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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

which is shown in Figure 5.7.

Figure 5.7 Powerlib Library Window

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5.4.3 Block Parameter Configurations

Modelling of each component of power system which would be required for the

power system analysis and study using Simpowersystem library blocks explained

along with the corresponding block parameters configurations. The main components

of power system such as Bus, Transmission Line, Source, Wind Farm, STATCOM etc

have been discussed.

Bus: This block is used to measure three phase voltages and currents in a circuit. So

it can be used as BUS for power system studies. Figure 5.8 and 5.9 represents the Bus

and its parameter window respectively. In Figure 5.9 it is observed that all the details

that are required for measurement needed to fill up.

Figure 5.8 Bus Representation

Figure 5.9 Bus Parameters

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Transmission Lines: This block models a three phase transmission line with single

PI section. The model consists of one set of RL series elements connected between

input and output terminals and two sets of shunt capacitances lumped at both ends of

the line which is shown in Figure 5.10. In transmission line block parameter, all the

necessary details of the line are entered as shown in Figure 5.11.

Figure 5.10 PI Section Transmission Line

Figure 5.11 Transmission Line Block parameter

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Transformer: Figure 5.12 and 5.13 shows the two winding three phase transformer

and this block implements three single-phase transformers to form three phase

transformers. The block model shown is step down transformer from 120 KV to 25

KV. But according to the requirement of the model the ratings can be adjusted.

Figure 5.12 Step Down Three Phase Transformer

Figure 5.13 Three Phase Transformer Block Parameter

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Grounding Transformer: This block implements a three phase transformer by using

three single phase transformers. Here the winding connection is set to ʏn to access the

neutral point of the Y. Also click measurements to none. Grounding transformer

representation and parameter window is shown in Figure 5.14 and 5.15.

Figure 5.14 Grounding Transformer

Figure 5.15 Grounding Transformer block parameter

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Three Phase Mutual Inductance: Three phase mutual inductance representation is

shown in Figure 5.16. This block implements three phase impedance with mutual

coupling between phases. Self impedance and mutual impedances are set by entering

positive and zero sequence parameters and shown in Figure 5.17.

Figure 5.16 Three phase Mutual Inductance

Figure 5.17 Three phase Mutual Inductance Block parameter

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Three Phase Programmable Voltage Source: This block implements a three –phase

zero- impedance voltage source and it is shown in Figure 5.18. The neutral is

accessible via input 1 of the block. Time variation for amplitude, phase and frequency

of the fundamental can be pre programmed which is shown in Figure 5.19.

Figure 5.18 Three phase Programmable Voltage Source

Figure 5.19 Three phase Programmable Voltage Source block parameters

Wind Farm: The wind farm block shown in Figure 5.20 constitutes subsystem

wherein six 1.5 MW rating Wind Turbine Generators are modelled which is shown in

Figure 5.21. As shown in Figure 5.22 the turbine details such as output power, wind

speed and pitch angle can be assigned according to the designed model.

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Figure 5.20 Wind Farm block

Figure 5.21 Wind Turbine Generator

Figure 5.22 Block parameter of Wind Turbine Generator

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Three Phase Fault: Using this block a fault can be created wherein the user can

create either LG or LLG or three phase fault according to requirement of the study of

the system. Figure 5.23 shows its representation and Figure 5.24 where any type of

short circuit can be created to see the performance and effects on the system

Figure 5.23 Fault Representation block

Figure 5.24 Three phase fault block parameter window

STATCOM: This power Electronic device is of phasor type representation used for

controlling reactive power and is represented in Figure 5.25. The converter rating can

be changed in the block parameter depending upon the user‟s application which is

shown in Figure 5.26. It can be made connected to the circuit with the help of manual

switch to No trip position, in contrast can be disconnected at Trip position.

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Figure 5.25 STATCOM Block (Phasor type)

Figure 5.26 Block parameter of STATCOM

Various other components of power system that are required for modelling the power

system can be obtained from the library and blocks can be chosen as discussed above.

