the control of DVR with bess

CONTROL OF DVR WITH BESS
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CHAPTER-1

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1. INTRODUCTION
1.1 INTRODUCTION:
Nowadays, modern industrial devices are mostly based on electronic devices such as
programmable logic controllers and electronic drives. The electronic devices are very sensitive to
disturbances and become less tolerant to power quality problems such as voltage sags, swells and
harmonics. Voltage dips are considered to be one of the most severe disturbances to the
industrial equipments.
Voltage support at a load can be achieved by reactive power injection at the load point of
common coupling. The common method for this is to install mechanically switched shunt
capacitors in the primary terminal of the distribution transformer. The mechanical switching may
be on a schedule, via signals from a supervisory control and data acquisition (SCADA) system,
with some timing schedule, or with no switching at all. The disadvantage is that, high speed
transients cannot be compensated. Some sag are not corrected within the limited time frame of
mechanical switching devices. Transformer taps may be used, but tap changing under load is
costly.
Voltage support at load can be achieved by reactive power injection at the load point of
common coupling. The common method for this is to install mechanically switched shunt
capacitors in the primary terminal of the distribution transformer.
The mechanical switching may be on a schedule, via signals from a supervisory control
and data acquisition (SCADA) system with some timing schedule, or on switching at all. The
disadvantage is that, high speed transients cannot be compensated within the limited time frame
of mechanical switching devices. Transformers taps may be used but tap changing under is
costly.
Another power electronic solution to the voltage regulation is the use of a dynamic
voltage restorer (DVR). DVRs are a class of custom power devices for providing reliable
distribution power quality. They employ a series of voltage boost technology using solid state
switches for compensating voltage sags/swells. The DVR applications are mainly for sensitive
loads that may be drastically affected by fluctuations in system voltage.

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They employ a series of voltage boost technology using solid state switches for
compensating voltage sags/swells. The DVR applications are mainly for sensitive loads that may
be drastically affected by fluctuations in system voltage.
Power quality problem encompass a wide range of disturbances as voltage sags/swells,
flickers, harmonic distortion, impulse transient and interruptions. Voltage sags occur at any
instant of time, with amplitudes ranging from 10-90% and duration is lasting for half a cycle to
one minute. Voltage swell, on the other hand, is defined as a swell increases in rms voltage or
current at the power frequency for durations from 0.5cycles to one minute typical magnitudes are
between 1.1 and 1.8 pu. Swell magnitude is also remaining voltage in this case always greater
than one.
Voltage swells are not as important as voltage sags because they are less common in
distribution systems voltage sag and swell can cause sensitive equipment to fail, or shutdown as
well as create a large current unbalance that could blow fuses or trip breakers. These effects can
be very expensive for the customer, ranging from minor quality variations to production down
time and equipment.

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CHAPTER-2

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2. POWER QUALITY
2.1 INTRODUCTION:
The contemporary container crane industry, like many other industry segments, is often
enamored by the bells and whistles, colorful diagnostic displays, high speed performance, and
levels of automation that can be achieved. Although these features and their indirectly related
computer based enhancements are key issues to an efficient terminal operation, we must not
forget the foundation upon which we are building. Power quality is the mortar which bonds the
Foundation blocks. Power quality also affects terminal operating economics, crane reliability,
our environment, and initial investment in power distribution systems to support new crane
installations. To quote the utility company newsletter which accompanied the last monthly issue
of my home utility billing: ‘Using electricity wisely is a good environmental and business
practice which saves you money, reduces emissions from generating plants, and conserves our
natural resources.’ As we are all aware, container crane performance requirements continue to
increase at an astounding rate. Next generation container cranes, already in the bidding process,
will require average power demands of 1500 to 2000 kW – almost double the total average
demand three years ago. The rapid increase in power demand levels, an increase in container
crane population, SCR converter crane drive retrofits and the large AC and DC drives needed to
power and control these cranes will increase awareness of the power quality issue in the very
near future.
2.2 POWER QUALITY PROBLEMS:
For the purpose of this article, we shall define power quality problems as:
‘Any power problem that results in failure or disoperation of customer equipment, Manifests
itself as an economic burden to the user, or produces negative impacts on the environment.
‘When applied to the container crane industry, the power issues which degrade power quality
include:

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 Power Factor
 Harmonic Distortion
 Voltage Transients
 Voltage Sags or Dips
 Voltage Swells
The AC and DC variable speed drives utilized on board container cranes are significant
contributors to total harmonic current and voltage distortion. Whereas SCR phase control creates
the desirable average power factor, DC SCR drives operate at less than this. In addition, line
notching occurs when SCR’s commutate, creating transient peak recovery voltages that can be 3
to 4 times the nominal line voltage depending upon the system impedance and the size of the
drives. The frequency and severity of these power system disturbances varies with the speed of
the drive. Harmonic current injection by AC and DC drives will be highest when the drives are
operating at slow speeds. Power factor will be lowest when DC drives are operating at slow
speeds or during initial acceleration and deceleration periods, increasing to its maximum value
when the SCR’s are phased on to produce rated or base speed. Above base speed, the power
factor essentially remains constant. Unfortunately, container cranes can spend considerable time
at low speeds as the operator attempts to spot and land containers. Poor power factor places a
greater KVA demand burden on the utility or engine-alternator power source. Low power factor
loads can also affect the voltage stability which can ultimately result in detrimental effects on the
life of sensitive electronic equipment or even intermittent malfunction. Voltage transients created
by DC drive SCR line notching, AC drive voltage chopping, and high frequency harmonic
voltages and currents are all significant sources of noise and disturbance to sensitive electronic
equipment.
It has been our experience that end users often do not associate power quality problems
with Container cranes, either because they are totally unaware of such issues or there was no
economic Consequence if power quality was not addressed. Before the advent of solid-state
power supplies, Power factor was reasonable, and harmonic current injection was minimal. Not
until the crane Population multiplied, power demands per crane increased, and static power
conversion became the way of life, did power quality issues begin to emerge. Even as harmonic

