The **UPFC** is installed for the purpose of multiple control functions, one of which will be the suppression of **low**-**frequency** **oscillations** occurring in the system. In literature [3-6] the effectiveness of improving the oscillation **damping** by a FACTS **supplementary** **damping** **controller** has been explored. Various feedback signals namely, deviation in generator rotor angle, deviations in real **power** flow through the transmission line, accelerating **power**, have been identified as capable of contributing direct electric **damping** torque to the electromechanical oscillation loop of the generator. The selection criteria chosen in these works consider the control cost, robustness of the feedback signal to variations of system operating conditions and local availability of signal. A judicious selection of the feed back signal can be done **based** on its capability in improving the **damping** of desired mode of oscillation. This work considers the deviation in rotor angle as input signal for the single machine infinite bus system aiming at improving the local mode of oscillation and the locally available **power** flow through the transmission line at which **UPFC** is connected, aiming at improving the poorly damped oscillation mode for the case of multi-machine. Thus these signals are capable of generating efficient database for the training of adaptive **controller**.

Show more
18 Read more

The eect of an Interline **Power** Flow **Controller** (IPFC) on **damping** **low** **frequency** **oscillations** has been implied in some papers, but has not been investigated in detail. This paper investigates the **damping** control function of an interline **power** ow **controller** installed in a **power** system. For this purpose, a single machine-innite bus model, integrated with IPFC, is used and the linearized model is established. Using this model, the Phillips-Heron model of the system for steady state digital simulations is derived. In this paper, the numerical results are presented using the MATLAB simulink toolbox, which shows the signicant eect of IPFC on **damping** inter-area **oscillations**.

Show more
The Benefits of Flexible AC Transmission **Systems** (FACTs) usages to improve **power** **systems** stability are well known [1], [2]. The growth of the demand for electrical energy leads to loading the transmission system near their limits. Thus, the occurrence of the LFO has increased. FACTs controllers has capability to control network conditions quickly and this feature of FACTs can be used to improve **power** system stability. The **UPFC** is a FACTS device that can be used to the LFO. The primarily use of **UPFC** is to control the **power** flow in **power** **systems**. The **UPFC** consists of two voltage source converters (VSC) each of them has two control parameters namely me, δe, mb and δb [3]. The **UPFC** used for **power** flow control, enhancement of transient stability, mitigation of system **oscillations** and voltage regulation [3]. A comprehensive and systematic approach for mathematical modeling of **UPFC** for steady-state and small signal (linearized) dynamic studies has been proposed in [4-7]. The other modified linearized Heffron-Philips model of a **power** system installed with **UPFC** is presented in [8] and [9]. For **systems** which are without **power** system stabilizer (PSS), excellent **damping** can be achieved via proper **controller** design for **UPFC** parameters. By designing a suitable **UPFC** **controller**, an effective **damping** can be achieved. It is usual that Heffron-Philips model is used in **power** system to study small signal stability. This model has been used for many years providing reliable results [10].

Show more
The Benefits of Flexible AC Transmission **Systems** (FACTs) usages to improve **power** **systems** stability are well known [1]. The growth of the demand for electrical energy leads to loading the transmission system near their limits. Thus, the occurrence of the LFO has increased. FACTs controllers has capability to control network conditions quickly and this feature of FACTs can be used to improve **power** system stability. The **UPFC** is a FACTS device that can be used to the LFO. The **UPFC** consists of two voltage source converters (VSC) each of them has two control parameters namely m e , δ e , m b and δ b [2]. The **UPFC** used for **power** flow

Show more
on transmission lines [9]. SVC controls reactive **power** by controlling the susceptance of passive devices. System voltage is controlled by controlling the reactive **power** and hence indirectly active **power** is controlled which results in **damping** of electromechanical **oscillations** [10-15]. **Damping** of electromechanical **oscillations** can be achieved through designing of appropriate external control for SVC. Proportional Integral (PI) and Proportional Integral Derivative (PID) controllers are the most frequently used conventional techniques available as an SVC external control. PI **controller** is the other commonly used scheme [16, 17]. Although the PI controllers present ease and simplicity of design, but their operating condition becomes less effective when the system conditions vary extensively or large disturbances take place [18]. To circumvent these drawbacks, recently, Fuzzy Logic Controllers (FLCs) and Artificial Neural Network Controllers (ANNCs) have been used for **oscillations** **damping** control in the **power** **systems** [19-23]. But majority of these artificial intelligence **based** control for SVC are designed for linearized **power** system and its control parameters are updated off-line. As **power** system is highly nonlinear and any vagueness in the system can drastically change its operating point. So these linear control designs may not give better performance under such circumstances.

