Synchronous Detection and Digital control of Shunt Active Power Filter in Power Quality Improvement

Synchronous Detection and Digital control of Shunt Active Power Filter in Power Quality Improvement

CHAPTER 1INTRODUCTION1.1 GeneralPower Quality is a set of electrical boundaries that allows apiece of equipment to function in its intended manner withoutsignificant loss of performance or life expectancy. Thethree phase power generated at the generating station is purelysinusoidal in nature[11][2]. Wide spread application of static powerelectronics converters, zero and negative sequence componentsoriginated by the use of single phase and unbalanced loads,reactive power, voltage sag, voltage swell, flicker, voltageinterruption etc. results voltage and current harmonics.The harmonics presence in the power lines results in variedproblems, like, greater power losses in distribution; problemsof electromagnetic interference in communication systems;and operation failures of protection devices, electronic equipmentsand, industrial processes. Due to these problems, thequality of the electrical energy delivered to the end consumersis, more than ever, an object of great concern. The passivefilters have been used as a conventional solution to solveharmonic currents problems, but they have disadvantages likeelectromagnetic interference, possible resonance, fixed compensation,bulkiness etc. To cope with these disadvantages,recent efforts have been concentrated on the development of Active Power Filters (APF) [9].The compensation strategy of Shunt Active Power Filter (SAPF) in two ways, Synchronous DetectionMethod (SDM) and digital control based on instantaneouspower theory (p-q theory). The control strategies of SAPFsystem are detailed in the second part of this paper. Simulationresults in the third part demonstrate a comparative studybetween the two methods and show the advantages of digitalcontrol over SDM.

1.2 POWER QUALITY1.2.1DefinitionPower Quality means to maintain purely sinusoidal current wave form in phase with a purely sinusoidal voltage wave form[11].Power Quality is a set of electrical boundaries that allows a piece of equipment to function in its intended manner without significant loss of performance or life expectancy[5].

1.2.2Power quality problemsDefinitions for power quality problems in power systems with non-sinusoidal waveforms and unbalanced loads are detailed in. The definitions and terminology used in conjunction with power quality are as follows:

A) 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. Theideal voltage is a single frequency sine wave of constant frequency and constant magnitude.

B) 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.

C) 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.

D) Voltage magnitude variation is the increase or decrease in voltage magnitude due to load variations, transformer tapchanging, switching of capacitor banks or reactors etc.E) Voltage frequency variation is the variation in frequency of supply voltage due to the imbalance between load and generation units.F) Current magnitude variation is the variation of the load current magnitude which alsoresults in voltage magnitude variations.G) 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.

H) 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.

I) Voltage fluctuation The fast variation in voltage magnitude is called voltage fluctuation or voltage flicker and can affect the performance of the equipment.

J) 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 contribute to harmonic distortion. The harmonic current components result in harmonic voltage components and hence a non-sinusoidal voltage in the system.

K) 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.

L) 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.M) 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.

N) 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.

0) Under voltages Short duration under voltages are known as voltage sags and longerduration under voltages are called under voltages. Voltage sag is a reduction in the supplyvoltage magnitude followed by a voltage recovery after a short period of time. Voltage sagsare mostly caused by short circuit faults in the system and by starting of large motors.

P) 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.

Q) 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.

1.2.3 SOLUTIONS TO POWER QUALITYPROBLEMSThere are two approaches to the mitigation of power quality problems. A) The first approach is called loadconditioning, which ensures that the equipment is lesssensitive to power disturbances, allowing the operationeven under significant voltage distortion.B) The othersolution is to install line conditioning systems thatsuppress or counteracts the power system disturbances.A flexible and versatile solution to voltage qualityproblems is offered by active power filters. Currently theyare based on PWM converters and connect to low andmedium voltage distribution system in shunt or in series.Series active power filters must operate in conjunctionwith shunt passive filters in order to compensate loadcurrent harmonics. Shunt active power filters operate as acontrollable current source and series active power filtersoperates as a controllable voltage source. Both schemesare implemented preferable with voltage source PWMinverters, with a dc bus having a reactive element such asa capacitor. Active power filters can perform one or moreof the functions required to compensate power systemsand improving power quality. As it will be illustrated inthis paper, their performance depends on the power ratingand the speed of response. The selection of the type of active power filter to improve power quality depends onthe source of the problem as can be seen in Table 1 [8] [3].Active FilterConnectionLoad on AC SupplyAC Supply on Load

Shunt-Current HarmonicFiltering.-Reactive currentCompensation.-Current unbalance.-Voltage Flicker.

SeriesCurrent harmonicfiltering.-Reactive currentcompensation.-Current unbalance.-Voltage Flicker.-Voltage unbalance-Voltage sag/swell.-Voltage unbalance.-Voltage distortion.-Voltage interruption.-Voltage flicker.-Voltage notching

Table1.2.3: The selection of the type of active power filter to improve power quality1.2.4 POWER QUALITY STANDARDSTo assure the harmonization of legislation within theEuropean Community, without which the free interchangeof goods and services would be affected, several directiveshave been released. One of such directives is the CouncilDirective 85/374, related to the liability for defectiveproducts. Its 2nd article defines electricity as product and inthis sense it becomes necessary to establish itscharacteristics [15].