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distortion and power Factor issues surfaced, no one was really prepared. Even today, crane
builders and electrical drive System vendors avoid the issue during competitive bidding for new
cranes. Rather than focus on Awareness and understanding of the potential issues, the power
quality issue is intentionally or unintentionally ignored. Power quality problem solutions are
available. Although the solutions are not free, in most cases, they do represent a good return on
investment. However, if power quality is not specified, it most likely will not be delivered.
Power quality can be improved through:
 Power factor correction,
 Harmonic filtering,
 Special line notch filtering,
 Transient voltage surge suppression,
 Proper earthing systems.
In most cases, the person specifying and/or buying a container crane may not be fully
aware of the potential power quality issues. If this article accomplishes nothing else, we would
hope to provide that awareness.
In many cases, those involved with specification and procurement of container cranes may not be
cognizant of such issues, do not pay the utility billings, or consider it someone else’s concern. As
a result, container crane specifications may not include definitive power quality criteria such as
power factor correction and/or harmonic filtering. Also, many of those specifications which do
require power quality equipment do not properly define the criteria. Early in the process of
preparing the crane specification:
 Consult with the utility company to determine regulatory or contract requirements that
must be satisfied, if any.
 Consult with the electrical drive suppliers and determine the power quality profiles that
can be expected based on the drive sizes and technologies proposed for the specific
project.

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 Evaluate the economics of power quality correction not only on the present situation, but
consider the impact of future utility deregulation and the future development plans for the
terminal
2.3THE BENEFITS OF POWER QUALITY:
Power quality in the container terminal environment impacts the economics of the terminal
operation, affects reliability of the terminal equipment, and affects other consumers served by the
same utility service. Each of these concerns is explored in the following paragraphs.
 ECONOMIC IMPACT:
The economic impact of power quality is the foremost incentive to container terminal
operators. Economic impact can be significant and manifest itself in several ways:
 POWER FACTOR PENALTIES:
Many utility companies invoke penalties for low power factor on monthly billings.
There is no industry standard followed by utility companies. Methods of metering and
calculating power factor penalties vary from one utility company to the next. Some utility
companies actually meter KVAR usage and establish a fixed rate times the number of KVAR-
hours consumed. Other utility companies monitor KVAR demands and calculate power factor. If
the power factor falls below a fixed limit value over a demand period, a penalty is billed in the
form of an adjustment to the peak demand charges. A number of utility companies servicing
container terminal equipment do not yet invoke power factor penalties. However, their service
contract with the Port may still require that a minimum power factor over a defined demand
period be met. The utility company may not continuously monitor power factor or KVAR usage
and reflect them in the monthly utility billings; however, they do reserve the right to monitor the
Port service at any time. If the power factor criteria set forth in the service contract are not met,
the user may be penalized, or required to take corrective actions at the user’s expense. One utility
company, which supplies power service to several east coast container terminals in the USA,
does not reflect power factor penalties in their monthly billings, however, their service contract
with the terminal reads as follows:

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‘The average power factor under operating conditions of customer’s load at the point
where service is metered shall be not less than 85%. If below 85%, the customer may be required
to furnish, install and maintain at its expense corrective apparatus which will increase the Power
factor of the entire installation to not less than 85%.
The customer shall ensure that no excessive harmonics or transients are introduced on to the
[utility] system. This may require special power conditioning equipment or filters.
The Port or terminal operations personnel, who are responsible for maintaining
container cranes, or specifying new container crane equipment, should be aware of these
requirements. Utility deregulation will most likely force utilities to enforce requirements such as
the example above.
Terminal operators who do not deal with penalty issues today may be faced with some
rather severe penalties in the future. A sound, future terminal growth plan should include
contingencies for addressing the possible economic impact of utility deregulation.
 SYSTEM LOSSES:
Harmonic currents and low power factor created by nonlinear loads, not only result in
possible power factor penalties, but also increase the power losses in the distribution system.
These losses are not visible as a separate item on your monthly utility billing, but you pay for
them each month. Container cranes are significant contributors to harmonic currents and low
power factor. Based on the typical demands of today’s high speed container cranes, correction of
power factor alone on a typical state of the art quay crane can result in a reduction of system
losses that converts to a 6 to 10% reduction in the monthly utility billing. For most of the larger
terminals, this is a significant annual saving in the cost of operation.
 POWER SERVICE INITIAL CAPITAL INVESTMENTS:
The power distribution system design and installation for new terminals, as well as
modification of systems for terminal capacity upgrades, involves high cost, specialized, high and
medium voltage equipment. Transformers, switchgear, feeder cables, cable reel trailing cables,
collector bars, etc. must be sized based on the kVA demand. Thus cost of the equipment is
directly related to the total kVA demand. As the relationship above indicates, kVA demand is

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inversely proportional to the overall power factor, i.e. a lower power factor demands higher kVA
for the same kW load. Container cranes are one of the most significant users of power in the
terminal. Since container cranes with DC, 6 pulses, SCR drives operate at relatively low power
factor.
The total kVA demand is significantly larger than would be the case if power factor
correction equipment were supplied on board each crane or at some common bus location in the
terminal. In the absence of power quality corrective equipment, transformers are larger,
switchgear current ratings must be higher, feeder cable copper sizes are larger, collector system
and cable reel cables must be larger, etc. Consequently, the cost of the initial power distribution
system equipment for a system which does not address power quality will most likely be higher
than the same system which includes power quality equipment.
 EQUIPMENT RELIABILITY:
Poor power quality can affect machine or equipment reliability and reduce the life of
components. Harmonics, voltage transients, and voltage system sags and swells are all power
quality problems and are all interdependent. Harmonics affect power factor, voltage transients
can induce harmonics, the same phenomena which create harmonic current injection in DC SCR
variable speed drives are responsible for poor power factor, and dynamically varying power
factor of the same drives can create voltage sags and swells. The effects of harmonic distortion,
harmonic currents, and line notch ringing can be mitigated using specially designed filters.
 POWER SYSTEM ADEQUACY:
When considering the installation of additional cranes to an existing power distribution
system, a power system analysis should be completed to determine the adequacy of the system to
support additional crane loads. Power quality corrective actions may be dictated due to
inadequacy of existing power distribution systems to which new or relocated cranes are to be
connected. In other words, addition of power quality equipment may render a workable scenario
on an existing power distribution system, which would otherwise be inadequate to support
additional cranes without high risk of problems.

