Thyristor Controlled Series Capacitor Model Research Articles

Modelling and utilisation of frequency responsive TCSC for enhancing the frequency response of a low inertia grid

The objective of this paper is to enhance the frequency resilience and wind penetration level of a low inertia power system by utilising frequency responsive Thyristor Controlled Series Capacitor (TCSC). In recent years, wind power integration has become prolific in numerous power grids around the world. As such, Synchronous Generators (SGs) are being substituted from the generation mix. Unlike conventional synchronous generators, variable speed Wind Turbine Generators (WTGs) generally do not participate in system frequency control without additional control strategy. When subjected to prolific wind generation and interconnection import from an adjacent grid, number of online SGs in a grid can be scant. During such a situation, a large contingency in the power importing zone may overload an AC interconnection. Consequently, the interconnection could trip due to loss of synchronism. It eventually may cause a system-wide blackout. In addition, due to the risk of network separation, non-synchronous wind penetration level is kept restricted in many power systems. To overcome these challenges, this paper proposes a frequency responsive TCSC model to increase interconnection transfer capability by reducing the line reactance. To this end, for determining optimal TCSC parameters, a strategy is outlined. Furthermore, a generalised expression is developed to find the maximum wind penetration level while maintaining the frequency response adequacy. The developed techniques are applied to a low inertia test system. Simulation results reveal that the risk of blackout is averted, and the maximum wind penetration level is significantly increased after deploying the frequency responsive TCSC.

Power flow control of power systems based on a simple TCSC model

Thyristor-Controlled Series Capacitor (TCSC) is used to control the active power flow in transmission lines in the power system to specific values. This paper proposes a simple modeling of TCSC into Newton-Raphson load flow algorithm in order to reduce the complexity and enhance the reusability of the original load flow code. TCSC is represented by two injected loads at the sending and auxiliary buses. These loads are calculated based on the specified active power while the reactive power is calculated based on the systems. The reactive loads are updated during the iterative process until the convergence is achieved. TCSC parameters are calculated based on the voltages of connected buses and the specified active power. This model solves the problem associated with the selection of proper initial values of the TCSC control parameter. The proposed TCSC model is validated using the standard IEEE 14-bus, IEEE 30-bus and IEEE 118-bus test systems.

Fuzzy based damping controller for TCSC using local measurements to enhance transient stability of power systems

This paper proposes a local fuzzy based damping controller (LFDC) for thyristor controlled series capacitor (TCSC) to improve transient stability of power systems. In order to implement the proposed scheme, detailed model of TCSC, based on actual behavior of thyristor valves, is adopted. The LFDC uses the frequency at the TCSC bus as a local feedback signal, to control the firing angle. The parameters of fuzzy controller are tuned using an off-line method through chaotic optimization algorithm (COA). To verify the proposed LFDC, numerical simulations are carried out in Matlab/Simpower toolbox for the following case studies: two-area two-machine (TATM), WSCC three-machine nine-bus and Kundur’s two-area four-machine (TAFM) systems under various faults types. In this regard, to more evaluate the effectiveness of the proposed method, the simulation results are compared with the wide-area fuzzy based damping controller (WFDC). Moreover, the transient behavior of the detailed and phasor models of the TCSC is discussed in the TATM power system. The simulation results confirm that the proposed LFDC is an efficient tool for transient stability improvement since it utilizes only local signals, which are easily available.

Effective oscillation damping of an interconnected multi-source power system with automatic generation control and TCSC

Abstract Stabilizing area frequency and tie-line power oscillations in interconnected power systems are main concerns that have received significant attention in automatic generation control (AGC) studies. This paper deals with modeling and simulation of thyristor controlled series capacitor (TCSC) based damping controller in coordination with AGC to damp the oscillations and thereby, improve the dynamic stability. The contribution of TCSC in tie-line power exchange is formulated analytically for small perturbation and a systematic method based on the Taylor series expansion is proposed for modeling of TCSC based damping controller. The integral gains of AGC and TCSC parameters are optimized simultaneously using an improved particle swarm optimization (IPSO) algorithm through minimizing integral of time multiplied squared error (ITSE) performance index. The performance of the proposed TCSC–AGC coordinated controller is compared with case of AGC alone. A two-area interconnected multi-source power system, including TCSC located in series with the tie-line, is studied considering nonlinearity effects of generation rate constraint (GRC) and governor dead band (GDB). Simulation results show that proposed controller shows greater performance in damping of the oscillations and enhancing the frequency stability. Furthermore, sensitivity analyses are carried out against system loading condition, parametric uncertainties, and different perturbation patterns to show the robustness of TCSC–AGC.