Show more
12 Read more

10 Read more

The dynamic characteristics of system can be influenced by location of eigenvalues, for a good system response in terms of overshoots/undershoot and settling time, a particular location for system eigenvalues is desired depending upon the operating conditions of the system. The **damping** **power** and the synchronizing **power** are related respectively, to real part and imaginary part of eigenvalue that correspond to incremental change in the deviation of the rotor speed and deviation of rotor angle[12], this Eigenvalue is known as electromechanical mode. **Power** oscillation **damping** can be improved if real part of eigenvalue associated with mode of oscillation can be shifted to left-side in complex s-plane as desired. This thesis present **controller** such that the closed loop designed system will have a desired degree of stability [13, and 14]. For the **power** system representation in state – space form, a closed loop gain matrix A-BK obtained by choosing the gain matrix K through state feedback control law U = −KX will have all its eigenvalue lies in left side of complex-plane. It is an easy task to design **power** oscillation **damping** **controller**. Making use of proposed **controller** design approach, **UPFC** **based** **power** oscillation **damping** **controller** is designed to **damping** of **low** **frequency** **power** **oscillations**. This has been attempted on a sample system. The expectation from **UPFC** **based** POD **controller** is to provide instantaneous solution to **power** oscillation **damping**, the settling time as obtained from response of system is expected to be as small as possible. For minimizing settling time real part of eigenvalue corresponding to mode of oscillation are required to be shifted more and more on LHS of complex plane, this will require control effort. There is a hardware limit of any designed **controller**, for the case of **UPFC**, in view of this, the control input parameters m e ,δ e and

Show more
A comprehensive and analytical approach for mathematical modeling of **UPFC** for steady state and linearised dynamic stability has been proposed. Several years the **power** system stabilizer act as a common control approach to damp the system **oscillations**. However, in some operating conditions, the PSS may fail to stabilize the **power** system, especially in **low** **frequency** **oscillations** . It is proved that the FACTS devices are very much effective in **power** flow control as well as **damping** out the swing of the system during fault. Among all FACTS devices the **UPFC** is the most popular **controller** for effective **damping**.

Show more
In recent years, new artificial intelligence-**based** approaches have been proposed to design a FACTS- **based** **supplementary** **damping** **controller**. These approaches include genetic algorithm [4], particle swarm optimization [5], differential evolution [6], and multi-objective evolutionary algorithm [7]. Since 1989, artificial neural networks (ANN) methodology has captured the interest in a large number of applications in electrical **power** engineering [8]. The applications include economical load dispatching, **power** system stabilizers (PSS), etc., The artificial neural network **controller** **based** on fuzzy control (**ANFIS** **controller**) is applied for FACTS device. For the design purpose MATLAB/SIMULINK model of the **power** system with **UPFC** **controller** is developed. Simulation results are presented at different operating conditions and under various disturbances to show the effectiveness of the proposed **controller**. And the results prove that the proposed **UPFC**-**based** **ANFIS** **controller** can improve transient stability and also can damp **power** oscillation more efficient than SSSC.

Show more
11 Read more

data concentrators that can be treated as integral parts of the WAM network. At the control center, the phasor data is first converted into the reference frame inde- pendent (RFI) output quantities (such as active **power**, reactive **power**, and voltage magnitude). In the case of output feedback control [29], [36] [37] [38] [39], the RFI output quantities measured are directly processed through a gain matrix to generate the WAC signals. On the other hand, an intermediate level of state estimation is required in the case of state feedback control [40], [41]. The state feedback **controller** generates WAC signals **based** upon the observable dynamic states of the system. The dynamic states of the system are determined by means of an extended Kalman filter (EKF) [42] or unscented Kalman filter (UKF) [43], [44]. Typically, the dynamic state estimation is carried by using subsystem models; therefore, the EKF/UKF algorithm employed should also have the capacity to dynamically determine the inputs to each subsystem [45]. After generating the WAC signals, those are transmitted to **power** system components (such as generators’ excitation **systems** [24] or FACTS devices [46]) via a WAC network. The implementation of the output feedback control is sim- pler than the implementation of the state feedback control since the former does not require any state estimator. However, the **controller** performance may be superior in the case of the state feedback control. This is because the system condition is more precisely addressed while designing and implementing the state feedback **controller**.