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 ENVIRONMENT:
No issue might be as important as the effect of power quality on our environment.
Reduction in system losses and lower demands equate to a reduction in the consumption of our
natural nm resources and reduction in power plant emissions. It is our responsibility as occupants
of this planet to encourage conservation of our natural resources and support measures which
improve our air quality

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CHAPTER-3

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3. DYNAMIC VOLTAGE RESTORER (DVR)
3.1 INTRODUCTION:
Among the power quality problems (sags, swells, harmonics…) voltage sags are the
most severe disturbances. In order to overcome these problems the concept of custom power
devices is introduced recently. One of those devices is the Dynamic Voltage Restorer (DVR),
which is the most efficient and effective modern custom power device used in power distribution
networks. DVR is a recently proposed series connected solid state device that injects voltage into
the system in order to regulate the load side voltage. It is normally installed in a distribution
system between the supply and the critical load feeder at the point of common coupling (PCC).
Other than voltage sags and swells compensation, DVR can also added other features like: line
voltage harmonics compensation, reduction of transients in voltage and fault current limitations
Fig 3.1 Location of DVR

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3.2 BASIC CONFIGURATION OF DVR:
The general configuration of the DVR consists of:
 An Injection/ Booster transformer
 A Harmonic filter
 Storage Devices
 A Voltage Source Converter (VSC)
 DC charging circuit
 A Control and Protection system
Fig 3.2 Schematic diagram of DVR

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3.3 EQUATIONS RELATED TO DVR:
Fig: 3.3 Equivalent Circuit diagram of DVR
The system impedance Zth depends on the fault level of the load bus. When the system
voltage (Vth) drops, the DVR injects a series voltage VDVR through the injection transformer so
that the desired load voltage magnitude VL can be maintained. The series injected voltage of the
DVR can be written as
3.4 OPERATING MODESOF DVR:
The basic function of the DVR is to inject a dynamically controlled voltage VDVR
generated by a forced commutated converter in series to the bus voltage by means of a booster
transformer. The momentary amplitudes of the three injected phase voltages are controlled such
as to eliminate any detrimental effects of a bus fault to the load voltage VL. This means that any

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differential voltages caused by transient disturbances in the ac feeder will be compensated by an
equivalent voltage generated by the converter and injected on the medium voltage level through
the booster transformer.
The DVR has three modes of operation which are: protection mode, standby mode,
injection/boost mode.
 PROTECTION MODE:
If the over current on the load side exceeds a permissible limit due to short circuit on the
load or large inrush current, the DVR will be isolated from the systems by using the bypass
switches (S2 and S3 will open) and supplying another path for current (S1 will be closed).
Fig 3.4 Protection Mode
 STANDBY MODE: (VDVR= 0)
In the standby mode the booster transformer’s low voltage winding is shorted through the
converter. No switching of semiconductors occurs in this mode of operation and the full load
current will pass through the primary.

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Fig 3.5 Standby Mode
 INJECTION/BOOST MODE: (VDVR>0)
In the Injection/Boost mode the DVR is injecting a compensating voltage through the
booster transformer due to the detection of a disturbance in the supply voltage.
3.5 VOLTAGE INJECTION METHODSOF DVR:
Voltage injection or compensation methods by means of a DVR depend upon the limiting
factors such as; DVR power ratings, various conditions of load, and different types of voltage
sags. Some loads are sensitive towards phase angel jump and some are sensitive towards change
in magnitude and others are tolerant to these. Therefore the control strategies depend upon the
type of load characteristics.
There are four different methods of DVR voltage injection which are
 Pre-sag compensation method
 In-phase compensation method
 In-phase advanced compensation method
 Voltage tolerance method with minimum energy injection
 PRE-SAG/DIP COMPENSATION METHOD:
The pre-sag method tracks the supply voltage continuously and if it detects any
disturbances in supply voltage it will inject the difference voltage between the sag or voltage at
PCC and pre-fault condition, so that the load voltage can be restored back to the pre-fault

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condition. Compensation of voltage sags in the both phase angle and amplitude sensitive loads
would be achieved by pre-sag compensation method. In this method the injected active power
cannot be controlled and it is determined by external conditions such as the type of faults and
load conditions.
VDVR =Vprefault - Vsag
Pre-Sag compensation method
 IN-PHASE COMPENSATION METHOD:
This is the most straight forward method. In this method the injected voltage is in phase with the
supply side voltage irrespective of the load current and pre-fault voltage. The phase angles of the
pre-sag and load voltage are different but the most important criteria for power quality that is the
constant magnitude of load voltage are satisfied.

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In-Phase compensation method
|VL|=|Vprefault|
One of the advantages of this method is that the amplitude of DVR injection voltage is
minimum for certain voltage sag in comparison with other strategies. Practical application of this
method is in non-sensitive loads to phase angle jump.
 IN-PHASE ADVANCED COMPENSATION METHOD:
In this method the real power spent by the DVR is decreased by minimizing the power
angle between the sag voltage and load current. In case of pre-sag and in-phase compensation
method the active power is injected into the system during disturbances. The active power supply
is limited stored energy in the DC links and this part is one of the most expensive parts of DVR.
The minimization of injected energy is achieved by making the active power component zero by
having the injection voltage phasor perpendicular to the load current phasor.
In this method the values of load current and voltage are fixed in the system so we can
change only the phase of the sag voltage. IPAC method uses only reactive power and
unfortunately, not al1 the sags can be mitigated without real power, as a consequence, this
method is only suitable for a limited range of sags

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 VOLTAGE TOLERANCE METHOD WITH MINIMUM ENERGY INJECTION:
A small drop in voltage and small jump in phase angle can be tolerated by the load itself.
If the voltage magnitude lies between 90%-110% of nominal voltage and 5%-10% of nominal
state that will not disturb the operation characteristics of loads. Both magnitude and phase are the
control parameter for this method which can be achieved by small energy injection.
Voltage tolerance method with minimum energy injection

