Low Frequency Power Oscillation Damping Enhancement and Voltage Improvement Using Unified Power Flow Controller (UPFC) in Multi-Machine Power System

The problem of low-frequency power swings is a matter of concern for power systems engineers in the operation and planning of power systems. Therefore, this paper is an investigation of the use of unified power flow controller (UPFC) that is suitably tuned to improve the damping of low frequency power oscillations present in Nigerian grid system. A large disturbance is initiated, during simulation in PSAT, in the network to induce nonlinear oscillations of the power system in order to ascertain the damping effect of UPFC. The dynamic responses of the system simulated show that the system is well damped and is stabilized at minimal time which confirms the robustness of the UPFC. Finally, a comparative study in a typical transient stability problem on IEEE 14-bus system using a UPFC model and the Nigerian high voltage interconnected system is used to illustrate the concepts presented in this paper. Key words: Power oscillation damping, power systems, unified power flow controller (UPFC), flexible AC transmission system (FACTS) devices, low frequency oscillation

The design of large interconnected power systems to ensure stable operation under wide variety of disturbances is a complicated problem. In recent years, technologically developments in Flexible AC Transmission Systems or FACTS devices provided better performance in enhancing power system stability. This paper has provided a general description of Single machine infinite bus system (SMIB) small signal stability in case of using Unified Power Flow Controller (UPFC). In this study, the small signal stability of the system is converted to a multi-objective optimization problem which leads to design a controller of UPFC in order to make higher damping torque. The Shuffled frog leaping algorithm or SFLA is used as an optimization tool to find the optimum parameters of the controller. Furthermore, the designed controller is compared with similar ones using PSO and QPSO optimization approaches and in addition with a PSS controller to show the remarkable robustness and higher performance of the method.

Flexible AC Transmission System (FACTS) controllers are advanced power electronic devices employed in electrical power systems to enhance system stability, reliability, and power transfer capabilities. These controllers enable dynamic and flexible control of various transmission parameters such as voltage, current, impedance, and phase angle, thereby improving the overall power system performance. FACTS devices are broadly classified into series, shunt, series- series, and series-shunt configurations, each designed to manage reactive power and regulate voltage either by injecting voltage in series or current in shunt with the transmission line. Well-known FACTS devices include Static Var Compensators (SVC), Static Synchronous Compensators (STATCOM), Thyristor Controlled Series Capacitors (TCSC), Static Synchronous Series Compensators (SSSC), and Unified Power Flow Controllers (UPFC), each serving specific roles in power flow control, voltage regulation, and transient stability enhancement. The integration of these controllers provides significant benefits such as increased transmission line capacity, improved voltage stability, minimized transmission losses, and damping of power system oscillations. They are capable of rapid response during transient disturbances, effectively mitigating voltage collapses and enhancing system resilience against faults and contingencies. FACTS controllers not only improve steady-state operational parameters but also address dynamic stability and transient conditions, enabling power systems to operate closer to their stability limits while maintaining security. Their deployment helps avoid costly infrastructural expansions by optimizing existing transmission assets, which is critical given environmental and economic constraints. Recent advances in semiconductor technologies and control algorithms have made FACTS devices more reliable, efficient, and adaptable to modern grids, including renewable integration and deregulated power markets. In summary, FACTS controllers play a vital role in modern power systems by providing flexible, efficient, and reliable solutions for power flow management, voltage control, and system stability enhancement, thereby supporting the evolving demands of today's complex electrical networks.

Ensuring the transient stability of the power system networks is one of the prime challenges in the highly interconnected power systems. Though the low-frequency oscillations are not very harmful initially, failure to damping out may lead the system to go out of synchronism. The employment of flexible AC transmission systems (FACTS) devices may suppress these oscillations effectively in addition to the enhancement of power transfer capability. Among many FACTS devices, unified power flow controller (UPFC) is one of the most sophisticated ones. Tuning the parameters of power system stabilizer (PSS) coordinated with UPFC for a stable system is a multi-objective optimization problem. This paper aims to optimize the parameters of power system stabilizer (PSS) of power network incorporating UPFC using support vector regression (SVR) in real time to damp out the small signal oscillations hence to enhance the transient stability. System eigenvalues obtained from SVR tuned UPFC coordinated PSS and the fixed gain conventional PSS are compared to investigate the efficacy of the proposed technique for different loading conditions. Besides, time domain simulation comparison proves the superiority of the proposed technique over the conventional one. Furthermore, the statistical performance measures for training and testing datasets provide confidence on the developed SVR model.

