BALANCING THE SUPPLY AND DEMAND USING

BALANCING THE SUPPLY AND DEMAND USING

FLEXIBLE RELIABLE INTELLIGENT ENERGY

DELIVERY SYSTEM

PROJECT REPORT (Phase – I)

Submitted by

L.KRISHNAVENI

Register No: 09MEPE010

in partial fulfilment for the award of the degree

of

MASTER OF ENGINEERING

in

POWER ELECTRONICS AND DRIVES

DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING

KARPAGAM UNIVERSITY

COIMBATORE – 641 021

DECEMBER 2010

KARPAGAM UNIVERSITY

COIMBATORE-641 021

FACULTY OF ENGINEERING

DEPARTMENT OF ELECTRICAL AND ELECTRONICS

ENGINEERING

PROJECT WORK

PHASE I

DEC 2010

This is to certify that the project entitled

“BALANCING THE SUPPLY AND DEMAND USING FLEXIBLE RELIABLE INTELLIGENT ENERGY DELIVERY SYSTEM”

is the bonafide record of project work done by

KRISHNAVENI L

Register No: 09MEPE010

of

MASTER OF ENGINEERING

in

POWER ELECTRONICS AND DRIVES

during the year 2010-2011

Project Guide Head of the Department

Prof. K. KEERTHIVASAN M. E., Prof. K. KEERTHIVASAN M. E., Associate Professor / Dept. of EEE Associate Professor / Dept. of EEE

Submitted for the Project Viva – Voce Examination held on _____________

INTERNAL EXAMINER EXTERNAL EXAMINER

BONAFIDE CERTIFICATE

This is to certify that this project report titled “BALANCING THE SUPPLY AND DEMAND USING FLEXIBLE RELIABLE INTELLIGENT ENERGY DELIVERY SYSTEM” is the bonafide work of KRISHNAVENI. L (09MEPE010) who carried out the research under my supervision. Certified further, that to the best of my knowledge the work reported herein does not form part of any other project report or dissertation on the basis of which a degree or award was conferred on an earlier occasion on this or any other candidate.

SIGNATURE

Prof. K. KEERTHIVASAN M. E.,

Associate Professor / Dept. of EEE

Karpagam University,

Coimbatore – 641 021

Submitted to the Viva-Voce Examination held on ……………

INTERNAL EXAMINER EXTERNAL EXAMINER

DECLARATION

I affirm that the thesis titled “BALANCING THE SUPPLY AND DEMAND USING FLEXIBLE RELIABLE INTELLIGENT ENERGY DELIVERY SYSTEM” being submitted in partial fulfilment for the award of MASTER OF ENGINEERING degree is the original work carried out by me. It has not formed the part of any other thesis submitted for award of any degree or diploma, either in this or any other University.

Signature of the Candidate

KRISHNAVENI. L Reg. No. : 09MEPE010

I certify that the declaration made above by the candidate is true.

Signature of the Guide

Prof. K. KEERTHIVASAN M. E.,

Associate Professor / Dept. of EEE

ACKNOWLEDGEMENT

Behind every achievement lies an unfathomable sea of gratitude to those who actuated it, without them it would never have into existence .To them we lay the word of gratitude imprinted within us.

I wish to express my sincere thanks to our respected DEAN Dr. G. Karuppusamy Ph. D., for all the blessing and help provided during the period of project work.

I wish to express my sincere thanks Prof. K. Keerthivasan, M. E., Associate Professor and Head of the Department of Electrical and Electronics Engineering, and my guide for the continuous help over the period of project work.

I express my sincere words of gratitude to our class counselor, other faculty members and staff members of the Department of Electrical and Electronics Engineering.

I would like to extend my warmest thanks to all our Lab Technicians for helping me in this venture. Unflinching support and encouragement from the members of my family and friends who helped me a long way to complete my project work. I must thank them all from the depths of my heart.

