71 CHAPTER 5 METHODOLOGY Modelling is a very important part of any engineering practice. Nowadays with the use of computers and powerful software extremely complex systems can be simulated and their performance can be predicted and monitored. This chapter deals with the virtual real world environment of power system through simulation studies. A brief detail about MATLAB and SIMULINK is discussed in this chapter. SimPowerSystems Library blocks and powerlib tools are used for modeling the system for analysis purpose as the study is on power systems. Modeling of wind and PV has been explained in detail using the tool. This chapter also presents the details of the wind farm of the study area. 5.1 Methodology Adopted for the Study The study area for the research considered is Nittur wind farm, Hassan, Karnataka. After visiting the wind farm some of the important observations were identified which are mentioned as follows. 1. The farm is presently using capacitor banks for reactive power support with the help of auto mechanical switches for maintenance of grid code. 2. The farm has to shut down when ever fault occurs at PCC to avoid voltage collapse causing heavy loss to the utility. 3. Due to the intermittent nature of wind the continuous switching operation occurrence induces harmonics in the system and wear and tear of the switches leads to frequent replacement of switches. 4. As the wind is seasonal, the grid aiding with this renewable DG is not reliable. With these observations lead the way to consider this as challenging study to give solutions for the issues and associated problems were formulated. After literature survey, it was found that STATCOM which belongs to FACTS family is the better option. The study would suggest the possibility of hybrid generation around the free land area of Nittur wind farm as the area is marshy land and belongs to forest department and felt suitable for installation of PV plant.
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CHAPTER 5
METHODOLOGY
Modelling is a very important part of any engineering practice. Nowadays with
the use of computers and powerful software extremely complex systems can be
simulated and their performance can be predicted and monitored. This chapter
deals with the virtual real world environment of power system through simulation
studies. A brief detail about MATLAB and SIMULINK is discussed in this chapter.
SimPowerSystems Library blocks and powerlib tools are used for modeling the system
for analysis purpose as the study is on power systems. Modeling of wind and PV has
been explained in detail using the tool. This chapter also presents the details of the
wind farm of the study area.
5.1 Methodology Adopted for the Study
The study area for the research considered is Nittur wind farm, Hassan, Karnataka.
After visiting the wind farm some of the important observations were identified which
are mentioned as follows.
1. The farm is presently using capacitor banks for reactive power support with the
help of auto mechanical switches for maintenance of grid code.
2. The farm has to shut down when ever fault occurs at PCC to avoid voltage
collapse causing heavy loss to the utility.
3. Due to the intermittent nature of wind the continuous switching operation
occurrence induces harmonics in the system and wear and tear of the switches
leads to frequent replacement of switches.
4. As the wind is seasonal, the grid aiding with this renewable DG is not reliable.
With these observations lead the way to consider this as challenging study to give
solutions for the issues and associated problems were formulated. After literature
survey, it was found that STATCOM which belongs to FACTS family is the better
option. The study would suggest the possibility of hybrid generation around the free
land area of Nittur wind farm as the area is marshy land and belongs to forest
department and felt suitable for installation of PV plant.
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Based on the problem formulation, the study was able to identify the objectives to
carry out this research work. To execute the defined objectives the study concentrated
to work on the tools of MATLAB/SIMULINK for simulation studies. Then the
knowledge of this simulation study was implemented to IEEE test system. The results
obtained after modelling and simulation of test system, gave a broad way to work on
the modelling and simulation of the real system. The results of the simulation studies
carried out for both test system and real system are discussed in the next chapter.
Using a practical load profile, real weather data and availability of land area of about
100 acres around the wind farm located near Nittur, Hassan, Karnataka, total capacity
of PV plant that could be installed is proposed. The total capacity was estimated
using the information on installed PV plants in Karnataka.
Simulation study of PV cell, PV module and PV array were carried out to evaluate the
number of arrays that are required to generate the possible estimated PV power plant
capacity. The overall cost of PV system and PV plant capacity are estimated. This
additional renewable energy system, which will compliment the facility well,
showcasing the latest in energy production technology with the existing wind plant,
will provide a reliable power supply. The following section discusses the features of
MATLAB/SIMULINK used as tool for simulation studies.
5.2 MATLAB
MATLAB is a numerical computation and simulation tool that was developed into a
commercial tool with a user friendly interface from the numerical function libraries
LINPACK and EISPACK, which were originally written in the FORTRAN
programming language. MATLAB essentially involves only a single data structure,
upon which all its operations are based. This is the numerical field, or, in other words,
the matrix. This is reflected in the name: MATLAB is an abbreviation for MATrix
LABoratory.