A. EN 50160Voltage Characteristics of Electricity Supplied by Public Distribution Systems This standard, CENELEC (European Committee for Electrotechnical Standardization) defines the main characteristics of the low and medium voltage supplied by public distribution networks at the PCC (point of common coupling) [15].

Table1.2.4 (A):Harmonic voltages at PCC until order 25 in percentage of the nominal voltage

This standard also establishes that voltage total harmonicdistortion (THD), including the first 40 harmonics, must notexceed 8%.

B. IEC 61000This set of IEC (International ElectrotechnicalCommission) standards [2-4] is concerned withelectromagnetic compatibility (EMC) and includes thefollowing parts:1. General General considerations, definitions andterminology: 61000-1-x.2. Environment Description of the environment,classification of the environment, compatibilitylevels: 61000-2-x.3. Limits Emission limits, immunity limits: 61000-3-x.4. Testing and Measurement Techniques Providestechniques and measurement rules in order to assurethe compliance with the other parts of the standard:61000-4-x.5. Installation and mitigation guidelines Providesguidelines in the application of equipment such asfilters, compensators, surge arresters, etc, in order tosolve the problems related with power quality:61000-5-x.6. Generic standards Sets up the required immunitylevels for general-purpose equipments or for specifictypes of equipment: 61000-6-x.9. Miscellaneous: 61000-9-x

Table1.2.4(B): Compatibility levels for individual harmonic voltages in public low-voltage Networks.

Table 1.2.4 (C): Compatibility levels for harmonics

Class 1- applies to protected networks and it has the lowest lower compatibility levels (lower than that publicnetworks). It concerns the use of devices and equipmentsvery sensitive to electric disturbances, v. g. technologicallaboratories instrumentation, certain automation andprotective equipments, specific computers, etc.Class 2- applies to PCC and to the internal connectingpoints in the general industrial environment. It also appliesto public networks.Class 3- is only applicable to internal connection pointsof the industrial environments. The compatibility level isgreater than that of the class 2 for certain disturbances. Thisclass should always be considered whenever one of theseconditions is met:- Most of the loads are fed through converters.- There are melting machines.- Large capacity drives are started up very often.- The loads change rapidly.

C. ANSI/IEEE 519-1992According to this standard, which is presently beingupdated, the distribution companies are responsible forkeeping the quality of voltage in all their systems. Thisstandard sets up the distortion limits for the different voltagelevels of the electric networks [15].

TABLE 1.2.4(D): Maximum distortion levels

1.3. MotivationFaster power quality improvement is a perquisite for industrial and consumer equipments and SAPF offers better performance than other state of the art compensation methods. It improves power quality by significantlyreducing the harmonic components in currents and correcting the power factor.

1.4.Organization of the projectThe project focus on synchronous detection and digital control of shunt active power filter in power quality improvement, where the main body of the project is preceded by detailed tables of contents including list of figures, tables, and glossary followed by units used in the report which is follower by appendices which contains the screen shots and explains some of the key technology elements and off the shelf components used in the project. The body of the project also contains details of development and deployment environment used during the implementation of the project, the test cases executed to validate the features of the project followed by conclusion.

Outlines of the projectChapter 1- explain the introduction of the project, definition power quality , power quality problems, power quality standards, solution to power quality problems , motivation of research workand organization of the projectChapter 2- explains which papers refer in this project(literature survey).Chapter 3- It explains the power filtersdefinition, classification and methods. It also explains the active power filter market and objectives of active power filter.Chapter 4- describe the simulation model of both p-q theory and SDM method, it indicates the proposed method of p-q theory and also objectives p-q theory.It also clearly explains the data flow diagrams of the overall project.Chapter 5-describe the MATLAB tool and SIMULINK software used in this project.Chapter 6-includes the results of simulation waveforms in p-q theory and SDM method with different compensation. It also include conclusion of the project.

1.5 Objectives of the project

1) Introduction of SAPF device can helps us to improve power quality. 2) Reducing the harmonic components in currents. 3) Correcting the power factor. 4) The result of SAPF simulation method shows that balancing the 3 phase sinusoidalsupply voltage. 5) It balances and reduces the values of the currents supplied by the source to the load. 6) It compensates dynamically, and instantaneously, the zero-sequence current.

CHAPTER 2LITERATURY SURVEYImpact of Distributed Power Flow Controller to Improve Power Quality Based on Synchronous Reference Frame Method Ahmad Jamshidi, S. Masoud Barakati, and M. Moradi Ghahderijani. IACSIT International Journal of Engineering and Technology, Vol. 4, No. 5, October 201[3].Distributed power flow controller (DPFC) which is similar to unified power flow controller (UPFC) in structure, is used to mitigate the voltage sag and swell as a power quality issue. Unlike UPFC, the common dc-link in DPFC, between the shunt and series converters is eliminated and three-phase series converter is divided to several single-phase series distributed converters through the transmission lineAlso to detect the voltage sags and determine the three single-phase reference voltages of DPFC, the synchronous reference frame method is proposed.The power quality enhancement of the power transmissionsystems is an vital issue in power industry. In this study, the, application of DPFC as a new FACTS device, in the voltage, sag and swell mitigation of a system composed of athree-phase source connected to a non-linear load through theparallel transmission lines is simulated in Mat lab/Simulinkenvironment.The voltage dip is analyzed by implementing athree-phase fault close to the system load. To detect thevoltage sags and determine the three single phase referencevoltages of DPFC, the SRF method is used as a detection anddetermination method. The obtained simulation results showthe effectiveness of DPFC in power quality enhancement,especially in sag and swell mitigation.