Date: KRISHNAVENI. L

ABSTRACT

This project proposes Flexible, Reliable and Intelligent ENergy Delivery system (FRIENDS) as a future power distribution system. In the FRIENDS new facilities called Quality Control Centers (QCCs), which consists of voltage control type inverters, Distributed Generators (DGs), Energy Storage Systems (ESSs), etc., are installed between distribution substation and customers. By controlling and operating those inverters and distributed generators in QCCs adequately, balancing the supply and demand can be realized. Particularly, when the power supply from the transmission network is interrupted, isolated local network which consists of some QCCs are composed in order to realize uninterruptible power supply. In the isolated network, the DG and ESS in QCCs are employed as backup generators. This project proposes a distributed and autonomous method for balancing the supply and demand during interruption period. This project also investigates the effectiveness of the proposed method through computational simulations.

LIST OF FIGURES

S.NO.

TITLE

PAGE. NO.

1. POWER SHARING TECHNIQUE 11

2. BLOCK DIAGRAM 13

3. BUILDING A SIMPLE MODEL 15

4. SIMULINK LIBRARY BROWSER 16

5. SIMULINK PARAMETERS 18

6. SCOPE 19

7. CONCEPT OF FRIENDS 20

8. OPERATION OF QCC 22

9. CIRCUIT DIAGRAM 23

10. SIMPLIFIED QCC MODEL 24

11. BLOCK DIAGRAM FOR FREQUENCY

CONTROL 25

12. BLOCK DIAGRAM FOR VOLTAGE

MAGNITUDE CONTROL 27

13. MATLAB CIRCUIT 29

14. OUTPUT WAVEFORM 30

LIST OF ABBREVIATIONS

ACE Area Control Error.

AGC Automatic Generation Control.

DG Distributed Generators.

ESS Energy Storage System.

FC Fuel Cell.

FFC Flat Frequency Control.

FRIENDS Flexible, Reliable and Intelligent Energy Delivery System.

GF Governor-Free Operation.

TBC Tie-line Bias Control.

TABLE OF CONTENTS

CHAPTER NO. TITLE PAGE NO.

Declaration 4

Acknowledgement 5

Abstract 6

List of Figures 7

List of Abbreviations 8

1. INTRODUCTION

1.1 Existing system 11 1.2 Proposed System 12 1.3 Block Diagram 13 1.4 Software Requirements 14

2. LITERATURE VIEW

2.1 Project Description 20

2.2 Operation and model of QCC 21

2.3 Circuit diagram 22

2.4 Role of QCC 24

2.5 Method for balancing supply and

Demand in isolated system 25

3. SIMULATION RESULTS AND 30

DISCUSSION

3.1 Simulation Circuit 29

3.2 Simulation Output Waveform 30

3.3 Work Planned for Phase – II 30

REFERENCE 31

CHAPTER - I

1. INTRODUCTION

RECENT deregulation in the electric power industry and pressing concerns about global environmental issues as well as an energy crisis have led to an increase in installation capacity of Distributed Generators (DGs) and Energy Storage Systems (ESSs). Enthusiastic R&Ds and price reductions are accelerating the pace of DG and ESS installation. However, reversal and/or unsteady power flows caused by DG output may hinder management of the voltage profile of distribution system, frequency control, etc. In the future, power distribution systems should be designed and constructed taking into account such technical problems. Another trend in the power industry is diversification of customer requirements for power quality level. Some customers require excellent power quality due to their high dependency on electricity, while other customers place more value not in quality but in cost. Future power systems, distribution systems in particular, will be required to become more favorable to both customers and DG/ESS.

Some new concepts regarding power distribution systems which can coexist with many DG/ESS systems have been developed, for example, Micro Grid, Custom Power Park, and Demand Area Power System and so on. The authors have also proposed a new power distribution system named Flexible, Reliable and Intelligent ENergy Delivery System (FRIENDS). In the FRIENDS, new facilities called Quality Control Center (QCC), which consists of power electronics devices, DGs, ESSs, etc., are installed between distribution substations and customers as shown (a QCC is assumed to be installed per one building in an urban area, for example). By controlling and operating those devices in a QCC adequately management and unbundling of power quality levels, power conditioning, advanced-demand side management, etc. can be realized.