Show more
123 Read more

Abstract: In this paper, use of the additional **supplementary** **damping** **controller** for unified **power** flow **controller** (**UPFC**) to damp out **low** **frequency** **oscillations** in a heavily loaded **power** system is investigated. Normal **damping** controllers are inferior when the **power** system is subjected to large and fast changing loads. In order to handle the situation, an additional **supplementary** **damping** **controller** for **UPFC** is designed using Fuzzy logic technique. The effectiveness of the proposed **controller** on **damping** **low** **frequency** **oscillations** is tested and demonstrated through simulation studies for single machine connected to infinite bus **power** system (SMIB). In addition **power** system response with **UPFC** **damping** **controller** & Fuzzy logic **based** **supplementary** **damping** **controller** (FLSDC) are compared at various loading conditions. It can be concluded that Fuzzy logic **based** **supplementary** **damping** **controller** improves greatly the system stability under heavily loaded conditions.

Show more
suitable remote signals coming from the whole system, as **supplementary** in- puts, for a separate better **damping** of specific inter-area modes, has been de- veloped. Each local PSS **controller** is designed separately for each of the inter- area modes of interest. The PSS **controller** uses only those local and remote input signals in which the assigned single inter-area mode is most observable and is located at a generator which is most effective in controlling that mode. The local PSS **controller**, designed for a particular single inter-area mode, also works mainly in a **frequency** band given by the natural **frequency** of the as- signed mode. The locations of the local PSS controllers are obtained **based** on the amplitude gains of the **frequency** responses of the best-suited measure- ment to the inputs of all generators in the interconnected system. For the se- lection of suitable local and **supplementary** remote input signals, the features or measurements from the whole system are pre-selected first by engineering judgment and then using a clustering feature selection technique. Final selec- tion of local and remote input signals is **based** on the degree of observability of the considered single mode in them.

Show more
154 Read more

The **power** transfer in a coordinated **power** system is compelled by transient stability, voltage soundness and small signal stability. These limitations limit a full use of accessible transmission passageways. Flexible AC Transmission **Systems** (FACTS) are the innovation that gives the required adjustments of the transmission usefulness so as, to completely use the current transmission offices and thus, limiting the gap between as far as possible and thermal limit. Modern **power** system has been connected by means of weak tie lines. **Low** **frequency** electromechanical **oscillations** are experienced among the group of interconnected generators. These **oscillations** create severe hazard to the normal operation of the **power** system. The **oscillations** residing within a plant are called local mode of **oscillations**. The range of **frequency** is in between 0.7– 2.0 Hz. The **oscillations** available in the interconnected **power** system are called inter-area mode **oscillations**. The range of **frequency** is in between 0.1–0.8 Hz. **Power** system stabilizers are also used to damp out **oscillations** and they cause large voltage variations with leading **power** factor operation and loose stability under severe disturbances. Fast development in the field of **power** electronics has opened new opportunities for the exercise of the Flexible AC Transmission System (FACTS) devices. Modulation of bus voltage, phase shift between the buses and the transmission line reactance are used to improve **power** system operation controllability and **power** transfer limits and they can be achieved by FACTS devices.

Show more
In recent years, the fast progress in the field of **power** electronics has opened new opportunities for the **power** industry via utilization of the controllable Flexible AC Transmission System devices like Unified **Power** Flow **Controller** which offer an alternative means to mitigate **power** system **oscillations** [5]. Oscillation Stability analysis and control has been an important subject in **power** system research and applications. The deregulation and competitive environment in the contemporary **power** networks [1, 2] will imply a new scenario in terms of load and **power** flow condition and so causing problems of line transmission capacity. But, nowadays, some problems exist like **power** system oscillation stability & refers to the **damping** of electromechanical **oscillations** occurring in **power** **systems** with oscillation **frequency** in the range of 0.2 Hz. to 2 Hz. These **low**-**frequency** **oscillations** are the consequence of the development of interconnection of large **power** **systems**. A **low** **frequency** oscillation in a **power** system constrains the capability of **power** transmission, threatens system security and damages the efficient operation of the **power** system [4].

Show more
16 Read more

Abstract––**Low** **frequency** electromechanical **oscillations** are inevitable characteristics of **power** **systems** and they greatly affect the transmission line transfer capability and **power** system stability. Traditionally, **power** system stabilizers (PSS) are being used to damp these **oscillations**. Unified **Power** Flow **Controller** (**UPFC**) is a well-known FACTS device that can control **power** flow in transmission lines. It can also replace PSS to damp **low** **frequency** **oscillations** effectively through direct control of voltage and **power**. In this paper a liberalized Philips-Heffron model of a (Single Machine– Infinite Bus) **power** system with a unified **power** flow **controller** is considered. The designed fuzzy-**based** **UPFC** **controller** adjusts four **UPFC** inputs by appropriately processing of the input error signal, and provides an efficient **damping**. The results of the simulation show that the **UPFC** with fuzzy-**based** controllers is effectively **damping** the LFO. Keywords—**Low** **frequency** **Oscillations** (LFO), Unified **Power** Flow **Controller** (**UPFC**), Fuzzy logic, **Damping** **controller**, Flexiable AC transmission System (FACTS)

