Post on 29-Jun-2020
1
POWER ELECTRONICS IN POWER SYSTEMS
- CONTROLLERS
By
JEC - STTP
Sasidharan Sreedharan
www.sasidharan.webs.com
2
Executive Summary
The work presents the application of power electronics in power system with special emphasis on artificial intelligence based controllers for renewable integration
JEC - STTP
Power Electronics in Power System
“POWER ELECTRONICS IN POWER SYSTEM – CONTROLLER”
JEC - STTP 3
Electric power systems are comprised of components that produce electrical energy and
transmit this energy to consumers.
A modern electric power system has mainly six main components:
• Power plants which generate electric power,
• Transformers which raise or lower the voltages as needed
• Transmission lines to carry power
• Substations at which the voltage is stepped down
for carrying power over the distribution lines
• Distribution lines
• Distribution transformers which lower the voltage
to the level needed for the consumer equipment.
Problem • We need to supply good quality power (possibly pure sinusoidal supply at rated voltage
and frequency) at minimum cost to consumers.
• But it is very difficult and challenging and duty of Power Electronics too.
• Power Electronics: is the electronics applied to conversion and control of electric
power
• Often Power Electronics applications in renewable integration of power system is by
embedding algorithm to an intelligent controller and hence the title
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POWER ELECTRONICS
IN POWER SYSTEM
- KEY DIAGRAM
Contents
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Part Topic
1 Challenges faced by the power sector
2 High Voltage Direct Current Transmission System (HVDC)
3 Flexible AC Transmission Systems (FACTS)
4 Custom Power Devices
5 Controllers for the grid integration of renewables
Conclusion Power Electronics in Smart Grid
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6
Presentation Objective &
Approach
• Identify the problems and challenges
faced by the power sector.
• Explore the possible power electronic
solutions to solve those problems.
7
PART- I
CHALLENGES FACED BY THE
ELECTRICAL POWER SECTOR
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Major Challenges faced by Electrical Power Sector
1. High reactive power losses & its management
2.Grid stability at large scale integration of renewables.
3. Limited transmission capacity
4. Power quality issues
5. Control of power flow
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INDIAN POWER GRID AT A GLANCE
http://www.srldc.org
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12
HIGH VOLTAGE DC CURRENT
TRANSMISSION (HVDC)
PART- II
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SOLUTION
HVDC is the only practical solution
to the above stated problems
HVDC Links In India
Asynchronous Connection and Bulk Power Transfer
1.Interconnection of non-
synchronous AC power systems, even at different frequencies.
2.Power transmission over long
undersea cable links.
3.Point-to-point, long-distance
transmission of large blocks of power.
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Advantages
• Voltage transformation
• Asynchronous Tie /Link
• Frequency as system-wide control signal
• Low losses (direct current)
• No limitations in length (Cables can be used over long
distances as there is no reactive power consumption)
Limitations
• Base costs for converter stations economically interesting only at
longer distances
• Point-to-point connection (multi-terminal possible with VSC -
HVDC)
Salient Features of HVDC Transmission
System
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HVDC Transmission System Model
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Source: http://www.ptd.siemens.de/artikel0506.html
HVDC EAST- SOUTH INTERCONNECTION IN INDIA
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Source: http://www.ptd.siemens.de/artikel0506.html
HVDC INSTALLATIONS
EAST- SOUTH INTERCONNECTION IN INDIA
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HVDC Topologies
Source: http://www.abb.com/hvdc
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HVDC Classic
• Mostly used for long distance point-to-point transmission
• Requires fast communication channels between two stations
• Large reactive power support at both stations
• Thyristor valves are commonly used.
• Line or phase commutated converters are used.
HVDC Light
Power transmission through HVDC utilizing voltage source converters
with insulated gate bipolar transistors (IGBT) which extinguishes the
current more faster and with less energy loss than GTOs.
• It is economical even in low power range.
