The document discusses power quality issues in power systems. It defines various power quality issues such as voltage fluctuations, sags, swells, interruptions, harmonic distortion, and current and voltage imbalances. It states that power quality is concerned with deviations from ideal sinusoidal voltages and currents. The sources of power quality issues are described as nonlinear loads containing power electronic devices, capacitor banks, and static converters, which can cause problems like harmonic resonance.
Cummins Power Generation is a world leader in the design and manufacture of power generation equipment, including PowerCommand standby and prime power systems. We also provide single–source warranty, planned maintenance, and round–the–clock emergency service 24 hours a day, seven days a week including back–up power rental through our network of distributors.
Management Information Systems In Applebee's & Dominos Pizza
Introduction:
The management information system (MIS) has a primary task of helping an organization become and stay efficient and effective. Managers use this computer-based system to organize, analyze, and execute plans to help the organization flow and accomplish its goals. The system can be used to study information in the form of employees, cost, profit, technology, procedures and documents.
Often MIS are much different from standard information systems because they study other information systems that are related to the operational tasks in an establishment. It is highly important for an organization to understand what MIS they need in order to remain competitive in the industry. Secondly, it is important for an organization to have a MIS which will promote both short term and long term organization goals. The improvement of technology over the years has allowed managers to make faster decisions based on the information that is collected by the system. However, this is also a negative aspect to the information systems. Situations can happen where imprecise reporting can take place thus leading to terrible decision making.
McDonald's History, Size, Growth, Menu, Acquisitions, Franchise Problem, Renovation, Moderation, Competitors, Way forward, competition with Starbucks. Did with Milena Price and Alzahra Alrasheed at the University of San Francisco.
During April 2011 the International Fund for Agriculture (IFAD) approved the implementation of the “Learning Routes: a Knowledge Management and Capacity Building Tool for Rural Development in East and Southern Africa (ROUTESA)” Programme, under the responsibility of PROCASUR Regional Corporation. During April 2011 both entities signed the Grant Agreement No. 1249 PROCASUR.
The first phase of ROUTESA finish by December 2014, after 3 years of implementation. This presentation presents main outputs of the Regional Workshop held simultaneously on the 3 of December in 4 different venues: Nairobi, Kigali, Kampala and Rome, partly through online conference.
Cummins Power Generation is a world leader in the design and manufacture of power generation equipment, including PowerCommand standby and prime power systems. We also provide single–source warranty, planned maintenance, and round–the–clock emergency service 24 hours a day, seven days a week including back–up power rental through our network of distributors.
Management Information Systems In Applebee's & Dominos Pizza
Introduction:
The management information system (MIS) has a primary task of helping an organization become and stay efficient and effective. Managers use this computer-based system to organize, analyze, and execute plans to help the organization flow and accomplish its goals. The system can be used to study information in the form of employees, cost, profit, technology, procedures and documents.
Often MIS are much different from standard information systems because they study other information systems that are related to the operational tasks in an establishment. It is highly important for an organization to understand what MIS they need in order to remain competitive in the industry. Secondly, it is important for an organization to have a MIS which will promote both short term and long term organization goals. The improvement of technology over the years has allowed managers to make faster decisions based on the information that is collected by the system. However, this is also a negative aspect to the information systems. Situations can happen where imprecise reporting can take place thus leading to terrible decision making.
McDonald's History, Size, Growth, Menu, Acquisitions, Franchise Problem, Renovation, Moderation, Competitors, Way forward, competition with Starbucks. Did with Milena Price and Alzahra Alrasheed at the University of San Francisco.
During April 2011 the International Fund for Agriculture (IFAD) approved the implementation of the “Learning Routes: a Knowledge Management and Capacity Building Tool for Rural Development in East and Southern Africa (ROUTESA)” Programme, under the responsibility of PROCASUR Regional Corporation. During April 2011 both entities signed the Grant Agreement No. 1249 PROCASUR.
The first phase of ROUTESA finish by December 2014, after 3 years of implementation. This presentation presents main outputs of the Regional Workshop held simultaneously on the 3 of December in 4 different venues: Nairobi, Kigali, Kampala and Rome, partly through online conference.
Il pollice schiaccia l'interruttore ed una stanza buia si illumina di luce: vi siete mai chiesti come viene prodotta l'energia elettrica e quali sono i passaggi che (da Thomas Edison) portano l'elettricità fino a casa o nella nostra azienda?
Grazie a questa simpatica infografica li scoprirete tutti!
Browse through our web pages as we are one of the leading saree exporters of the country. You may also check out our local store and shop at wholesale rates.
A Low Impact Solution for Increasing Existing Structural LoadsUretek Mid-Atlantic
Using a minimally invasive structural resin, Uretek Mid-Atlantic was able to increase the load bearing capacity of existing foundations for a factory expansion.
Procasur Africa was invited to organize and chair the Break Out session on Successful Strategies of Land Access for the New Generations at the ILC organized Global Land Forum Break Out Session: Successful Strategies of Land Access for the New Generations, held in Dakar, Senegal on the 13th of May 2015.