Adaptive RTRL based neurocontroller for damping subsynchronous oscillations using TCSC

Modern interconnected electrical power systems are complex and require perfect planning, design and operation. Hence the recent trends towards restructuring and deregulation of electric power supply has put great emphasis on the system operation and control. Flexible AC transmission system (FACTS) devices such as thyristor controlled series capacitor (TCSC) are capable of controlling power flow, improving transient stability and mitigating subsynchronous resonance (SSR). In this paper an adaptive neurocontroller is designed for controlling the firing angle of TCSC to damp subsynchronous oscillations. This control scheme is suitable for non-linear system control, where the exact linearised mathematical model of the system is not required. The proposed controller design is based on real time recurrent learning (RTRL) algorithm in which the neural network (NN) is trained in real time. This control scheme requires two sets of neural networks. The first set is a recurrent neural network (RNN) which is a fully connected dynamic neural network with all the system outputs fed back to the input through a delay. This neural network acts as a neuroidentifier to provide a dynamic model of the system to evaluate and update the weights connected to the neurons. The second set of neural network is the neurocontroller which is used to generate the required control signals to the thyristors in TCSC. This is a single layer neural network. Performance of the system with proposed neurocontroller is compared with two linearised controllers, a conventional controller and with a discrete linear quadratic Gaussian (DLQG) compensator which is an optimal controller. The linear controllers are designed based on a linearised model of the IEEE first benchmark system for SSR studies in which a modular high bandwidth (six-samples per cycle) linear time-invariant discrete model of TCSC is interfaced with the rest of the system. In the proposed controller, since the response time is highly dependent on the number of states of the system, it is often desirable to approximate the system by its reduced model. By using standard Hankels norm approximation technique, the system order is reduced from 27 to 11th order by retaining the dominant dynamic characteristics of the system. To validate the proposed controller, computer simulation using MATLAB is performed and the simulation studies show that this controller can provide simultaneous damping of swing mode as well as torsional mode oscillations, which is difficult with a conventional controller. Moreover the fast response of the system can be used for real-time applications. The performance of the controller is tested for different operating conditions.

Output feedback SSR damping controller design based on modular discrete-time dynamic model of TCSC

This paper presents the use of a modular, sample invariant, six samples per cycle, discrete-time model of a thyristor controlled series capacitor (TCSC) for output feedback-based subsynchronous resonance (SSR) damping controller (SSDC) design. An SSDC is used to alleviate the instability of torsional modes caused by external fixed capacitors used in conjunction with a TCSC. It is found that damping torque analysis-based design of an SSDC using a non-local signal like generator slip is straightforward and the resulting SSDC has a simple compensator structure. On the other hand, the residues and pole-zero configuration with the line current magnitude as a feedback signal are such that it is relatively more difficult to obtain a robust design, especially if several subsynchronous torsional modes are present. Eigenvalue analysis and digital simulation studies indicate that the TCSC model can accurately predict the behaviour of a TCSC with and without a damping controller.

Analytical Modeling of TCSC Dynamics

This paper presents an analytical, linear, state-space model of a thyristor-controlled series capacitor (TCSC). First, a simplified fundamental frequency model of TCSC is proposed and the model results are verified. Using frequency response of the nonlinear TCSC segment, a simplified nonlinear state-space model is derived, where the frequency of the dominant TCSC complex poles shows linear dependence on the firing angle. The nonlinear element is linearised and linked with the ac network model and the TCSC controller model that also includes a phase-locked-loop (PLL) model. The model is implemented in MATLAB and verified against PSCAD/EMTDC in the time and frequency domains for a range of operating conditions. The model is sufficiently accurate for most control design applications and practical stability issues in the subsynchronous range.

Modeling and simulation of SVC and TCSC to study their limits on maximum loadability point

This paper presents the steady-state modeling of static var compensator (SVC) and thyristor controlled series capacitor (TCSC) with their control and limits. Handling of limits and control mode switching are presented and discussed. Bifurcation analysis is applied in order to find the optimal location and rating of these devices and a continuation power flow is used to evaluate the effects of these devices on system loadability. Eigenvector analysis applied at the maximum loading point is used to rank the most critical voltage buses. After that, it would be possible to optimize location, sizing and control modes of SVC and TCSC in order to achieve maximum enhancement of system loadability. The models and methodology for placing and designing SVC and TCSC are tested in a 173 bus AC/DC system. Performance factors are defined to evaluate the efficiency of SVC and TCSC on different conditions.

Resistive Behavior of Thyristor-Controlled Series Capacitors at Subsynchronous Frequencies

The thyristor-controlled series capacitor (TCSC) does not have resistive main components in ideal form. Yet, a resistive behavior has been reported at subsynchronous frequencies for this device. The paper investigates the source of this resistance and suggests a way to compute it when a periodic steady state can be found or approximated for the test circuit. The results are compared with two methods proposed by other research groups, one for frequency response and the other for dynamic modeling of TCSC, which are also examined as to their treatment of the resistive behavior. Finally, three open-loop firing schemes are compared with respect to the impedance they present to subsynchronous currents.

Modeling and simulation of SVC and TCSC to study their limits on maximum loadability point

This paper presents the steady state modeling of static var compensator (SVC) and thyristor controlled series capacitor (TCSC) with their control and limits. Handling of limits and control mode switching are presented and discussed. Bifurcation analysis is applied in order to find the optimal location and rating of these devices and a continuation power flow is used to evaluate the effects of these devices on system loadability. Eigenvector analysis applied at the maximum loading point is used to rank the most critical voltage buses. After that, it would be possible to optimize location, sizing and control modes of SVC and TCSC in order to achieve maximum enhancement of system loadability. The models and methodology for placing and designing SVC and TCSC are tested in a 173 bus AC/DC system. Performance factors are defined to evaluate the efficiency of SVC and TCSC on different conditions.