After the study of all the blocks that are required for the desired power system, next

step is to modelling the power system.

Powergui: The Powergui block is necessary for simulation of any SIMULINK model

containing SimPowerSystems blocks. It is used to store the equivalent SIMULINK

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circuit that represents the state-space equations of the model. Rules to be followed

when using this block in a model are as follows:

Always place the Powergui block at the top level of diagram for optimal

performance. However, user can place it anywhere inside subsystems for their

convenience; its functionality will not be affected.

There can be a maximum of one Powergui block per model

Must name the block powergui

Figure 5.27 shows the representation of Powergui block which is essential to include

in the model created for study purpose. Figure 5.28 shows various power system

analysis that can be performed from Powergui block parameter.

Figure 5.27 Powergui Block

Figure 5.28 Analysis tools from Powergui block parameter

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5.5 Wind System Modeling using MATLAB/SIMULINK

As discussed in previous sections usage of SimPowerSystems software for Modelling

requires MATLAB and SIMULINK.

In addition to SimPowerSystems software, the physical modelling product family

requires other products for modelling and simulating mechanical and electrical

systems. There are also a number of closely related tool boxes and other products

from the MathWorks that can be used with SimPowerSystems software.

The graphical user interface makes use of the SIMULINK functionality to

interconnect various electrical components.

The electrical components are grouped in a library called blocks and it is shown

Figure 5.29. Each component is represented by a special icon having one or several

inputs and outputs corresponding to the different terminals of the component.

Figure 5.29 Power system components library

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To build a required model, first step is to copy the blocks from the SIMULINK

Library Browser to the new model window as explained earlier. The power library

and the new model window are shown in Figure 5.30

Figure 5.30 Power system components library and new model window

The blocks that are needed to build the model on the new untitled file are to be

carried out. The step by step procedure is as follows:

Select the Sources library in the SIMULINK Library Browser.

Right click on the block to be used.

Select “open to untitled”.

Then the selected block will gets added to the „untitled‟ file as shown in Figure 5.31

and 5.32. Like this any block that need to be loaded, to create a model can be added

to the untitled file for simulation.

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Figure 5.31 Three phase π section line selection to add to new model in

untitled file

Figure 5.32 Loading of selected file to untitled file from the

simpowersystem library

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Similarly by following above steps required power system can be created

which includes the following components which were clearly explained in

previous subchapter.

Bus

Transmission line

Ground

Three-Phase Source

Load

Wind Farm

STATCOM

To show how the components are loaded to the untitled file, STATCOM block and

wind farm block are taken as example and are shown in Figure 5.33 and 5.34

respectively.

Figure 5.33 STATCOM loaded to untitled model

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Figure 5.34 Wind Farm loaded to Untitled new Model

After selecting the required power system components from the simpowersystem

library, desired model can be obtained. The modelling of a sample system is

modeled with the help of procedure explained which is shown in Figure 5.35.

Figure 5.35 Sample Power System Model

Once the power system is modelled next step is to simulate the system and if there are

no errors the results are observed from relevant scopes which are explained in the next

coming section.

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5.6 PV System Modelling with MATLAB/SIMULINK

PV module represents the fundamental power conversion unit of a PV generator

system. The output characteristics of PV module depends on the solar insolation, the

cell temperature and output voltage of module. Since PV module has nonlinear

characteristics, it is necessary to model it for the design and simulation of maximum

power point tracking (MPPT) for PV system applications.

However, the SimPowerSystem tool in Matlab/SIMULINK package offers wind

turbine models but no PV model to integrate with current electronics simulation

technology. Thus, it is difficult to simulate and analyze in the generic modelling of

PV power system. This motivates to develop a generalized model for PV cell, module

and array using Matlab/ SIMULINK.

This model of PV cell, PV characteristics module and PV array was based on a

MATLAB model from ECEN2060. The MATLAB window is shown in Figure 5.36.

