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This paper presents the impact of simultaneous and coordinated control of the unified power flow controller (UPFC) and the doubly-fed induction generator (DFIG) on the multi-machine power system`s dynamic stability. All UPFC`s main basic PI controllers and its Power Oscillation Damping (POD) supplementary controller have been used. A more complete model of DFIG and both Rotor-Side Converter (RSC) and Grid-Side Converter (GSC) dynamics with their PI controllers are considered, too. UPFC and DFIG controllers are simultaneously coordinated and optimized with compromising between their control variables parameters. Particle Swarm Optimization (PSO) algorithm is used to optimize the objective function based on eigenvalues and damping ratio to reach the best parameters and variables of controllers of both UPFC and DFIG. During the studies of permanent and dynamic state, the thermal capacity of the lines and the nominal values of UPFC have also been considered. Simulation results in a 39-bus 10-machine New-England power system show the capability of the applied method. The results demonstrate that coordinated control of UPFC and DFIG tend to more damping system modes oscillation and more stability in the power system. [ABSTRACT FROM AUTHOR]

Summary: Flexible alternating‐current transmission system (FACTS) devices as power electronic‐based technologies have been developed to improve the performance of power systems. This paper proposes a probabilistic framework for optimal allocation of unified power flow controller (UPFC) as one of the most beneficial FACTS devices to increase the reliability of the power system. For this purpose, the expected power not served (EPNS) is considered as a reliability index that is obtained based on the summation of required load shedding in all buses during single contingencies, including transmission lines and generators outage. Power demands and wind speed are considered as uncertain input variables. In addition, the correlations among these variables are included in the proposed study method. The well‐known particle swarm optimization (PSO) algorithm is used to optimize the proposed objective function. Also, the firefly algorithm (FA) is implemented to determine the total amount of load shedding for the calculation of EPNS, considering each possible generated solution by the PSO. The k‐means based data clustering method (DCM) is used for probabilistic evaluation of the problem, for the first time. Also, the correlations among uncertain input variables are modeled with the Cholesky decomposition method. Extraction of statistical information of UPFC parameters for improving power system reliability in a probabilistic framework is one of the most important achievements of the proposed method. This information is very important in deciding on the UPFC sizing. In order to evaluate the effectiveness of the proposed method, the IEEE 14‐bus and 30‐bus test systems have been used. [ABSTRACT FROM AUTHOR]

A unified power flow controller (UPFC) combines the advantages of various flexible alternating current transmission system (FACTS) devices into a powerful format. Using a 500 kV power grid, this study evaluates the selection and use of a UPFC to improve transmission capacity. The “UPFC unit capacity control proportionality coefficient” is introduced to quantify the control effect of the UPFC, and an optimal calculation method for the UPFC capacity is presented. Following the proposal of a UPFC site selection process, the data of an existing power grid is used to conduct simulations. The simulation results show that the UPFC has a strong ability to improve transmission capacity, and its use is greatly advantageous. Additionally, by applying the proposed selection method, the control effect and economic benefits of the UPFC can be comprehensively considered during project site selection. These findings have a guiding significance for UPFC site selection in ultra-high voltage power grids.

The unified power flow controller (UPFC) is recognized as one of the most promising flexible ac transmission system (FACTS) devices for modern power systems, due to its versatile functionalities. Based on typical operation conditions, this paper investigates the global and local power flow operation rules of the UPFC embedded transmission system theoretically. First, the detailed global power flow model (GPFM) and the local power flow model (LPFM) are established concerning several selected critical points (SCPs) in the system. The theoretical power flow operation rules for the ranges, the movements and the trajectories of GPFM and LPFM are analyzed, respectively. Then, the case study is performed based on the proposed simplified model, and the results are analyzed from GPFM and LPFM perspectives respectively. The operation rules and the power flow ranges is studied. Further case studies based on the proposed original mathematical model are also carried out, and the results are listed from different viewpoints of two-dimensional planes and three-dimensional spaces. All types of results are also analyzed from GPFM and LPFM perspectives, which verify that the UPFC is adaptive to various operation conditions for power flow regulation.

In this paper, a student psychology‐based optimization algorithm (SPBOA)‐based proportional‐integral‐derivative (PID) controller is implemented for load frequency control (LFC) of an isolated hybrid power system (IHPS) and a grid‐connected HPS (GHPS) models. In the designed models, a combined‐cycle gas turbine, a diesel engine generator, a wind turbine generator and a solar photovoltaic generating unit are used as the main power generating units. A superconducting magnetic energy storage is used with IHPS model to improve the dynamic stability of the studied system. A single area power system is connected with IHPS model through a tie‐line to form a GHPS. In the GHPS, a thyristor‐controlled series controller and a unified power flow controller are associated with the tie‐line power flow control. In this work, electric vehicle is also connected as a load to both the IHPS and GHPS models. The output profile of the proposed SPBOA‐based PID controller of both models is compared with whale optimization algorithm (WOA) and quasi‐oppositional‐based WOA (QOWOA). The performance of IHPS and GHPS models are studied under the different load perturbations. The robustness analysis and frequency domain analysis in terms of Bode plot are also shown in favor of the SPBOA method. [ABSTRACT FROM AUTHOR]

