GUJARAT TECHNOLOGICAL UNIVERSITY
GOVERNMENT ENGINEERING COLLEGE
A Project Report
“AUTOMATIC GENERATION CONTROL IN Restructure Power System”
BE Semester – IV
Sr. No Name of Student Enrollment Number
1 Surati Nirmit 150600109059
2 Upadhyay Prem 150600109062
3 Darji Ayush 150600109014
4 Pancholi Dhaval 150600109022
Prof. A. N. Christian Sir COURSE CO-COORDINATOR
Prof. N.S.Desai HEAD OF THE DEPARTMENT
Table of contents
List of Figures
Chapter 1 Introduction to Automatic Generation Control 1
1.1 Basics about AGC 1
1.1.1 Generator model 1
1.1.2 Load model 2
1.1.3 Prime-mover model 3
1.1.4 Governor model 3
1.1.5 Tie-line model 4
Chapter 2 Restructured Power System 8
2.1 Vertically Integrated Utility Structure 8
2.2 Structure of Deregulated Industry 9
2.2.1 Different entities in deregulated environment 2.3 Reasons for restructuring 10
2.4 Traditional vs. Restructured Scenario 2.5 Concept of DISCO Participation Matrix (DPM) Chapter 3 Simulation of Automatic Generation Control 12
3.1 MATLAB model of AGC 12
3.2 Results for different cases 13
3.2.1 Case 1: Application of 0.1 Pu Mw load change at time t=0 sec 13
3.2.2 Case 2: Application of 0.2 Pu Mw load change at time t=0 sec 15
3.2.3 Case 3: Application of 0.2 Pu Mw load change at time t=1 sec
3.2.4 Case 4: Application of 0.1 Pu Mw load change at time t=2 sec
: Chapter 4 Future scope 19
Modern power system consists of a number of utilities interconnected together and power is exchanged between utilities over the tie-lines by which they are connected. In order to achieve the interconnected operation of a power system, an electric energy system must be maintained at a desired operating level characterized by nominal frequency, voltage profile and load flow configuration. This is achieved by close control of real and reactive powers generated through the controllable sources of the system. Automatic Generation Control (AGC) plays a significant role in the power system for close control of real power by maintaining scheduled system frequency and tie-line power flow during normal operating condition and also in the event of load perturbations. The traditional AGC two-area system is modified to take into account the effect of bilateral contracts on the dynamics. The concept of DISCO participation matrix to simulate these bilateral contracts is introduced and reflected in the two-area block diagram. In this minor project report responses for state variables subject to load perturbations is optimized using optimal control design.
LIST OF FIGURES
1.1 Mechanical and electrical torques in a generating unit
1.2 Relationship between Mechanical and electrical power and speed change
1.3 Block diagram of rotating mass and load as seen by prime-mover output
1.4 Prime-mover model
1.5 Prime-mover – generator – load model
1.6 Isochronous governor
1.7 Governor with speed-droop feedback loop
1.8 Block diagram of governor with droop
1.9 Block diagram of governor, prime-mover and rotating mass
1.10 Block diagram of inter connected areas
2.1 Vertically Integrated Industry
2.2 Deregulated Industry
2.3 Schematic of two-area system in restructured environment
3.1 MATLAB model of two-area AGC system
3.2 Results for case-1
3.3 Results for case-2
3.4 Results for case-3
3.5 Results for case-4
Introduction to automatic generation control
1.2 Basics about AGC
1.2.1 Generator model
(Fig.1.1: Mechanical and electrical torques in a generating unit)
? = rotational speed (rad/sec)
? = rotational acceleration
? = phase angle of a rotating machine
Tnet = net accelerating torque in a machine
Tmech= mechanical torque exerted on the machine by the turbine
Telec =electrical torque exerted on the machine by the generator
Pnet = net accelerating power
Pmech =mechanical power input
Pelec= electrical power output
I = moment of inertia for the machine
M = angular momentum of the machine
?Pmech – ?Pelec = Ms??
(Fig.1.2: Relationship between Mechanical and electrical power and speed change)
1.2.2 Load model
The loads on a power system consist of a variety of electrical devices. Some of them are purely resistive, some are motor loads with variable power frequency characteristics, and others exhibit quite different characteristics. Since motor loads are a dominant part of the electrical load, there is a need to model the effect of a change in frequency on the net load drawn by the system. The relationship between change in load due to the change in frequency is given by
?PL(freq) = D??