Figure 5.36 MATLAB window

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The SIMULINK model of a PV cell is shown in Figure 5.37. The description of each

block of the PV cell model is shown in Figure 5.38. The P-V power and I-V

characteristics represents X-Y plot of its inputs in a MATLAB window and

workspace block to save the input as an N-dimensional array and are discussed in

results and discussion chapter. These PV cells are grouped together to obtain PV

modules. The SIMULINK model of PV module is shown in Figure 5.39.

Figure 5.37 PV Cell SIMULINK Model

Figure 5.38 Description of each block of the PV Cell Model

ECEN2060

PV cell characteristics

Vpv

PV

To WorkspaceProduct

PV power

1e-9*(exp(u/26e-3)-1)

PN-junction characteristic

1/1000

Insolation to

ISC current gain

1000

Insolation

I-V characteristic

ISC

Id

Ipv

Ipv

Ppv

Ppv

Vpv

Vpv

PV cell characteristic

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Figure 5.39 PV Module SIMULINK Model

Depending upon the requirement of PV system the modules are classified as current

input PV module as shown in Figure 5.40 and voltage input PV module as shown in

Figure 5.41. The current input module is well suited for the case when modules are

required to be connected in series and share the same current. Whereas the voltage

input module is suited for the case when modules are needed to be connected in

parallel and share the same voltage.

Figure 5.40 Current input PV Module

Figure 5.41 Voltage input PV Module

Based on the requirement data sheet in MATLAB/SIMULINK window is filled

accordingly. The parameters for the study are conFigured on the basis of ECEN2060

details and the window parameter is shown in Figure 5.42. The modules are finally

connected together to obtain PV array. Here six module output are added with

summer to show how the output can be increased as shown in Figure 5.43.

ECEN2060

PV Module Characteristics

Vpv

Vpv

Insolation

Ipv

Ppv

PV module (V)

PV1

PV power

Insolation

I-V characteristic

Vpv

Vpv

Ipv

PV Module characteristic

Characteristic

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Figure 5.42 Parameters to be configured in a PV Model block

Figure 5.43 PV Array Model

ECEN2060

6-module PV Array

XY power

XY V-I

PV

To Workspace

Product

Ipv

Insolation

Vpv

Ppv

PV module (I)

PV6

Ipv

Insolation

Vpv

Ppv

PV module (I)

PV5

Ipv

Insolation

Vpv

Ppv

PV module (I)

PV4

Ipv

Insolation

Vpv

Ppv

PV module (I)

PV3

Ipv

Insolation

Vpv

Ppv

PV module (I)

PV2

Ipv

Insolation

Vpv

Ppv

PV module (I)

PV1

Ipv Ramp

1000

Insolation

Add

Ipv

Ipv

Vpv

Vpv

Ppv

Ppv

6 Module PV Array

characteristic

Characteristic

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5.7 Scope Details

After modelling, the simulation is carried out for analysing the system. If there exists

any error in the model, simulation terminates showing the related compilation errors

that needed to be corrected for the modelling. Simulation time for analysis can be

selected suitably. Finally to observe the results scopes are used as explained in

previous chapter.

For this study details like Bus voltage V, current I, real power P and reactive power Q

at PCC are required and hence they are measured and selected for modelling in the

scope. Figure 5.44 shows the bus scope and Figure 5.45 shows the measurement of all

the parameters of the bus. Similarly wind speed, real power, reactive power and pitch

angle measurements are required and hence scopes were modelled according to the

requirements which are shown in Figures 5.46 and 5.47. Finally from STATCOM t

he measurements such as voltage and reactive power are necessary for the study and

hence scopes are modelled as shown in Figures 5.48 and 5.49.

Figure 5.44 Bus Scope details

Figure 5.45 Measurement of various parameters of the bus

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Figure 5.46 Wind Turbine Scope details

Figure 5.47 Measurement of various parameters of wind turbine

Figure 5.48 STATCOM Scope details

Figure 5.49 Measurement of various parameters of STATCOM