A Review of Long-Distance UHVDC Technology - A future Energy Disrupter

Optimal transmission conversion from alternating current to high voltage direct current transmission systems for limiting short circuit currents

Nowadays electromechanical oscillations of lower frequencies (LFO) have become a quite common phenomenon in modern power systems, posing a major threat to stability and security of the systems. For mitigation of these oscillations to improve system stability, Power System Stabilizers (PSS) are provided in power systems. However, in cases of certain faults and increased loading in a transmission line, equipping power systems with only PSS might not be enough. For better controllability as well as improved stability, Flexible AC Transmission System (FACTS) technologies are predominantly used in power systems. With unified use of FACTS devices along with PSS, there is improvement not only in just control of the power flow and response but also further enhancement in power system stability by damping out oscillations. Thyristor Controlled Series Capacitor (TCSC) is a modern versatile FACTS device extensively used in power systems for its effectiveness in rapid regulation of voltage, maintenance of balance in power flow and hence leading to greater stability limits as compared to other FACTS devices. However the linear control methods might not be effective in design of coordinated parameters. Hence taking nonlinearities in power system into consideration, a robust and unique evolutionary optimization technique termed as ‘Spider Monkey Algorithm’ is used for dynamic tuning of PID specifications of PSS for improvement of system stability to a much greater extent. The SMO based PID controller is designed and compared with conventional PID for justification and validation of the enhancement achieved, in terms of transient stability performance using MATLAB/SIMULINK environment by subjecting it to non linear loading conditions. The results demonstrate greater transient performance and immense potential of dynamically tuned SMO technique based PSS-PID of the two machine system as compared to the conventional PSS based PID controller.

This paper presents a comprehensive performance analysis of power systems incorporating High Voltage Direct Current (HVDC) transmission lines, with a focus on the impact of integrating advanced Flexible AC Transmission Systems (FACTS) devices, namely Static Synchronous Series Compensator (SSSC) and Static Synchronous Compensator (STATCOM). This study evaluates key performance parameters, including Total Power Loss (TPL), Voltage deviation (Vdev), transmission efficiency, and corona loss, across three configurations, HVDC alone, HVDC with SSSC, and HVDC with STATCOM. Through simulations conducted using MATLAB or Simulink, the results demonstrate that the addition of SSSC and STATCOM significantly improves system performance by reducing power losses, enhancing voltage stability, and optimizing transmission efficiency. The analysis reveals that HVDC systems with SSSC outperform other configurations in terms of power loss reduction and voltage stability, while STATCOM improves voltage regulation and minimizes deviations. This study highlights the benefits of incorporating SSSC and STATCOM into HVDC systems for enhancing power system efficiency, stability, and operational reliability.

The deregulation of the energy-supply industry has increased the importance of security in an electric power system (EPS). The analysis of transient stability in electric power systems plays an important role in this issue. Since an analytical solution to a set of EPS differential equations does not exist, many approaches for finding a solution were developed in the past. Existing methods can be divided into three types. First are the so-called time-domain (T-D) digital simulations that numerically integrate differential equations and obtain a solution in the form of a system trajectory. The second approach uses direct methods that employ Lyapunov energy functions. In addition to information on systems stability, these methods can also provide stability margin estimation and various stability indices that help to identify a critical operation point. They are less accurate but substantially faster than T-D simulations. Complementary characteristics, speed and accuracy, are combined in hybrid methods, which emerged by combining digital simulation and direct methods. This paper gives an insight into all three methods for cases when transient stability assessment of power systems with FACTS (flexible AC transmission systems) is under discussion. The discussion focuses on direct methods and the derivation of appropriate energy functions that embed the action of FACTS devices. In this sense we provide methods for the implementation of the FACTS effect in energy functions.

