Graphical explanation of the damping torque analysis method and its applications in multi‐machine power systems

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 study presents coordinate control tuning of power system stabilizer (PSS) with series and shunt FACTS controllers. Here thyristor controlled series compensator (TCSC) and static synchronous compensator (STATCOM) based controllers are coordinated to enhance the damping of power system inter area oscillations. The design of proposed damping controller is formulated as an optimization problem and the controller gains of a linearized power system are optimized instantaneously using genetic algorithm (GA). Here the power system employed with PSS and STATCOM as well as TCSC. The coordinated tuning among the damping controllers is performed on the linearized power system model. Finally, the proposed coordinated controller performance is tested with both eigen value analysis and time domain simulations. Three different control schemes are employed on the test system and the simulation results are compared.

This paper investigates three polynomial strategies in damping oscillations in a horizontal axis turbine plant power systems, to demonstrate the influence of the introduction of the STATCOM in the power system, a comparative study is implemented using various polynomial algorithm control approaches to a horizontal wind axis turbine power system incooperating a static synchronous compensator (STATCOM). The proposed controllers' designs are based on a linear time invariant model of the plant and state feedback scheme. First, the linearized mathematical model of STATCOM is derived. Then, using polynomial algorithms as a state feedback algorithm, a state feedback control law is derived. The proposed control strategy is tested on SMIB power system with wind turbine by digital computer simulations using matlab/simulink and a power analysis toolbox. Comparison of the polynomial matching results of the controllers establishes the superb nature of polynomial approximation approach.

A static synchronous series compensator (SSSC) has the ability to emulate a reactance in series with the connected transmission line. A static synchronous compensator (STATCOM) is able to provide the reactive power to an electricity network. When fed with some supplementary signals from the connected power system, both SSSC and STATCOM are able to participate in the power system inter-area oscillation damping by changing the compensated reactance or the provided reactive power. This paper analyses the influence of SSSC and STATCOM on power system small signal stability. The damping controller schemes for SSSC and STATCOM are presented and discussed. The IEEE 39-bus New England system model as the test system is built in DIgSIELNT PowerFactory, in which the damping control strategies for both SSSC and STATCOM are validated by time domain simulations and modal analysis. Furthermore, comparison studies show that the SSSC is a better solution in term of equipment capabilities and costs.

This paper proposes a method to select the supplementary input signal for systems equipped with static synchronous compensators (STATCOM) to damp inter-area mode(s). Input-output observability-controllability analysis, minimum singular value, right half plane zeros and relative gain array are used to assess the most appropriate supplementary input signal. The open-loop frequency of the system is shown to examine the sensitivity of the selected supplementary input signal to inter-area mode. The method is applied to select the input signal for a small power system equipped with a single STATCOM and for a large power system equipped with two STATCOMs.

Recently, the large-scale integration of power electronic-based renewable energy power plants has changed the operation and response mechanism of the power system, resulting in several emerging oscillation issues that have seriously been threatening the system's stability. It helps us to recognize the similarities and differences among the triggering causes and formation mechanisms of oscillation scenarios. Following several typical oscillation events in the real world and the timescale decomposition method, this paper comprehensively reviews the wide-bandwidth oscillation study from the aspects of the analysis methods, possible cause, mechanism, and mitigation solution. The paper provides a perspective to classify the oscillations in the modern power systems on the basis of the oscillation frequency and the main oscillation module. This classification framework involves not only emerging oscillations in the power system with large-scale renewable energy sources integration but also includes typical oscillations in traditional power systems. It also systematically presents the relative relationship, development process, and inner influence between emerging oscillations and typical oscillations. Based on this review, the future research is suggested to focus on the relationship between different analytical methods or oscillation mechanisms, as well as the stability risk assessment of hybrid alternating current and direct current power systems.

In electromechanical oscillation damping within power system, power system stabilizers (PSSs) are often deployed. However, a PSS is less effective in damping interarea oscillation and is limited by changes in network configuration due to weak tie-lines and load variations. Consequently, this paper presents a wide-area coordination approach that damps interarea oscillations using FACTS devices and phasor measurement units. We selected a static synchronous compensator (STATCOM) and static series synchronous compensator (SSSC) for realistic power system interarea oscillation damping. The performance of the coordinated FACTS installed in a power system depends on their suitable locations, sizes, tuned parameters, and remote input signal selection. Hence, we formulated a multiobjective problem to provide the STATCOM and SSSC's optimal solutions using multiobjective particle swarm optimization. In addition, we employed a participation factor to select suitable generator speed deviations as the wide area stabilizing signal. The proposed approach was tested on different configurations of the Kundur $2$-area $4$-machine test system within MATLAB and Psat environments. The outcome of the nonlinear simulation proved that the multimachine power system stability was enhanced.

Application of subsynchronous damping controller (SSDC) to STATCOM

In the category of small signal stability problem, one of the major causes of unpredictability of power transfer in the inter-connected power system is due to low frequency oscillations (LFO). These oscillations in the inter-connected power system, affects the power transfer capability and thereby, needed to be suppressed. To damp the oscillation and protect the power system, power system stabilizers are used. In this study, a Kho-Kho optimization (KKO) based proportional integral derivative (PID) power system stabilizer is put forward which can suppress the LFO in the inter-connected power system. Optimization methods are widely being used to solve number of optimization problem. Therefore, in this work the specification of the stabilizer are calibrated using KKO technique by optimizing a objective function constructed using the Integral time square error (ITSE) of the speed deviation. To test the effectiveness of the designed optimal controller, a one machine infinite bus (OMIB) with IEEE type DC-1 exciter unit is also taken into consideration. The superiority of the proposed technique is examined by comparing the obtained results with some other existing techniques.