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CHAPTER-4

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4. VOLTAGE SAG & SWELL
4.1 VOLTAGE SAG DEFINITIONS:
Over the last fifteen years, based on how the power quality instruments measure voltage
sags and swells the definitions have been developed. Power system communities state sags or
dips as a reduction in voltage below a user- defined low limit for between one cycle and 2.55
seconds. Surges are now called as swells, except that the voltage exceeds a particular user-
defined high limit. While different definitions pertaining to the amplitude and duration are still in
use, the IEEE 1159-1995 Recommended Practice on Monitoring Electric Power Quality has
defined them as follows:
Sag (dip) can be defined as, “A decrease to between 0.1 and 0.9 pu in rms voltage or current at
the power frequency for durations of 0.5 cycles to 1 minute.”
Fig 4.1 Voltage Sag Depiction

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With respect to an outage or interruption, sag is differentiated by the amplitude being greater
than or equal to 0.1 per unit (of nominal voltage). The IEEE 1159 document further categorizes
the duration values into: Instantaneous, momentary, and temporary, as illustrated in the
following table1.
IEEE definitions of Voltage Sags and Voltage Swells
It is blatant from the previous definitions that both voltage sag and voltage dip relate to the same
disturbance. Moreover, IEC states that “voltage sag is an alternative name for the phenomenon
voltage dip.
Categories and Characteristics of Power Systems Electromagnetic Phenomena

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4.2AMPLITUDE LIMITS OF VOLTAGE SAG:
The duration and amplitude value limits that are likely to cause problems with
equipments are already defined by both the ANSI C84.1-1989 Utility Power Profile and the
CBEMA (Computer and Business Equipment Manufacturers Association) curve. The smaller the
amplitude of a sag or higher the value of a swell, the shorter the duration should be for
equipment to follow through the disturbance, as in the following table derived from such. The
typical industrial utility power after building line losses is in the range of +6%, -13% from the
nominal value.
Amplitude limits of Voltage Sag
4.3 EFFECTSOF VOLTAGE SAG:
The prime interest about voltage sags is their effect on sensitive electrical devices, such as
personal computers, adjustable speed drives, programmable logic controllers, and other power
electronic equipment. The least sensitive loads failed when the voltage dropped to 30 % of the
specified voltage. On the other hand, the most sensitive components failed when the voltage
dropped to 80-86 % of rated value. From the test results, the calculated sag threshold to affect
production at the utility PCC - point of common coupling was 87 % of the nominal voltage for
more than 8.3 ms.

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Voltage Sag Classification based on type of Sag, duration and magnitude.
Classifications of Voltage Sags
The power system voltage can be given by a sine wave. A reduction in the amplitude of the
waveform indicates a Voltage Sag. Shows the voltage waveform during voltage sag.The sag
magnitude is characterized by the amplitude of the instantaneous voltage.
Fig 4.2 Classification of Voltage Sags

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 A TYPICAL VOLTAGE SAG WAVEFORM:
Fig 4.3 A Typical Voltage Sag Waveform
 GENERAL CAUSES AND EFFECTS OF VOLTAGE SAGS:
There are various causes of voltage sags in a power system. Voltage sags can be caused
by lightning faults on the transmission or distribution system or by switching of loads with large
amounts of initial starting or inrush current such as motors, transformers, and large dc power
supply.

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 VOLTAGE SAGS DUE TO FAULTS:
One of the major factors critical to the operation of the power plant is voltage sags due to
faults. The magnitudes of the voltage sags can be equal in each phase or unequal depending on
the types of the fault such as symmetrical or unsymmetrical, respectively. For faults in the
transmission system, customers do not experience interruption since transmission systems are
looped or networked.
At a certain point in the system parameters affecting the sag magnitude due to faults are:
 Distance to the fault
 Fault impedance
 Type of fault
 Pre-sag voltage level
 System configuration, System impedance and Transformer connections.
 CLASSIFICATIONOF EQUIPMENTS USED FORVOLTAGE SAG MITIGATIONS:
A greater awareness of voltage quality has been created with the recent growth in the
use of digital computers and PWM adjustable speed drives. Voltage dips and its associated phase
angle jumps can cause equipment to fail or malfunction which in turn can lead to production
downtime. Since a very long time interval is needed to restart industrial processes, these effects
can be greatly expensive for the clients/customers who are continuously seeking for cost
effective sag mitigation techniques. These interests have resulted in the development of power
electronics based devices with sag mitigation capability. These devices can be classified into two
classes, namely Custom Power Devices and Power Line conditioners.

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Fig 4.4 Custom Power Distribution System
N G Hingorani put forward the idea of custom power devices in 1995 as shown in the figure
above. Like Flexible AC Transmission Systems (FACTS), the term custom power devices relates
to the use of power electronics controllers in a distribution system, to deal with various power
quality problems. Just as FACTS improves the power transfer capabilities and stability margins,
custom power devices ascertain that customers get pre-specified quality and reliability of supply.
Without significant effect on the terminal voltages this pre-specified quality may contain a
combination of the following, low phase unbalance, no power interruptions, low flicker at the
load voltage, low harmonics distortion in load voltage, magnitude and duration of over voltages
and under voltages within specified limits, acceptance of fluctuations and poor power factor
loads.
Custom Power Devices are recently being developed under the Custom Power Program initiated
by the Electric Power Research Institute (EPRI). Typical custom power applications include the

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Dynamic Voltage Restorer (DVR), Distribution Static Compensator (D-STATCOM), Solid State
Fault Current Limiter (SSFCL). These devices are also known as source side solutions.
There are many types of Custom power devices like those listed below:
 Active Power filters(APF)
 Battery Energy storage systems(BESS)
 Distributed Static Compensators(DSTATCOM)
 Distribution series Capacitors(DSC)
 Dynamic Voltage Restorer(DVR)
 Super conducting Magnetic Energy systems(SEMES)
 Static Electronics Tap Changers(SETC)
 Solid State Transfer Switches (SSTS)
 Solid state Fault Current Limiters(SSSFCL)
 Static VAR Compensators(SVC)
 Thyristor Switched Capacitors(TSC)
4.4 VOLTAGE SWELL:
A swell is the reverse form of a Sag, having an increase in AC Voltage for a duration of
0.5 cycles to 1 minute's time. For swells, high-impedance neutral connections, sudden large load
reductions, and a single-phase fault on a three phase system are common sources. Swells can
cause data errors, light flickering, electrical contact degradation, and semiconductor damage in
electronics causing hard server failures. Our power conditioners and UPS Solutions are common
solutions for swells.
Swell can be defined as, “An increase to between 1.1 pu and 1.8 pu in rms voltage or current at
the power frequency durations from 0.5 to 1 minute