• Real and reactive power is controlled independently in two HVDC
light converters.
• Controls AC voltage rapidly.
• No contribution to short circuit current.
• No need to have fast communication between two converter stations.
• Operates in all four quadrants.
• PWM scheme is used.
HVDC Technologies
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MATLAB MODEL OF 1000MW HVDC TRANSMISSION SYSTEM
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HVDC PLACEMENT ANALYSIS IN POWER SYSTEM
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HVDC PLACEMENT IN POWER SYSTEM
(Power Flow Analysis)
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HVDC PLACEMENT IN POWER SYSTEM
(Voltage Profile)
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HVDC PLACEMENT IN POWER SYSTEM
(Power Flow Profile)
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HVDC WORLD WIDE INSTALLATIONS
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• The power system can be stabilized and the
transmission limitations on the AC line can be
increased by using HVDC .
• A HVDC transmission line costs less than an AC line
for the same transmission capacity.
• However, the terminal stations are more expensive in
the HVDC case due to the fact that they must
perform the conversion from AC to DC and vice
versa.
• The "break-even distance“ for long overhead lines
is > 700 km
CONCLUSION - HVDC
• HVDC can control/ transmit contracted amounts of power and alleviate unwanted
loop flows.
• An HVDC link can alternatively be controlled to minimize total network losses
• An HVDC link can never be overloaded
• The HVDC damping controller is a standard feature in many HVDC projects in
operation. It normally takes its input from the phase angle difference in the two
converter stations. (see fig.)
27
PART- III
FLEXIBLE AC TRANSMISSION SYSTEMS
(FACTS)
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Flexible AC Transmission System
Alternating current
transmission systems
incorporating power
electronics-based and
other static controllers to
enhance controllability
and increase power
transfer capability
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Sub-synchronous resonance
• Resonant frequencies below the
fundamental.
• Occurs due to interaction between
series capacitors and nearby
turbine‐generators
Role of FACTS
• Dynamic: – Transient and
dynamic stability
– Sub synchronous oscillations
– Dynamic overvoltage and under voltages
– Voltage collapse
– Frequency collapse
• Steady-State:
– Uneven power flow
– Excess reactive power flows
– Voltage capability
– Thermal capability
30 JEC - STTP
31
Benefits of FACTS Control of power flow
– Contractual Power Flow
– Increase the loading capability of lines to their
thermal capabilities.
– Increase the system security through raising the
transient stability limit, limiting short-circuit currents and
overloads, managing cascading blackouts and damping
electromechanical oscillations of power systems and
machines.
Provide secure tie line connections to neighboring utilities
and regions thereby decreasing overall generation
reserve requirements on both sides.
– Provide greater flexibility in new generation.
– Reduce reactive power flows, thus allowing the lines to
carry more active power. JEC - STTP
FACTS Devices
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• Static VAR Compensator - SVC
• Thyristor Controlled Series Compensator - TCSC
• Thyristor Controlled Phase Angle Regulator - TCPAR
• Static Synchronous Compensator - StatCom
• Solid State Series Compensator - SSSC
• Unified Power Flow Controller - UPFC
Shunt connected controllers
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Series connected controllers
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Combined shunt and series connected controllers
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Other controllers
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FACTS devices are solid-state converter that have the capability of control of various electrical parameters in transmission circuit Thyristor Controlled Series
Compensator (TCSC)
Static VAR Compensator (SVC)
Unified Power Flow Controller (UPFC)
Static Compensator (STATCOM)
Static Synchronous Series Compensator (SSSC), etc
37
etc etc
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FLEXIBLE AC TRANSMISSION SYSTEM
38 JEC - STTP
•(TG- Turbine Governor; AVR-Automatic Voltage regulator; C-Synchronous Compensator)
CASE STUDY: SVC PLACEMENT IN KERALA GRID
39 JEC - STTP
SVC
SVC
SVC
SVC
CASE STUDY: SVC PLACEMENT IN KERALA GRID
40
0.00
1.00
2.00
3.00
4.00
5.00
6.00
1 3 5 7 9 11 13 15 17 19 21 23 25
Rea
l pow
er l
oad
(pu
)
Bus no.