A review of a quasi-static and a dynamic TCSC model

Two major thyristor controlled series capacitor (TCSC) models are reviewed and a comparison based on digital simulation is carried out showing the steady state reactance and the dynamic behavior obtained with them. Some simpler and equivalent expressions are developed.

A study of thyristor controlled series capacitor models for power system stability analysis

The thyristor-controlled series capacitor (TCSC) is promising as a powerful device to increase power transfer capability and transient stability. The basic configuration of the TCSC consists of a series of capacitors connected antiparallel with thyristor-controlled reactors, so that firing angle control of the thyristors makes the TCSC capable of achieving impedance control in a wide range with quick response. It is important to clarify the relationship between the fundamental reactance of the TCSC and the firing angle of the thyristors, thus leading to practical applications of the TCSC for enhancement of power transfer capability and transient stability in transmission lines. Two relationship equations for the TCSC's fundamental reactance have already been proposed. One is the relationship equation derived from a TCSC circuit whose source is a voltage. The other is the relationship equation derived from a TCSC circuit whose source is a current. For TCSC installed in a transmission line, it is clear which equation is more adequate for analyzing power system stability. In this paper, the authors determine whether either of the equations is valid for analyzing a power system stability. 1. In the steady state, the TCSC fundamental reactance is analyzed and compared with the two equations and EMTP. It is clear that the TCSC reactance based on current source is adequate. 2. The swing angle of a generator when the firing angle is stepped up is analyzed with EMTP and an analytical model using the TCSC model based on current source. It is shown that the proposed model is effective for power system stability analysis. © 1999 Scripta Technica, Electr Eng Jpn, 129(1): 20–28, 1999

SSR analysis with dynamic phasor model of thyristor-controlled series capacitor

In their previous work, the authors have studied the phasor dynamics of thyristor-controlled series capacitors (TCSCs), and derived associated models for studying power swing oscillations in power systems. This paper presents the use of a dynamic phasor model of the TCSC in studies of subsynchronous resonance (SSR). Their earlier dynamic phasor models of the TCSC are further simplified here, and tested at typical subsynchronous frequencies. The phasor model of the TCSC is directly compatible with the conventional models used for the other system components relevant to SSR. The proposed approach to SSR analysis is an attractive alternative to approaches based on sampled-data models, and to torque-per-unit-velocity methods. The dynamic phasor approach has been tested on the IEEE first benchmark SSR model, showing outstanding agreement with more computationally demanding alternative methods for eigenvalue analysis.

Loop current characteristics of a thyristor-controlled series capacitor

This paper presents the results of an investigation on the loop current of a thyristor-controlled series capacitor (TCSC). The knowledge of loop current characteristics is important for understanding analytically the equivalent impedance of TCSC, estimating harmonics produced by TCSC, and determining ratings of the TCSC circuit components. However, little has been written on the loop current of TCSC circuit. Therefore, using a laboratory-scale TCSC installed on a laboratory power system, the TCSC currents and voltages were measured and analyzed to investigate the behavior of loop current. A mathematical model of TCSC was also developed to compare to the experimental results and further clarify the relationship between loop current and steady-state impedance characteristics, including effects of TCSC circuit component size on the characteristics. Capacitor voltage harmonics and their impact on the power system were also investigated. ©1998 Scripta Technica, Electr Eng Jpn, 125(1): 37–46, 1998

系統安定度解析のためのサイリスタ制御直列コンデンサモデルの検討

The thyristor-controlled series capacitor (TCSC) is promising as a powerful device to increase power transfer capability and transient stability. The basic configuration of the TCSC consists of a series of capacitors connected antiparallel with thyristor-controlled reactors, so that firing angle control of the thyristors makes the TCSC capable of achieving impedance control in a wide range with quick response. It is important to clarify the relationship between the fundamental reactance of the TCSC and the firing angle of the thyristors, thus leading to practical applications of the TCSC for enhancement of power transfer capability and transient stability in transmission lines. Two relationship equations for the TCSC's fundamental reactance have already been proposed. One is the relationship equation derived from a TCSC circuit whose source is a voltage. The other is the relationship equation derived from a TCSC circuit whose source is a current. For TCSC installed in a transmission line, it is clear which equation is more adequate for analyzing power system stability. In this paper, the authors determine whether either of the equations is valid for analyzing a power system stability. 1. In the steady state, the TCSC fundamental reactance is analyzed and compared with the two equations and EMTP. It is clear that the TCSC reactance based on current source is adequate. 2. The swing angle of a generator when the firing angle is stepped up is analyzed with EMTP and an analytical model using the TCSC model based on current source. It is shown that the proposed model is effective for power system stability analysis. © 1999 Scripta Technica, Electr Eng Jpn, 129(1): 20–28, 1999