Show more
The **frequency**-**based** stabilizer is dependent on terminal **frequency** which is derived from terminal current and voltage. Its main advantage is sudden phase shift in transient condition. The improvement of stability under high communication delays is discussed in [18]. The authors of [19], discusses the eigen values of three different **power** system and the accuracy, convergence and consistency of eigen value calculations and alternative methods are discussed. H∞ loop shaping techniques are introduced to design robust PSS for SMIB designing. The selection of weighting functions is shown for the **controller**. Various operating parameters are compared with the conventional model in [20].

Show more
Abstract— This paper presents a systematic procedure for modeling and simulation of a **power** system equipped with FACTS type Gate Controlled Series Compensator (GCSC) **based** stabilizer **controller**. Single Machine Infinite Bus (SMIB) **power** system was investigated for evaluation of GCSC stabilizing **controller** for enhancing the overall dynamic system performance. PSO algorithm is employed to compute the optimal parameters of **damping** **controller**. Eigenvalues of system under various operating condition and nonlinear time domain simulation is employed to verify the effectiveness and robustness of GCSC stabilizing **controller** in **damping** **low** **frequency** **oscillations** (LFO) modes.

Show more
FACTS (Flexible AC Transmission System) technology **based** on high speed **power** electronic devices is intro- duced for the improvement of controllability and opti- mal usage of the existing **power** system capacities. The latest generation of FACTS controllers uses the Solid State Synchronous Voltage Sources (SVS) concept that is introduced by L.Guygyi. The SVS acts like an best alternator means it generates 3-ø balanced voltages of variable phase angle and amplitude having funda- mental **frequency**. Voltage source converters (VSC) are used to implement SVS. In order to damp this in- ter area mode **oscillations** FACTS controllers [1] such as Unified **power** flow controllers(**UPFC**),Static series syn- chronous compensator (SSSC)[5],Static synchronous compensator (STATCOM)[6] etc. are used. The **UPFC** is one of the most flexible device, which is a grouping of SSSC and STATCOM, DC link capacitor acts as com- mon between both shunt and series converters. In this paper, a new control method using unified **power** flow controllers (**UPFC**) along with superconducting mag- netic energy storage system (SMES) [2,3,7,9] using fuzzy logic **controller**

Show more
To have sustainable growth and social progress, it is necessary to meet the energy need by utilizing the renewable energy resources like wind, biomass, hydro, co-generation, etc In sustainable energy system, energy conservation and the use of renewable source are the key paradigm. The need to integrate the renewable energy like wind energy into **power** system is to make it possible to minimize the environmental impact on conventional plant[1]. The integration of wind energy into existing **power** system presents a technical challenges and that requires consideration of voltage regulation, stability, **power** quality problems. The **power** quality is an essential customer- focused measure and is greatly affected by the operation of a distribution and transmission network. The issue of **power** quality is of great importance to the wind turbine [2]. There has been an extensive growth and quick development in the exploitation of wind energy in recent years. The individual units can be of large capacity up to 2 MW, feeding into distribution network, particularly with customers connected in close proximity [3]. Today, more than 28 000 wind generating turbine are successfully operating all over the world. In the fixed-speed wind turbine operation, all the fluctuation in the wind speed are transmitted as fluctuations in the mechanical torque, electrical **power** on the grid and leads to large voltage fluctuations. During the normal operation, wind turbine produces a continuous variable output **power**. These **power** variations are mainly caused by the effect of turbulence, wind shear, and tower-shadow and of control system in the **power** system. Thus, the network needs to manage for such fluctuations.

Show more
generation control scheme in electric **power** **systems**. Among the various types of load **frequency** controllers, the most widely employed is the conventional proportional integral (PI) **controller**. The PI, PID and Fuzzy-PID and **ANFIS** controllers are very simple for implementation and gives better dynamic response, but their performance deteriorate when the complexity in the system increases due to disturbance like load variation . Therefore, there is need of controllers which can overcome these problems. The artificial intelligent controllers like fuzzy and neural control approaches are more suitable in this respect. Literature survey shows that most of earlier work in the area of LFC pertains to interconnected reheat thermal **power** system. In this paper, the performance evaluation **based** on **ANFIS**, Fuzzy-PID and conventional PID for two area thermal interconnected system.

Show more