Control of Shunt Active Filters for Power Quality Improvement.Mr.B.Dastagiri Reddy, V.Naga Bhaskar Reddy, Mr.K.Rajasekhara Reddy,DRDO Sponsored Eighth Control Instrumentation System Conference, CISCON-2011(An International Conference)[4].Active filtering of electric power has nowbecome a mature technology for various power qualityproblems such as harmonics, reactive power, unbalance,neutral current, voltage sag/swell and poor voltageregulation. Different configurations and control algorithmsfor power filters are used to eliminate these power qualityproblems. The work presented in this investigation consistsof various aspects on design and control of shunt activefilter (AF) for 3-wire system.In this paper, the performance of AF underdifferent load dynamics is verified using SRF controlalgorithm. AF is operated in UPF mode, ZVR mode andalso under distorted supply mains conditions. Moreover,SRF control scheme is best suited under distorted supplyconditions. In all the cases, AF has yielded thesatisfactory response with self supported DC busvoltage.Using Active Power Filters to Improve Power Quality. Luis A. Morn(1) Juan W. Dixon(2) Jos R. Espinoza(1) Rogel R. Wallace(1)[8].

This paper describes different power quality problems in distribution systems and their solutions with power electronics based equipment. Shunt, hybrid and series active power filters are described showing their compensation characteristics and principles of operation. Different power circuits topologies and control scheme for each type of active power filter are analyzed. The compensation characteristics of each topology with the respective control scheme are proved by simulation and experimentally.In this paper the use and advantages of applying active power filters to compensation power distribution systems has been presented. The principle of operation of shunt, series, and hybrid active power filters has been presented. Also, a brief description of the state of the art in the active power filter market has been described. The shunt active power filter performance under fault power distribution system was discussed. Simulation and experimental results proved the viability of using active power filters to compensate active power filter.

DSP Based Digital Controller for Shunt Active Power Filter to Improve Power Quality.Ginnes K John1, Sindhu M R2, and Manjula G Nair3. International Journal of Recent Trends in Engineering, Vol 2, No. 7, November 200[5].Power quality has been very interesting research area for past many years. Current harmonics are one of the most significant power quality issues, which is usually resolved by using shunt passive filters or shunt active filters. In this paper ICOS algorithm based shunt active filter is implemented in analog circuit and tested for a nonlinear load. The test results show that it can compensate for current harmonics. The algorithm was implemented digitally by dsPIC 30F 4011microcontroller with help of MPLAB C30 Compiler.Shunt active filter for powerquality improvement, E. W. J. M. Joo Afonso, Maurcio Aredes, International Conference UIE 2000 Electricity for a Sustainable Urban Development Lisboa, Portugal, Nov. 2000[1].This paper describes the development of a low cost shunt active power filter with digital control, which allows dynamic power factor correction and both harmonics and zero-sequence current compensation. The active filter controller is based on the instantaneous power theory (p-q theory) and was implemented using a standard 16 bits microcontroller. The p-q theory is introduced followed by the presentation of some active power filters topologies. Then a brief description of the implemented solution is made, including references to software tools used for simulation and system development. Experimental results are also presented, showing the good performance of the developed active filter.This paper presents a shunt active power filter as a reliable and cost-effective solution to power quality problems.The active filter controller is based on the p-q theory, which proved to be a powerful tool, but simple enough they allow the digital implementation of the controller using a standard and inexpensive microcontroller with minimum additional hardware.The filter presents good dynamic and steady-state response and it can be a much better solution for power factor and current harmonics compensation than the conventional approach

Active Power Filter for Nonlinear AC Loads.Janko Nastran, Member, IEEE, Rafael Cajhen, Matija Seliger, and Peter Jereb, Member, IEEE transactions on power electronics, vol. 9, no. 1, january 1994[9].This paper describes an active power filter fornonlinear ac loads with the power part carried out in the bridgeconnection. A theoretical approach to the implementation of thecurrent reference is given for this original solution of the serialactive filter. The paper also provides experimental results of thefilter application on two specific nonlinear loads, i.e., on theohmic load, fed over a pair of anti parallel thyristor , and onthe accumulator feeder.The required modification of the input load current can be activated by the power filter only when capacitor C ischarged with a particular voltage.CHAPTER 3POWER FILTER3.1 FILTERA filter is a circuit that is designed to pass a specified band of frequencies while attenuating all the signals outside that band .It is a frequency selective circuit[1]. There are two types of filters1) Passive power filter2) Active power filter1) Passive power filterPassive filters have been most commonly used to limit the flow of harmonic currents in distribution systems they are usually custom designed for the application. However, their performance is limited to a few harmonics and they can introduce resonance in the power system. Passive filter networks use only passive elements such as resister, inductors & capacitors.2) Active power filterIt is a type of analog electronic filter that uses active components such as amplifier and Transistors. Active filters, different from the passive ones, have the capability to dynamically adjust to the conditions of the system in terms of harmonics and reactive power compensation.