Base case (with out wind)
Base case (with wind)
Maximum penetration (with controller)
0.95
0.97
0.99
1.01
1.03
1.05
1.07
1.09
1.11
1 2 3 4 5 6 7 8 9 10111213141516171819202122232425
Bu
s volt
age
(pu
)
Bus no.
Base Case (with out wind)Base case (with wind)Maximum penetration (with controller)
0.00
1.00
2.00
3.00
4.00
5.00
6.00
7.00
1 3 5 7 9 11 13 15 17 19 21 23 25
Rea
l pow
er g
ener
atio
n (
pu
)
Bus no.
Base case (with out wind)
Base case (with wind)
Maximum penetration (with controller)
-15
-10
-5
0
5
10
15
-6 -5 -4 -3 -2 -1 0
Eigen value(0 to-5)
Eigenvalue (Real part)
Eig
enval
ue
(Im
agin
ary p
art)
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Wind Farm Bus : 1,21
Slack Bus : 5
CASE STUDY: SVC PLACEMENT IN KERALA GRID
41
PART- IV
CUSTOM POWER DEVICES
(Power Quality Solutions)
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Custom Power & FACTS
• Similar to FACTS for the transmission systems, the term custom power (CP)
means the use of power electronic controllers for distribution systems.
• Custom power devices enhances the quality and reliability of power that are
delivered to customers.
• There is also a concept called “Custom Power Park” that can serve customers
who demand a high quality of power and ready to pay a premium price for the
service.
• Custom power assures the pre-specified quality/ specifications:
– Reduce the Frequency of rare power interruptions.
– Magnitude and duration of over and under voltages within specified
limits.
– Low harmonic distortion in the supply voltage.
– Low phase unbalance.
– Low flicker in the supply voltage.
– Frequency of specified voltage with specified limits
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Custom Power Devices
• Customer power devices can be classified in to two main types.
– Reconfiguring type
– Compensating type
• Reconfiguring type - Changes the network topology or re-configure the next
work by altering the network.
– Solid State Current Limiter (SSCL)
– Solid State Circuit Breaker (SSCB)
– Solid State Transfer Switch (SSTS)
• Compensating devices - Compensate a load, by correcting power factor,
balancing an unbalanced load or improve the quality of the supply voltage
– Distribution STATCOM (D-STATCOM)
– Dynamic Voltage Restorer (DVR)
– Unified Power Quality Conditioner (UPQC)
(D-STATCOM is a shunt device used for load compensation, dynamic and static voltage control. DVR is a series connected
device used for voltage compensation. UPQC is a combination of D-STATCOM and DVR.)
.
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Solid State Current Limiter
• The major components are an inductor, pair of opposite poled switches (GTOs or IGBTs) and a snubber circuit.
• Snubber circuit is a series RC circuit which prevents a huge sudden voltage rise across the inductor.
• Current limiter is connected in series with the feeder such that it can restrict the fault current in case of a fault downstream.
• During the normal operation the opposite poled switches remained closed. JEC - STTP 44
Solid State Circuit Breaker
• Same topology as that of SSCL, except the current limiting
inductor is connected in series with the thyristor pair.
• These thyristor pair is switched on simultaneously with the
bidirectional switch and switch off upon detection of fault.
• This will force the current to flow through the thyristors and
current limiting inductors.
• The thyristor pair is blocked after few cycles if the fault still
persists.
• In this case, the current through the thyristor will cease to flow in
the next available zero crossing.
• There still might be a small amount of current flow through the
snubber circuit which can be easily interrupted by a mechanical
switch.