The utilization of renewable energy sources for energy transition is gaining significant popularity due to pollution control and other environmental benefits. To move toward green energy generation, the integration of renewable energy sources with the existing conventional grid plays a key role. The performance of a modern interconnected power system, particularly with a high penetration of renewable energy sources, is significantly impacted by power system oscillations. Flexible Alternating Current Transmission System (FACTS) devices are recommended to improve control framework performance, and the power system stabilizer is the customary controller for damping such oscillations. FACTS offer a powerful strategy as they can control transport voltage, transmission line impedance, and power flows. This paper presents an efficient control scheme that combines four FACTS controllers: the static VAR compensator for controlling reactive power in control frameworks, the unified power flow controller for managing active and reactive power flows on transmission lines, the static synchronous compensator for maintaining system voltage stability, and the static synchronous series compensator for controlling transmission line impedance. To address the challenges posed by the variability of renewable energy sources such as wind and solar, the ant colony optimization algorithm is employed to optimally tune the controllers’ parameters. By generating controlled voltage and interfacing with the transmission line, these controllers enhance system stability, even under fluctuating renewable energy inputs. The IEEE 30-Bus system was used for simulation and control design, demonstrating the effectiveness of this approach in damping inter-area oscillations and improving the stability and resilience of a renewable-energy-integrated power system.

With the expansion of electric power systems, the size and complexity of the network is increased. One of the most important drawbacks of network expansion is the reduction in the damping torque of the whole system. The lack of damping torque can lead to fluctuations and instability in the power system. With regard to this problem, power system stabilizers (PSSs) have been widely utilized to improve power system stability. However, due to some drawbacks of the conventional PSSs, the need for finding a better substitution still remains. Therefore, in this paper, the application of a static synchronous compensator (STATCOM) to improve dynamic stability of a multimachine electric power system is presented and a supplementary stabilizer based on the STATCOM is incorporated. Intelligence optimization methods such as particle swarm optimization and genetic algorithms are considered for tuning the parameters of the proposed stabilizer. Several nonlinear time-domain simulation tests visibly show the ability of the STATCOM in damping power system oscillations.

A number of techniques have been proposed to dampen the power system oscillations in the electric power systems. Flexible alternating current transmission system (FACTS) devices are becoming one of them. Among the FACTS family, the static synchronous compensator (STATCOM), a shunt connected FACTS device, has been widely used to provide smooth and rapid steady state, limit transient voltage, and improve the power system stability and performance by absorbing or injecting reactive power. However, the influence ability depends on its placement, control signal, and place of receiving-signal in the network. In order to satisfy these issues, this paper proposes a method for optimal setting and signal position of the STATCOM into the multi-machine power systems with the aim for damping the electromechanical oscillations. This method is developed from the energy approach based on Gramian matrices considering multiple tasks on the Lyapunov equation, in which the observability Gramian matrix is used to seek an optimal location for STATCOM placement. The another is the controllability one used to determine the best local input signal placement that is chosen as a feedback signal for the power oscillation damping (POD) of STATCOM. In addition, the Krylov-based model reduction method is introduced to shorten the calculation time. The proposed method has been verified on the IEEE 24-bus system by analyzing the small-signal stability to search several feasible placements, and then the transient stability is analyzed to compare and determine an optimal placement through testing various cases. The obtained result is also compared with other optimal method.

Comparing strategies to damp electromechanical oscillations through STATCOM with multi-band controller

Scope of this paper is to present a design process of a supervisory control scheme that optimally coordinates a parallel operation of FACTS devices and an HVDC link to synchronously counteract inter-area oscillations in a power system. The control system is based on Linear Quadratic Gaussian (LQG) optimal control theory. The scheme provides coordinating control signals to the power electronic devices to coherently damp electromechanical oscillations inherent in the system. The scenarios considered involve transient disturbances, signal time delays and reduced system inertia. The feasibility of the proposed scheme is validated on a two-area network incorporating HVDC link, TCSC and SVC devices. The modelling was performed in MATLAB and DIgSILENT simulation environments. Main outcome from this research is the demonstration of improved performance and robustness measures achieved by the novel control scheme, utilizing flexible transmission assets to effectively damp power oscillations in inter-connected power systems.

In order to mitigate inter-area oscillations in power systems, a new self-tuning method based on the Lyapunov stability theory is proposed to tune parameters of a proportional-integral-derivative controller. The proportional-integral-derivative controller tuned by this method is implemented in on-line mode in order to enhance the damping of a static synchronous series compensator. In addition, an auto-tuning neuron composed of only one neuron is used to approximate the complex dynamic of a controlled power system. A two-area four-machine power system is used to demonstrate the performance of the proposed approach. All the simulations show that the proposed self-tuning proportional-integral-derivative controller can effectively damp out the inter-area oscillations.