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Modular multilevel converter based unified power flow controller (MMC-UPFC) can provide flexible power regulation and plays an important role in the smart grid and future distribution networks. PI controller is widely adopted in the Unified power flow controller (UPFC) control. However, it is often difficult to figure out a pair of stable control parameters with good dynamic performance. A passive sliding mode control strategy of MMC-UPFC is proposed in this paper to achieve the advantages of both the passive controller and sliding mode controller. The proposed passive sliding mode control strategy has a fast response speed and is not sensitive to system parameter variation. Since unbalance grid voltage conditions are common in the modern distribution networks, an unbalanced grid treatment strategy is also presented with the series side of MMC-UPFC. Negative sequence components of the grid voltages are detected by the cross-decoupling method with second order generalized integrator and then compensated by the series side of MMC-UPFC. The series side converter controls the power flow and treats unbalanced grid conditions simultaneously. The efficiency of the general device is increased thus. A 27-level MMC-UPFC simulation system is built based on the Shanghai UPFC Project and validate the proposed approach.

More than one hundred countries are using wind energy due to their easy implementation, cheap energy, and high energy efficiency. Implementation of FACTS devices in Wind Energy Conversion Systems (WECS) has been dramatically improved due to cooperative and accurate performance of FACTS devices. However, dealing with wind turbine faults promptly is crucial. Short-term and long-term faults may have excessive voltage changes and inconstant active and reactive power injection into transmission line. In this paper, robustness and flexibility of SSSC, STATCOM, and UPFC FACTS devices connecting to a 9 MW SCIG-based wind farm under different time-domain fault conditions is investigated. Variety of system scenarios under fault conditions are surveyed in order to find the best Fault Ride Through (FRT) scheme for the system. To carry out this study, same rating and capacity is considered for all three FACTS devices which are employed at the grid-connected point of WECS to mitigate FRT problem. Moreover, the best compromised control mode of FACTS devices is sought by a power flow analysis. Additionally, to obtain a more perceivable view over the technical issues related to the voltage sag support, performance of FACTS devices is analyzed and compared with each other through the paper and at the final stage. A complete digital simulation of the system is executed in the MATLAB/SIMULINK environment and the results are presented to authenticate the performance of devices.

This paper proposes a multiobjective improved particle swarm optimisation (IPSO) for placing and sizing the series modular multilevel converter-based unified power flow controller (MMC-UPFC) FACTS devices to manage the transmission congestion and voltage profile in deregulated electricity markets. The proposed multiobjective IPSO algorithm is perfect for accomplishing the close ideal distributed generation (DG) sizes while conveying smooth assembly qualities contrasted with another existing algorithm. It tends to be reasoned that voltage profile and genuine power misfortunes have generous upgrades along ideal speculation on DGs in both the test frameworks. The proposed system eliminates the congestion and the power system can be easily used to solve complex and non-linear optimisation problems in a real-time manner.

Unified power flow controller(UPFC) is the most advance flexible ac transmission system(FACTS). Active/reactive power balance for UPFC is analyzed in this paper when it is working in power flow control mode, and an improved real time power coordinate control strategy is proposed in paper. In the parallel converter control loops, an improved real-time dynamic feed forward method is added to reduce over voltage caused by imbalance power. The results of hardware-in-loop simulation based RT-LAB platform show that this new coordinate control strategy，comparing with the conventional one, can decrease excessive voltage excursions of the send terminal ac voltage and DC-link voltage and improve the control performance during power flow changing or system occurring fault.

In this paper, a stochastic sensitivity algorithm is introduced to optimize the location of unified power flow controller (UPFC) in large scale power grid. The stochastic sensitivities are defined as the total operation cost of power system to control parameters of UPFC. Firstly, probability optimal power flow (POPF) model with power system’s randomness is established. Then point estimate method (PEM) is utilized to solve the above problem, so that the stochastic sensitivities of UPFC in all possible transmission lines could be obtained. Finally, by sorting the influence degree of UPFC at different locations to cumulative distribution function (CDF) of operation cost, the optimal location for UPFC could be selected correspondingly. To this end, IEEE-5 and IEEE-14 systems are employed to verify our proposed approach. The results show that installing UPFC by the method in this paper could significantly reduce the probability distribution of operation cost in higher region. [ABSTRACT FROM AUTHOR]

The conventional highly composite and interrelated power systems sometimes consist of thousands of buses and hundreds of alternators, which need improvement in electric power consumption, consistency maintains, and security. To meet the ever-growing good quality power demand, the improvement of conventional transmission methods and the formation of new concepts that might allow the optimum utilization of accessible power with no reduction of system reliability are of the utmost importance. But due to high complexity, these system responses are oscillatory in nature. If this system oscillation is damped somehow such that the system achieves a new steady operating condition within the transient period, then the system becomes stable. A stable power system requires that the system oscillations should die immediately. This paper proposed a novel control strategy based on a lead-lag based stable controller for a unified power flow controller (UPFC) for faster damping of inter-area oscillations of the system. Each design has been successfully simulated in MATLAB Simulink platform. [ABSTRACT FROM AUTHOR]