Where, D is expressed as percent change in load divided by percent change in frequency.
?Pelec = ?PL + D??
Whrere, ?PL = Non frequency sensitive load change and
D?? = Frequency sensitive load change
By including this in the block diagram results in the new block diagram shown in figure below.
(Fig.1.3: Block diagram of rotating mass and load as seen by prime-mover output)
1.2.3 Prime mover model
The prime mover driving a generator unit may be a steam turbine or a hydro turbine.
(Fig.1.4: Prime-mover model)
The combined prime-mover-generator-load model for a single generating unit can be given by
(Fig.1.5: Prime-mover, generator, load model)
1.2.4 Governor model
There are two types of governors:
(Fig.1.6: Isochronous governor)
The speed-measurement device’s output ? is compared with a reference ?ref to, produce an error signal ??. The error ?? is negated and then amplified by a gain Kg and integrated to produce a control signal ?Pvalve which causes the main steam-supply valve to open (?Pvalve position) when ?? is negative.
Governor with speed-droop feedback loop
To be able to run two or more generating units in parallel on a generating system, the governors are provided with a feedback signal that causes the speed error to go to zero at different values of generator output. This can be accomplished by adding a feedback loop around the integrator as shown in Figure.
(Fig.1.7: Governor with speed-droop feedback loop)
Block diagram is reduced as shown in the figure below.
(Fig.1.8: Block diagram of governor with droop)
Combined block diagram of generator, load and governor is shown in the figure below.
(Fig.1.9: Block diagram of governor, prime-mover and rotating mass)
1.2.5 Tie-line model
The power flowing across a transmission line can be modeled using the DC load flow method and is given by
Ptie flow = 1Xtie?1-?2This tie flow is a steady-state quantity. For purposes of analysis here, we will perturb the equation above to obtain deviations from nominal flow as a function of deviations in phase angle from nominal.
?Ptie flow = Ts??1-??2Where, T=377*1/Xtie (for 60Hz system)
(Fig.1.10: Block diagram of inter connected areas)
RESTRUCTURED POWER SYSTEM
2.1 Vertically integrated utility structure
The electric power industry has over the years been dominated by large utilities that had an overall authority over all activities in generation, transmission and distribution of power within its domain of operation. Such utilities have often been referred to as vertically integrated utilities. Such utilities served as the only electricity provider in a region and were obliged to provide electricity to everyone in the region.
The typical structure of a vertically integrated electric utility is shown in figure below. In the figure, the money flow is unidirectional, i.e. from the consumer to the electric company. Similarly, the information flow exists only between the generators and the transmission systems.
In vertically integrated utilities, it was often difficult to segregate the costs involved in generation, transmission or distribution. So, the utilities often charged their customers an average tariff rate depending on their aggregated cost during a period.
(Fig.2.1: Vertically Integrated Industry)
The state electricity boards (SEB) in India were examples of a vertically integrated utility; they are now being restructured.
2.2 Structure of a Deregulated Industry
One of the principal characteristics of a competitive structure is the identification and separation of the various tasks which are normally carried out within the traditional organization so that these tasks can be open to competition whenever practical and profitable. This process is called unbundling. An unbundled structure contrasts with the so-called vertically integrated utility of today where all tasks are coordinated jointly under one umbrella with one common goal, that is, to minimize the total costs of operating the utility. One of the first steps in the restructuring process of the power industry has been the separation of the transmission activities from the electricity generation activities.
On the other hand, the transmission system has significant economies of scale (i.e., it is economical to have a common bulk transmission system of a large capacity rather than individual small capacity transmission links). Consequently it was suited to be a natural monopoly and a separate entity. It was felt necessary to introduce regulation in transmission so as to prevent it from overcharging for its services. The transmission system thus became a neutral, natural monopoly subject to regulation by public authorities. And to overcome the monopolistic characteristic, the trend has been to establish new legal and regulatory frameworks offering third parties “open access” to the transmission network subject to technical constraints.
An important point to note is that the restructuring process was however not uniform in all countries. While in many instances, it started with the breaking up of a large vertically integrated utility, in certain other instances restructuring was characterized by the opening up of small municipal monopolies to competition.