Power electronics devices are widely used in different fields and for different practical applications. Theexpansion of their field of applications is related to the knowledge of the device behavior and of theirperformances. One of the most interesting field of application is load compensation, i.e. active filtering of loadharmonics, load unbalance and / or load power factor compensation. Both items require a proper drive of powerelectronics apparatus. This result can be easily obtained by designing specific software programmes. Thedevelopment of these programmes can be satisfactorily made only on the basis of the theoretical knowledge and ofthe preliminary evaluation of mathematical models of power electronics devices. It is well-known that these devicesmake largely use of solid-state semiconductor switches. They have non-linear electric characteristics that lead tocomplicate analytical expressions of mathematical models. An important step for solving many practical problemsis researches devoted to evaluate solutions of non linear system of differential equations that depict mathematicalmodels of such devices. It is indeed not easy to get general solutions of these problems but it can be considered aremarkable research effort to try to find solutions for specific devices. In order to obtain these results, integraltransformations are sometimes useful, because operations in complex domains make it possible to find easier solutions in analytical closed form.[11]Figure 3.1.(A):Block diagram of a simple power system Figure.3.1.(B) Block diagram of a simple power system With APF ON with APF OFF

Figure 3.2:Classification of active filters according to rating 3.2 Classification of active filters according to ratingi) Low power applications: It is concerned with systems of power ratings below 100kVA, mainly in residential areas, commercial buildings and hospitals. These dynamic active filters are high pulse number PWM VSI or CSI. Their response time is relatively much faster ranging from tens of microseconds to milliseconds and can be used for single phase and three phase systems.

(ii)Medium power applications: are used in three phase systems ranging from 100kVA to10MVA (for current harmonic compensation). Speed of response is in the range100ms-1 sec.

(iii) High power applications: Implementation of very high power dynamic filter isextremely ineffective because of the lack of high switching frequency power devicesthat can control the current flow at high power ratings. This is a major limitation forsuch systems. Here, response time is in the range of tens of seconds.33However, the rating of active filters is very close to load rating (up to 80%) and hence costof shunt active filters is high. They are difficult to be implemented in large scale.3.3 Methods of active power filterA) Shunt active power filterB) Series active power filter

3.3.1 .SHUNT ACTIVE POWER FILTERA shunt active filter is an inverter driven by a pulse-width modulation technique (PWM) and placed in parallelwith a load. The shunt active filter injects a harmonic currents with thesame amplitude of those of the load into the ac system but with opposite phase displacement. The filter control is implemented through a detection and extraction circuit of the load harmonic currents [6]. At steady state,ideally, the compensating current can be supposed to be dependent on the load current by means of a propertransfer function, representing the selected control technique of active filter. With this simplification the analysis ofthe compensation characteristics of filters is straightforward, if reference is made to the equivalent circuits at thedifferent harmonics. [8]The shunt active power filter, with a self-controlled dc bus, has a topology similar to that of a static compensator (STATCOM) used for reactive power compensation in power transmission systems. Shunt active power filters compensate load current harmonics by injecting equal but opposite harmonic compensating current. In this case the shunt active power filter operates as a current source injecting the harmonic components generated by the load but phase shifted by 180 [1].

Figure 3.3.1: Configuration of a shunt active filter system

3.3.2 .SERIES ACTIVE POWER FILTERSeries active power filters were introduced by the end of the 1980s and operate mainly as a voltage regulator and as a harmonic isolator between the nonlinear load and the utility system. The series connected filter protects the consumer from an inadequate supply voltage quality. This type of approach is especially recommended for compensation of voltage unbalances and voltage sags from the ac supply and for low power applications and represents economically attractive alternatives to UPS, since no energy storage (battery) is necessary and the overall rating of the components is smaller. The series active filter injects a voltage component in series with the supply voltage and therefore can be regarded as a controlled voltage source, compensating voltage sags and swells on the load side. [8][1].A series active filter has to be placed in series between the ac source and the load in order to force the source current to become sinusoidal. The approach is based on a principleof harmonic isolation by controlling the output voltage of the series active filter. In other words, the series activefilter has to present high impedance to harmonic currents and then it is able to block these currents from the load tothe ac source and from the ac source to the load [1].