The presentation covers the identification and analysis of successful strategies of land access for rural youth in different regions (specifically in Latin America and the Caribbean and Africa) by presenting main approaches, types of intervention and lessons learned from PROCASUR and the International Fund of Agricultural Development - IFAD's experiences;
Presents two good practices of land access for rural youth in Bolivia and Senegal; and
Approaches, strategies and policies to secure and promote youth access to land.
Please click on the following link! For more on Procasur Africa's work with Rural Youth and Agriculture in Africa: http://africa.procasur.org/en/learning-routes/lr-sorted-by-theme/rural-youth/148-148
Estratto dalle viscere della terra, il gas metano raggiunge le nostre case e le nostre aziende: semplice, no? Ma dalla Russia, dall'Algeria oppure dalla Norvegia, la strada che il metano deve percorrere per arrivare in Italia è lunga e tortuosa.
Basta un'infografica ed i passaggi diventano semplici!
An outline the uses and applications for high density polyurethane resins, in geotechnical applications. The presentation uses examples from previous projects and information about how the material interacts with various soils.
MITIGATING ELECTRICAL DISTURBANCES WITH HYBRID DISTRIBUTION TRANSFORMERijscmcj
Hybrid transformers (HT) have the advantages of the conventional transformer, the regulatory abilities of
power electronic converters, and reduce the impact of the grid. The impacts of the existing grid are
voltage sag, voltage swell, harmonic distortion, and voltage unbalanced. The power electronic converter
has a controllable advantage such as regulating the voltage and can transfer only a fraction of the power.
The aim of the paper is to augment the conventional power distribution transformer with a partially rated
power electronic module to enhance flexibility and introduce new features to the distribution transformer.
In this paper, the proposed back-to-back converter included an active front rectifier and a modular
multilevel converter (MMC) was simulated by MATLAB/Simulink software. The proposed back-to-back
converter was used at the primary side of the distribution transformer to compensate for the voltage sag
and swell issues. The simulation results were obtained under different conditions such as various supply
voltages and various loads. Hence, the proposed system has the ability to regulate the output voltage
under various conditions with ±10%.
Electrical Engineering: An International Journal (EEIJ)ijccmsjournal
Hybrid transformers (HT) have the advantages of the conventional transformer, the regulatory abilities of
power electronic converters, and reduce the impact of the grid. The impacts of the existing grid are
voltage sag, voltage swell, harmonic distortion, and voltage unbalanced. The power electronic converter
has a controllable advantage such as regulating the voltage and can transfer only a fraction of the power.
The aim of the paper is to augment the conventional power distribution transformer with a partially rated
power electronic module to enhance flexibility and introduce new features to the distribution transformer.
In this paper, the proposed back-to-back converter included an active front rectifier and a modular
multilevel converter (MMC) was simulated by MATLAB/Simulink software. The proposed back-to-back
converter was used at the primary side of the distribution transformer to compensate for the voltage sag
and swell issues. The simulation results were obtained under different conditions such as various supply
voltages and various loads. Hence, the proposed system has the ability to regulate the output voltage
under various conditions with ±10%.
MITIGATING ELECTRICAL DISTURBANCES WITH HYBRID DISTRIBUTION TRANSFORMERijscmcj
Hybrid transformers (HT) have the advantages of the conventional transformer, the regulatory abilities of
power electronic converters, and reduce the impact of the grid. The impacts of the existing grid are
voltage sag, voltage swell, harmonic distortion, and voltage unbalanced. The power electronic converter
has a controllable advantage such as regulating the voltage and can transfer only a fraction of the power.
The aim of the paper is to augment the conventional power distribution transformer with a partially rated
power electronic module to enhance flexibility and introduce new features to the distribution transformer.
In this paper, the proposed back-to-back converter included an active front rectifier and a modular
multilevel converter (MMC) was simulated by MATLAB/Simulink software. The proposed back-to-back
converter was used at the primary side of the distribution transformer to compensate for the voltage sag
and swell issues. The simulation results were obtained under different conditions such as various supply
voltages and various loads. Hence, the proposed system has the ability to regulate the output voltage
under various conditions with ±10%
Voltage Flicker Analysis and its Mitigation by STATCOM for Power Quality Impr...IJMTST Journal
Voltage flicker is considered as one of the most severe power quality problems (especially in loads like electrical arc furnaces) and much attention has been paid to it lately. The reason for this disturbance is mainly due to the large nonlinear loads such as electric arc furnaces. Due to the latest achievements in the semiconductors industry and consequently the emergence of the compensators based on voltage source converters, FACTS devices have been gradually noticed to be used for voltage flicker compensation. This paper covers the contrasting approaches; dealing with the voltage flicker mitigation in three stages and assessing the related results in details. Initially, the voltage flicker mitigation, using FCTCR (Fixed Capacitor Thyristor Controlled Reactor), was simulated. Secondly, the compensation for the Static Synchronous Compensator (STATCOM) has been performed. The voltage flicker compensation by 8– pulse as well as 12 – pulse static synchronous compensator (STATCOM) has been performed. This paper deals with the voltage flicker mitigation and reduction in total harmonic distortion (THD) and compared the results in detail. The obtained results show that STATCOM is very efficient and effective for the compensation and mitigation of voltage flicker and harmonics all the simulation results have been performed on the MATLAB Software.