1.1 EXISTING SYSTEM

ELECTRIC FIELD

Nowadays in modern world every new object will be created daily, that all new objects are only depend on the electrical sources. The main problem of our electrical source is power interruption, not balancing the supply and demand

UPS

It is defined as a system which is designed to provide power during all periods. Where in the normal or prime source of power is outside acceptable limits without causing disruption of the flow of acceptable power to the load. Two major categories are there i) on line system, ii) off line system.

POWER SHARING TECHNIQUES

Using this technique the heavy demand problem can be solved by this way. Here we consider two areas from the distribution station the power flow in the normal condition.

During interruption period area 1 show the power 1 to 2 up to 50%. If else more than 50% utilized, automatically the power interrupted.

Fig. 1 Power sharing technique

DISADVANTAGES OF EXISTING SYSTEMS

· It is very expensive.

· Heavy demands are not balanced properly.

· Early the demand occurs the device gets damaged.

1.2 PROPOSED SYSTEM

This project proposes a new concept Flexible Reliable and Intelligent Electrical Energy Delivery System. In the FRIENDS new facilities called Quality Control Centers (QCCs), which consists of power electronics devices, Distributed Gnerators (DGs), Energy Storage Systems (ESSs) etc., are installed between distribution substation and customers. When the power supply from the transmission network is interrupted, isolated local network which consists of some QCCs are composed in order to realize uninterruptible power supply. In the isolated network, the DG and ESS in QCCs are employed as backup generators.

In this Chapter, the authors aim at developing the frame of a new electric power delivery system for the next generation which differs from the present power delivery system. The purpose of the FRIENDS is to develop a desirable structure for future power delivery systems where dispersed power generation resources and energy storage systems are allocated near the demand side, and to develop reliable and energy conservation oriented operating strategies of the power system, taking into consideration ways of enhancing service to consumers through intelligent functions. The FRIENDS is a new concept made up by integrating a number of research concepts which have been investigated individually, and adding more reliable and flexible functions. In other words, by dispersed power generation resources, energy storage systems, demand side control, power electronics technologies, high level communication technologies and dispersed intelligent facilities, etc.,

This system is expected to attain the following functions:

Large Energy Storage

(1) Flexibility in reconfiguration of the system.

(2) Reliability in supply with reduced need for scheduled

(3) Multi-menu service to allow consumers to select the quality of electric power and the supplier,

(4) Load leveling and energy conservation.

(5) Enhancement of information services to customers.

(6) Efficient demand side management. outage. Quality of electric power and the supplier.

1.2.1 ADVANTAGES OF PROPOSED SYSTEM

· Meet out heavy demand can be balanced easily

· Fault identification is easy

· Fault analysis and rectification is simple.

1.3 BLOCK DIAGRAM

			TRANSMISSION LINE		LOAD
	3 PHASE SOURCE

			THREE PHASE INVERTER

Fig. 2 Block diagram

1.4 SOFTWARE REQUIREMENTS

• MATLAB 7.0

MATLAB

MATLAB is a high-performance language for technical computing. It integrates computation, visualization, and programming in an easy-to-use environment where problems and solutions are expressed in familiar mathematical notation.

Typical uses include:

• Math and computation
• Algorithm development
• Modeling, simulation, and prototyping
• Data analysis, exploration, and visualization
• Scientific and engineering graphics
• Application development, including Graphical User Interface building

MATLAB is an interactive system whose basic data element is an array that does not require dimensioning. This allows you to solve many technical computing problems, especially those with matrix and vector formulations, in a fraction of the time it would take to write a program in a scalar non-interactive language such as C or FORTRAN.