This article proposes a real-time power system stabilizers (PSS) parameter optimization technique employing extreme learning machine (ELM) to enhance overall system stability by damping out the low-frequency oscillations. It models two electric networks, i.e., single machine infinite bus systems where the first network's synchronous machine is equipped with a PSS only, and the second network's synchronous machine is equipped with a unified power flow controller coordinated PSS. It uses diverse loading conditions to investigate the performance of the proposed ELM model-tuned PSS technique and compares it with conventional PSS and the referenced works in terms of the eigenvalues and minimum damping ratios. Additionally, the satisfactory values of the well-known statistical performance indices including the root mean squared error (RMSE), mean absolute percentage error, RMSE-observations-to-standard deviation ratio, coefficient of determination (R2), Willmott's index of agreement, and Nash–Sutcliffe model efficiency coefficient provide confidence in the developed technique in predicting PSS parameters. Besides, comparisons of results from time-domain simulation demonstrate the ELM model tuned system's superiority over the conventional approach for both test cases. Furthermore, the ELM models require less than a cycle to predict PSS parameters for any loading condition that endorses the developed technique's real-time application. [ABSTRACT FROM AUTHOR]

Due to the intermittent nature of renewable sources, miss-matching between power generation and load power causes a deviation from the desired voltage and frequency in power supply. To solve this problem, a new control technique has been proposed for the power flow control with the unified power flow controller (UPFC) in grid-connected hybrid renewable energy systems such as photovoltaic-wind. The proposed control technique combines the binary version of the grey wolf optimization (bGWO) and recurrent neural network (RNN). Here, bGWO is utilized to generate the dataset of control signals for shunt and series converters of the UPFC. Based on the accomplished dataset, the RNN technique performs and predicts the optimal control signals of the UPFC. Likewise, the proposed control scheme regulates the voltage deviation and minimizes the power losses simultaneously. Then, the proposed model is executed in Matrix Laboratory/Simulink working stage and the execution is assessed with the existing techniques such as fuzzy logic controller, improved particle swarm optimization and grey wolf optimization. The optimized gain parameters and elapsed time of the proposed and existing technique is also analysed. The optimized gain parameters such as KpKi of the proposed hybrid technique are 2.5 and 150. The elapsed time of the proposed technique is 30.15sec. Overall, the comparison results demonstrate the superiority of the proposed technique and confirm its potential to solve the above-mentioned problems. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The Flexible AC Transmission System (FACTS) devices are being commissioned in electrical power systems across the globe owing to the vast array of benefits they offer. The optimal performance of the FACTS devices can be harnessed only if they are installed at a strategic location. In this paper, the authors suggest the merit of multiobjective cuckoo search (MOCS) algorithm in mitigation of transmission losses by strategically installing unified power flower controller (UPFC) at an optimal location. Active power loss and reactive power loss reduction is the multiobjective optimization considered for the study. The Pareto-optimal technique is employed to extract the Pareto-optimal solution for the multiobjective problem considered. The Fuzzy logic method is utilized to yield the best-compromise solution from the pool of Pareto-optimal solution. The proposed approach is tested on a standard IEEE 30 bus test system. Furthermore, the efficacy of the MOCS algorithm is demonstrated by comparing the results with that of multiobjective particle swarm optimization (MOPSO). [ABSTRACT FROM AUTHOR]

This study aims to improve oscillation damping and the rate of integration of wind energy into the grid. To this end, this study focuses on selecting the optimal location of flexible alternating current transmission system (FACTS) devices, such as the static synchronous series compensator, the static synchronous parallel compensator, and the unified power flow controller (UPFC). This study proposes new methods to determine the optimal locations of FACTS devices in the transmission system. To further improve power oscillation damping and the rate of integration of wind energy, FACTS devices were combined with a multiband power system stabiliser (MBPSS) at each synchronous machine. The MBPSS is an advanced power system damping controller that offers clear advantages over conventional power system stabilisers in the damping of low‐frequency oscillatory modes. A comparative study was performed on the two‐zone, four‐machine (Kundur) multi‐machine test network containing a wind farm to select the best combination of FACTS devices with the MBPSS. The results indicate that a combination of UPFC with MBPSS is favourable in terms of improving stability and increasing the rate of integration of wind energy into the grid. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Power quality becomes the most significant concerns for many reasons as the dependence of electricity is increasing in this modern society. In fact that less quality of power will generate some considerable losses in terms of economy in few moments. The potential power quality issues were flicker, voltage dips, supply and harmonic interruptions. The quality of power might be enhanced with the use of some filtering approaches and some compensators. This work presents a unique framework of optimal utilization of the unified power flow controller (UPFC). The UPFC's inverter series is then controlled so as to perform the following functions: load reactive power sharing with the shunt inverter and compensation of voltage sag/swell. A cuckoo search optimization-based maximum power point tracking algorithm is employed for providing best fitness function for varying duty cycles. The approach of active power filter is widely employed in the harmonic compensation of voltage swell/sag. The proposed system also provides low rate of total harmonic distortion. MATLAB/Simulink-based simulation results are discussed to support the developed concept. [ABSTRACT FROM AUTHOR]