Voltage instability and voltage collapse have been considered as a major threat to present power system networks due to their stressed operation. It is very important to do the power system analysis with respect to voltage stability. Flexible AC Transmission System (FACTS) is an alternating current transmission system incorporating power electronic-based and other static controllers to enhance controllability and increase power transfer capability. A FACTS device in a power system improves the voltage stability, reduces the power loss and also improves the load ability of the system. FACTS have made the power systems operation more flexible and secure. Amongst the several FACTS controllers, the Unified Power Flow Controller (UPFC) is most effective to improve the enhancement of voltage stability and reduces the power loss. This study investigates the application of Particle Swarm Optimization (PSO) to find sizing of Unified Power Flow Controller (UPFC) device to minimize the voltage stability index, total power loss, load voltage deviation, and cost of FACTS devices to improve voltage stability in the power system. A new model is proposed in this thesis to improve existing power-based model by using the Norton Equivalent Theorem. The proposed model can be integrated with the Equivalent Current Injection (ECI) power flow model easily. By ECI algorithm, it is much quickly and precisely to implement power flow calculations. Finally It is observed from the results that the voltage stability margin is improved, the voltage profile of the power system is increased and real power losses also reduced by optimally sizing UPFC device in the power system. Index Terms: Voltage stability, Unified Power Flow Controller (UPFC), Equivalent -Current Injection (ECI), Modified particle swarm optimization (MPSO)

The successful application of the unified power flow controller (UPFC) provides a new control method for the secure and economic operation of power system. In order to make the full use of UPFC and improve the economic efficiency and static security of a power system, a preventive security-constrained power flow optimization method considering UPFC control modes is proposed in this paper. Firstly, an iterative method considering UPFC control modes is deduced for power flow calculation. Taking into account the influence of different UPFC control modes on the distribution of power flow after N-1 contingency, the optimization model is then constructed by setting a minimal system operation cost and a maximum static security margin as the objective. Based on this model, the particle swarm optimization (PSO) algorithm is utilized to optimize power system operating parameters and UPFC control modes simultaneously. Finally, a standard IEEE 30-bus system is utilized to demonstrate that the proposed method fully exploits the potential of static control of UPFC and significantly increases the economic efficiency and static security of the power system.

Güç sistemlerinin sürekli ve geçici durum çalışmalarında Esnek AC İletim Sistemi (FACTS) cihazları tercih edilmektedir. FACTS cihazları içerisinde kontrol etme yeteneği en güçlü olan Birleştirilmiş Güç Akışı Kontrolü (UPFC)’dir. UPFC bara gerilimlerini reaktif güce bağlı olarak kontrol ederken, iletim hattını empedans ve akıma göre kontrol etmektedir. Bu çalışmada, Uluslararası Elektrik Elektronik Mühendisliği (IEEE) 14 baralı güç sisteminde UPFC’nin statik ve dinamik gerilim kararlılığı analizleri gerçekleştirilmiştir. Sürekli ve geçici durum için gerilim kararlılığı çalışma limitlerinin geliştirilmesi ve sistemin kararlı bölgede kalması için UPFC ile birlikte Enerji Depolama Sistemi (EDS) elemanlarından yakıt hücresi kullanılmıştır. UPFC-EDS ile sistemin gerilim-maksimum yüklenme parametre değerlerinin yanı sıra bara gerilim profilleri analiz edilmiştir. UPFC ile yakıt hücresinin birlikte kullanılması durumunda sistemin yüklenme parametre değerinin arttığı ve bara gerilim profillerinin iyileştiği görülmüştür.

Nowadays distributed generation systems such as photovoltaic power generation systems and wind power generation systems have been on the increase. The increase of distributed generation systems causes the reverse power flow and the voltage rise in power distribution systems. By the way, the leading currents by the installed compensation capacitors cause the voltage rise and increase of the power loss in distribution line. The authors have proposed the node voltage control and line loss suppression methods using Unified Power Flow Controller (UPFC). This paper presents the comparison of the arrangement and capacity of UPFC for the distribution system control. The proper arrangement for reducing the converter capacity is derived. The effectiveness of the proposed theory is verified by experiments.