MATLAB - SIMULINK

Simulink is an environment for multi domain simulation and Model-Based Design for dynamic and embedded systems. It provides an interactive graphical environment and a customizable set of block libraries that let you design, simulate, implement, and test a variety of time-varying systems, including communications, controls, signal processing, video processing, and image processing.

• Introduction and Key Features
• Creating and Working with Models
• Defining and Managing Signals
• Running a Simulation
• Analyzing Results

Simulink is a software package for modeling, simulating, and analyzing dynamical systems. It supports linear and nonlinear systems, modeled in continuous time, sampled time, or a hybrid of the two. Systems can also be multirate, i.e., have different parts that are sampled or updated at different rates. For modeling, Simulink provides a graphical user interface (GUI) for building models as block diagrams, using click-and-drag mouse operations. With this interface, you can draw the models just as you would with pencil and paper (or as most textbooks depict them). Simulink includes a comprehensive block library of sinks, sources, linear and nonlinear components, and connectors. You can also customize and create your own blocks, Models are hierarchical. This approach provides insight into how a model is organized and how its parts interact. After you define a model, you can simulate it, using a choice of integration methods, either from the Simulink menus or by entering commands in MATLAB's command window. The menus are particularly convenient for interactive work, while the command-line approach is very useful for running a batch of simulations (for example, if you are doing Monte Carlo simulations or want to sweep a parameter across a range of values). Using scopes and other display blocks, you can see the simulation results while the simulation is running. In addition, you can change parameters and immediately see what happens, for "what if" exploration. The simulation results can be put in the MATLAB workspace for post processing and visualization. And because MATLAB and Simulink are integrated, you can simulate, analyze, and revise your models in either environment at any point.

Building a Simple Model

This example shows you how to build a model using many of the model building commands and actions you will use to build your own models. The instructions for building this model in this section are brief. The model integrates a sine wave and displays the result, along with the sine wave. The block diagram of the model looks like this.

Fig.3

To create the model, first type simulink in the MATLAB command window.

On Microsoft Windows, the Simulink Library Browser appears.

On UNIX, the Simulink library window appears.

To create a new model, select Model from the New submenu of the Simulink library window's File menu. To create a new model on Windows, select the New Model button on the Library Browser's toolbar. Simulink opens a new model window.

To create this model, you will need to copy blocks into the model from the following

Simulink block libraries:

• Sources library (the Sine Wave block)
• Sinks library (the Scope block)
• Continuous library (the Integrator block)
• Signals & Systems library (the Mux block)

To copy the Sine Wave block from the Library Browser, first expand the Library Browser tree to display the blocks in the Sources library. Do this by clicking on the Sources node to display the Sources library blocks. Finally, click on the Sine Wave node to select the Sine Wave block. Here is how the Library Browser should look after you have done this.

Fig. 4

Now drag the Sine Wave block from the browser and drop it in the model window. Simulink creates a copy of the Sine Wave block at the point where you dropped the node icon.

To copy the Sine Wave block from the Sources library window, open the Sources window by double-clicking on the Sources icon in the Simulink library window. (On Windows, you can open the Simulink library window by right-clicking the Simulink node in the Library Browser and then clicking the resulting Open Library button.)

Simulink displays the Sources library window. Now drag the Sine Wave block from the Sources window to your model window. Copy the rest of the blocks in a similar manner from their respective libraries into the model window. You can move a block from one place in the model window to another by dragging the block. You can move a block a short distance by selecting the block, then pressing the arrow keys. If you examine the block icons, you see an angle bracket on the right of the Sine Wave block and two on the left of the Mux block. The > symbol pointing out of a block is an output port; if the symbol points to a block, it is an input port. A signal travels out of an output port and into an input port of another block through a connecting line. When the blocks are connected, the port symbols disappear.