Figure 3.3.2:Configuration of a series active filter system

3.3.3. Active power Filter MarketMany different electrical companies are offering powerline conditioner or active power filter equipment tocompensate power quality problems. Based on state of theart power electronic technology, they have developeddifferent system to compensate not only current harmonic,but also flicker compensation and voltage regulation.Specially Siemens, ABB, Hitachi, Fuji and many othercompanies are offering power line conditioners to improvepower quality. These power line conditioners are based inshunt active power filter and series active power filtertopologies. Specially Siemens has developed bothapproaches as well as ABB.Currently active power line conditioner are typicallybased on IGBT or GTO thyristors voltage source PWMconvertersand connected to low and medium voltagedistribution systems in shunt, series or both at the sametime. In comparison to conventional passive LC filters,active power filters offer very fast control response andmore flexibility in defining the required control tasks for aparticular application. Some of the active power filtersavailable in the market and in use to compensate powerdisturbance problems are described below.The selection of equipment for improvement of powerquality depends on the source of the problem. In case of them Siemens Power Conditioner (SIPCON), which is based onstandard IGBT drive-converters, the series-connected PowerConditioner, also called Dynamic Voltage Regulator,(DVR) is most preferable to protect the consumer fromsupply voltage disturbances. However, if the objective is toreduce the network perturbations due to distorted loadcurrents the shunt-connection (also called DSTATCOM), ismore appropriate. Many shunt active filter consisting of PWM invertersusing IGBTs or GTO Thyristors have been operatingproperly in Japan, with a rating capacity which ranges from10 kVA to several MVA. Fuji Electric has developed andintroduced in the market shunt active power filters with rated power between 50 and 400 kVA for low voltageapplication. For a specific application, Toshiba hasdeveloped a shunt active power filter based on three voltagefed PWM inverters using GTO thyristors, each of which israted at 16 MVA. The three active power filters are used tocompensate the fluctuating reactive current and negativesequence current component generated by the Japanesebullet trains. In this case, the purpose of the shunt activepower filters with a total rating power of 48 MVA is tocompensate for voltage regulation, voltage variation andunbalance at the terminals of the 154 kV power systems toimprove the power quality. In this particular application,the active filters are effective in compensating not only voltage regulation, but also in reducing the voltageunbalance from 3.6% to 1 %. Also, CEGELEC hasdeveloped shunt active power filters based on GTO voltagesource inverters [8].The use of such system developed byCegelec in collaboration with Electricite de France (EDFs)R&D Group is to control interference in the Paris masstransit authority network, which was caused by the 15 kVbus bar. In this case, by using a GTO active power filter, thegeneral harmonic distortion in the current was reducedfrom 5.8 % to 2 %.Another Japanese company named Meiden, hasdeveloped the Multi-Functional Active Filter, also based onvoltage-fed PWM IGBTs inverters. This is a shunt activepower filter designed to compensate current harmonics,power factor and voltage regulation. Current harmoniccompensation is possible from the second component to the25th. The rated powerof the different models rangebetween 50 to 1000 kVA. The standard specifications ofthese active power filters are the followings: Number of phases: 3-phase and three wires [8]. Input voltage: 200, 210, 220 10%, 400,420, 440 10 %, 6600 10 %. Frequency: 50/60 Hz 5 %. Nos. of restraint harmonic orders: 2 to 25 th. Harmonic restraint factor: 85 % or more atthe rated output. Type of rating: continues. Response: 1 ms or less.

CHAPTER 4high Level DesignDesign is one of the most important phases of software development. The design is a creative process in which a system organization is established that will satisfy the functional and non-functional system requirements. Large Systems are always decomposed into sub-systems that provide some related set of services. The output of the design process is a description of the Software architecture.A robust watermarking algorithm for JPEG images need to be designed in which the watermark can be embedded in a predictable manner in compressed-encrypted byte stream by exploiting the homomorphic property of the cipher scheme.4.1 Design ConsiderationsThe purpose of the design is to plan the solution of the problem specified by the requirements document. This phase is the first step in moving from problem to the solution domain. The design of the system is perhaps the most critical factor affecting the quality of the software and has a major impact on the later phases, particularly testing and maintenance. System design describes all the major data structure, file format, output as well as major modules in the system and their Specification is decided.4.1.1 Development MethodsThe development method used in this software design is the functional development method. Digital control of SAPF based on p-q theory Control of SAPF system using synchronous Detection method (SDM)

4.2. P Q THEORY4.2.1. Principles of p-q theoryThe Generalized Theory of the Instantaneous Reactive Power in Three-Phase Circuits", proposed by Akagiet al., and also known as the p-q theory, is an interesting tool to apply to the control of active power filters, or even to analyze three-phase power systems in order to detect problems related to harmonics, reactive power and unbalance[12].The p-q theory implements a transformation from a stationary reference system in a-b-c coordinates, to a systemwith coordinates --0. It corresponds to an algebraic transformation, known as Clarke transformation, whichalso produces a stationary reference system, where coordinates - are orthogonal to each other, and coordinate 0corresponds to the zero-sequence component. The zero sequence component calculated here differs from the oneobtained by the symmetrical components transformation, or Fortescue transformation, by a 3 factor. The voltages and currents in --0 coordinates are calculated as follows: [7][1].

=A*(1)=A*Where,

A =

Is the Clarke transmission matrix, and,

A. Instantaneous Zero-Sequence Power

(2)

Mean value of the instantaneous zero-sequencepower. It corresponds to the energy per time unity thatis transferred from the power source to the loadthrough the zero-sequence components of voltage andcurrent.-Alternating value of the instantaneous zero-sequencepower. It means the energy per time unity that is exchangedbetween the power source and the load through the zero-sequence components of voltage andcurrent.The zero-sequence power exists only in three-phase systems with neutral wire. Moreover, the systems must have both unbalanced voltages and currents, or the same third order harmonics, in both voltage and current, for at least one phase. It is important to notice that cannot exist in apower system without the presence of. Since clearly an undesired power component (it only exchanges energy with the load, and does not transfer any energy to the load), both and must be compensated[15].