To relieve congestion due to open‐access feature in competitive power system framework, utilities plan flexible alternating current transmission systems (FACTS), ensuring improved utilization and performance of the transmission infrastructure. However, high‐investment cost restricts implementation to single type of FACTS' planning in a time. Therefore, successive planning of another FACTS to delay transmission expansion results in multi‐type FACTS planning. Consequently, to optimise performance, subsequent planning must coordinate with existing FACTS. The main objective of this study is to implement coordination of multi‐type FACTS for available transfer capability (ATC) enhancement. A hybrid real power flow performance index (PI) and particle swarm optimisation (PSO), coordinate thyristor control series compensator (TCSC) in the first planning horizon with static synchronous series compensator (SSSC) and unified power flow controller (UPFC), in the second horizon. The PI–PSO‐based multi‐type FACTS coordination improves ATC of multilateral power transfers in a standard 9‐buses test network. Results show that multi‐type FACTS achieved higher ATC; such that enhanced ATC by TCSC–SSSC ranges between 8.06–69.34% while the TCSC–UPFC ranges between 11.85–71.59% for various power transfer transactions. A comparison of the three coordination schemes shows that the scheme with more decision parameters provides superior loadability and transfer capability improvement. [ABSTRACT FROM AUTHOR]

A major role is played by the analysis of power system security in heightening system security and in system collapse condition avoidance. This article presents a cutting edge mechanism which is devised applying transmission line loadings as well as variance in bus voltage magnitude. The use of flexible alternating current transmission systems devices improves the objectives of generation fuel charges in addition to the severity index proposed which were investigated considering the contingency circumstances of generator(s) or/and transmission channel(s). To boost system security in spite of contingency circumstances in the existence of unified power flow controller or UPFC, it would be most appropriate to pinpoint a most advantageous position to install aforementioned device. We propose a model of UPFC where power insertion is done by using voltage source. Also a procedure to incorporate the same and a strategy to find optimum position has been proposed which uses line overload sensitivity indices. This work mainly focused on establishment of available transfer capability on the heavily congested line. The proposed congestion management scheme alleviates the heavy stress in transmission line and provides an ample corridor for the power to flow. Biogeography‐based optimization or BBO in short, is a technique which is a growing recognized optimization method which has been lucratively engaged in solving intricate optimization problem in dissimilar fields. The BBO provides better results than the metaheuristic counter parts such as Genetic Algorithm and Particle Swarm Optimization. The effectiveness of proposed BBO has been tested on standard IEEE 30 bus system and the results are compared with classic methods and other metaheuristic methods. This is established through the MATLAB package. Improved bus voltage profile was also attained and it can be inferred from the outcome that the prospective approach can drastically enhance security of power system when comparing with other optimization methods. [ABSTRACT FROM AUTHOR]

Abstract Forced oscillations (FOs), or low-frequency oscillations (LFOs) caused by periodic, continuous, small power disturbances, threaten the security and stability of power systems. Flexible AC transmission system (FACTS) devices can effectively mitigate LFOs via stability control. We propose a novel method that mitigates FOs by shifting the resonant frequency. Based on the features of the linearized swing equation of a generator, a resonant frequency shift can be achieved by controlling the synchronous torque coefficient using a unified power flow controller (UPFC). Because of the resonance mechanism, the steady-state response of an FO can be effectively mitigated when the resonant frequency changes from the original one, which was close to the disturbance frequency. The principle is that a change in resonant frequency affects the resonance condition. Simulations are conducted in a single-machine infinite-bus (SMIB) system, and the simulation results verify that the method is straightforward to implement and can significantly mitigate FOs. The controller robustness when the resonant frequency is not accurately estimated is also analyzed in the simulations.

Abstract With an aim to improve the transient stability of a DFIG wind farm penetrated multimachine power system (MPN), an adaptive fractional integral terminal sliding mode power control (AFITSMPC) strategy has been proposed for the unified power flow controller (UPFC), which is compensating the MPN. The proposed AFITSMPC controls the dq- axis series injected voltage, which controls the admittance model (AM) of the UPFC. As a result the power output of the DFIG stabilizes which helps in maintaining the equilibrium between the electrical and mechanical power of the nearby generators. Subsequently the rotor angular deviation of the respective generators gets recovered, which significantly stabilizes the MPN. The proposed AFITSMPC for the admittance model of the UPFC has been validated in a DFIG wind farm penetrated 2 area 4 machine power system in the MATLAB environment. The robustness and efficacy of the proposed control strategy of the UPFC, in contrast to the conventional PI control is vindicated under a number of intrinsic operating conditions, and the results analyzed are satisfactory.