Power Quality Improvement by UPQC based on Voltage Source ConvertersIJRST Journal
In modern power system consists of wide range of electrical, electronic and power electronic equipment in commercial and industrial applications. Since most of the electronic equipment’s are nonlinear in nature these will induce harmonics in the system, which affect the sensitive loads to be fed from the system. These problems are partially solved with the help of LC passive filters. However, this kind of filter cannot solve random variation in the load current wave form and voltage wave form. Active filters can resolve this problem. However, the cost of active filters is high. They are difficult to implement in large scale. Additionally, they also present lower efficiency than shunt passive filters. One of the many solutions is the use of a combined system of shunt and active series filters like Unified Power Quality Conditioner (UPQC) which aims at achieving a low cost under highly effective control. The UPQC device combines a shunt active filter together with a series active filter in a back-to-back configuration, to simultaneously compensate the supply voltage and the load current or to mitigate any type of voltage and current fluctuations and power factor correction in a power distribution network, such that improved power quality can be made available at the point of common coupling. The control strategies are modeled using MATLAB/SIMULINK. The performance is also observed under influence of utility side disturbances such as harmonics and voltage sags. The simulation results are compared without and with UPQC for the verification of results.
Il pollice schiaccia l'interruttore ed una stanza buia si illumina di luce: vi siete mai chiesti come viene prodotta l'energia elettrica e quali sono i passaggi che (da Thomas Edison) portano l'elettricità fino a casa o nella nostra azienda?
Grazie a questa simpatica infografica li scoprirete tutti!
Browse through our web pages as we are one of the leading saree exporters of the country. You may also check out our local store and shop at wholesale rates.
A Low Impact Solution for Increasing Existing Structural LoadsUretek Mid-Atlantic
Using a minimally invasive structural resin, Uretek Mid-Atlantic was able to increase the load bearing capacity of existing foundations for a factory expansion.
Procasur Africa was invited to organize and chair the Break Out session on Successful Strategies of Land Access for the New Generations at the ILC organized Global Land Forum Break Out Session: Successful Strategies of Land Access for the New Generations, held in Dakar, Senegal on the 13th of May 2015.
The presentation covers the identification and analysis of successful strategies of land access for rural youth in different regions (specifically in Latin America and the Caribbean and Africa) by presenting main approaches, types of intervention and lessons learned from PROCASUR and the International Fund of Agricultural Development - IFAD's experiences;
Presents two good practices of land access for rural youth in Bolivia and Senegal; and
Approaches, strategies and policies to secure and promote youth access to land.
Please click on the following link! For more on Procasur Africa's work with Rural Youth and Agriculture in Africa: http://africa.procasur.org/en/learning-routes/lr-sorted-by-theme/rural-youth/148-148
Estratto dalle viscere della terra, il gas metano raggiunge le nostre case e le nostre aziende: semplice, no? Ma dalla Russia, dall'Algeria oppure dalla Norvegia, la strada che il metano deve percorrere per arrivare in Italia è lunga e tortuosa.
Basta un'infografica ed i passaggi diventano semplici!
An outline the uses and applications for high density polyurethane resins, in geotechnical applications. The presentation uses examples from previous projects and information about how the material interacts with various soils.
MITIGATING ELECTRICAL DISTURBANCES WITH HYBRID DISTRIBUTION TRANSFORMERijscmcj
Hybrid transformers (HT) have the advantages of the conventional transformer, the regulatory abilities of
power electronic converters, and reduce the impact of the grid. The impacts of the existing grid are
voltage sag, voltage swell, harmonic distortion, and voltage unbalanced. The power electronic converter
has a controllable advantage such as regulating the voltage and can transfer only a fraction of the power.
The aim of the paper is to augment the conventional power distribution transformer with a partially rated
power electronic module to enhance flexibility and introduce new features to the distribution transformer.
In this paper, the proposed back-to-back converter included an active front rectifier and a modular
multilevel converter (MMC) was simulated by MATLAB/Simulink software. The proposed back-to-back
converter was used at the primary side of the distribution transformer to compensate for the voltage sag
and swell issues. The simulation results were obtained under different conditions such as various supply
voltages and various loads. Hence, the proposed system has the ability to regulate the output voltage
under various conditions with ±10%.
Electrical Engineering: An International Journal (EEIJ)ijccmsjournal
Hybrid transformers (HT) have the advantages of the conventional transformer, the regulatory abilities of
power electronic converters, and reduce the impact of the grid. The impacts of the existing grid are
voltage sag, voltage swell, harmonic distortion, and voltage unbalanced. The power electronic converter
has a controllable advantage such as regulating the voltage and can transfer only a fraction of the power.
The aim of the paper is to augment the conventional power distribution transformer with a partially rated
power electronic module to enhance flexibility and introduce new features to the distribution transformer.
In this paper, the proposed back-to-back converter included an active front rectifier and a modular
multilevel converter (MMC) was simulated by MATLAB/Simulink software. The proposed back-to-back
converter was used at the primary side of the distribution transformer to compensate for the voltage sag
and swell issues. The simulation results were obtained under different conditions such as various supply
voltages and various loads. Hence, the proposed system has the ability to regulate the output voltage
under various conditions with ±10%.