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Solid State Transfer Switch
• Used to transfer power from the preferred to alternative sources in case of a
problem in the preferred feeder (e.g. voltage sag or swell, fault on the
feeder).
• This switch could be used to protect sensitive loads.
• The main component of SSTS is two pair of opposite poled switch
(thyristors).
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Compensating Custom Device -
DSTATCOM
• Distribution Static Compensator (DSTATCOM) is basically
the same as STATCOM used in the transmission system,
except the switches used here are high speed medium power.
Load compensating DSTATCOM
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DSTATCOM
• Distribution STATCOM (DSTATCOM) exhibits high speed
control of reactive power to provide voltage stabilization,
flicker suppression, and other types of system control.
• The compensator must inject current such that Is becomes
fundamental and positive sequence.
• In addition to those the compensator can also make the
current Is to be in phase with bus voltage at Bus-2.
• DSTATCOM is compensating load current.
• As far as the utility is concerned Load along with the
DSTACOM is drawing a unity power factor and balanced
current at fundamental frequency.
• The desired performance of the DSATCOM is that it
generates a current If such that it cancels the reactive,
harmonic components and balanced the load current. JEC - STTP 48
DSTATCOM - Analysis
Example: Consider the following circuit in which
the voltage sources is considered to be stiff.
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DSTATCOM operating in the
current control mode
DSTATCOM
• The DSTACOM injects
currents that cancel
harmonics from load current
and also balance the load.
• It also forces the current draws
from the source to be in phase
with the voltage at PCC, i.e.
draws current at unity power
factor (only real current).
• Power supplied by the sources
is constant, the power supplied
by the DSTATCOM has zero
mean.
• DSTATCOM neither absorbs or
injects real power to the load. JEC - STTP 50
Voltage Regulating DSTATCOM
• The basic idea in this kind of schemes is to inject the current id in such a
way that the voltage vt follows a specified reference.
• The DSTACOM should operate in such a manner that it does not inject or
absorb any real power in the steady state.
• The magnitude of the terminal voltage can be arbitrarily chosen.
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52
Matlab Model of DSTATCOM
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Case Study-Arc Furnace
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For weak distribution systems where the operation of arc furnaces causes
significant power quality problems, a high performance flicker compensation
device is necessary.
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• The flicker caused by the arc furnace operation was measured by use of
a flicker meter.
In this application, the flicker suppression realized was 58% on
average with utilization of the DSTATCOM. http://www.donsion.org
Dynamic Voltage Regulator (DVR)
• A Dynamic Voltage Regulator is used to protect sensitive loads from sag/swell or disturbances in the supply voltage.
Vl=Vt+Vf
• Where Vl is the load bus voltage, Vt is the terminal voltage and Vf is the DVR
voltage.
• DVR can regulate the bus voltage to any arbitrary value by measuring terminal
voltage and supplying the balance voltage Vf.
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Dynamic Voltage Regulator (DVR)
Unified Power Quality Conditioner (UPQC)
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• A device that is similar in construction to a Unified Power flow
Conditioner (UPFC).
• The UPQC, just as in a UPFC, employs two voltage source inverters
(VSIs) that are connected to a d.c. energy storage capacitor.
• One of these two VSIs is connected in series with a.c. line while the
other is connected in shunt with the a.c. system.
• A UPQC that combines the operations of a Distribution Static
Compensator (DSTATCOM) and Dynamic Voltage Regulator (DVR)
together
Unified Power Quality Conditioner (UPQC)
• One of the serious problems in electrical systems is the increasing number of
electronic components that injects harmonics in the distribution system.
• The device that can be used for this purpose is unified power quality conditioner
(UPQC)
• If the source voltage is unbalanced and distorted, the terminal voltage will also be
unbalanced and distorted and all the customers connected to the feeder will be
affected.
• All the loads connected to the feeder, including unbalanced and nonlinear loads,
will have a balanced sinusoidal voltage.
• It will not be possible to correct the unbalance and distortion produced by source using this device.