Now it's time to connect the blocks. Connect the Sine Wave block to the top input port of the Mux block. Position the pointer over the output port on the right side of the Sine wave block. Notice that the cursor shape changes to cross hairs. Hold down the mouse button and move the cursor to the top input port of the Mux block. Notice that the line is dashed while the mouse button is down and that the cursor shape changes to double-lined cross hairs as it approaches the Mux block. Now release the mouse button. The blocks are connected. You can also connect the line to the block by releasing the mouse button while the pointer is inside the icon. If you do, the line is connected to the input port closest to the cursor's position.

If you look again at the model at the beginning of this section, you'll notice that most of the lines connect output ports of blocks to input ports of other blocks. However, one line connects a line to the input port of another block. This line, called a branch line, connects the Sine Wave output to the Integrator block, and carries the same signal that passes from the Sine Wave block to the Mux block. Drawing a branch line is slightly different from drawing the line you just drew. To weld a connection to an existing line, follow these steps:

1. First, position the pointer on the line between the Sine Wave and the Mux block.

2. Press and hold down the Ctrl key (or click the right mouse button). Press the mouse button, then drag the pointer to the Integrator block's input port or over the Integrator block itself.

3. Release the mouse button. Simulink draws a line between the starting point and the Integrator block's input port. Finish making block connections.

Now, open the Scope block to view the simulation output. Keeping the Scope window open, set up Simulink to run the simulation for 10 seconds. First, set the simulation parameters by choosing Simulation Parameters from the Simulation menu.

On the dialog box that appears, notice that the Stop time is set to 10.0 (its default value).

Fig. 5

Close the Simulation Parameters dialog box by clicking on the OK button. Simulink

applies the parameters and closes the dialog box.

Choose Start from the Simulation menu and watch the traces of the Scope block's input.

Fig. 6

The simulation stops when it reaches the stop time specified in the Simulation

Parameters dialog box or when you choose Stop from the Simulation menu.

To save this model, choose Save from the File menu and enter a filename and location.

CHAPTER - II

2.1 DESCRIPTION OF FRIENDS CONCEPT

Fig. 7. Concept of FRIENDS

One of the key functions in power quality management is to improve the reliability of power supplies. The FRIENDS aims to realize an uninterruptible power supply by using the DG/ESS as backup generators. Particularly, when power supply from the transmission network is interrupted, some QCCs are interconnected with each other and constitute an isolated local network to supply electricity for customers without interruptions.

Since the capacity of an isolated FRIENDS network is much smaller than the already existing bulk transmission power system, balancing the supply and demand in an isolated system with multiple backup resources becomes a more difficult operation. For this difficult and complicated situation, we can consider two approaches: communication-based approach and communication-less approach. The former approach can realize sub-optimal balancing (for example, effective load assignment to multiple backup resources); however, the dynamic behavior of balancing strongly depends on the communication delay. The latter approach, on the other hand, can realize the stable dynamic performance and show a high fault tolerance against the communication failures. Considering the main motive of isolated operation—improvement in supply reliability—this paper proposes a novel distributed and autonomous (communication-less) method for balancing the supply and demand in an isolated system.

Some autonomous (communication-less) balancing methods for an isolated system in which a multiple DG/ESS is utilized as backup generators have been proposed based on the conventional frequency control scheme. A basic idea employed in these past works is to implement a speed droop characteristic in the output control system of DG/ESS. Most past works aim to balance the supply and demand within an isolated local network. Our method, on the other hand, aims to achieve not only a balance within the local QCC network but also a balance within each QCC. This is because every QCC is assumed to be responsible for feeding its own customers in the FRIENDS concept. The novel control method for realizing the above-mentioned balancing scheme is proposed in this paper.

Furthermore, this paper also investigates the effectiveness of the proposed method through various computational simulations.