The building of additional transmission network to meet the demand of the everincreasing load is expensive, and time consuming. An alternative to constructing new lines is the incorporation of the Flexible Alternating Current Transmission System (FACTS); in which a Unified Power Flow Controller (UPFC) is a member of the ménage, which can be modelled as a combination of Static Var Compensator and Thyristor Control Series Compensator. This study determines the optimal location of the UPFC by randomly adding loads to the existing transmission network until the Fast Voltage Stability Index of one of the lines is at a critical point. This is the vital line in which UPFC components are added. The sizing of the components of the UPFC is determined using Artificial Bee Colony algorithm. The IEEE 30-bus network is exploited as the test bed. The results obtained reveal that the optimal positioning and sizing of the UPFC for the purpose of maximizing loadability of the grid when load angles are assumed to be negligible are the same as when the load angles are considered. The loadability of the test bed when UPFC is not injected in the grid is 440.376 MW, whereas, it is 837.915 MW when the UPFC is optimally located and sized; and this represents 90.27 %. The sizes of the shunt and series components of the UPFC that assist in realizing this maximization are -0.2780 pu and 0.1000 pu respectively. [ABSTRACT FROM AUTHOR]

Currently, transmission grids are subject to experience more operation and control difficulties. The use of power flow controllers (PFCs) can ease such difficulties. However, most competent PFCs need to be used. Cost‐wise, the power transistor assisted Sen transformer (TAST) is attractive as compared to the unified PFC (UPFC). However, while the UPFC has three control parameters, the TAST has only two. The UPFC can regulate the voltage of its shunt bus while the TAST cannot. The main objective of this study is to investigate the extent to which the TAST and UPFC are comparable when used for power flow control. Power flow control is performed in this study for congestion management using a TAST/UPFC in a modified IEEE‐118 bus system. A TAST/UPFC is optimally located using sensitivity analysis. For the sake of validation, results are obtained using both load flow analysis and voltage vector analysis. With only two control parameters, the performance of the TAST is found very closely comparable to that of the UPFC. Accordingly, the TAST can competently replace the UPFC for application of power flow control, at a far lower cost. Nonetheless, appropriate limited angle TAST is a suitable substitute for the TAST at a further lower cost. [ABSTRACT FROM AUTHOR]

Summary: The proposed work aims to achieve an optimal balance between the power availability and cost incurred for the same through a novel technique by configuring a new hybrid form of Antlion, Salpswarm and Mothflame optimizations together. The analysis of power system comprising of pre‐determined number of buses, lines and specific line and bus parameters is performed. A detailed study of the types, operation and response of power electronic device aided flexible ac transmission devices (FACTS) is carried out. The article deals with the implementation of such controllers in a bus system to improve the system loadability. Two types of FACTS devices namely Thyristor Controlled Series Capacitor, Static Var Compensator and Unified Power Flow Controller are used in single and multiple type combinations in an IEEE 6 Bus system for improvement of the system loadability. The incorporation of new devices comes with extra cost involvement and the economics play a vital role in the power system studies. Therefore, the use of such controllers should be done in an optimal way. The main aim of this work is to optimize the location, type and rating of the FACTS devices and also maintain the system parameters like voltage stability and thermal loading within prescribed limits. [ABSTRACT FROM AUTHOR]

Due to the low converters rating and cost of doubly fed induction generator (DFIG) along with its ability to function under variable wind speed, DFIG has been widely employed in wind energy conversion systems (WECSs). Unfortunately, the performance of DFIG is sensitive to the variation in the operating conditions and disturbance events at the grid side. This includes wind gust, voltage fluctuation and faults at the point of common coupling of the DFIG and the grid. In this study, a model‐free adaptive control (MFAC) is developed for a unified power flow controller (UPFC) in order to improve the overall dynamic performance of a DFIG‐based WECS during wind gusts and enhance the fault ride through capability of the DFIG during various disturbance events. The effective performance of the proposed controller is assessed through a comparison with a conventional proportional–integral (PI) controller optimised by a modified flower pollination algorithm. Results reveal the superiority of the proposed UPFC‐MFAC technique over the conventional PI controller currently used in most of the UPFC‐WECS applications. [ABSTRACT FROM AUTHOR]

Generally, the mathematical formulation of the dynamics governing multi‐area power systems with Unified Power Flow Controller (UPFC) is a challenging task owing to the presence of both differential and algebraic sub‐systems. The proposed research work attempts to integrate the two subsystems by replacing the algebraic subsystem with a differential approximant that leads to a non‐linear system of differential equations. Solution of the proposed model with a properly chosen Lyapunov function produce a nonlinear control signal which damps inter‐area oscillations effectively. The non‐linear control signal is realised using the backstepping method. Moreover, the new formulation enables utilisation of the law for uncertain parameters using the standard parametric feedback form, such that the advantage of such a controller is unaffected by these parameters. In addition to this major contribution, full utilisation of UPFC, by using a lone multi‐variable PI controller which eliminates negative interaction between the controllers, is also achieved. Empirical verification of the proposed approach is done by simulating various scenarios with varying degrees of complexity – from dual area power networks to 39 buses New England system. The results of the experiments indicate the efficacy of the method. [ABSTRACT FROM AUTHOR]

