques succeeded.

Significance of Harmonic Filters by Computation of Short-Time Fourier Transform-Based Time–Frequency Representation of Supply Voltage

The nonlinear characteristics of power electronic-based loads in a power system contribute a major role in the harmonics’ injection and other power quality disturbances. This affects the quality of the power supplied to consumers by distribution systems. Flexible AC transmission system (FACTS) devices at the transmission level and custom power devices at the distribution level are used for an effective power transfer. In addition to these devices, filters play a prominent role in distribution systems. This paper aims to analyze the supply voltage in the time–frequency domain to perceive the variations in signal strength, explaining the role and significance of filters in mitigating or reducing harmonics. This paper presents the significance of harmonic filters in terms of signal-processing terminology. This depicts the prominent role of filters in improving the power quality by harmonic reduction or elimination, depending upon the requirement. The mathematical transform used in this approach is the short-time Fourier transform, which results in transforming the signal into a domain giving information about time and frequency. A MATLAB Simulink environment and ‘spectrogram’ were used to simulate harmonic signals, and we analyzed them using a short-time Fourier transform. Different windows were used with varying window size lengths.

A vertical and horizontal crossover sine cosine algorithm with pattern search for optimal power flow in power systems

Most of the energy consumption is now being used to supply human demand for electricity, which has increased the burden of power system planning to some extent, and thus, researchers proposed solutions to the optimal power flow (OPF) problem. In such a background, flexible AC transmission system (FACTS) devices are widely used in modern power systems to alleviate human power demand and improve network congestion problems. This research proposes a better-quality sine cosine algorithm (CPSCA) based on a crossover mechanism and pattern search algorithm for optimizing multiple objectives, such as system generation cost and transmission losses when we have multiple types of FACTS devices in the power system. The proposed method uses sine and cosine theory and evolutionary strategy to continuously sample and update the framework and improve the quality of the solutions. The method uses a class of vertical and horizontal crossover operators and pattern-shifting techniques to find the optimal solution set. In addition, the Weibull probability density function was used in this study to model uncertainty in wind energy, while direct costs, penalty costs, and standby costs were considered in constructing the target model. Various types of FACTS devices, such as thyristor-controlled series compensators, thyristor-controlled phase shifters, and static reactive power compensators, are also inserted into the model as power in the target optimization problem. The proposed algorithm has experimented on an IEEE30 bus test system. Based on the experimental results, CPSCA achieves an optimal total cost of 806.0225 $/h. In terms of power loss of the bus system, CPSCA reduces the total power loss value from 2.042 MW to 1.41 MW compared to the original sine cosine algorithm, which is a 31% improvement and has an optimal power loss value. Therefore, the simulation results demonstrate that the proposed algorithm is an effective technique for optimizing the optimal power flow of the entire power system and FACTS equipment.

Transient stability enhancement using optimized PI tuning of static synchronous series compensator in wind power conversion system

Power systems are expanding comprehensively with the increase in load demand from both residential and industrial usage. Renewable energy is penetrating the power system to satisfy the power needs of the load demand. With its potential to generate power and compensate for a large portion of the load demand, wind generators make a major renewable power contribution. Power oscillations inherent in wind generator integration with the grid are a power quality issue to be addressed. Oscillation damping using flexible AC transmission system (FACTS) devices is a relevant solution for the power quality issue. There are multiple reasons for power oscillation. Mainly, power systems encounter fault conditions. The faults can be cleared, and the power system tries to retain stability. Sometimes, the system fails due to a longer settling time. A series-connected FACTS device utilized as a series compensator is referred to as a static synchronous series compensator (SSSC). Controlling the flow of electricity over a transmission line using this method is incredibly efficient. The capacity to switch between a capacitive and an inductive reactance characteristic is necessary. The SSSC regulates the flow of power in transmission lines to which it is linked by adjusting both the magnitude of the injected voltage and the phase angle of the injected voltage in series with the transmission line. This allows the SSSC to manage the power flow in the transmission lines. It does it by inserting a voltage that can be controlled into a transmission line in series with the fundamental frequency. This paper develops the optimally tuned SSSC in the wind-integrated grid system to dampen the oscillation. Teacher–learner-based optimization (TLBO) and gray wolf optimization (GWO) algorithms are used to tune the PI controller to improve the damping response. The obtained results show that the damping performance of the proposed controller is better than that of the other traditional controllers.

Power Quality Enhancement in a Wind Farm Connected Grid with a Fuzzy-based STATCOM

Integrating wind farms with electricity transmission networks presents several problems, and power quality plays a vital role among these. This study proposed a novel fuzzy logic controller to reduce the effect of power quality issues in such applications and investigated two different FACTS (Flexible AC Transmission System) devices, the Static Var Compensator (SVC) and the Static Synchronous Compensator (STATCOM). The fuzzy logic controller was designed as a voltage controller to improve power quality. Detailed analysis was carried out to investigate the successful mitigation of voltage sag/swell, active and reactive power improvement, and voltage flickers control by two controllers in a Multi-Terminal Load (MTL) system consisting of wind generators. The results were verified in MATLAB simulations, and a comparison was performed between the proposed shunt controllers. Furthermore, the design of a fuzzy interference system based on Vref (reference voltage) and the voltage measured at STATCOM location signals was investigated and compared with the SVC in terms of voltage sag, voltage swell, voltage flickers, and Total Harmonic Distortions (THD). The proposed fuzzy system was compared with a PI-based STATCOM and SVC. The power quality issues were exacerbated when using Multi-Terminal Load (MTL) in the transmission network.

Synchronized Control Strategy of UPQC to Mitigate the Sag and Swell of Voltage

AbstractThis paper demonstrates efficacy of the control strategy of Unified Power Quality Conditioner (UPQC) for improvement of three‐phase power quality. UPQC contains a couple of active power filters (APF), one is connected in series and another is shunt. Series APF belongs to the Flexible AC Transmission System (FACTS), it is a promising device for the improvement of transmission efficiency. The Voltage Source Converter (VCS) acts as the brain of series APF while the shunt APF is another part of the UPQC. This series‐connected component injects the compensating voltages that are generated by voltage source inverter (VSI). The entire system of UPQC (series and shunt APF) deals with the voltage dip and voltage swell on the consumer end of the network. Among the major advantages of the system is that this conditioner can captivate or insert true power. It can inject the voltage from 0° to 360° as per the phase angle requirement of the base voltage. It is the major reason why it can work in three different modes. This series APF acts as an active power deliverer for sag condition in the aspect of voltage. The Matlab/Simulink software is used to investigate the analysis and results.