MITIGATING ELECTRICAL DISTURBANCES WITH HYBRID DISTRIBUTION TRANSFORMERijscmcj
Hybrid transformers (HT) have the advantages of the conventional transformer, the regulatory abilities of
power electronic converters, and reduce the impact of the grid. The impacts of the existing grid are
voltage sag, voltage swell, harmonic distortion, and voltage unbalanced. The power electronic converter
has a controllable advantage such as regulating the voltage and can transfer only a fraction of the power.
The aim of the paper is to augment the conventional power distribution transformer with a partially rated
power electronic module to enhance flexibility and introduce new features to the distribution transformer.
In this paper, the proposed back-to-back converter included an active front rectifier and a modular
multilevel converter (MMC) was simulated by MATLAB/Simulink software. The proposed back-to-back
converter was used at the primary side of the distribution transformer to compensate for the voltage sag
and swell issues. The simulation results were obtained under different conditions such as various supply
voltages and various loads. Hence, the proposed system has the ability to regulate the output voltage
under various conditions with ±10%
Voltage Flicker Analysis and its Mitigation by STATCOM for Power Quality Impr...IJMTST Journal
Voltage flicker is considered as one of the most severe power quality problems (especially in loads like electrical arc furnaces) and much attention has been paid to it lately. The reason for this disturbance is mainly due to the large nonlinear loads such as electric arc furnaces. Due to the latest achievements in the semiconductors industry and consequently the emergence of the compensators based on voltage source converters, FACTS devices have been gradually noticed to be used for voltage flicker compensation. This paper covers the contrasting approaches; dealing with the voltage flicker mitigation in three stages and assessing the related results in details. Initially, the voltage flicker mitigation, using FCTCR (Fixed Capacitor Thyristor Controlled Reactor), was simulated. Secondly, the compensation for the Static Synchronous Compensator (STATCOM) has been performed. The voltage flicker compensation by 8– pulse as well as 12 – pulse static synchronous compensator (STATCOM) has been performed. This paper deals with the voltage flicker mitigation and reduction in total harmonic distortion (THD) and compared the results in detail. The obtained results show that STATCOM is very efficient and effective for the compensation and mitigation of voltage flicker and harmonics all the simulation results have been performed on the MATLAB Software.
Power Quality Improvement by UPQC based on Voltage Source ConvertersIJRST Journal
In modern power system consists of wide range of electrical, electronic and power electronic equipment in commercial and industrial applications. Since most of the electronic equipment’s are nonlinear in nature these will induce harmonics in the system, which affect the sensitive loads to be fed from the system. These problems are partially solved with the help of LC passive filters. However, this kind of filter cannot solve random variation in the load current wave form and voltage wave form. Active filters can resolve this problem. However, the cost of active filters is high. They are difficult to implement in large scale. Additionally, they also present lower efficiency than shunt passive filters. One of the many solutions is the use of a combined system of shunt and active series filters like Unified Power Quality Conditioner (UPQC) which aims at achieving a low cost under highly effective control. The UPQC device combines a shunt active filter together with a series active filter in a back-to-back configuration, to simultaneously compensate the supply voltage and the load current or to mitigate any type of voltage and current fluctuations and power factor correction in a power distribution network, such that improved power quality can be made available at the point of common coupling. The control strategies are modeled using MATLAB/SIMULINK. The performance is also observed under influence of utility side disturbances such as harmonics and voltage sags. The simulation results are compared without and with UPQC for the verification of results.
A Voltage Controlled Dstatcom for Power Quality Improvementiosrjce
Due to increasing complexity in the power system, voltage sag is becoming one of the most significant
power quality problems. Voltage sag is a short reduction voltage from nominal voltage, occurs in a short time.
If the voltage sags exceed two to three cycles, then manufacturing systems making use of sensitive electronic
equipments are likely to be affected leading to major problems. It ultimately leads to wastage of resources (both
material and human) as well as financial losses. This is possible only by ensuring that uninterrupted flow of
power is maintained at proper voltage levels. This project tends look at the solving the sag problems by using
custom power devices such as Distribution Static compensator (D-STATCOM).Proposed scheme follows a new
algorithm to generate reference voltage for a distribution static compensator (DSTATCOM) operating in
voltage-control mode. The proposed scheme ensures that unity power factor (UPF) is achieved at the load
terminal during nominal operation, which is not possible in the traditional method. Also, the compensator
injects lower currents therefore, reduces losses in the feeder and voltage-source inverter. Further, a saving in
the rating of DSTATCOM is achieved which increases its capacity to mitigate voltage sag. Nearly UPF is
maintained, while regulating voltage at the load terminal, during load change. The state-space model of
DSTATCOM is incorporated with the deadbeat predictive controller for fast load voltage regulation during
voltage disturbances. With these features, this scheme allows DSTATCOM to tackle power-quality issues by
providing power factor correction, harmonic elimination, load balancing, and voltage regulation based on the
load requirement.