New approach for optimal UPFC placement using hybrid immune algorithm in electric power systems

UPFC (Unified power flow controller) is one of the most powerful and complex FACTS (Flexible AC transmission system) devices in a power system today. It is primarily used for simultaneous or independent control of real and reactive power in transmission lines for flexible, reliable and economic operation and loading of power systems. In this paper, the effectiveness of UPFC has been explored in transmission system network when subjected to three phase to ground fault condition. The comparison has been made between VSI (Voltage Source Inverter) based UPFC and ZSI (Z-Source Inverter) based UPFC. From the results so obtained, it has been established that the performance of ZSI based UPFC is superior as compared to that of VSI based UPFC.

The introduction of the flexible AC transmission system (FACTS) in the power system reduces the losses, reduces the cost of the generation, improves the stability and also improves the load capability of the system. Some application of the Flexible AC transmission system (FACTS) technologies to existing high voltage power system has proves the use of FACTS technology may be a cost effective option for power delivery system enhancement. Amongst various power electronic devices unified power flow controller (UPFC) may be considered to be a capable of regulating the power flow and minimizing the power loss simultaneously. Since for the cost effective application of the FACTS technology a proper selection of the number and the placement of these devices is required. The main aim of this paper is to propose the methodology based on the genetic algorithm, able to identify the optimal number and the location of the UPFC devices in an assigned power system network for maximizing system capabilities. In order to validate the usefulness of the approach suggested here is , a case study using a IEEE 30-bus power system is presented and discussed.

In this paper, multi – type Flexible AC Transmission System (FACTS) devices are optimally located for enhancing the loadability of an existing power network within the security margins. Line Stability Index is used to determine the critical lines of the system in increased loading of transmission lines and is used to determine the optimal location of FACTS devices. Differential Evolution Algorithm (DE) is used to determine the optimal location and control parameter settings of the FACTS devices. Among the various FACTS devices, Unified Power Flow Controller (UPFC) and Thyristor Controlled Series Capacitor (TCSC) are chosen and modeled for steady state studies. IEEE- 30 bus test system is used for simulation studies and the results are compared with Genetic Algorithm (GA) to show the advantage and feasibility of the DE approach. Further the results demonstrate that the system loadability can be increased by optimal location and control parameter settings of the multi – type FACTS devices.

– The unified power flow controller (UPFC) is the most versatile and complex power electronic equipment that has emerged as the indispensable equipment for the control and optimization of power flow in electrical power transmission system. In this manuscript is investigated the control of real and reactive power flow through a transmission line with the use of UPFC at the sending end. Computer simulation using MATLAB Simulink is done and the behavior of the UPFC is studied. In the UPFC based control of transmission line parameter control systems, it is observed that whenever the SSSC sources some real power into the transmission line it is manifested as a voltage drop across the DC link. Reactive power demand is indicated as fall in the bus bar AC voltage. The fall of the DC link voltage is an indication of real power demand from the receiving end. Similarly a fall of the bus bar AC voltage is an indication of reactive power demand from the receiving end. Fuzzy Logic and PI controllers are used in this works, the control of DC voltage, AC voltage and power transfer.

A generalized approach for determination of optimal location and performance analysis of FACTs devices

In this paper, a fully fledged optimal power flow (OPF) algorithm with flexible AC transmission systems (FACTS) devices has been developed and presented aiming at the advancement of how FACTS equipment impacts on the security and economy of the wider power network. The proposed modelling uses Newton’s method along with Lagrangian multipliers, leading to an ecient algorithm that can handle practical power networks independence of initial settings of FACT controllers parameters. Newton’s method provides a suitable vehicle for incorporating the newly developed nonlinear, linearized FACTS models. In this paper, mainly a firing angle-based thyristor controlled series compensators (TCSC) model, a coordinated two-voltage source unified power flow controller (UPFC) model have been developed and presented in details and can easily be extended to other modern FACTS devices such as interline power flow controller (IPFC) and generalized unified power flow controller (GUPFC). The proposed model has capability of converting multi-objective functions into single objective and also can be extended to multiple multi-type FACTS devices. The performance of the proposed model has been validated for IEEE 30 bus system and the solutions so obtained are presented in detail.