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Fig: 4.5 Voltage Swell
It is important to note that, much like sags, swells may not be apparent until results are seen.
Having your power quality devices monitoring and logging your incoming power will help
measure these events.
 OVER-VOLTAGE:
Over-voltages can be the result of long-term problems that create swells. Think of an
overvoltage as an extended swell. Over-voltages are also common in areas where supply
transformer tap settings are set incorrectly and loads have been reduced. Over-voltage
conditions can create high current draw and cause unnecessary tripping of downstream circuit
breakers, as well as overheating and putting stress on equipment. Since an overvoltage is a
constant swell, the same UPS and Power Conditioners will work for these. Please note however
that if the incoming power is constantly in an overvoltage condition, the utility power to your
facility may need correction as well. The same symptoms apply to the over-voltages and swells
however since the overvoltage is more constant you should expect some excess heat. This
excess heat, especially in data center environments, must be monitored.

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If you are experiencing any of these power quality problems we have solutions ranging
from Power Conditioners / Voltage Regulators to traditional UPS Systems and Flywheel UPS
Solutions. Do not hesitate to call on us.
 SWELL CAUSES:
As discussed previously, swells are less common than voltage sags, but also usually
associated with system fault conditions. A swell can occur due to a single line-toground fault on
the system, which can also result in a temporary voltage rise on the unfaulted phases. This is
especially true in ungrounded or floating ground delta systems, where the sudden change in
ground reference result in a voltage rise on the ungrounded phases. On an ungrounded system,
the line-to ground voltages on the ungrounded phases will be 1.73 pu during a fault condition.
Close to the substation on a grounded system, there will be no voltage rise on unfaulted phases
because the substation transformer is usually connected delta-wye, providing a low impedance
path for the fault current. Swells can also be generated by sudden load decreases. The abrupt
interruption of current can generate a large voltage, per the formula: v = L di/dt, where L is the
inductance of the line, and di/dt is the change in current flow. Switching on a large capacitor
bank can also cause a swell, though it more often causes an oscillatory transient.
4.5 SOLUTIONS:
The first step in reducing the severity of the system sags is to reduce the number of faults.
From the utility side, transmission-line shielding can prevent lighting induced faults. If tower-
footing resistance is high, the surge energy from a lightning stroke is not absorbed quickly into
the ground. Since high tower-footing resistance is an import factor in causing back flash from
static wire to phase wire, steps to reduce such should be taken. The probability of flashover can
be reduced by applying surge arresters to divert current to ground. Tree-trimming programs
around distribution lines are becoming more difficult to maintain, with the continual reductions
in personnel and financial constraints in the utility companies. While the use of underground
lines reduces the weather-related causes, there are additional problems from equipment failures
in the underground environment and construction accidents. The solutions within the facility are
varied, depending on the financial risk at stake, the susceptibility levels and the power
requirements of the effected device. Depending on the transformer configuration, it may be

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possible to mitigate the problem with a transformer change. "It is virtually impossible for an
SLTG condition on the utility system to cause voltage sag below 30% at the customer bus, when
the customer is supplied through a delta-wye or wye-delta transformer.
For wye-wye and delta-delta connections two phase-to-phase voltages will drop to 58% of
nominal, while the other phase-to-phase is unaffected. However, for delta-wye and wye-delta
connections, one phase-to-phase voltage will be as low as 33% of nominal, while the other two
voltages will be 88% of nominal. It is the circulating fault current in the delta secondary
windings that results in a voltage on each winding. Another possible solution is through the
procurement specification. If a pre-installation site survey is done, the distribution curve and
probability of the sags and/or swells can be determined. The user then specifies such information
in the equipment procurement specifications. Only equipment with acceptable ride through
characteristics would then be used. When neither of the above solutions are practical or adequate,
some form of additional voltage regulator are required to maintain constant output voltage to the
effected device, despite the variation in input voltage. Each type has its own disadvantage and

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advantages for a given application. The utility companies can add dynamic voltage restorers,
static condensers, fault current limiters, and/or high-energy surge arresters. Since these are
beyond the control of the end user of the electricity, the following concentrates on "in-the-
facility" solution. These include: Ferro resonant transformers, magnetically controlled voltage
regulators (3-10 cycle response); electronic tap switching transformers (1-3 cycles); shielded
isolation transformers; static transfer switches (within 4 milliseconds); static UPSs; and, rotary
UPSs.
 NEWER SOLUTIONS:
EPRI has been working with PSEG and Westinghouse Electric Corp to develop an active
power line conditioner, which will combine active harmonic filtering, line voltage regulation and
transient voltage surge protection in a single compact unit. To date, 5KVA, 50KVA and
150KVA units are available. Several successfully applications of superconductivity magnetic-
storage systems have been carried out in the United States. The stored energy that is provided by
the batteries in a static UPS, or the inertia of the motor in a MG set, is instead provided by
current stored in a superconductive magnetic system. This energy can be quickly coupled back
into the system, when the AC input power is inadequate.

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CHAPTER-5

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5. RELIZATION OF COMPENSATION TECHNIQUE
5.1 DISCRETE PWM-BASED CONTROL SCHEME:
In order to mitigate the simulated voltage sags in the test system of each compensation
technique, also to compensate voltage sags in practical application, a discrete PWM-based
control scheme is implemented, with reference to DVR. The aim of the control scheme is to
maintain a constant voltage magnitude at the sensitive load point, under the system disturbance.
The control system only measures the rms voltage at load point, for example, no reactive power
measurement is required.
The DVR controller scheme implemented in MATLAB/SIMULINK. The DVR control
system exerts a voltage angle control as follows: an error signal is obtained by comparing the
reference voltage with the rms voltage measured at the load point. The PI controller processes the
error signal and generates the required angle δ to drive the error to zero, for example; the load rms
voltage is brought back to the reference voltage.
It should be noted that, an assumption of balanced network and operating conditions are
made. The modulating angle δ or delta is applied to the PWM generators in phase A, whereas the
angles for phase B and C are shifted by 240° or -120° and 120° respectively.
VA = Sin (ωt +δ)
VB=Sin (ωt+δ-2π/3)
VC = Sin (ωt +δ+2π/3

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Fig 5.1 firing angle controller schemes
Fig 5.2 Simulink model of DVR controller

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5.2 TESTS SYSTEM FOR DVR:
Fig 5.3 Single line diagram of test system
Single line diagram of the test system for DVR is composed by a 13 kV, 50 Hz
generation system, feeding two transmission lines through a 3- winding transformer connected in
Y/Δ/Δ, 13/115/115 kV. Such transmission lines feed two distribution networks through two
transformers connected in Δ/Y, 115/11 kV. To verify the working of DVR for voltage
compensation a fault is applied at point X at resistance 0.66 U for time duration of 200 ms. The
DVR is simulated to be in operation only for the duration of the fault.