FRIENDS is a new power delivery concept which intend to attain the following functions by using dispersed power generators & energy storage systems (DGS), power electronics technologies, communication technologies and intelligent facilities, etc. Namely,

(1) Flexibility in reconfiguration of the system in normal and fault states,

(2) High reliability in power supply,

(3) Multi-menu services or customized power quality services to allow consumers to select the quality of electric power and the supplier, normal and fault states,

(4) Load leveling and energy conservation,

(5) Enhancement of information services to customers,

(6) Efficient demand side management, etc. With FRIENDS, the power system can be operated without interrupting power supply by flexibly changing the distribution system configurations after occurrence of a fault. Further, each consumer can select the quality of electrical power independently through the Qquality Control Center (QCC). More specifically, multiple power quality services named “customized power quality services” for each consumer can be provided. In addition, since DGSs are allocated on the demand side of the FRIENDS, we can also expect energy conserving measures due to the Demand Side Management (DSM). To operate the FRIENDS efficiently, such electronics technologies play important roles as static protection scheme, micro-computers (work stations) and data communication lines which connect computers and supply various types of information to each customer.

2.2. OPERATION AND MODEL OF QCC

2.2.1 Operational Policy

In the concept of FRIENDS, QCCs are interconnected by high voltage distribution feeders and constitute a local network in which every QCC becomes a node (loop configuration is Fig. 2. Operation of QCC in (a) normal state and in (b) isolated operation also permitted). This local network interconnects to the transmission or sub transmission system through distribution substations. In a normal state, every QCC supplies the customer with power which is fed from the transmission networks through the high voltage distribution feeders and the DG/ESS in the QCC [Fig. 2(a)]. When a fault occurrence interrupts the power supply to some QCCs, they are disconnected from the other QCCs and constitute a local system as shown in Fig. 2(b). A detailed method for constituting a local system was proposed in [6].

In the local system, each QCC basically supplies energy for its own loads. Only when the capacity of backup generators (DG/ESS) in the QCC is insufficient, the other QCCs in the local system compensate for the shortage of capacity. This operational policy is based on the concept that every QCC is responsible for the power supply in its service area (principle of self-supply).

Fig. 8. Operation of QCC in (a) normal state and in (b) isolated operation.

2.3 CIRCUIT DIAGRAM (Internal Composition of QCC)

Fig. 9. Internal composition of QCC

2.3.1 QCC MODEL

As a circuit configuration of QCC, this paper employs a so-called UPS-type QCC in which two inverters (Inverter 1 and Inverter 2), DG, and ESS share a dc bus as shown in Fig. 3. The UPS-type QCC can provide four types of quality power levels: ordinary quality, high quality, super premium quality, and dc.. The ordinary quality is distinguished from the other qualities by supply reliability, that is, supply for the ordinary quality is stopped by turning off the thyristor switch when the total capacity of backup generators in the isolated system is insufficient. Therefore, the ordinary quality load is supplied with the lowest price. Furthermore, since the super premium quality and dc are distinguished from the others by waveform quality, the prices for these qualities should be set at relatively expensive. In a normal state, the Inverter 1 is driven in the current control mode to supply or draw adequate power to or from the dc bus.

The voltage supplied to the ordinary and high quality loads is provided by the main grid. When a fault occurs and the isolated system is constituted, the control mode of Inv.1 in the isolated system is changed to the voltage control mode. That is, the voltage supplied to the ordinary and high quality loads is provided by the Inverter 1. A detailed control method of the Inv.1 during the isolated operation is proposed in next section.

Here, the super premium and dc lines are supplied from the dc bus through the Inverter 2 and the dc-dc converter, respectively, in both normal state and isolated operation. Therefore, this paper uses a simplified QCC model as shown in Fig. 10 because fault occurrence has less effect on the super premium and dc quality levels. In this simplified model, the super premium and dc loads are not considered and the high and ordinary quality loads are considered as a single impedance load. Furthermore, the DG and ESS which are modeled by a current source are assumed to be interconnected to the ac system through the Inverter 1 and reactor L.

Fig. 10. Simplified QCC model.