In the modern power system the reactive power compensation is one of the main issues, the transmission of active power requires a difference in angular phase between voltages at the sending and receiving points (which is feasible within wide limits), whereas the transmission of reactive power requires a difference in magnitude of these same voltages (which is feasible only within very narrow limits). The reactive power is consumed not only by most of the network elements, but also by most of the consumer loads, so it must be supplied somewhere. If we can't transmit it very easily, then it ought to be generated where it is needed." (Reference Edited by T. J. E. Miller, Forward Page ix).Thus we need to work on the efficient methods by which VAR compensation can be applied easily and we can optimize the modern power system. VAR control technique can provides appropriate placement of compensation devices by which a desirable voltage profile can be achieved and at the same time minimizing the power losses in the system. This report discusses the transmission line requirements for reactive power compensation. In this report thyristor switched capacitor is explained which is a static VAR compensator used for reactive power management in electrical systems.
Seminar Topic For Electrical and Electronics Engineering (EEE)
The transformers are an integral part of the power system. In transformers, the main consequence of harmonic
currents is an increase in losses, mainly in windings, because of the deformation of the leakage fields. Higher losses mean that
more heat is generated in the transformer so that the operating temperature increases, leading to deterioration of the insulation
and a potential reduction in lifetime. Due to the non-linear loads, the transformers are much affected by the distorted currents
and supply voltages which largely reduce its efficiency due to overheating. Nonlinear loads cause harmonics to flow in the power
lines which can overload wiring and many desktops, personal computers present nonlinear loads to the AC supply because of
their power supplies design (capacitor input power supply). In power transformers, the main consequence of harmonic currents
is an increase in losses, mainly in windings, because of the deformation of the leakage fields. Higher losses mean that more heat
is generated in the transformer so that the operating temperature increases, leading to deterioration of the insulation and a
potential reduction in lifetime. As a result, it is necessary to reduce the maximum power load on the transformer, a practice
referred to as de-rating, or to take extra care in the design of the transformer to reduce these losses. To estimate the de-rating of
the transformer, the load’s K Factor may be used. Thus analysing this problem and reducing the losses of the transformer has
become a major area of research in today’s scenario. This report includes the effects of non-sinusoidal supply voltage on the
transformer excitation current and the core losses which includes eddy current and hysteresis losses.
IRJET-Review on Power Quality Enhancement in weak Power Grids by Integration ...IRJET Journal
Prathmesh Mayekar, Mahesh Wagh, Nilkanth Shinde "Review on Power Quality Enhancement in weak Power Grids by Integration of Renewable Energy Technologies", International Research Journal of Engineering and Technology (IRJET), Volume2,issue-01 April 2015.e-ISSN:2395-0056, p-ISSN:2395-0072. www.irjet.net
Abstract
During Last decade power quality problems has become more complex at all level of power system. With the increased use of sophisticated electronics, high efficiency variable speed drive, power electronic controllers and also more & more non-linear loads, Power Quality has become an increasing concern to utilities and customers. The modern sensitive, Non-linear and sophisticated load affects the power quality. This paper deals with the issues of low power quality in weak power grids. Initially the various power quality issues are discussed with their definition or occurrence and then finally the solution to mitigate this power quality issues are discussed. The innovative solutions like integration of renewable energy systems along with energy storage to enhance power quality by interfacing with custom power devices are explained in detail. Nearly all sorts of solution for mitigating power quality issue require some sort of DC source for providing active power, which can be supplied by renewable energy source. Also the various energy storage systems are studied.
IRJET-Review on Power Quality Enhancement in weak Power Grids by Integration ...
Survey of dc motor
1. Abstract When we say that an electric motor
is a device that transforms electric power into
mechanical power, we say two things. First, that
the motor is ?and behaves as ?a transformer.
Second, that it stands at the dividing line
between electrical and mechanical phenomena.
In the case of permanent magnet motors, this
power transformation works in both directions
so that the electrical impedance depends on the
mechanical load, while the mechanical behavior
of the motor depends on the conditions at the
electrical end. This being the case, it should be
possible to represent a motor ?s mechanical
load, on the electrical side, by a set of familiar
electrical components such as capacitors or
resistors.
Introduction
The metric system of units has undergone a
number of changes in its history, of which the
latest is the SI (Systeme International d’Unites).
This system has become popular in most of the
industrialized world, largely because it is a
coherent system, in which the product or
quotient of two or more units is the unit of the
resulting quantity. Certain simplifications result
from using this form of the metric system.
In the Sl system, force IS measured in Newtons
(N) and distance in meters (m). Consequently,
the units of torque are Nm (see Table 1.). If a
motor shaft rotates at an angular velocity of
ωM radians per second, with torque TM, the
mechanical power output will be equal to the
product TM, and ωM and the units will be watts
if TM is in Nm.
Motor manufacturers usually specify a torque
constant (KT) and a voltage constant (KV) for
their motors. These constants have different
values when the torque and speed are
measured in
English units, but they have the same numerical
value when Sl units are used. This becomes
obvious when you consider that the electrical
input power must be equal to the mechanical
output power:
where VA is the internally generated armature
voltage, or back emf. and IA IS the armature
current. (See Figure 1–1 for definition of motor
terms.)
NOTE: The dimensions are M (mass), L (length), and
T (time). The gram (g) is a unit of mass and the gram-force
(gf) is a unit of force. The pound (lb) and the
ounce (oz) are included as units of force only.