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CHAPTER-6

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6. PULSE WIDTH MODULATOR
6.1 PULSE WIDTH MODULATOR:
So, how do we generate a PWM waveform? It's actually very easy, there are circuits
available in the TEC site. First you generate a triangle waveform as shown in the diagram below.
You compare this with a d.c voltage, which you adjust to control the ratio of on to off time that
you require. When the triangle is above the 'demand' voltage, the output goes high. When the
triangle is below the demand voltage, the
When the demand speed it in the middle (A) you get a 50:50 output, as in black. Half the
time the output is high and half the time it is low. Fortunately, there is an IC (Integrated circuit)
called a comparator: these come usually 4 sections in a single package. One can be used as the
oscillator to produce the triangular waveform and another to do the comparing, so a complete
oscillator and modulator can be done with half an IC and maybe 7 other bits.
The triangle waveform, which has approximately equal rise and fall slopes, is one of the
commonest used, but you can use a saw tooth (where the voltage falls quickly and rinses slowly).
You could use other waveforms and the exact linearity (how good the rise and fall are) is not too
important.

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Traditional solenoid driver electronics rely on linear control, which is the application of a
constant voltage across a resistance to produce an output current that is directly proportional to
the voltage. Feedback can be used to achieve an output that matches exactly the control signal.
However, this scheme dissipates a lot of power as heat, and it is therefore very inefficient.
A more efficient technique employs pulse width modulation (PWM) to produce the
constant current through the coil. A PWM signal is not constant. Rather, the signal is on for part
of its period, and off for the rest. The duty cycle, D, refers to the percentage of the period for
which the signal is on. The duty cycle can be anywhere
from 0, the signal is always off, to 1, where the signal is constantly on. A 50% D results in a
perfect square wave.
A solenoid is a length of wire wound in a coil. Because of this configuration, the solenoid
has, in addition to its resistance, R, a certain inductance, L. When a voltage, V, is applied across
an inductive element, the current, I, produced in that element do not jump up to its constant
value, but gradually rises to its maximum over a period of time called the rise time. Conversely, I
do not disappear instantaneously, even if V is removed abruptly, but decreases back to zero in
the same amount of time as the rise time.

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Therefore, when a low frequency PWM voltage is applied across a solenoid, the current
through it will be increasing and decreasing as V turns on and off. If D is shorter than the rise
time, I will never achieve its maximum value, and will be discontinuous since it will go back to
zero during V’s off period In contrast, if D is larger than the rise time, I will never fall back to
zero, so it will be continuous, and have a DC average value. The current will not be constant,
however, but will have a ripple.
At high frequencies, V turns on and off very quickly, regardless of D, such that the
current does not have time to decrease very far before the voltage is turned back on. The
resulting current through the solenoid is therefore considered to be constant. By adjusting the D,
the amount of output current can be controlled. With a small D, the current will not have much

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time to rise before the high frequency PWM voltage takes effect and the current stays constant.
With a large D, the current will be able to rise higher before it becomes constant.
Static friction, stiction, and hysteresis can cause the control of a hydraulic valve to be
erratic and unpredictable. Stiction can prevent the valve spool from moving with small input
changes, and hysteresis can cause the shift to be different for the same input signal. In order to
counteract the effects of stiction and hysteresis, small vibrations about the desired position are
created in the spool. This constantly breaks the static friction ensuring that it will move even
with small input changes, and the effects of hysteresis are average out.
Dither is a small ripple in the solenoid current that causes the desired vibration and there
by increases the linearity of the valve. The amplitude and frequency of the dither must be
carefully chosen. The amplitude must be large enough and the frequency slow enough that the
spool will respond, yet they must also be small and fast enough not to result in a pulsating
output.
The optimum dither must be chosen such that the problems of stiction and hysteresis are
overcome without new problems being created. Dither in the output current is a byproduct of low
frequency PWM, as seen above. However, the frequency and amplitude of the dither will be a
function of the duty cycle, which is also used to set the output current level. This means that low
frequency dither is not independent of current magnitude. The advantage of using high frequency
PWM is that dither can be generated separately, and then superimposed on top of the output
current.

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This allows the user to independently set the current magnitude (by adjusting the D), as
well as the dither frequency and amplitude. The optimum dither, as set by the user, will therefore
be constant at all current levels.
6.2 PWM Controller Features:
This controller offers a basic “Hi Speed” and “Low Speed” setting and has the option to
use a “Progressive” increase between Low and Hi speed. Low Speed is set with a trim pot inside
the controller box. Normally when installing the controller, this speed will be set depending on
the minimum speed/load needed for the motor. Normally the controller keeps the motor at this
Low Speed except when Progressive is used and when Hi Speed is commanded . Low Speed can
vary anywhere from 0% PWM to 100%.
Progressive control is commanded by a 0-5 volt input signal. This starts to increase
PWM% from the low speed setting as the 0-5 volt signal climbs. This signal can be generated
from a throttle position sensor, a Mass Air Flow sensor, a Manifold Absolute Pressure sensor or
any other way the user wants to create a 0-5 volt signal. This function could be set to increase
fuel pump power as turbo boost starts to climb (MAP sensor). Or, if controlling a water injection
pump, Low Speed could be set at zero PWM% and as the TPS signal climbs it could increase
PWM%, effectively increasing water flow to the engine as engine load increases. This controller
could even be used as a secondary injector driver (several injectors could be driven in a batch
mode, hi impedance only), with Progressive control (0-100%) you could control their output for
fuel or water with the 0-5 volt signal.
Progressive control adds enormous flexibility to the use of this controller. Hi Speed is
that same as hard wiring the motor to a steady 12 volt DC source. The controller is providing
100% PWM, steady 12 volt DC power. Hi Speed is selected three different ways on this
controller: 1) Hi Speed is automatically selected for about one second when power goes on. This
gives the motor full torque at the start. If needed this time can be increased ( the value of C1
would need to be increased). 2) High Speed can also be selected by applying 12 volts to the High
Speed signal wire. This gives Hi Speed regardless of the Progressive signal.