B. Instantaneous Real Power (p) (3)

Mean value of the instantaneous real power. It correspondsto the energy per time unity that is transferredfrom the power source to the load, in a balanced way,through the a-b-c coordinates (it is, indeed, the onlydesired power component to be supplied by the powersource).Alternating value of the instantaneous real power. It isthe energy per time unity that is exchanged betweenthe power source and the load, through the a-b-c coordinates.Since does not involve any energy transferencefrom the power source to load, it must becompensated.

C. Instantaneous Imaginary Power q )(4)

-Alternating value of instantaneous imaginary power.

The instantaneous imaginary power, q, has to do withpower (and corresponding undesirable currents) that is exchangedbetween the system phases, and which does notimply any transference or exchange of energy between thepower source and the load.Rewriting equation (4) in a-b-c coordinates the followingexpression is obtained:(5)This is a well known expression used in conventionalreactive power meters, in power systems without harmonicsand with balanced sinusoidal voltages. These instruments, of the electrodynamics type, display the mean value of equation(5). The instantaneous imaginary power differs fromthe conventional reactive power, because in the first case all the harmonics in voltage and current are considered.In the special case of a balanced sinusoidal voltagesupply and a balanced load, with or without harmonics, is equal to the conventional reactive powerIt is also important to note that the three-phase instantaneouspower ( ) can be written in both coordinates systems,a-b-c and --0, assuming the same value:

Thus, to make the three-phase instantaneous power constant,it is necessary to compensate the alternating powercomponents and. Since, as seen before, it is not possibleto compensate only, all zero-sequence instantaneouspower must be compensated.Moreover, to minimize the power system currents, theinstantaneous imaginary power, q, must also be compensated.The compensation of the p-q theory undesired power components ( , and q) can be accomplished with the use of an active power filter. The dynamic response of this active filter will depend on the time interval required by its control system to calculate these values[15].4.2.2. Proposed Method

Fig. 4.2.2: Operation of Three Phase Shunt Active Power Filter.

The compensation principle of a three phase shunt active power filter. The source is a balanced Y-connected three-phase voltage source where the phase voltages are while the nonlinear loads connected to each phase produces nonlinear load currents .When the SAPF block is not operating the nonlinear load current are themselves the line currents , which causes degradation in power factor and introduces harmonic distortion. When the SAPF block is operating it injects currents equal in magnitude but in phase opposition to harmonic currentin each of the lines. This compensates the harmonic distortion and makes the source current balanced sinusoidal while the load current remains nonlinear. The SAPF block is basically divided into two parts. The first part is a control block which does necessary computations and operations to generate the compensation current reference. This reference is fed to the IGBT based Voltage Source Inverter (VSI). A dc capacitor usually works as the source of power for the VSI.

4.2.3. The p-q theory applied to SAPF

Figure 4.2.3: SimulinkModel for Instantaneous power Theory (p-q theory) with SAPFThe only desirable quantity among all the power componentsobtained through the p-q theory is because itcorresponds to the energy transferred from the supply to theload. To compensate all the other quantities SAPF is used.Watanabe et al. presented a convenient way to compensateby delivering it from the power source to the active filterthrough coordinates, so that the active filter can supplythis power to the load through the 0 coordinate (see Fig.4.2.3) in abalanced way. Also the active filter capacitor can compensateand. The instantaneous imaginary power (q), which includesthe conventional reactive power, can be compensated withoutany capacitor .So for a three-phase system with balancedsinusoidal voltages, the supply currents are also sinusoidalbalanced, and in phase with the voltages. Thus, the powersupply now considers the nonlinear load as a purely resistive symmetrical load. The reference compensation currents in thecoordinatescan be calculated from [10].

=

Whereare the powers to be compensated. Also,the reference compensation current in the 0 coordinate is itself,, since all the instantaneous zero sequencepower will be compensated. In order to obtain the referencecompensation currents in the a-b-c coordinate inverse Clarketransformation is applied[13][10].

=

When the currents are fed to the VSI it generates theexact replica of these currents but in magnitude equal to theoriginal line currents. These replicated compensation currentsare then injected to the system to obtain in-phase sinusoidalsource currents with the line voltages that is to conform powerquality.This theory is based on time-domain, what makes it validfor operation in steady-state or transitory regime, as wellas for generic voltage and current power systemwaveforms, allowing to control the active power filters inreal-time. Another important characteristic of this theoryis the simplicity of the calculations, which involves onlyalgebraic calculation (exception done to the need ofseparating the mean and alternated values of the calculated power components)[12].