The major advantage of MATLAB is the interaction with the special toolbox
SIMULINK. This is a tool for constructing simulation programs based on a graphical
interface. The simulation runs under MATLAB and an easy interconnection between
MATLAB and SIMULINK is ensured.
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5.3 SIMULINK
SIMULINK is advanced software which is increasingly being used as a basic building
block in many areas of research. As such, it holds a great potential in power system
example to demonstrate the features and scope of SIMULINK based model for
transient stability analysis.
SIMULINK is an interactive environment for modelling, analyzing and simulating a
wide variety of dynamic systems. The complete system can be illustrated in terms of
SIMULUNK blocks in a single integral model. One of the most important features of
SIMULINK is that it is being interactive, which is proved by the display of signals at
each and every terminal. A parameter within any block can be controlled from a
MATLAB command line or through an m-file program. This is used for the transient
stability study since the power system configuration differs before, after and during
the fault. Loading conditions and control measures can also be implemented
accordingly.
5.3.1 Simulation and Model Design
SIMULINK is a block diagram environment for multi domain simulation and Model-
Based Design. It supports system-level design, simulation, automatic code generation,
continuous test and verification of embedded systems. SIMULINK provides a
graphical editor, customizable block libraries, and solvers for modelling and
simulating dynamic systems. It is integrated with MATLAB, enabling to incorporate
MATLAB algorithms into models and export simulation results to MATLAB for
further analysis. Key Features are as follows
Graphical editor for building and managing hierarchical block diagrams
Libraries of predefined blocks for modelling continuous-time and discrete-
time systems
Simulation engine with fixed-step and variable-step Ordinary Differential
Equations (ODE) solvers
Scopes and data displays for viewing simulation results
Project and data management tools for managing model files and data.
Model analysis tools for refining model architecture and increasing simulation
speed
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MATLAB Function block for importing MATLAB algorithms into models.
Legacy Code Tool for importing C and C++ code into models
SIMULINK turns the computer into a laboratory for modelling and analyzing systems
that would not be possible for practical otherwise. SIMULINK provides with the tools
to model and simulate almost any real-world problem. It provides a graphical user
interface (GUI) for building models as block diagrams.
SIMULINK also includes a comprehensive block library of sinks, sources, linear and
nonlinear components, and connectors. If these blocks do not meet the needs,
however, there is a possibility to create user‟s own blocks. The interactive graphical
environment simplifies the modelling process, eliminating the need to formulate
differential and difference equations in a language or program.
Models are hierarchical, so user can build models using both top-down and bottom-up
approaches. User can view the system at a high level, and then double-click blocks to
see increasing levels of model detail. This approach provides insight into how a model
is organized and how its various parts interact.
5.3.2 Tool for Simulation and Analysis
After defining a model, user can simulate its dynamic behaviour using a choice of
mathematical integration methods, either from the SIMULINK menus or by entering
commands in the MATLAB command window. The menus are convenient for
interactive work, while the command line is useful for running a batch of simulations.
Using scopes and other display blocks, user can see the simulation results while the
simulation runs. User can then change parameters and see what happens for “what if”
exploration.
SIMULINK software is tightly integrated with the MATLAB environment. It requires
MATLAB to run, depending on it to define and evaluate model and block parameters.
SIMULINK can also use many MATLAB features. Because MATLAB and
SIMULINK are integrated, user can simulate, analyze, and revise their models in
either environment at any point.
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User needs MATLAB running before they can open the SIMULINK Library Browser.
The following procedure is required to open SIMULINK library.
Start MATLAB, and then in the MATLAB Command Window, enter
SIMULINK.
The SIMULINK Library Browser opens.
User can also open the SIMULINK Library Browser from the MATLAB
tool strip, by clicking the SIMULINK Library button.
If user has not already loaded SIMULINK, a short delay occurs while it
loads.
Once the above procedure is carried out General SIMULINK Library Browser
window opens which is shown in Figure 5.1.
Figure 5.1 General SIMULINK Library Browser window
To create a new SIMULINK Model, from the SIMULINK Library browser, the steps
involved are as follows:
From the SIMULINK Library Browser menu, select File> New> Model.
An empty model opens in the SIMULINK Editor. In the SIMULINK Editor,
select File > Save.
In the Save As dialog box, enter a name of the model, and then click Save.
SIMULINK saves the model.
Figure 5.2 shows the new SIMULINK model named untitled, which has to be saved
according to the users choice.