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CHAPTER-7

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7. MATLAB
7.1 INTRODUCTION:
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 Data acquisition 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 no interactive language such as C or FORTRAN.
The name Matlab stands for matrix laboratory. Matlab was originally written to provide
easy access to matrix software developed by the LINPAC and eispack projects. Today, Matlab
engines incorporate the lapack and blas libraries, embedding the state of the art in software for
matrix computation.
MATLAB has evolved over a period of years with input from many users. In university
environments, it is the standard instructional tool for introductory and advanced courses in
mathematics, engineering, and science. In industry, Matlab is the tool of choice for high-
productivity research, development, and analysis.
MATLAB features a family of add-on application-specific solutions called toolboxes.
Very important to most users of Matlab, toolboxes allow you to learn and apply specialized
technology. Toolboxes are comprehensive collections of Matlab functions (M-files) that extend
the Matlab environment to solve particular classes of problems. Areas in which toolboxes are
available include signal processing, control systems, neural networks, fuzzy logic, wavelets,
simulation, and many others.

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The Mat lab system consists of five main parts:
Development Environment this is the set of tools and facilities that help you use Matlab
functions and files. Many of these tools are graphical user interfaces. It includes the Matlab
desktop and Command Window, a command history, an editor and debugger, and browsers for
viewing help, the workspace, files, and the search path.
The Mat lab Mathematical Function Library This is a vast collection of computational
algorithms ranging from elementary functions, like sum, sine, cosine, and complex arithmetic, to
more sophisticated functions like matrix inverse, matrix eigenvalues, Bessel functions, and fast
Fourier transforms.
The Mat lab Language this is a high-level matrix/array language with control flow
statements, functions, data structures, input/output, and object-oriented programming features. It
allows both "programming in the small" to rapidly create quick and dirty throw-away programs,
and "programming in the large" to create large and complex application programs.
Mat lab has extensive facilities for displaying vectors and matrices as graphs, as well as
annotating and printing these graphs. It includes high-level functions for two-dimensional and
three-dimensional data visualization, image processing, animation, and presentation graphics. It
also includes low-level functions that allow you to fully customize the appearance of graphics as
well as to build complete graphical user interfaces on your Mat lab applications.
The Mat lab Application Program Interface (API). This is a library that allows you to
write C and FORTRAN programs that interact with Matlab. It includes facilities for calling
routines from Matlab (dynamic linking), calling Matlab as a computational engine, and for
reading and writing MAT-files.

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7.2 SIMULINK:
INTRODUCTION:
Simulink is a software add-on to Mat lab which is a mathematical tool developed by The
Math works, (http://www.mathworks.com) a company based in Natick. Matlab is powered by
extensive numerical analysis capability.
Simulink is a tool used to visually program a dynamic system (those governed by
Differential equations) and look at results. Any logic circuit, or control system for a dynamic
system can be built by using standard building blocks available in Simulink Libraries. Various
toolboxes for different techniques, such as Fuzzy Logic, Neural Networks, dsp, Statistics etc. are
available with Simulink, which enhance the processing power of the tool. The main advantage is
the availability of templates / building blocks, which avoid the necessity of typing code for small
mathematical processes.
7.3 CONCEPT OF SIGNAL AND LOGIC FLOW:
Fig. 7.1 Simulink library browser
In Simulink, data/information from various blocks are sent to another block by lines
connecting the relevant blocks. Signals can be generated and fed into blocks dynamic /
static).Data can be fed into functions. Data can then be dumped into sinks, which could be
scopes, displays or could be saved to a file. Data can be connected from one block to another,

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can be branched, multiplexed etc. In simulation, data is processed and transferred only at discrete
times, since all computers are discrete systems. Thus, a simulation time step (otherwise called an
integration time step) is essential, and the selection of that step is determined by the fastest
dynamics in the simulated system.
 CONNECTING BLOCKS:
Fig. 7.2 Connecting blocks
To connect blocks, left-click and drag the mouse from the output of one block to the
input of another block.

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 SOURCES AND SINKS:
The sources library contains the sources of data/signals that one would use in a dynamic
system simulation. One may want to use a constant input, a sinusoidal wave, a step, a repeating
sequence such as a pulse train, a ramp etc. One may want to test disturbance effects, and can use
the random signal generator to simulate noise. The clock may be used to create a time index for
plotting purposes. The ground could be used to connect to any unused port, to avoid warning
messages indicating unconnected ports.
The sinks are blocks where signals are terminated or ultimately used. In most cases, we
would want to store the resulting data in a file, or a matrix of variables. The data could be
displayed or even stored to a file. The stop block could be used to stop the simulation if the input
to that block (the signal being sunk) is non-zero. Figure 3 shows the available blocks in the
sources and sinks libraries. Unused signals must be terminated, to prevent warnings about
unconnected signals.
Fig. 7.3 Sources and sinks

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 CONTINUOUS AND DISCRETE SYSTEMS:
All dynamic systems can be analyzed as continuous or discrete time systems. Simulink
allows you to represent these systems using transfer functions, integration blocks, delay blocks
etc.
Fig. 7.4 continous and descrete systems

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 NON-LINEAR OPERATORS:
A main advantage of using tools such as Simulink is the ability to simulate non-linear
systems and arrive at results without having to solve analytically. It is very difficult to arrive at
an analytical solution for a system having non-linearities such as saturation, signup function,
limited slew rates etc. In Simulation, since systems are analyzed using iterations, non-linearities
are not a hindrance. One such could be a saturation block, to indicate a physical limitation on a
parameter, such as a voltage signal to a motor etc. Manual switches are useful when trying
simulations with different cases. Switches are the logical equivalent of if-then statements in
programming.
Fig. 7.5 simulink block
 MATHEMATICAL OPERATIONS:
Mathematical operators such as products, sum, and logical operations such as and, or,
etc.can be programmed along with the signal flow. Matrix multiplication becomes easy with the
matrix gain block. Trigonometric functions such as sin or tan inverse (at an) are also available.
Relational operators such as ‘equal to’, ‘greater than’ etc. can also be used in logic circuits

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Fig. 7.6 Simulink math blocks
 SIGNALS & DATA TRANSFER:
In complicated block diagrams, there may arise the need to transfer data from one portion
to another portion of the block. They may be in different subsystems. That signal could be
dumped into a goto block, which is used to send signals from one subsystem to another.
Multiplexing helps us remove clutter due to excessive connectors, and makes matrix
(column/row) visualization easier.