4.2.3. (A) Calculation of p-q theoryThe p-q theory calculations are done in the shunt activepower filter controller block. The controller allows, in asystematic way, and according to the receivedinformation, to verify the needing of compensationcurrents by the active filter. The controller receives theinformation of phase voltages, load currents and DCvoltage, and based on its control algorithm, proceeds tothe calculations of the p-q theory values, generating, ornot, the necessary reference compensation currents,which are injected in the power system by the inverter block [12]

Figure 4.2.3(A): Calculation of p-q theory

Figure 4.2.4:p-q Theory without Shunt Active Power Filter for load set A

Figure 4.2.5:p-q Theory without Shunt Active Power Filter for load set B

4.3. Objectives of p-q theory

1) It compensates dynamically the harmonic currents;2) It corrects dynamically the power factor;3) It compensates dynamically, and instantaneously, thezero-sequence current;4)It balances and reduces the values of the currentssupplied by the source to the load;5) It turns the instantaneous three-phase power that sourcedelivers to load into a constant value (the source onlydelivers conventional active power).

4.4. Synchronous Detection MethodControl of APF system using SDM: Figure showsthe control circuit of an APF system using SDM. Thecontrol circuit consists of an outer voltage control loopand two inner current control loops. The outer controlloop is used to maintain the capacitor voltage constantand to determine the amplitude of the mains currentsrequired in an APF system. SDM method is basicallyused for the determination of amplitude of the sourcecurrents. [4] [11].In the SDM, it is assumed that the three-phase main currentsare balanced after compensation, and it tries to determine thatrequired amplitude of the main currents.

Where are the amplitude of respectively .From here, the balanced line currents can be determined.

The compensation current reference is thus,

The compensation current references ,and are fed to the VSI which supplies the replica of these currents to the line. Since the PWM VSI is assumed to be instantaneous to track the compensation currents, it is modeled as a current amplifier with unity gain.[11][7].

Figure 4.4: Simulink Model Developed for SDM with SAPF

4.5.Architecture StrategiesThe architectural design process is concerned with establishing a basic structural framework for a system. It involves identifying the major components of the system and communications between these components. The initial design process of identifying these sub-systems and establishing a framework for sub-system control and communication is called architecture design and the output of this design process is a description of the software architecture. The architecture of the proposed approach is

Fig 4.5: System power components in a-b-c coordinatePower Quality means to maintain purely sinusoidal current wave form in phase with a purely sinusoidal voltage wave form. Power quality improvement using traditional compensation methods include many disadvantages like electromagnetic interference, possible resonance, fixed compensation, bulkiness etc. So power system and power electronic engineers need to develop adjustable and dynamic solutions using custom power devices. These power conditioning equipments use static power electronic converters to improve the power quality of distribution system customers.

4.6. Data Flow DiagramsA Data Flow Diagram (DFD) is a graphical representation of the "flow" of data through an information system. Data Flow models are used to show how data flows through a sequence of processing steps. The data is transformed at each step before moving on to the next stage. These processing steps or transformations are program functions when Data Flow diagrams are used to document a software design. DFD diagram is composed of four elements, which are process, data flow, external entity and data store. The DFD can be decomposed into three levels such as level 0, level 1

4.6.1. Data Flow Diagram Level 0The level-0 is the initial level DFD and its generally called as the context level diagram.

Non linear load connected each phaseSource VoltagesVa,Vb,Vc

Nonlinear load currents Ia,Ib,IcProduces

SAPF operating NO YES

Ia,Ib,Ic themselves line current ,,SAPF injects Ica,Icb,Icc equal in magnitude

Phase opposition to harmonic current in each lines

Degration in PF &harmonic distortion Causes

Compensate harmonic distortion

Source current balanced sinusoidal

Stop

Figure4.6.1: Data Flow Diagram Level 04.6.2 Data Flow Diagram Level 1The Level-1 DFD gives more information than the level-0 DFD. The Figure shows the Level-1 DFD.

transferred energy from supply to load

delivers from power source to active filter

Active filter supply power to load

Balanced Sinusoidal Voltage

Capacitor Compensate&

Imaginary power q compensate without capacitor

Sinusoidal balanced supply current & in phase with voltage

Figure 4.6.2: Data Flow Diagram Level 1The power components obtained through the p-q theory is p because it corresponds to the energy transferred from the supply to the load. To compensate all the other quantities SAPF is used. To compensate by delivering it from the power source to the active filter through alpha and betacoordinates, so that the active filter can supply this power to the load through the 0 coordinate in a balanced way. Also the active filter capacitor can compensateand . The instantaneous imaginary power (q), which includesthe conventional reactive power, can be compensated withoutany capacitor. So for a three-phase system with balancedsinusoidal voltages, the supply currents are also sinusoidalbalanced, and in phase with the voltages.

4.7.Detailed DesignOnce the high level design is completed the next stage is to perform detailed design of the software. While the high level design focuses on the tasks to be performed, the detailed design concentrates on how these can be performed. Detailed design is a phase where in the internal logic of each of the modules specified in high-level design is determined. In this phase details and algorithmic design of each of the modules is specified. Other low-level components and subcomponents are also described in this section. Each subsection of this section will refer to or contain a detailed description of system software component. Each subsection of this section refers to or contains a details description of a system software component. The Algorithm has the following operations on: Synchronous Detection Method (SDM) Digital control based on instantaneouspower theory (p-q theory).4.7.1. Functional Description of the ModulesThis section provides the complete description of all the modules use as part of this project.Introduction: To improve the power quality of distribution system customers. The devices include Active Power Filter (APF), dynamic voltage restorer (DVR) and Unified Power Quality Conditioner (UPQC). APF is a compensator used to eliminate the disturbances in current. There are basically two types of APFs: the shunt type and the series type. This paper examines the control of Shunt Active Power Filter (SAPF) from two different aspects: Synchronous Detection Method (SDM) and digital control based on instantaneous power theory (p-q theory).Purpose:Power quality improvement using traditional compensation methods include many disadvantages like electromagnetic interference, possible resonance, fixed compensation, bulkiness etc. So power system and power electronic engineers need to develop adjustable and dynamic solutions using custom power devices. These power conditioning equipments use static power electronic converters to improve the power quality of distribution system customers this work shows that digital control provides better power quality improvement than SDM.