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The SIMULINK Library Browser displays the block libraries installed on the
computer. User can start to build models by copying blocks from a library into a
SIMULINK Editor Model window. For example, in the Library Browser shown in
Figure 5.3 the Sine Wave block is selected. Similarly other blocks according to the
model need to be created are selected.
Figure 5.2 New SIMULINK Model
Figure 5.3 Sine wave block from library
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Once all the blocks are selected and the model is developed then last step is to
simulate the model. Before simulating a model, simulation options are required to
setup. For this specific options, such as the stop time and solver, using the model
configuration parameters dialog box as shown in Figure 5.4. For example, in the Stop
time field, user can enter as 20 and in the Max step size field as 0.2. Then once
clicked OK the SIMULINK software updates the parameter values with changes and
close the configuration parameters dialog box which is shown as in Figure 5.4.
Figure 5.4 Configuration Parameters Window
After entering relevant configuration parameter, model is ready to simulate the simple
model and visualize the simulation results. The simple procedure is as follows:
In the SIMULINK Editor, select Simulation > Start. The simulation runs. The
simulation stops when it reaches the stop time specified in the configuration
parameters dialog box. Alternatively, controlling the simulation is possible by
clicking the Start simulation button and Pause simulation button on the
SIMULINK Editor toolbar.
Double-click the Scope block. The Scope window opens and displays the
simulation results.
From the Scope block toolbar, click the Parameters button. Select the Style
tab. The Scope Parameters dialog box displays Figure editing options.
Change the appearance of the Figure. For example, select white for the Figure
color and Axes background color. To see the changes, click Apply.
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Figure 5.5 shows the window of option for style changes of scope parameters. The
scope block displays its input with respect to simulation time and it also display
signals generated during simulation.
Figure 5.5 Style changes of scope parameters
The Scope block can have multiple axes (one per port) and all axes have a common
time range with independent y-axes. The scope block allows the user to adjust the
amount of time and the range of input values displayed. User can move and resize the
Scope window and can modify the scope's parameter values during the simulation.
If the signal is continuous, the scope produces a point-to-point plot. If the signal is
discrete, the scope produces a stair-step plot. Figure 5.6 shows the scope and its
various parameters.
Figure 5.6 Scope Parameters
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5.4 SimPowerSystems
SimPowerSystems software and other products of the physical modeling product
family work together with SIMULINK software to model electrical, mechanical, and
control systems. SimPowerSystems software operates in the SIMULINK
environment.
SimPowerSystems provides component libraries for modelling and simulating
electrical power systems. It includes models of three-phase machines, electric
drives, FACTS, and wind power generators. Abstracted models of power
electronics components are also included, enabling to assess the impact of
switching events on system-level behaviour. These components are used to model
the generation, transmission, distribution, and consumption of electrical power.
SimPowerSystems models can be discretized to speed up simulations and
configured for phasor simulation, which helps t o determine the transient stability
of electrical power systems. Key features of SimPowerSystems are:
Application-specific models, including common AC and DC electric drives,
flexible AC transmission systems and wind-power generators
Discretization and phasor simulation models for fast model execution
Ideal switching algorithm for fast simulation of power electronic devices
Functions for obtaining equivalent state-space representations of circuits
Tools for computing load flow and for initializing models of three-phase
networks with machines
Frequency domain analysis methods, including FFT and harmonics
Demonstration models of key electrical technologies
5.4.1 Role of Simulation in Design
SimPowerSystems software is a modern design tool that allows scientists and
engineers to rapidly and easily build models that simulate power systems. It uses the
SIMULINK environment, allowing the user to build a model using simple click and
drag procedures. Not only user can draw the circuit topology rapidly, but analysis of
the circuit can include its interactions with mechanical, thermal, control, and other
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disciplines. This is possible because all the electrical parts of the simulation interact
with the extensive SIMULINK modelling library. Since SIMULINK uses the
MATLAB® computational engine, designers can also use MATLAB toolboxes and
SIMULINK blocksets. SimPowerSystems software belongs to the physical modelling
product family and uses similar block and connection line interface.
5.4.2 SimPowerSystems Library
SimPowerSystems libraries contain models of typical power equipment such as
transformers, lines, machines and power electronics. These models are proven ones
coming from text books, and their validity is based on the experience of the Power
Systems Testing and Simulation Laboratory of Hydro-Québec, a large North
American utility located in Canada.
The SimPowerSystems main library, powerlib, organizes its blocks into libraries
according to their behaviour. The powerlib library window displays the block library
icons and names. Double-click a library icon to open the library and to access the
blocks. The main powerlib library window also contains the Powergui block that
opens a graphical user interface for the steady-state analysis of electrical circuits