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Fig.7.7 signals and systems
 MAKING SUBSYSTEMS:
Drag a subsystem from the Simulink Library Browser and place it in the parent block
where you would like to hide the code. The type of subsystem depends on the purpose of the
block. In general one will use the standard subsystem but other subsystems can be chosen. For
instance, the subsystem can be a triggered block, which is enabled only when a trigger signal is
received.
Open (double click) the subsystem and create input / output PORTS, which transfer
signals into and out of the subsystem. The input and output ports are created by dragging them
from the Sources and Sinks directories respectively.

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When ports are created in the subsystem, they automatically create ports on the external
(parent) block. This allows for connecting the appropriate signals from the parent block to the
subsystem.
 SETTING SIMULATION PARAMETERS:
Running a simulation in the computer always requires a numerical technique to solve a
differential equation. The system can be simulated as a continuous system or a discrete system
based on the blocks inside. The simulation start and stop time can be specified. In case of
variable step size, the smallest and largest step size can be specified. A Fixed step size is
recommended and it allows for indexing time to a precise number of points, thus controlling the
size of the data vector. Simulation step size must be decided based on the dynamics of the
system. A thermal process may warrant a step size of a few seconds, but a DC motor in the
system may be quite fast and may require a step size of a few milliseconds.
Fig. 7.8 Simulation Parameters

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CHAPTER-8

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8. RESULT
8.1 CIRCUIT DIAGRAM:
Fig.8.1 MATLAB-based model of the BESS-supported DVR-connected system.

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8.2 RESULT:
Fig.8.2 Dynamic performance of DVR with in-phase injection during voltage sag and swell
applied to critical load.

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Fig. 8.3Dynamic performance of DVR during harmonics in supply voltage applied to critical
load.

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Fig. 8.4Dynamic performance of the capacitor-supported DVR during voltage sag applied to
critical load.

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Fig. 8.5Dynamic performance of the capacitor-supported DVR during voltage swell applied
to critical load.

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CHAPTER-9

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9 ADVANTAGES,APPLICATIONS & FUTURE SCOPE
9.1 ADVANTAGES:
 It is less expensive
 Small in size
 Better power effective device as compare to other links UPS, SMES, DSTATCOM.
 Fast response
 Less Maintenance
9.2 APPLICATIONS:
 Transmission
 Distribution
 Non-Linear loads
 Communication Network
 Process industries
 Precise manufacturing process
9.3 FUTURE SCOPE:
 Study and control of power quality issues for deregulated power system.
 Soft computing techniques developed can be further used in various fields of power
system like – power system dynamics & stability, smart grid, power system state
estimation, economic dispatch and optimal power flow.

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CHAPTER-10

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10. CONCLUSION & REFERENCES
10.1 CONCLUSION:
The operation of a DVR has been demonstrated with a new control technique using
various voltage injection schemes. A comparison of the performance of the DVR with
different schemes has been performed with a reduced-rating VSC, including a capacitor-
supported DVR. The reference load voltage has been estimated using the method of unit
vectors, and the control of DVR has been achieved, which minimizes the error of voltage
injection. The SRF theory has been used for estimating the reference DVR voltages. It is
concluded that the voltage injection in-phase with the PCC voltage results in minimum rating
of DVR but at the cost of an energy source at its dc bus.

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10.2 REFERENCES:
 M. H. J. Bollen, Understanding Power Quality Problems—Voltage Sags and
Interruptions. New York, NY, USA: IEEE Press, 2000.
 Ghosh and G. Ledwich, Power Quality Enhancement Using Custom Power Devices.
London, U.K.: Kluwer, 2002.
 M. H. J. Bollen and I. Gu, Signal Processing of Power Quality Disturbances. Hoboken,
NJ, USA: Wiley-IEEE Press, 2006.
 IEEE Recommended Practices and Recommendations for Harmonics Control in Electric
Power Systems, IEEE Std. 519, 1992.
 M. Vilathgamuwa, R. Perera, S. Choi, and K. Tseng, “Control of energy optimized
dynamic voltage restorer,” in Proc. IEEE IECON, 1999, vol. 2, pp. 873–878.
 J. G. Nielsen and F. Blaabjerg, “A detailed comparison of system topologies for dynamic
voltage restorers,” IEEE Trans. Ind. Appl., vol. 41, no. 5,pp. 1272–1280, Sep./Oct. 2005.
 D. M. Vilathgamuwa, H.M.Wijekoon, and S. S. Choi, “A novel technique to compensate
voltage sags in multiline distribution system—The interline dynamic voltage restorer,”
IEEE Trans. Ind. Electron., vol. 53, no. 5, pp. 1603–1611, Oct. 2006.
 K. Jindal, A. Ghosh, and A. Joshi, “Critical load bus voltage control using DVR under
system frequency variation,” Elect. Power Syst. Res., vol. 78, no. 2, pp. 255–263, Feb.
20M. R. Banaei, S. H. Hosseini, S. Khanmohamadi, and G. B.Gharehpetian “Verification
of a new energy control strategy for dynamic voltage restorer by simulation,” Simul.
Model. Pract. Theory, vol. 14, no. 2, pp. 112–125,Feb. 2006.08
 A. Ghosh, A. K. Jindal, and A. Joshi, “Design of a capacitor supported dynamic voltage
restorer for unbalanced and distorted loads,” IEEE Trans. Power Del., vol. 19, no. 1, pp.
405–413, Jan. 2004.

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