2.4 ROLE OF QCC

Capacity (MW & MWH) and functions of QCC must be changed according to the types and amounts of electrical power demand of the area where QCC is installed. Namely, several types of QCCs must be designed according to the demand types of electrical power. Among many kinds of classification candidates, let us assume QCC can be classified into the following three types depending on its size.

(a) Substation type QCC

(b) Regional type QCC

(c) Personal type QCC

These types of QCCs are used properly in the specified region by taking installation costs, characteristics of the types and benefits to be expected into consideration. The characteristics of the above three types are summarized according to where they are installed: that is, industrial region, region of office buildings, commercial area, condominium park and residential area.

2.5 METHOD FOR BALANCING THE SUPPLY AND DEMAND IN AN ISOLATED SYSTEM

2.5.1 DECOUPLING

Let us define a voltage provided by the Inv.1 in the isolated system is given by the equation

V_inv = ( V₀+∆v ) sin {2Л (f₀+∆f)} t (2.1)

Where V₀ and f₀ are the base value of voltage amplitude and frequency, and ∆v and ∆f are deviations of amplitude and frequency from the base values, respectively. When a load in the isolated system changes, voltage drop along the transformers and the reactor L also changes. As a result, voltage at the point of common coupling (PCC) changes and real and reactive power flows among QCCs emerge. In order to satisfy the operational policy described in Section II-A, it is necessary to adjust ∆f and ∆v adequately so that the receiving or sending power becomes zero. As is well-known, real and reactive power flows have

stronger coupling with voltage phase angles and amplitude, respectively. Therefore, in this paper, the mechanisms for balancing real and reactive powers are designed separately considering these coupling features.

Fig.11. Block diagram for frequency control.

2.5.2 REAL POWER BALANCING

The control system for achieving real power balancing is shown in Fig. 11. The proposed method consists of three sub-control systems which correspond to short-term, medium-term, and long-term balancing, respectively.

2.5.2.1 SHORT-TERM BALANCING (GOVERNOR-FREE)

As stated above, operational policy of the isolated system is based on the principle of self-supply; however, the DG and ESS might not respond to rapid and/or large load changes due to their slow response or capacity constraint. In order to mitigate the burdens

of DG and ESS, the proposed method is designed so that the short-term component of load changes can be compensated by all QCCs in the isolated system. Allocation of short-term components to every QCC is autonomously decided by the same mechanism as a governor-free operation employed in the conventional bulk power system. More specifically, the frequency deviation is adjusted proportionally to the difference between actual real power supply through Inverter 1 (P_DG+P_ESS-P_DCL) and its reference value as shown in (2):

∆f = k_p{ P_ref - ( P_DG+P_ESS-P_DCL) } (2.2)

Here, P_DG and P_ESS are output of DG and ESS, P_DCL is a power consumed by the super premium and dc load. k_p is a positive proportional gain and is equivalent to speed regulation in the conventional frequency drooping characteristic of a generator. The short-term load allocation mechanism realized by (2) is called Governor-Free operation (GF) in this paper.

2.5.2.2 MEDIUM-TERM BALANCING (TBC)

The purpose of a governor- free operation is to temporarily compensate for a steep load change by all QCCs in the isolated system. Therefore, compensation by the other QCCs should be readjusted so that the principle of self-supply can be achieved. This readjustment is called medium-term balancing in this paper. The principle of self-supply is very similar to the concept of tie-line bias control (TBC) which has been applied in the conventional automatic generation control (AGC) scheme. Therefore, this paper applies the TBC mechanism as medium-term balancing.