Applying the the same principle to the familiar
electrical transformer yields the turns ratio:
Figure 1 shows this series RLC circuit is an
excellent model of a dc motor loaded with an
essentially inertial load. Here, J is the total
moment of inertia, including the rotor’s JM.
2. Thus, the non-dimensional turns ratio N1/N2 is
analogous to the dimensional torque (or
voltage) constant KTV. Furthermore, equations
(2) and (4) give us a clear hint that the angular
velocity (ωM) is analogous to voltage, while the
torque (TM) is analogous to current.
The units of Km may be either Nm/A. or
Vsec/rad. Thus, specifying both KT and KV for a
motor is like measuring and specifying both the
voltage ratio and the current ratio of a
transformer, and can only make sense where
redundancy is required.
LITERATURE REVIEW
Power quality issues and remedies are relevant
research topics and a lot of advanced
researches are being carried out in this area.
These issues are mainly due to increased use of
power electronic devices, nonlinear loads and
unbalance in power systems. Dynamic loads
cause power quality problems usually by
voltage or current variations such as voltage
dips, fluctuations, momentary interruptions,
oscillatory transients, harmonics, harmonic
resonance etc.[2]. Various publications define
power quality in different aspects.
According to IEEE Recommended Practice for
Monitoring Power Quality (IEEE Std 1159-
1995), Power quality is defined as “concept of
powering and grounding sensitive equipment in
a manner that is suitable for operation of that
equipment.”
Power quality issues- Definitions
Definitions for power quality issues in power
systems with non sinusoidal waveforms and
unbalanced loads are detailed in [5-9]. The
definitions and terminology used in conjunction
with power quality are as follows:
Voltage quality can be interpreted as the quality
of voltage delivered by the utility to the
consumers and is concerned with the deviations
of the voltage from the ideal one. The ideal
voltage is a single frequency sine wave of
constant frequency and constant magnitude.
Current quality deals with the deviations of the
current from the ideal one which should be
sinusoidal wave current of constant frequency
and required magnitude and should also be in
phase with the supply voltage. Voltage quality
deals with what the utility delivers to the
customer and current quality deals with what
the customers take from the utility and are
mutually dependent.
Power quality is the combination of voltage
quality and current quality. Power quality is
concerned with deviations of voltage and/or
current from the ideal. 7 Voltage magnitude
variation is the increase or decrease in voltage
magnitude due to load variations, transformer
tap–changing, switching of capacitor banks or
reactors etc.
Voltage frequency variation is the variation in
frequency of supply voltage due to the
imbalance between load and generation units.
Current magnitude variation is the variation of
the load current magnitude which also results in
voltage magnitude variations.
Current phase variation – Ideally, the voltage
and current waveforms should be in phase so
that the power factor perceived by the source is
unity. Deviation from this situation is termed as
current phase variation.
Voltage and current imbalances – Voltage
imbalance in three phase systems where the
rms values of the voltages in each phase or the
phase angle differences between consecutive
phases are not equal, can affect the ratio of
negative sequence and positive sequence
voltage components. This can result in large
differences between the highest and lowest
values of voltage magnitude and phase
difference. The voltage imbalance leads to large
load current imbalances.
Voltage fluctuation –The fast variation in
voltage magnitude is called voltage fluctuation
or ‘voltage flicker’ and can affect the
performance of the equipment.
Harmonic voltage distortion – The ideal voltage
waveform is a sinusoidal wave of constant
frequency. But, when there is voltage
distortion, it may be a sum of sine waves with
frequencies which are multiples of fundamental
frequency. These non-fundamental components
3. contribute to harmonic distortion. The
harmonic current components result in
harmonic voltage components and hence a
non-sinusoidal voltage in the system.
Harmonic current distortion – Harmonic current
distortion is the complementary phenomenon
of harmonic voltage distortion. They are
mutually dependent as harmonic voltage
distortion is mainly due to non-sinusoidal load
currents.
Inter-harmonic voltage and current components
are generated by equipment such as cyclo-converters,
heating controllers and arc
furnaces, which generate current components
at such frequencies which are not integral
multiples of fundamental frequency. In fact,
there may be sub-harmonic frequency currents
as well. These inter-harmonic components can
cause resonance between the line inductances
and capacitor banks. The sub-harmonic currents
can lead to saturation of transformers and in
turn to damage of synchronous generators and
turbines.
Voltage notching - In three phase converters
during commutation from one device to
another, short circuits for short durations can
cause voltage reduction or notching. Voltage
notching leads to higher order harmonics.
Interruptions – Supply interruption is a
condition in which the voltage at the supply
terminals is close to zero or less than 10%
according to IEEE Standard 1159 -1995. Faults
or protection equipment mal-tripping can cause
interruptions.
Under voltages –Short duration under voltages
are known as voltage sags and longer duration
under voltages are called under voltages.
Voltage sag is a reduction in the supply voltage
magnitude followed by a voltage recovery after
a short period of time. Voltage sags are mostly
caused by short circuit faults in the system and
by starting of large motors.
Over voltages- Over voltages of very short
duration and high magnitude are called
transient over voltages/voltage spikes/voltage
surges. Over voltages with duration between
one cycle and one minute are called voltage
swells or temporary power frequency over
voltages. Longer duration over voltages are
called over voltages. Over voltages are caused
by lightning strokes, switching operations,
sudden load reduction, single phase short
circuits and nonlinearities.
