Generator Excitation Control System Research Articles

Computation of Delay-Dependent Stability Regions for Electric Power Systems with Time Delay

Bu çalışma, bir özdeğer izleme yöntemi kullanarak güç sistem dengeleyici (GSD) ve otomatik gerilim regülatörü (OGR) içeren zaman gecikmeli jeneratör uyarma kontrol sisteminin zaman gecikmeleri düzleminde kararlılık bölgesini elde etmeyi ve zaman gecikmesine bağlı kararlılık analizini incelemektedir. Elektrik güç sistemlerinde gerilim ve frekans kararlılığının sürdürülmesi bakımından haberleşme alt yapısına ve ölçme sistemlerine ihtiyaç duyulmaktadır. Ancak, haberleşme alt yapısı ve ölçme sistemlerinden dolayı sistemin dinamik davranışını ve kararlılığını olumsuz etkileyen zaman gecikmeleri meydana gelmektedir. Bu çalışmada, jeneratör uyarma kontrol sisteminin durum denklem modellerini kullanarak özdeğerlerini ve bu özdeğerlere karşılık gelen zaman gecikmesi değerlerini belirleyen bir yöntem kullanılmıştır. Ayrıca, bu gecikme değerleri kullanılarak gecikmeye bağlı bir kararlılık bölgesi elde edilmiştir. Kararlılık analizleri için, GSD ve OGR içeren tek makineli sonsuz baralı (TMSB) bir güç sistemi seçilmiştir. Gecikmeye bağlı kararlılık bölgelerinin doğruluğu, zaman düzleminde gerçekleştirilen benzetim çalışmaları ve zaman gecikmeli sistemlerin köklerini kompleks düzlemde hesaplayan QPmR (the quasi-polynomial mapping-based root finder) algoritması ile gösterilmiştir.

Research on excitation system of synchronous generator

With the rapid development of power grid, large capacity units are continuously put into operation, which makes the small interference. This paper analyzes the influence of different regulation modes of AC exciter excitation system on the performance of generator excitation control system, demonstrates that PID excitation regulation can effectively improve the quality of excitation control, and simulation test is an effective measure to adjust the parameters of excitation system.

Delay margin computation of generator excitation control system by using fractional order controller

This article is devoted to stability analysis of generator excitation control system that has some time delay with fractional order proportional integral derivative controller by using direct method. When the time delay exceeds certain critical values, the excitation control system becomes unstable. In order to obtain more delay margin, in control part of the system, fractional order proportional integral derivative controller is used. A formulation is obtained to find out the maximum time delay which is known as delay margin with which the system can tolerate without any loss in its stability. All the possible stability regions analytically in the parametric space of the time delay is obtained by using an exact method and it is presented in this study. The method is formulated in frequency domain. The time-domain simulations are implemented to validate theoretical delay margin results in Matlab/Simulink. When it is compared with previous researches in literature, better stability margin is obtained. The results have shown that fractional order PID controller gives wide stability area than integer order PID controller.

Stability analysis of damping compensated generator-excitation control system with time-varying delays

In this paper, a simplified analysis procedure is presented to ascertain delay-dependent stability of a typical damping compensated closed-loop generator-excitation control system operated in a smart grid environment. In closed-loop control of dynamic systems, it is inferred that the use of smart grid technology encompassing complex sensor/measurement circuits, signal conditioning systems, and data transfer through open communication links as feedback loops introduces time-delays in the feedback path. These delays are time-varying in nature, and invariably they exert a destabilising effect to the overall performance of the closed-loop system. Using Lyapunov-Krasovskii functional approach combined with appropriate inequalities, a less conservative analysis is presented in this paper to assess delay-dependent stability of the generator-excitation control system under study. The derived stability criterion is expressed as a set of solvable linear matrix inequality (LMI) conditions so that they can be solved readily using standard numerical packages. Using a standard bench-mark system, the proposed analysis is validated through simulation studies.

Stability analysis of damping compensated generator-excitation control system with time-varying delays

Stability analysis of damping compensated generator-excitation control system with time-varying delays

A Discrete Delay N-decomposition Approach for Delay-Dependent Stability of Generator Excitation Control System with Constant Communication Delays

<p>This paper deals with problem of delay in stability analysis of network controlled generator excitation system. Delays exist in communication channel in network based control between system and controller. A discrete delay N-decomposition is used to compute delay margin for generator excitation system with constant delay which is easier when compared to analytical method. A Lyapunov krasovskii function is constructed for given time delay generator excitation system and linear matrix inequalities techniques are used. Generator excitation system is employed with proportional integral controller, delay margin calculated for various values of gain of proportional integral controller. Theoretically obtained results are verified using simulation studies.</p>

Delay-Dependent Stability of Networked Generator-Excitation Control Systems: An LMI based Approach∗∗This work was carried out at the Dept. of Electrical and Electronics Engineering, Pondicherry Engineering College, Puducherry 605014.