Copyright of Electric Power Automation Equipment / Dianli Zidonghua Shebei is the property of Electric Power Automation Equipment Press and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Optimal reactive power dispatch is one of the key factors to attain cost-effective and stable functioning of power system. It is a complicated non-linear optimization issue with a combination of discrete and continuous control variables. Due to this complex feature of optimal reactive power dispatch, optimization technique has become an efficient method to solve this problem. In this work, Kinetic Gas Molecule Optimization algorithm with Pareto optimality is proposed for solving multi-objective optimal reactive power dispatch problem. The presentation of Kinetic Gas Molecule Optimization is improved by computing inertia weight and acceleration coefficients dynamically rather than a fixed value. Because of this reason, the searching capability of the particles in each iteration is improved. However, to improve the power system performance in optimal reactive power dispatch scenario, additional flexible AC transmission system devices like static VAR compensator, thyristor-controlled series compensator, and unified power flow controller are introduced to provide stable results when compared to conventional output because flexible AC transmission system devices are capable of controlling the flow of real power and reactive power. These details are implemented and tested on IEEE 30-bus test system with various objectives. The performance of proposed method is validated from MATLAB, which shows the value of power loss as 4.3583 and voltage deviation as 0.26499 with cost of US$469.6417 per MVAR, which shows considerably superior results when compared with implemented particle swarm optimization results. The proposed method provides an efficient result for solving multi-objective optimal reactive power dispatch issues. [ABSTRACT FROM AUTHOR]

A valid damping of oscillations is an upcoming extensive challenge while maintaining the stability of the power system. This oscillation generally occurs due to the fluctuation raised, when two systems are interconnected. This paper addresses the oscillation occurred in the power system as the main challenge, which thus performs an effective simulation in 68-bus system. Here, it promotes a sufficient CC with two FACTS devices such as TCSC and UPFC, which are connected with PSS. Further, it adopts firefly algorithm to enable the CC among the FACTS devices. To the next of the simulation, this paper compares the performance of the FF- CC with conventional optimisations include GSO, PSO, GA and ABC algorithms to enable CC. Further, it provides a detailed analysis of the impact of PSS and loading effects on CC. As a result, the performance of FF-CC hands over the stable power system with powerful damping of oscillations, after comparing it with the existing methods. Abbreviations: ABC, Artificial Bee Colony; ICA, Imperialist Competitive Algorithm; AVR, Automatic Voltage Regulators; NETS, New England test system; BFOA, Bacteria Foraging Optimization Algorithm; NYPS, New York power system; BSO, Bacterial Swarm Optimization; PSO, Particle Swarm Optimization; CC, Coordinated Control; PSS, Power System Stabilizers; COA, Chaotic Optimization Algorithm; STATCOM, Static Synchronous Compensator; CS, Cuckoo Search; SSSC, Static Synchronous Series Compensator; FACTS, Flexible Alternating Current Transmission System; SVC, Static Var Compensator; GA, Genetic Algorithm; TCSC, Thyristor Controlled Series Capacitor; GSO, Gravitational Search Algorithm; UPFC, Unified Power Flow Controller [ABSTRACT FROM AUTHOR]

Power system security analysis plays key role in enhancing the system security and to avoid the system collapse condition. In this paper, a novel severity function is formulated using transmission line loadings and bus voltage magnitude deviations. The proposed severity function and generation fuel cost objectives are analyzed under transmission line(s) and/or generator(s) contingency conditions. The system security under contingency conditions is analyzed using optimal power flow problem. An improved teaching learning based optimization (ITLBO) algorithm has been presented. To enhance the system security under contingency conditions in the presence of unified power flow controller (UPFC), it is necessary to identify an optimal location to install this device. Voltage source based power injection model of UPFC, incorporation procedure and optimal location identification strategy based on line overload sensitivity indexes are proposed. The entire proposed methodology is tested on standard IEEE-30 bus test system with supporting numerical and graphical results.

The nature of power system restoration problem involves status assessment, optimization of generation capability and load pickup. This paper proposes the evaluation of Power System Restoration Indices (PSRI) based on the Automatic Generation Control (AGC) assessment of interconnected power system in a deregulated environment. The PSRI are useful for system planners to prepare the power system restoration plans and to improve the efficiency of the physical operation of the power system with the increased transmission capacity in the network. The stabilization of frequency and tie-line power oscillations in an interconnected power system becomes challenging when implemented in the future competitive environment. This paper also deals with the concept of AGC in two-area reheat power system having coordinated control action with Redox Flow Battery (RFB) and Unified Power Flow Controller (UPFC) are capable of controlling the network performance in a very fast manner and improve power transfer limits in order to have a better restoration. In addition to that a new Proportional–Double Integral (PI2) controller is designed and implemented in AGC loop and controller parameters are optimized through Bacterial Foraging Optimization (BFO) algorithm. Simulation results reveal that the proposed PI2 controller is that it has good stability during load variations, excellent transient and dynamic responses when compared with the system comprising PI controller. Moreover the AGC loop with RFB coordinated with UPFC has greatly improved the dynamic response and it reduces the control input requirements, to ensure improved PSRI in order to provide the reduced restoration time, thereby improving the system reliability.