In brief, Electric utilities are expected to split apart into unbundled companies, with each utility re-aligning itself into several other companies that respectively focus on each part of the new industry, i.e., power delivery and retailing. This is known as Deregulation.
Under deregulation, the vertically integrated utility, one giant company that generates, transmits, distributes and sells electricity in coordinated manner will become thing of the past. To function in an open access system, such utilities will have to rearrange their operational organization to match the unbundled functions they must perform. Each part of the company will need to work in its new form. Generation will have to compete in the competitive power generation market place. T ; D will have to operate as an open provider of delivery services. Competition will be present in retailing.
Generally, the governments advocating deregulation want competition in energy production, and they want to see significant levels of customer choice in the retail market for electricity. At the same time, it recognizes that it is best to have only one transmission and one distribution system in any one area. The figure below shows the typical structure of a deregulated electricity system with links of information and money flow between various players. The configuration shown in the figure is not a universal one. There exist variations across countries and systems.
(Fig.2.2: Deregulated Industry)
Different power sellers will deliver their product to their customers (via retailers), over a common set of T ; D wires. These operations are supervised by an independent system operator (ISO). The generators, T ; D utility and retailers communicate with the ISO. Mostly, customers communicate with a retailer, demanding energy. The retailer contacts the generating company and purchases the power from it and makes it transferred to its customer’s place via regulated T & D lines. The ISO is the one responsible for keeping track of various transactions taking place between various entities. A customer can also enter into a bi-lateral contract with a generator directly for supply of the required energy.
2.2.1 Different entities in deregulated environment:
The introduction of deregulation has brought several new entities in the electricity market place, while on the other hand redefining the scope of activities of many of the existing players. Variations exist across market structures over how each entity is particularly defined and over what role it plays in the system.
However, on a broad level, the following entities can be identified as shown in the figure below:
Genco:- is an owner-operator of one or more generators that runs (Generating Company)them and bids the power into the competitive marketplace. Genco sells energy at its sites in the same manner that a coal mining company might sell coal in bulk at its mine.
Transco:- moves power in bulk quantities from where it is producedto where it is delivered. The Transco owns and maintains the transmission facilities, and may perform many of the management and engineering functions required to ensure the system can Transcocontinue to do its job. In most deregulated industry structures, the (Transmission Company)Transco owns and maintains the transmission lines under monopoly franchise, but does not necessarily operate them. That is done by Independent System Operator (ISO). The Transco is paid for the use of its lines. In some countries, Transo itself acts as a system operator.
It is the monopoly franchise owner-operator of the local power
Disco:- delivery system, which delivers power to individual businesses and (Distrubution Company) homeowners. In some places, the local distribution function is combined with retail function, i.e. to buy wholesale electricity either through the spot market or through direct contracts with gencos and supply electricity to the end use customers. In many other cases, however, the disco does not sell power. It only owns and operates the local distribution system, and obtains its revenues by ‘renting’ space on it, or by billing for delivery of electric power.
Resco:- It is the retailer of electric power. Many of these will be the retail departments of the former vertically integrated utilities. Others will (Retail Energy be companies new to the electric industry that believe they are (Service Company) good at selling services. Either way, a resco buys power from gencos and sells it directly to the consumers.
ISO:- The ISO is an entity entrusted with the responsibility of ensuring the reliability and security of the entire system. It is an independent authority and does not participate in the electricity (Independent System market trades. It usually does not own generating resources, Operator) except for some reserve capacity in certain cases. In order to maintain the system security and reliability, the ISO procures various services such as supply of emergency reserves, or reactive power from other entities in the system.
Customer:- A customer is an entity, consuming electricity. In deregulated markets, a customer has several options for buying electricity. Itmay choose to buy electricity from the spot market by bidding for purchase, or may buy directly from a genco or even from the local distribution company.
2.3 Reasons for restructuring
The reasons for initiating the idea of deregulation (we will henceforth use the word deregulation to describe changes in power system structures; however, it will be clear that these changes involve changes in regulations rather than deregulation! In some countries, these changes are also described as”liberalisation”) in power industry are many.