• There are two ways of connecting a UPQC. – The series device is placed before the shunt
– The shunt device is placed before the series device.
• Usually, the inverter realizing the series device is supplied with a dc capacitor. Similarly, the shunt inverter is also supplied with a capacitor.
• In UPQC, these inverters are supplied by a common capacitor
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Custom Power Park (CPP)
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Custom Power Park (CPP)
• A custom power park control center is fully loaded with a DSTACOM, a DVR and a stand by generator.
• The DSATCOM eliminates harmonics and/or unbalance, while the DVR eliminates any sag or distortion.
• Here the electrical power to the park is supplied through two feeders that are joined together via a SSTS.
• The SSTS ensures that the feeder with higher voltage selected in less than half a cycle in the case of a voltage dip or (sag).
• The SSTS can also be used to protect the loads in the park from dynamic over
voltage.
• DSTACOM when operated in voltage control mode and can provide reactive
power support to the park and maintain voltage.
• There are three different grades of power can be supplied to the park’s
customers.
– Grade A
– Grade AA
– Grade AAA
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Custom Power Park (CPP)
• Grade A: The basic quality power in the park.
– Since the SSTS protect the incoming feeders, the quality of power is usually better than the one from normal utility supply.
– In addition this grade has the benefit of low harmonic power due to the presence of DSTATCOM.
• Grade AA: This includes all the features of Grade A + – It also receives the benefits of standby generator which can be brought into
service with in 10-20 seconds (e.g. serious emergency such as power failure in both feeders).
• Grade AAA: This includes all the features of Grade AA+ It enjoys the benefits of receiving distortion and dip free voltage due to the presence of DVR.
– Semiconductor plant AAA
– Hospital both AA and AAA
– Shopping malls and office buildings AA
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PART- V
CONTROLLER FOR THE GRID INTEGRATION OF
RENEWABLES
The Work Presents the development of particle swarm optimization
based controller for maximizing the wind energy penetration in power
system.
63
(Controller/Algorithm)
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Controller Schematic
1. Consumer loads are changing instantaneously.
2. The nature of grid hence is very dynamic.
3. We have to supply power at the minimal cost to the consumers.
4. Wind is abundantly available and cost/unit is very less; and is also green.
5. Wind power has to be increased in the grid.
6. But as the wind share increases, there arise lots of instability problems in grid (Voltage and frequency).
7. So the question finally arises
HOW MUCH MAXIMUM WIND SHARE WE CAN ALLOW AT ANY TIME?
WHAT ARE THE METHEDOLOGIES AND TECHNIQUES FOR MAXIMIZING WIND PENETRATION
64
The Wind Penetration Controller Problem
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Control bus
Wind Farm Control
Pw Nf
1-Xn
1-X3
GN
1-X2
1-X1
G3 G2 G1
Market Analyzer and Planner
1+Y1 1+Y2
L1
1+Y3
1+Yn
L2 L3 LN
OPF
FACTS Controller Optimizer
Storage requirement
calculator
Contingency analysis
Combined load increase and generation
displacement method
Load increase method
Generation displacement
method
Voltage SSSA
Single
Objective
Multi
Objective
TSA
Optimization
Stability
Data bus Implemented Yet to implement
Grid Control
65 JEC - STTP
The Complete Wind Penetration Controller
Maximize
Pw; Real power output of all the wind farms to the grid by adjusting the grid parameters
Subject to
1. Power flow constraints Nodal power balance constraints
Active power generation limit constraints
Reactive power generation limit constraints
Voltage limit constraints
Line limit constraints
2. Wind generation constraints
3. Grid Stability Constraints Voltage stability constraints
Angle stability constraints
4. FACTS Controller Constraints
66 JEC - STTP
Controller Problem Description
67
It was developed in 1995 by J. Kennedy and R. Eberhart
PSO is a robust stochastic optimization technique base on the movement and intelligence of swarms.