Abstract In this paper, using Lyapunov-Krasovskii functional approach combined with Wirtinger inequality, a less conservative stability criterion (sufficient condition) in linear matrix inequality (LMI) framework is presented for ascertaining the delay-dependent stability of a network controlled generator-excitation control system. A PI controller based generator-excitor control system (Automatic Voltage Regulator (AVR)) with time-invariant feedback loop delays is considered for the stability analysis. The delay-dependent stability problem is formulated by mathematically modeling of the closed-loop system as a linear retarded continuous-time delay-differential equation with incremental system variables as state variables. Subsequently, by using the LMI based stability criterion, maximum allowable bound of the network delay that the closed-loop system can accommodate without losing stability is computed for various subset of the controller parameters. The effectiveness of the proposed result is validated on a bench-mark AVR system with simulation results.

Effect of load increase and power system stabilizer on stability delay margin of a generator excitation control system

This paper studies the impact of load increase and a power system stabilizer (PSS) on the stability delay margin of a single-machine-infinite-bus system including an automatic voltage regulator. An analytical method is proposed to determine the stability delay margin of the excitation control system. The proposed method first eliminates transcendental terms in the characteristic equation of the excitation system without making any approximation and transforms the transcendental characteristic equation into a regular polynomial. The key result of the elimination process is that the real roots of the new polynomial correspond to the imaginary roots of the transcendental characteristic equation. With the help of the new polynomial, it is also possible to determine the delay dependency of system stability and the root tendency with respect to the time delay. Delay margins are computed for various loading conditions and PSS gains. It is observed that the delay margin generally decreases as the PSS gain and load demand increase, resulting in a less stable system.

Computation of Stability Delay Margin of Time-Delayed Generator Excitation Control System with a Stabilizing Transformer

This paper investigates the effect of time delays on the stability of a generator excitation control system compensated with a stabilizing transformer known as rate feedback stabilizer to damp out oscillations. The time delays are due to the use of measurement devices and communication links for data transfer. An analytical method is presented to compute the delay margin for stability. The delay margin is the maximum amount of time delay that the system can tolerate before it becomes unstable. First, without using any approximation, the transcendental characteristic equation is converted into a polynomial without the transcendentality such that its real roots coincide with the imaginary roots of the characteristic equation exactly. The resulting polynomial also enables us to easily determine the delay dependency of the system stability and the sensitivities of crossing roots with respect to the time delay. Then, an expression in terms of system parameters and imaginary root of the characteristic equation is derived for computing the delay margin. Theoretical delay margins are computed for a wide range of controller gains and their accuracy is verified by performing simulation studies. Results indicate that the addition of a stabilizing transformer to the excitation system increases the delay margin and improves the system damping significantly.

Research on DSP-Based Automatic Excitation Regulator in Small Rural Hydropower Station

Excitation regulator has played an important role to ensure that generator run safely and stably. However, in some remote areas, the rural small generator excitation control system is very backward, and it has hindered the development of Chinese agriculture and the pace of new countryside construction. This paper introduced a kind of structure and basic principle of DSP-based automatic excitation regulator, which was applied to rural small generator. We chose TMS320LF2407A chip as the core of regulator control system; the regulator adjusted PWM based on PID control strategy to control the exciting current. The theoretical analysis showed that the regulator had the characteristics of simplicity and reliability, well dynamic and static characteristics, and it could also adjust its own state quickly. The result was applicable to small rural hydropower station.

Models of generator excitation control systems in dynamic security analyses of electric power interconnections

This paper presents models of generator excitation control systems used in dynamic security analyses of electric power interconnections. The general structure and functional block diagram of generator excitation control systems are given, as well as a review of the current state within the electrical power system of Serbia. The model used for analyses of short-term dynamics where transient stability analyses are dominant, has been presented. The model used in the analyses of long-term dynamics, has also been presented. After verification based on experimental measurements, these models have been incorporated into appropriate computer programs for dynamic security analyses of electric power interconnections. These computer programs have been developed at the 'Nikola Tesla' Institute and some typical examples of their application have been provided.

Design and Construction of Pic-Based Excitation Control System for Generator

The main objective of this PIC-based excitation control system is to control the terminal voltage by adjusting the generator exciter voltage. Unlike the conventional control system, the PIC-based excitation control system is constructed to reduce the number of components and thus the amount of design work and wiring required for the system. As a consequence, this is constructed to be low cost and high performance. In this work, this design is based on the construction of switched mode power supply (SMPS). MOSFET IRF840 is used as switching element to control the field excitation through the field coil. PIC16F628 microcontroller is used as excitation controller and performs the modulator function in firmware. In this modulator function, Pulse Skipping Modulation (PSM) which generates train of pulses to turn IRF840 (switching device) on/off in order to reach the desired output voltage of the generator is used. In the PIC-based excitation control system, PIC microcontroller senses the feedback voltage and compares this voltage with reference voltage by using onboard reference and two comparators. In this control system, PIC microcontroller generates a train of pulses to turn MOSFET (IRF840) on/off to control the field excitation of the generator. This excitation control system provides 10% voltage regulation from no load and provides the continuous maximum current up to 8A at maximum rating of 32, 63, 125 and 250 Vdc.