Following are the main reasons:
1. The need for regulation changed: Most of the the major electrical infrastructure was paid for, decades ago. The revenues gained by the electric utilities was invested to renew their system, and the level of risk in doing so was less as compared to that existed in the initial era. Being a proved technology, the risk involved in investing money in such a technology was nullified. The electricity could now be thought of as an essential commodity, which can be bought and sold in the marketplace in a competitive manner, just like other commodities.
2. Ideological Reason: Privatization usually the motive was the government’s firm conviction that private industry could do a better job of running the power industry. This belief, of course came from better privatization experiences of the other industries. Deregulation does not necessarily have to be a part of privatization efforts.
3. Cost is expected to drop: Competition is expected to bring innovation, efficiency, and lower costs.
4. Customer focus will improve: Although monopoly franchise utilities have an obligation to serve all customers, that does not promote the proactive attention to customer needs. A monopoly franchise utility listens to its customers when they explain their needs, and then responds. A competitive electric service company anticipates customer’s needs and responds in advance. The technological advances that will be applied under deregulation, address customer service. More important gain of competition in the electricity market is the customer value rather than lowering the cost.
5. Encouragement for innovation: The regulatory process and the lack of competition gave electric utilities no incentive to improve on yesterday’s performance or to take risks on new ideas that might increase customer value. If a new idea succeeded in cutting costs, the utility still made only its regulated rate of return on investment; if it didn’t work, the utility would usually have to ‘eat’ a good deal of the failed attempt, as imprudent expenses.
2.4 Traditional vs. Restructured Scenario
The traditional power system industry has a “vertically integrated utility” (VIU) structure. In the restructured or deregulated environment, vertically integrated utilities no longer exist. The utilities no longer own generation, transmission, and distribution; instead, there are three different entities, viz., GENCOs (generation companies), TRANSCOs (transmission companies) and DISCOs (distribution companies).
As there are several GENCOs and DISCOs in the deregulated structure, a DISCO has the freedom to have a contract with any GENCO for transaction of power. A DISCO may have a contract with a GENCO in another control area. Such transactions are called “bilateral transactions.” All the transactions have to be cleared through an impartial entity called an independent system operator (ISO).
2.5 Concept of DISCO Participation Matrix (DPM)
In the restructured environment, GENCOs sell power to various DISCOs at competitive prices. Thus, DISCOs have the liberty to choose the GENCOs for contracts. They may or may not have contracts with the GENCOs in their own area. This makes various combinations of GENCO-DISCO contracts possible in practice. We introduce the concept of a “DISCO participation matrix” (DPM) to make the visualization of contracts easier. DPM is a matrix with the number of rows equal to the number of GENCOs and the number of columns equal to the number of DISCOs in the system. Each entry in this matrix can be thought of as a fraction of a total load contracted by a DISCO (column) toward a GENCO (row). Thus, the ijth entry corresponds to the fraction of the total load power contracted by DISCO j from a GENCO i. The sum of all the entries in a column in this matrix is unity. DPM shows the participation of a DISCO in a contract with a GENCO; hence the name “DISCO participation matrix.”
The notation follows along the lines of 1, 2. Consider a two-area system in which each area has two GENCOs and two DISCOs in it. Let GENCO, GENCO, DISCO, and DISCO be in area I and GENCO, GENCO, DISCO , and DISCO be in area II as shown in Fig.
(Fig.2.3: Schematic of two-area system in restructured environment)
The corresponding DPM will become
Where cpf refers to “contract participation factor.”
SIMULATION OF AUTOMATIC GENERATION CONTROL
3.1 MATLAB model of AGC
(Fig.3.1: MATLAB model of AGC system)
3.2 Results for different cases
3.2.1 Case 1: – Application of 0.1 Pu Mw load change at time t=0 sec
MATLAB results for case-1
Fig.3.2: Results for case-1)
3.2.2 Case 2: – Application of 0.2 Pu Mw load change at time t=0 sec
MATLAB results for case-2
(Fig.3.3: Results for case-2)
3.2.3 Case 3: – Application of 0.2 Pu Mw load change at time t=1 sec
MATLAB results for case-3
(Fig.3.4: Results for case-3)
3.2.4 Case 4: – Application of 0.1 Pu Mw load change at time t=2 sec
(Fig.3.5: Results for case-4)
Tie Line Control
Power flow control between two area AGC
Simulation of two area AGC
Different cases of two area AGC & its Simulation
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