First, the area control error ( ACEp) is calculated based on a frequency deviation determined by (2) and the difference between receiving real power (P_QCC) and its reference value (P*_QCC) which corresponds to the tie-line bias in TBC:

ACEp = - Kp ∆f + (P_QCC + P*_QCC) (2.3)

Kp = (1/ Kp ) + Dp (2.4)

Here, P*_QCC is set to zero in order to eliminate the real power flow among QCCs. Kp is the power-frequency constant of QCC which is determined by Kp and load-frequency characteristic Dp. Then, the reference for the DG/ESS’s output (P_ref) is determined by a PI control whose input is ACEp :

P_ref = . ACEp + ∫ ACEp dt (2.5)

where and are the positive control gain used in the Proportional Integrator control.

2.5.3 REACTIVE POWER BALANCING

Fig. 12. Block diagram for voltage magnitude control.

As stated in the previous section, voltage magnitude at the PCC also changes when the connected load changes. Therefore, reactive power flows among the QCCs appear as real power flows do. In order to stabilize voltage magnitude at the PCC and eliminate the reactive power flows among QCCs, this paper will apply the idea of Q-TBC which has been recognized as TBC for reactive power. More specifically, the receiving real power P_QCC in TBC is replaced with the receiving reactive power q _QCC and the subsequent frequency deviation in TBC is replaced with a deviation of voltage at the PCC from its reference. The area-control error of reactive power (ACEq) can be calculated for the above values:

ACEq = - Kq ( V_LV – V_LV0 ) + ( q_QCC – q*_QCC) 2.6)

Here, Kq represents the relation between reactive power and voltage magnitude, q*_QCC is the reference value for and is defined as zero for eliminating the reactive power flow. The inverter’s output voltage magnitude is then determined by the PI control whose input is ACEq:

∆v = 9_q1.ACEq + 9_q2 ∫ ACE_q dt (2.7)

Where 9_q1 and 9_q2 are positive control gains used in the PI control.

Adjustment of the reactive power by inverters is free from constraints of the DG response and energy capacity of the ESS; therefore, this control does not need the GF mechanism.

This paper assumes that reactive power is exchanged among QCCs only when the current capacity of Inv.1 is deficient. Specifically, when q_inv has increased over its limit (q_inv – limit ) which is determined by the current capacity of inverter and/or the inverter real power output (see Section III-D), q*_QCC is adjusted to exchange reactive power among QCCs. Stable reactive power exchanges among QCCs require a steady state deviation of voltage magnitude at the PCC. In order to maintain the PCC voltage within its allowable range, an integral controller is employed parallel to (6).

POWER SYSTEM AND POWER ELECTRONICS

Power Electronics is a field which combines Power (electric power), Electronics and Control systems. Power engineering deals with the static and rotating power equipment for the generation, transmission and distribution of electric power. Electronics deals with the study of solid state semiconductor power devices and circuits for Power conversion to meet the desired control objectives (to control the output voltage and output power).

Power electronics may be defined as the subject of applications of solid state power semiconductor devices (Thyristors) for the control and conversion of electric power. Power electronics deals with the study and design of Thyristorised power controllers for variety of application like Heat control, Light/Illumination control, and Motor control – AC/DC motor drives used in industries, High voltage power supplies, Vehicle propulsion systems, High voltage direct current (HVDC) transmission.

BACK UP SOURCE

· Backup generators like Diesel generators …etc

· PV CELL

PV CELL

Renewable energy resources will be an increasingly important part of power generation in the new millennium. Besides assisting in the reduction of the emission of greenhouse gases, they add the much needed flexibility to the energy resource mix by decreasing the dependence on fossil fuels. Due to their modular characteristics, ease of installation and because they can be located closer to the user, PV systems have great potential as distributed power source to the utilities.

CHAPTER - III

3.1 SIMLATION CIRCUIT

Fig.13

3.2 SIMULATION OUTPUT WAVEFORM

Time in seconds

Fig.16 Output waveform

3.3 WORK PLANNED FOR PHASE - II

In future method for real power and reactive power variation will be identify during transient conditions. The variation parameters are compensated by using software PSCAD / EMTDC. This project will develop by hardware components and it is mainly applicable to bulk power transmission system etc…

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