To maintain the voltage stability in the power system it is necessary to balance the flow of real and reactive power which can be achieved by the compensation techniques in the power system. Reactive power plays an important role to maintain the voltage stability in the power system because the flow of reactive power is depends upon the voltage magnitude, in case of voltage magnitude dips the unbalance of reactive power flow will occurs which results in overall instability of the power system So, there is need to design an model which can compensate the reactive power in the system to maintain the system voltage. STATCOM is one of the FACTs device used to maintain the flow of reactive power and hence, voltage stability in power system (Hingorani and Gyugyi, Understanding FACTS: concepts and technology of flexible AC transmission systems, [1]). This paper describes the mathematical modeling with inherent controlling capability of STATCOM helps to compensate the reactive power flow in the system which maintain the voltage stability. This will approach to the DFIG based wind farms using STATCOM also had been applied for offshore wind power plants to satisfy the grid codes (Tanaka et al., Reactive power compensation capability of a STATCOM based on two types of modular multilevel cascade converters for offshore wind application, 2017, [2], Ushkewar and Bodke, Compensation of reactive power in DFIG based wind farm using STATCOM, 2018, [3], Pereira et al., STATCOM to improve the voltage stability of an electric power system with high penetration of wind generation, 2016, [4]).

This paper focuses on the effective utilization of Flexible AC Transmission System (FACTS) and High Voltage Direct Current (HVDC) interconnection link for the improvement of voltage profile, stability and loss allocation in heavily loaded as well as contingent conditions of the network. The weakest bus interconnection has been replaced by FACTS and HVDC link and a study has been carried out to prove their effectiveness in an interconnecting network under deregulated environment. The IEEE 14 bus system, operating with common loads and generators is used to demonstrate the usefulness of FACTS and HVDC link. A new voltage stability index (VSI) has been proposed in this paper for stability analysis with HVDC and FACTS. A comparative analysis between FACTS and HVDC has also been presented in this paper, for their comparison, in field of power quality and cost efficiency.

This paper discusses and compares different control techniques for damping undesirable electromechancial oscillations in power systems by means of power system stabiliser (PSS) and series/shunt FACTS (flexible AC transmission system) controllers. The linearised model of the power system is derived with FACTS controllers and the problem is formulated as an optimisation problem to maximise the damping ratio of the power system. Particle swarm optimisation (PSO) technique is applied to tune the controller parameters of the PSS and FACTS controllers. The following FACTs controllers are taken for analysis: (i) static Var compensator (SVC); (ii) static compensator (STATCOM); (iii) thyristor controlled series capacitor (TCSC); and (iv) unified power flow controller (UPFC). The time domain simulation results are carried out using EUROSTAG 4.3, which provides necessary information about the dynamic reactive power support required by shunt FACTS controllers and the dynamic MVA rating of series FACTS controllers for small signal/transient stability enhancement.

The paper describes the coordination control of PSS (power system stabilizer) and FACTS (flexible AC transmission system) devices in order to improve low-frequency oscillation followed by disturbances. The PSS is generally used to mitigate the low-frequency oscillation and the FACTS is used to enhance the transfer capacity for the transmission line in power system. In order to improve small signal and transient stability in power system, the paper proposes the combination of the PSS and FACTS. The performances of the proposed method are carried out by time-domain simulation with single- machine connected to infinite bus system.

Damping of power system oscillations between interconnected areas is very important for the system secure operation. Power system stabilizer (PSS) and flexible AC transmission systems (FACTS) devices are used to enhance system stability. In large systems multi-machine, using only conventional PSS may not provide sufficient damping for inter- area oscillations. In these cases, FACTS power oscillation damping controllers are effective solutions. But uncoordinated local control of FACTS devices and PSS's may cause destabilizing interactions. In this paper, using objective function which maximizes the function, the total damping ratios of the system are optimized and dynamic stability of the system will be improved. In this method all the operation conditions are considered. Simulation results for a large system and different operation conditions of the system shows that this method has a good efficiency and can be effective solution for this problem in a large system. This method can be effective for the coordinating of multi-controllers in large power systems.