PSO applies the concept of social interaction to problem solving.
It uses a number of agents (particle) than constitute a swarm moving around the search space looking for the best solution.
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Particle Swarm Optimization
68
IEEE 14-bus Test System
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•(TG- Turbine Governor; AVR-Automatic Voltage regulator; C-Synchronous Compensator)
WFPI Rank-1 for Bus No: 3
Case Study- IEEE 14 bus System
Problems in Wind
Farm Integration
Small Scale Impacts
• Branch flows and node voltages
• Protection schemes and fault
currents
• Power Quality
Large Scale Impacts
Power system dynamic
stability
Frequency control and load
following
Reactive power and voltage
control
Wind speed
Interconnection
bus strength
Interconnection
cable length
Wind farm
size
69 JEC - STTP
70
GRID
STABILITY
Angle Voltage
Fast voltage
stability Index
Line stability
factor
Small signal
stability analysis
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71 JEC - STTP
Methodology
Connect Wind
Farm at the
best suitable
bus.
Formulate
DFIG based
Wind Farm
model.
Using PSO,
calculate the
optimal grid
and FACTS
controller
settings
Obtain
maximum
wind
penetration
limit
Methodology
72
Objective Function
Constraints
GRID STABILITY CONSTRAINTS
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Detailed Problem Formulation
73 JEC - STTP
SVC is used for wind penetration maximization.
The location of the SVC is judged by conducting the static voltage
stability analysis and the setting is done by using PSO
Bus number Normalized tangent vector near collapse
point
14 0.015802
10 0.01404
13 0.013938
9 0.013764
FACTS Controller Placement
74
0.00
0.50
1.00
1.50
2.00
2.50
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Rea
l pow
er l
oad (
pu
)
Bus no.
Base case (with out wind)
Base case (with wind)
Maximum penetration (with
controller)
0.00
0.50
1.00
1.50
2.00
2.50
3.00
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Rea
l p
ow
er g
ener
atio
n (p
u)
Bus no.
Base case (with out wind)
Base case (with wind)
Maximum penetration (with
controller)
-15
-10
-5
0
5
10
15
-6 -5 -4 -3 -2 -1 0
eigen…
Eigen value (Real
part)
Eig
en v
alu
e (I
mag
inar
y p
art)
0.95
0.97
0.99
1.01
1.03
1.05
1.07
1.09
1.11
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Bu
s volt
age
(pu
)
Bus no.
Base case (with out wind)Base case (with wind)Maximum penetration (with controller)
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SVC
Bus:10,14
Analysis Results
Power Electronics in Smart Grid
JEC - STTP 75
Smart Grid
JEC - STTP 76
• The Smart Grid is a combination of hardware, management and reporting software, built atop an intelligent communications infrastructure.
• In the world of the Smart Grid, consumers and utility companies alike have tools to manage, monitor and respond to energy issues.
• The flow of electricity from utility to consumer becomes a two-way conversation, saving consumers money, energy, delivering more transparency in terms of end-user use, and reducing carbon emissions.
• The Smart Grid in large, sits at the intersection of Energy, IT and Telecommunication Technologies.
• Smart Grid Consists of the following
– Transmission Optimization
– Demand Side Management
– Distribution Optimization
– Asset Optimization
What is Smart Grid ? What is Smart Grid
JEC - STTP 77
Demand Optimization Smart Metering –
Automatic, Time of Use, Consumer Communication & Load Control
Communications : Automated Metering Infrastructure (AMI) – LAN, WAN etc.
DRMS (Demand Response Management Sytem)
Elements of Smart Grid
It is having the following GIS (geo-spatial Information Systems),
AMI,
SAP (ERP),
OMS (Outage management System),
DMS (Distribution Management System),
EMS (Energy Management System),
DRMS (Demand Response management
System).
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80
Regards
Sasidharan Sreedharan
www.sasidharan.webs.com
JEC - STTP