Electromagnetic compatibility (EMC) – EMC is
defined by IEC (International Electrotechnical
Commission) as the ability of a device,
equipment or system to function satisfactorily
in its electromagnetic environment without
introducing intolerable electromagnetic
disturbances to anything in that environment
.
Sources of power quality issues
The increasing cost of energy led to the
introduction of efficient adjustable speed drives
using static power converters in 1970’s. This
brought about a wide change in application of
utilisation equipment in industrial power
systems. To minimise the electrical energy
costs, which are made up of kVA demand and
kWh charges, users began to apply capacitors in
their system to lower the demand charges.
Wide usage of capacitor banks with static
power 9 converters introduced harmonic
resonance problems. The causes of these power
quality problems are generally complex and
difficult to detect. In earlier days, the main
sources of waveform distortion were electric
arc furnaces, fluorescent lamps, electrical
machines and transformers.
(i) Arc-furnace: In Arc furnace, the voltage-current
characteristics of electric arcs are highly
nonlinear. Following arc ignition, the voltage
decreases due to the short-circuit current,
which is limited only by the power system
impedance.
(ii) Fluorescent lamp: In a fluorescent lamp, the
voltage builds up in each half cycle till it emits
light. Its current is limited by the non-linear
reactive ballast and hence distorted.
4. (iii) Rotating machines: They also generate
harmonics because the windings are embedded
in slots which are not exactly sinusoidally
distributed and mmf becomes distorted.
Generally, harmonics produced by rotating
machines are considered negligible compared
to those produced by other sources. Also, large
generators are usually connected to power grid
through delta-connected transformers thus
blocking the flow of third harmonic current.
(iv) Power transformers: They use magnetic
materials that are operated often in the
nonlinear region for economic purposes
resulting in the distorted (mainly third
harmonics) transformer magnetizing current
even if the applied voltage is sinusoidal. Large
numbers of power electronic loads installed in
power systems, also generate harmonics. Major
sources are identified as Desktop computers,
TVs, Fax Machines, Copiers, Microwave ovens,
Electric vehicle battery chargers, Thyristor
converters, UPS, ASDs, Welding machines, Static
var compensators, Inverters, SMPS, Fluorescent
lighting etc. The switching or commutation of
power semiconductor devices generates
voltage or current transients that are
characterized by a spectrum of frequencies.
Static VAR compensators are balanced three-phase
devices that use thyristors to control the
conduction time of shunt capacitors or
inductors during each half cycle in order to
maintain a desired terminal voltage. It
generates non sinusoidal currents Harmonics is
considered to be a major power quality issue.
The generation of harmonic currents by typical
harmonic loads are illustrated in the following
subsection.
Typical harmonic generating loads Of the
several harmonic producing loads such as
transformers, arc furnaces, welding equipments
etc., for the purpose of this work, it is decided
to consider four types of widely used loads,
both steady state and dynamic, which will
introduce non sinusoidal currents in three
phase AC network. The major harmonic loads
considered in this work are:
(a) Three phase diode bridge rectifier
(b) Three phase thyristor converter
(c) DC motor drive and
(d) Induction motor drive
OPERATIONAL PRINCIPLES
The proposed converter is depicted in Fig. 1. It
is derived from a flyback converter whose two
transformers are connected in series input and
parallel output. The upper transformer T1 is
used for delivering energy stored in the dc link
capacitor C1 to the output. The lower
transformer T2 delivers the input energy
directly to the output, as well as dc-link energy,
and has an additional function to limit the
current charging into the link capacitor by
controlling the input-current dead zone.
Accordingly, the proposed converter shows
different operations depending on the input-current
flow that is influenced by the voltage
applied to the anode of D2. Fig. 2 depicts a
powerflow diagram of the proposed converter.
The power flow is controlled by the imaginary
switch S, which is on or off based on the
relationship between the rectified line voltage
Vg and the link voltage VC1 scaled by k. k is a
constant value between 0 and 1 that is
determined by the primary inductances of the
two transformers. If Vg is greater than kVC1,
the switch S is on, and the input power is
supplied to the link capacitor and output stage.
In the opposite case, power transmission from
the ac line is stopped, and the output power is
supplied only by the link capacitor. Because the
decision of the switching point of S varies
according to the link capacitor voltage level, the
charge current of the link capacitor can be
further reduced as the link capacitor voltage is
increased. It follows that an excessive
5. increase of the link voltage can be suppressed.
Fig. shows the simplified diagram of the
proposed converter when the main switch Q is
turned on. Assuming that the anode voltage of
D2 is lower than the cathode voltage, D2 is
blocked, and the anode voltage ofD2 can be
written as follows by applying Kirchhoff’s
voltage law (KVL) along C1, L2, and L3:
where L2 and L3 are primary inductances of T1
and T2, respectively. Therefore, the critical
rectified line voltage Vg,critical that determines
the diode state is defined as
Introducing N, the inductance ratio of L2 to L3,
(2) can be rewritten as
DCM condition is successfully satisfied by
selecting the inductance ratio of L2 to L3.
