Thesis-1: Automatic Generation Control (AGC) – Part_1

Posted: June 26, 2012 in Electrical Engineering, Electrical Thesis, Thesis Papers
Tags: , , , , , , , , ,

This is a thesis of a recently passed Electrical Engineer (secret name). I’ll publish it sequentially. May be it will be published in 7/8 parts and this is the 1st one. Here is the 1st chapter of the thesis. I’ll publish a chapter in each part. Let us start with chapter 1….


1.1.   Introduction

Modern power system networks are required to carry more power to meet the ever-growing demand of electrical energy. As the construction of new transmission facilities is time consuming and expensive, the existing transmission corridors are often required to transmit increasingly more amount of power remote generation points to consumption points over a long distance.

Successful operation of a power system depends largely on the engineer’s ability to provide reliable and uninterrupted service to the loads. The reliability of the power supply implies much more than merely being available. Ideally, the loads are fed at constant voltage and frequency at all times. In practical terms this means that both voltage and frequency must be held within tolerance so that consumer’s equipment may operate satisfactorily. We discuss about frequency.

The primary function of an electric power system is to provide the real and reactive power demand by the various load connected to the system. The supplied power, in addition to continuity, must also meet certain minimum requirement in to quality, such as, (a) Constant frequency, (b) Constant voltage and (c) High reliability. Since the power system is a complex quantity, it is important to observe that changes in the real power output of electric generator affect, essentially, only the frequency, and changes in the reactive power affect, essentially, only the voltage in the system. The problem of controlling the reactive power balance in the system is often referred to as ‘the excitation control’ [1, 4].


1.2.   Automatic Generation Control (AGC)

If the load on the system is increased, the turbine speed drops before the governor can adjust the input of the stream to the new load. As the change in the value of speed diminishes, the error signal becomes smaller and the position of the governor fly balls gets closer to the point required to maintain a constant speed. However, the constant speed will not be the point, and there will be an offset. One way to restore the speed or frequency to its nominal value is add an integrator. The integral unit monitors the average error over a period of time and will overcome the offset. Because of its ability to return a system to its point, integral action is also known as the reset action. Thus as the system load changes continuously, the generation is adjusted automatically to restore the frequency to the nominal value. This scheme is known an the automatic generation control (AGC) [5].

1.3. Theory of This Research

The power oscillations occur when there are system disturbances such as sudden load-changes or faults. The damping of the system must be such that the synchronous generators can of the transmission line experiences sudden load perturbations, the generators need continuous control to suppress undesirable oscillations in the system [4, 13].

In electric generation, system disturbances caused by the load fluctuations result in changes to the desired frequency value. Load frequency control (LFC), or Automatic generation control (AGC), is very important issue in power system operation and control for supplying sufficient and both good quality and reliable electric power [13].

There are many investigations in the area of Automatic Generation Control (AGC) of an isolated power system have been reported and number of control strategic have been proposed to achieve improved system performances by the researches in the past [13, 2]. Due to the nonlinearities of various components of power systems, a linear model obtained by linearization around an operating point is usually adopted for the controller design. However because of the inherent characteristics of changing loads, the operating point of a power system may change very much during a daily cycle [13].

Most of them adopt a simplified approach. Investigations have that following sudden load change in a single power system the frequency undergoes a fluctuation which persists for a very long time. This fluctuation is very poorly damped. Since these oscillations are the result of imbalance of power [16, 12]. Automatic generator control adjusts the generation automatic to restore the frequency to the nominal value as the system load changes continuously [2].

The first attempt to control the frequency was via the flywheel governor of the synchronous machine, and was found to be insufficient. Then a supplementary control was added to the governor by means of a single directly proportion to frequency deviation plus it’s integral. The proportional plus integral control scheme constitutes the classical approach to the automatic generation control of power systems.

The proportion integral control is successful in achieving zero stead-state error in the frequency of the system, but exhibits relatively poor dynamic performance as evident by large overshoot and transient frequency oscillations. Moreover the transient settling time is relatively large. The application of optimal control techniques, the controller design normally based on a fixed parameter model of the system derived by a linearization process. Power system parameter is a function of the operating point. Therefore, as the operating control change system performance with controllers designed for a specific operating point most likely will not be satisfactory. Fixed integral gain control performance over a wide range off nominal operating conditions. The variable gain is applied then small overshoot and transient frequency less oscillations.

1.4. Objective of This Research

The main purpose of this research is to propose some variable gain control of AGC of single area power system. Transient performance of the system can be greatly improved and overshoot of the transient frequency deviations can be reduction by a variable parameter of intelligent controllers [3].

In this research, some comprehensive variable intelligent controllers for an AGC have to propose to restore the frequency automatically to the nominal value there is a change in the system load. The main objectives of this research are given below:

  1. At first generator load control loops
  2. Next, power system control
  3. Then, module of single area power system
  4. Then, Integral Gain control of Automatic Generation Control (AGC)
  5. Finally, Adaptive  fuzzy logic controller

1.5. Organization of This Research

Power system load are sensitive to frequency and the aggregate load change follows the frequency deviation. When a generator unit is tripped or additional load is added to the system, the power mismatch is initially compensated by an extraction of kinetic energy from the system inertial storage that causes a system frequency drop. As the frequency decreases the power consume by the loads also decreases. Equilibrium for large system can be obtained when the frequency sensitive reduction of loads balances the power output of the tripped unit. This effect could stop the frequency decline in less than couple of seconds.

This automatic adjustment of generation by free governor action is known as primary frequency regulation. The objective of the follow up control especially under normal change of load, are to return frequency to schedule, to minimize production cost, and to operate the system at an adequate level of security. Automatic Generation Control (AGC) (also know as secondary frequency regulation) is a closed-loop control system that partially replaces this manual control.

This form of generation control has become essential to the real-time operation and control of isolated and of interconnected power systems and operates in widely varying power system control environment ranging from autonomous to strongly interconnected systems with hierarchic multi-level control.

Chapter 2, There is a brief discussion about a general overview of the load dependency and control loop system (P-f and Q-V). The relationship between load and real power i.e. frequency is described. Also short notes about the interaction among P-f and Q-V control loops are given.

Chapter 3, Represents power system modeling. In this chapter, generator model, load model, governor model, turbine model are described in details.

Chapter 4, Illustrates the single area power system with uncontrolled and controlled case elaborately. The dynamic equations of the single area power system are given in state-space form in this chapter.

Chapter 5, In this chapter discusses constant gain KI of Automatic Generation Control, variable gain KI of Automatic Generation Control, Compare between constant and variable gain, Effect of Variable Load.

And much more things are added in this thesis paper….

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