Flexible AC transmission systems have shown effective functionalities in promoting the system operation security and service reliability. Facing with series-compensated lines, subsynchronous resonance (SSR) may jeopardise the stability and mechanical facilities. The control strategy and simulation model of a unified power flow controller (UPFC) based on the dq decoupling control are deduced and constructed. Considering the impacts of grid-connected wind farms, SSR characteristics of the series-compensated system with UPFC are studied by the complex torque coefficient method and time-domain simulation. The results verify the capability of UPFC in attenuating SSR in wind farm integrations by utilising subsynchronous damping controllers coordinated with UPFC's main controllers. It also suggests that the shunt transformer−converter has a slight effect on SSR, whereas the series transformer−converter affects the system resonance characteristics significantly. Simulations are carried out on a typical power system model integrated with wind turbines.

In order to release the capability restriction of the North–South transmission channels in the 500 kV power grid of Fujian Province, this article studies the application of unified power flow controller (UPFC) to improve the transmission capability under steady-state security restriction with N−1 principle. On the basis of analysis of principle and structure of UPFC, a simplified equivalent model of UPFC is constructed and used in BPA simulation software. The optimal installation scheme and the minimal capacity required of UPFC are determined by comparing the results of power flow calculation in various schemes. The research result shows that the application of UPFC can effectively reduce the N−1 overload problem of the North–South transmission channels, and has a great economic advantage over the traditional solution. Finally, based on the technical and economic analysis, this study puts forward suggestions on the construction of UPFC in the Fujian 500 kV power grid.

The extensive usage of power electronic components creates harmonics in the voltage and current, because of which, the quality of delivered power gets affected. Therefore, it is essential to improve the quality of power, as we reveal in this paper. The problems of load voltage, source current, and power factors are mitigated by utilizing the unified power flow controller (UPFC), in which a combination of series and shunt converters are combined through a DC-link capacitor. To retain the link voltage and to maximize the delivered power, a PV module is introduced with a high gain converter, named the switched clamped diode boost (SCDB) converter, in which the grey wolf optimization (GWO) algorithm is instigated for tracking the maximum power. To retain the link-voltage of the capacitor, the artificial neural network (ANN) is implemented. A proper control of UPFC is highly essential, which is achieved by the reference current generation with the aid of a hybrid algorithm. A genetic algorithm, hybridized with the radial basis function neural network (RBFNN), is utilized for the generation of a switching sequence, and the generated pulse has been given to both the series and shunt converters through the PWM generator. Thus, the source current and load voltage harmonics are mitigated with reactive power compensation, which results in attaining a unity power factor. The projected methodology is simulated by MATLAB and it is perceived that the total harmonic distortion (THD) of 0.84% is attained, with almost a unity power factor, and this is validated with FPGA Spartan 6E hardware.

Highlights • MGGP-A novel intelligence approach optimizes the PSS coordinated UPFC parameters. • Standard statistical performance measures validate the proposed technique. • Results are compared with fixed gain conventional PSS and the referenced work. Abstract The coordination of flexible AC transmission systems (FACTS) with power system stabilizers (PSS) can significantly enhance the overall network stability by damping out the low-frequency oscillations (LFO). This paper proposes a multi-gene genetic programming (MGGP) approach to optimize PSS parameters coordinated with unified power flow controller (UPFC) to enhance power system stability by damping out LFO. The obtained results (minimum damping ratio, eigenvalues and time domain simulations) of the proposed MGGP approach are compared with the results of the conventional fixed gain model, the single-gene genetic programming (SGGP) approach and the referenced work to inquire the efficacy of the proposed approach for various operating conditions of the considered electric network. Besides, the acceptable values of standard statistical performance measures in estimating UPFC-PSS parameters provide confidence on the evolved MGGP models. Furthermore, the proposed approach requires a minimal time (∼less than a cycle) to estimate the key parameters that signal the real-time application of the proposed technique. [ABSTRACT FROM AUTHOR]

In the context of flexible operation and bidirectional line flows in modern transmission systems, suitable line flows are essential for safe, secure and stable power systems. Improper line flows may deteriorate stability and longevity of transmission lines. To avoid line outage and faults, improvement in thermal margin of conductors by regulating line flows is a practical consideration. To maintain and control the line flows, the unified power flow controller (UPFC) is the most appropriate compensating device. Thus, in this study, line flows are considered as state variables to optimise several functions, like, voltage deviation index, active and reactive power losses, temperature of conductors and cost of UPFC. The UPFC is modelled with practical losses like switching, coupling and internal transmission losses. Suitable line flows are obtained for the 30‐bus and 57‐bus test systems by applying an adaptive‐version of the wind‐driven optimisation (AWDO) algorithm. The AWDO is designed using two innovative tuning parameters: a decaying friction coefficient to reduce the probability of stagnation, and an adaptive velocity function to maintain diversity. The results are compared among different cases of line flows, validating the necessity of the technical challenge. The performance of AWDO is compared with other techniques, suggesting its superiority over other methods. [ABSTRACT FROM AUTHOR]