There are two types of oscillation damping controller in power system which are power system stabilizer (PSS) and flexible ac transmission systems (FACTS). Numerous works have been carried out on the damping of power system low frequency oscillations. This paper addresses an extensive literature review on coordination problem in single-machine and multi-machine power system. It also reviews various types of FACTS controllers. Various methods are proposed in order to enhance the dynamic performance of a power system for coordinated control between FACTS and PSS controller in power system models.

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.

This paper presents a sequential based Newton- Raphson power flow algorithm for reliable and efficiently handling power systems with embedded FACTS (Flexible AC Transmission Systems) devices. Computation and control of power flow in power systems with embedded FACTS devices appear to be fundamental for power system analysis and planning purposes. A power injection model for conventional FACTS devices such as SVC (Static Var Compensator) and TCSC (Thyristor Controlled Series capacitor) as well as modern FACTS devices such as STATCOM (Static Series Compensator) SSSC (Static Synchronous Series Compensator) and UPFC (Unified Power Flow Controller) is derived. Also a power injection model of conventional HVDC (High Voltage Direct Current) is obtained. Then a sequential power flow algorithm (two step algorithm) is adopted. The proposed injection models and sequential power flow algorithm have been programmed and systematically tested in a number of systems. The results of Ward-Hale network are reported which clearly illustrates the Capabilities and generalization of the proposed algorithm.

This paper presents Ant Colony Algorithm (ACA) based approach for the allocation of FACTS (Flexible AC Transmission System) devices for the improvement of Power transfer capacity in an interconnected Power System. The ACA based approach is applied on IEEE 30 BUS System. The system is reactively loaded starting from base to 200% of base load. FACTS devices are installed in the different locations of the power system and system performance is noticed with and without FACTS devices. First, the locations, where the FACTS devices to be placed is determined by calculating active and reactive power flows in the lines. Ant Colony Algorithm is then applied to find the amount of magnitudes of the FACTS devices. This approach of ACA based placement of FACTS devices is tremendous beneficial both in terms of performance and economy is clearly observed from the result obtained.

This work deals with the simultaneous coordinated tuning of the FACTS (flexible AC transmission systems) POD power oscillation damping) controller and the conventional PSS (power system stabilizer) controllers in multimachine power systems. Using the linearized system model and the parameter-constrained nonlinear optimization algorithm, interactions among FACTS controller and PSS controllers are considered. Furthermore, their parameters are optimized simultaneously. Simulation results of multimachine power system validate the efficiency of this new approach. The proposed algorithm is an effective method for the tuning of multicontrollers in large power systems.

With the advent of modernization, the demand for electricity is increasing exponentially. Low frequency electromechanical oscillations have posed a major challenge to the power transfer capabilities and stability of modern power system. For the effective mitigation of these electromechanical oscillations, a coordinated design of Power System Stabilizer (PSS) and Static Var Compensator (SVC) is proposed for a two machine system, with the application of a novel optimization technique called Gravitational Search Algorithm (GSA).PSS helps in the effective damping of electromechanical oscillations and enhancement of transient stability. However, at times only use of PSS in long transmission lines is not enough. FACTS devices is a recent technology that is being used extensively to improve controllability in power flow. Unified use of PSS along with a unique Flexible AC Transmission System (FACTS) device named SVC can result in improvement in reliability, controllability and reduction of power system oscillations thus further improving the system stability. Furthermore the PID controller of PSS is tuned dynamically using a global search technique called Gravitational Search Algorithm (GSA) for the system to respond effectively to non linearities present in power system. The results show the robustness and the flexibility of the new GSA based PID controller over a wide range of faults by effectively reducing oscillations. The system stability is improved to a great extent in terms of rise time, settling time and peak overshoot. Furthermore the GSA optimized PID controller gives much minimized THD as compared to conventional PID. For the justification and validation of the GSA technique in attaining enhanced stability, the two machine system is introduced with single phase triple L-G fault. The conventional PID based PSS simulation results are compared with GSA optimized PID based PSS simulation results using MATLAB.