Because the main switch carries input inductor
current as well as load current, the current
stress is heavy in general. Accordingly, it is
important to choose a proper value to make the
current stress as low as possible. Referring to
this, the maximum current stress can be written
as follows:
where V3 is calculated from (10) with the peak
value of the minimum line voltage. Fig. 8 shows
the maximum current stress according to
calculated (L1,N) pairs satisfying DCM, which
shows that lower current stress can be obtained
by selecting N to be as small as possible.
Therefore, the (L1,N) = (43 μH, 1.6) pair is used
for the design, and the power factor is
predicted to be about 0.95 from (3), (4), and
Fig. shows the reset time plots of ID3 and ID4
divided
by (1 − Dmax)Ts according to the transformer
turns ratios of n1 and n2 from (23) and (24). In
this figure, the minimum transformer turns
ratios of T1 and T2 are found to be 7.8 and 7.4,
respectively, and n1 = 8 and n2 = 8 are used in
the prototype converter. With these design
parameters, the calculated maximum link
voltage is about 395 V, and the maximum
switch voltage stress is calculated as 475 V. The
key component parameters used in the
prototype.
Experimental Results
A three-level AC–DC converter is proposed.
The proposed converter integrates the
operation of the boost power factor correction
and the three-level AC–DC Converter. There is
only a single stage power factor correction
converter; it is operated with two independent
controllers. One controller is used to perform
PFC and regulate the voltage across the primary
side DC-bus capacitors. The other controller is
used to regulate the output voltage, by sending
appropriate gating signals.
6. Fig, integrates an AC–DC boost PFC converter
into a three-level DC–DC converter. The AC–DC
boost section consists of an input diode bridge,
boost inductor Lin, boost diode Dx1, and switch
S4, which is shared by the multilevel DC–DC
section.
When S4 is off, it means that no more energy
can be captured by the boost inductor. In this
case, diode Dx2 prevents input current from
flowing to the midpoint of capacitors C1 and C2
and diode Dx1
Conducts and helps to transfer the energy
stored in the boost inductor Lin to the DC bus
capacitor. Diode Dx3 bypasses Dx2 and makes a
path for circulating current.
Although there is only a single
converter, it is operated with two independent
controllers. One controller is used to perform
PFC and regulate the voltage across the primary
side DC-bus capacitors by sending appropriate
gating signals to S4. The other controller is used
to regulate the output voltage by sending
appropriate gating signals to S1 to S4. It should
be noted that the control of the input section is
decoupled from the control of the DC–DC
section and thus can be designed separately.
The gating signal of S1, however, is dependent
on that of S4, which is the output of the input
controller; how this signal is generated is
discussed in detail later in this project.
The gating signals for S2 and S3 are
easier to generate as both switches are each ON
for half a switching cycle, but are never ON at
the same time. Typical converter waveforms are
shown in Fig
1) Reduced cost compared to two-stage
converters: Although the proposed converter
may seem expensive, the reality is that it can be
cheaper than a conventional two-stage
converter. This is because replacing a switch
and its associated gate drive circuitry with four
diodes reduces cost considerably even though
the component count seems to be increased
this is especially true if the diodes are ordered
in bulk numbers.
2) Better performance than a single-stage
converter: The proposed single-stage converter
can operate with a better input power factor for
universal input line applications than a single-controller,
single-stage because it does have a
dedicated controller for its input section that
can perform PFC and regulate the DC-bus
voltage. The presence of a second controller
also allows the converter to operate with better
7. efficiency and with less output ripple as each
section of the converter can be made to
operate in an optimal manner.
3) Improved light-load efficiency: The proposed
converter can be designed so that it has a
conventional DC-bus voltage of 400 V. Since the
converter is a multilevel converter, a 400 V DC
bus means that each switch will be exposed to a
maximum voltage of 200 V. Having 200 V across
a MOSFET device instead of 400 V (as is the case
with two-level converters) results in a 75%
reduction in turn on losses when the converter
is operating under light-load conditions and
there is an insufficient amount to current
available to discharge the switch output
capacitances before the switches are turned on.
4) Increased design flexibility: Since the
converter is a multilevel converter, it can be
operated with high dc-bus voltage (800 V),
standard dc-bus voltage (400 V), or any dc-bus
voltage 400 V < Vbus <800 V. There are
advantages to operating with high dc-bus
voltage or with standard dcbus voltage. The fact
there is flexibility in the level that the dc-bus
voltage is set means that there is considerable
flexibility in the design of the converter.
CONCLUSION
In this paper a review of position control
methods for the fundamentals of various
techniques have been introduced, mainly back-
EMF schemes and estimators, as a useful
reference for preliminary investigation of
conventional methods. Advances in the position
control and applications were also discussed. To
provide insight in control techniques and their
benefits a classification of existing methods and
newer methods were presented with their
merits and drawbacks. From the above
discussion, it is obvious that the control for
BLDC motors using position sensors, such as
shaft encoders, resolvers or Hall-effect probes,
can be improved by means of the elimination of
these sensors to further reduce cost and
increase reliability. Furthermore, sensorless
control is the only choice for some applications
where those sensors cannot function reliably
due to harsh environmental conditions and a
higher performance is required.As a result be
believe that designing applications with our
motors is simpler and less risky.
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