A Field Test of Diesel Generator Excitation Control System Using Real Time Simulator

The excitation control system of an emergency diesel generator is classified as a kind of safety-related system. Compared with other control systems in a power plant, this system is required to be more reliable and have better performance. KEPCO Research Institute successfully developed the excitation control system for a diesel generator. This paper presents its field test results by using a real time simulator on a nuclear power plant.

Stability analysis of a generator excitation control system with time delays

This paper investigates the effect of time delays on the stability of generator excitation control system. The time delays are due to the use of measurement devices, communication links for data transfer, and controller processing time. The stability with respect to the time delay is theoretically analyzed and a formula to determine the maximum amount of time delay known as delay margin that the system can tolerate without losing its stability is presented. It is found that the excitation control system becomes unstable when the time delay crosses certain critical values, delay margins for stability. The time-domain simulations of Matlab/Simulink are used to validate theoretical delay margin results.

직접 순시전압 제어기법에 의한 동기발전기의 고성능 여자 제어시스템

This paper presents a simple, robust excitation control system for synchronous generator using direct instantaneous voltage control(DIVC) method DIVC method can operate as maximum dynamics of power conversion system without any control gains such as PID controller. And the transient overshoot of generator voltage can be suppressed with a simple time constant. The proposed control scheme is verified by the computer simulation and experimental results in prototype generation system.

ATP modelling and field tests of the ac voltage regulator in the Palmar hydroelectric power plant

This paper presents a detailed description of a synchronous generator excitation control system in the Palmar power plant, Uruguay. It also describes the most important aspects of the Alternative Transients Program (ATP) modelling of the ac voltage regulator and exciter. Some records of time response of the excitation control system to step change in input are included. Some results of ATP simulations of the field tests mentioned before are included. Finally a comparison was made between the obtained results from simulations and those obtained from field tests in order to validate the models developed.

Installation of an integrated turbine-generator control system for a pulp mill

A British Columbian pulp mill had experienced the spiral of death many times when the turbine-generator controls were unable to survive the loss of utility tie-line connections. The mill has two high-efficiency rotary turbine-generator units rated 32.2 MVA each and a heat sink capable of generating 47 MW, approximately 87% of the mill power needs, though only 44 MW was being produced. The mill believed that with a load rejection strategy the mill had the potential to continue operation after the loss of a utility tie. In order to ride through the loss of the utility and to fully utilize the process heat sink, the mill needed to replace the 1960s-era turbine-generator control system supplied by the turbine-generator original equipment manufacturer. A triple modular redundant control system for each unit was installed. These systems integrate turbine governor controls and generator excitation control system in a single digital control. The systems are connected in order to jointly coordinate dispatch of real and reactive power demands and achieve load control for the mill. In a staged test, the mill was able to survive the loss of a utility tie-line, and has increased total generation. The new system completely automates the startup, loading, and synchronizing of both generators.

DSP-BASED H∞ CONTROLLED DIGITAL AUTOMATIC VOLTAGE REGULATOR FOR USE ON ENGINE GENERATOR

This paper presents a DSP-based high performance digital automatic voltage regulator (D-AVR) for use on engine generator. The H∞ control approach is applied to the engine generator excitation control system (ECS) for the purpose of tracking a r.m.s. of sinusoidal ac voltage to a specified value. Since the implementation of the control laws has tended to the digital microprocessor, the paper extends the reformulized H∞ control to the discrete time domain. The design procedure of H∞ based ECS is explained for the purpose of constructing robust, low noise, and high performance tracking system. Simulation and experimental results show that the proposed scheme can supply a high-quality voltage power source in the presence of load disturbance.

Discretization of power system transfer functions

This paper compares two methods for obtaining a discrete-time mathematical model for digital control design of a power system. The usual approach has been to use the shift operator q, or its equivalent z-transform, but this gives numerical difficulties with the small sampling periods which are now becoming usual with modern control hardware. It is shown, by means of the example of the identification of a generator excitation control system, that these problems can be avoided by the use of the delta operator /spl delta/ instead. Calculations show that the /spl delta/-operator formulation also reflects the frequency and dynamic response of the system more accurately and conveniently.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Development of advanced generator excitation control regulator (PSVR) for improving voltage stability of a bulk power transmission system

Earlier generator excitation control systems were based on AVR control of generator terminal voltage. This system cannot accommodate reactive power up to the facility limit even when the power system voltage decreases to the limit for stable operation. An attempt was made to develop an advanced excitation control system (PSVR) to achieve higher constant sending end voltage of power stations. The intent was to apply the system to the generator connected to a 500-kV system which contributes most effectively to the voltage stability of a bulk power transmission system. This PSVR produces higher control gains than the AVR, and the following functions were adopted: (1) AVR gain reduction circuit; (2) phase compensation circuit; and (3) damping improvement by enlarging the limiter of the PSS. In addition, various functions were provided, e.g., voltage slope characteristics to balance the reactive power of adjacent generators and PSVR output and terminal voltage limiter to stabilize the generator operation. Before application to a real system, a transient response test was performed by combining the PSVR and a generator simulator to verify the damping improvement and stability of the voltage control.