This article proposes a state-variable stabilizing control algorithm for unified power flow controller in a multi-machine power system. This stabilizing control is activated in the transient state of the power system and is complementary to the main steady-state control designed for power flow regulation. The stabilizing control algorithm proposed in this article is derived for a non-linear multi-machine system model in order to maximize the damping of power swings in a power system. This article also shows that the effects of multiple control devices on power swing damping are additive, i.e. each new device added to power system network increases damping. [ABSTRACT FROM AUTHOR]

The unified power flow controller (UPFC) is an excellent flexible alternating current transmission device, which has a wide range application in the power system. It can be expected that more UPFC engineering applications will be introduced to the power system in the future, and they will have an unignorable impact on the power grid. It is of great significance to analyse the influence of UPFC on power system energy conservation. First of all, the basic characteristics of UPFC are briefly introduced. Secondly, the influence of voltage quality, reactive power index, and energy saving after UPFC is introduced to the power system is analysed in detail from reactive power compensation and power flow regulation. Finally, comparison simulation of a three-machine nine-node system is simulated, the simulation results show that the power system with UPFC introduced can make the power flow distribution more reasonable, reduce the voltage sag, improve the voltage quality, and power transmission capacity, thus reducing the loss of the power system. [ABSTRACT FROM AUTHOR]

The unified power flow controller (UPFC) is the third generation of flexible AC transmission systems. It can control the power flow and voltage of the power system quickly and flexibly that has an advantage in compensating the AC transmission system in real time. The world's first 500 kV UPFC project is under construction in Jiangsu Province of China. On the paralleled converter side, it is connected to the 500 kV Mudu substation by using a gas insulated transmission line, and the series converter side is connected to the 500 kV Meili substation through a 500 kV double-circuit overhead transmission line. In order to optimise insulation design of the UPFC system and ensure the safety operation of the power system, it is essential to analyse the characteristics of lightning overvoltage. Considering the invaded path of lightning surges in the UPFC system, a detailed model was established by using Electro-Magnetic Transient Program/Alternative Transients Program in this study. The lightning overvoltage level at key nodes of the UPFC system was presented. The check calculation for the configuration and protection level of ZnO arresters were also carried out. The obtained results can provide a reference for insulation coordination design of the 500 kV UPFC project. [ABSTRACT FROM AUTHOR]

In order to release the capability restriction of the North–South transmission channels in the 500 kV power grid of Fujian Province, this article studies the application of unified power flow controller (UPFC) to improve the transmission capability under steady-state security restriction with N−1 principle. On the basis of analysis of principle and structure of UPFC, a simplified equivalent model of UPFC is constructed and used in BPA simulation software. The optimal installation scheme and the minimal capacity required of UPFC are determined by comparing the results of power flow calculation in various schemes. The research result shows that the application of UPFC can effectively reduce the N−1 overload problem of the North–South transmission channels, and has a great economic advantage over the traditional solution. Finally, based on the technical and economic analysis, this study puts forward suggestions on the construction of UPFC in the Fujian 500 kV power grid. [ABSTRACT FROM AUTHOR]

Flexible AC transmission systems have shown effective functionalities in promoting the system operation security and service reliability. Facing with series-compensated lines, subsynchronous resonance (SSR) may jeopardise the stability and mechanical facilities. The control strategy and simulation model of a unified power flow controller (UPFC) based on the dq decoupling control are deduced and constructed. Considering the impacts of grid-connected wind farms, SSR characteristics of the series-compensated system with UPFC are studied by the complex torque coefficient method and time-domain simulation. The results verify the capability of UPFC in attenuating SSR in wind farm integrations by utilising subsynchronous damping controllers coordinated with UPFC's main controllers. It also suggests that the shunt transformer−converter has a slight effect on SSR, whereas the series transformer−converter affects the system resonance characteristics significantly. Simulations are carried out on a typical power system model integrated with wind turbines. [ABSTRACT FROM AUTHOR]

The electricity demands and transactions in power markets increase frequently. Hence existing power networks must be enhanced for better utilization. In this work, Artificial Bee Colony Algorithm (ABC) is proposed for enhancing and controlling power flow using Flexible AC Transmission System (FACTS) controllers. The objectives considered are enhancement of system loadability, reduction of Installation cost of devices and reduction of transmission loss. Three types of FACTS devices such as Static VAR Compensator (SVC), Thyristor Controlled Series Compensator (TCSC) and Unified Power Flow Controller (UPFC) are used. The optimal location and parameter setting of FACTS devices is achieved using ABC algorithm. In this paper two cases are considered: i) single type i.e. same type of FACTS device, and ii) multi type i.e. combination of SVC, TCSC, UPFC. The proposed algorithm is implemented on 6 bus, IEEE 30, IEEE 57 and IEEE 118 bus systems using MATLAB platform. The power flows are analyzed. The results obtained are compared with existing literature. The results indicate that the proposed algorithm gives better improvement in system loadability, reduction of transmission loss and installation cost. Hence the proposed algorithm will be useful in restructuring power networks. [ABSTRACT FROM AUTHOR]