Input: sinusoidal source voltage.Output: sinusoidal balanced source current.Algorithm:Phase voltage are Va,Vb,VcNonlinear load currents are Ia,Ib,IcStep 1: The source is a balanced Y-connected three-phase voltage source areVa,Vb,VcStep 2: The nonlinear loads connected to each phase produces Ia,Ib,Ic.Step 3: The SAPF block is not operating the nonlinear load current are themselves theline currents Isa,Isb,IscStep 4: It causes degradation in power factor and introduces harmonic distortion.Step 5: When the SAPF block is operating it injects currents Ica,Icb,Iccequal in magnitude.Step 6: In phase opposition to harmonic current in each of the lines.Step 7: This compensates the harmonic distortion.Step 8: Makes the source current balanced sinusoidal while the load current remains nonlinear.

is the mean value. is the alternated value of the instantaneous zero-sequence power.P is the instantaneous mean value.is the instantaneous alternated value of the real power.

Algorithm 2Step 1:The power components obtained through is p because it corresponds to the energy transferred from the supply to the load.Step 2: To compensate all the other quantities SAPF is used.Step 3: To compensate by delivering it from the power source to the active filter through alphaand betacoordinates.Step 4: The active filter can supply this power to the load through the 0 coordinate in a balanced way.Step 5:The active filter capacitor can compensate and Step 6:The instantaneous imaginary power (q), which includes the conventional reactive power, can be compensated without any capacitor.Step 7: Three-phase system with balanced sinusoidal voltages, the supply currents are also sinusoidal balanced, and in phase with the voltages.

CHAPTER 5: ABOUT MATLABINTRODUCTIONTOMATLAB5.1.MATLAB1 MATLAB is a software package for computation in engineering, science, and applied mathematics. It offers a powerful programming language, excellent graphics, and a wide range of expert knowledge. MATLAB is published by and a trademark of The Math Works, Inc.2 It provides interactive environment that enables to perform computations faster than other numerically oriented languages like C++ and FORTRAN.3 Here, in our project we are using the MATLAB7.1 version.

5.1.1.SIMULINKComputersimulationisawidelyacceptedtoolforanalysisanddesignofelectricalsystems,thelargeinterconnectedpowersystems.DigitalsimulationtoolslikeMATLABofferaconvenientmechanismtosolvetheseproblems.Itcanbeusedinalmostallfieldofscience,engineeringandinanyotherfieldinwhichextensivemathematicalsimulationandvisualreferencerequired.MATLABoffersexcellentplottingfeaturesandgraphicshandlingtechniquessothattheusercanhaveavisualreference.SIMULINK (Simulation and Link) works with MATLAB to offer modeling, simulating, and analyzing of dynamical systems under a graphical user interface (GUI) environment. The construction of a model is simplified with click-and-drag mouse operations. SIMULINK includes a comprehensive block library of toolboxes for both linear and nonlinear analyses. Models are hierarchical, which allow using both top-down and bottom-up approaches. As SIMULINK is an integral part of MATLAB, it is easy to switch back and forth during the analysis process and thus, the user may take full advantage of features offered in both environments.

5.1.2SIMPOWERSYSTEMSSimPowerSystemsandSimMechanicsofthePhysicalModellingproductfamilyworktogetherwithSimulinktomodelelectrical,mechanical,andcontrolSystems.

5.1.2.1.TheRoleofSimulationinDesignElectricalpowersystemsarecombinationsofelectricalandelectromechanicaldeviceslikemotorsandgenerators.Engineersworkinginthisdisciplineareconstantlyimprovingtheperformanceofthesystems.RequirementsfordrasticallyimprovedefficiencyhaveforcedpowersystemdesignerstousepowerelectronicDevicesandsophisticatecontrolsystemconceptsthattaxtraditionalanalysistoolsandTechniques.Furthercomplicatingtheanalystsroleisthefactthatthesystemisoftensononlinearthattheonlywaytounderstanditisthroughsimulation. Landbasedpowergenerationfromhydroelectric,steam,orotherdevicesarenottheonlyuseofpowersystems.Acommonattributeofthesesystemsistheiruseofpowerelectronicsandcontrolsystemstoachievetheirperformanceobjectives.SimPowerSysemsisamoderntoolthatallowsscientistsandengineerstorapidlyandeasilybuildmodelsthatsimulatepowersystems.SimPowerSystemsusestheSimulinkenvironment,allowingyoutobuildamodelusingsimpleclickanddragprocedures.Notonlycanyoudrawthecircuittopologyrapidly,butyouranalysisofthecircuitcanincludeitsinteractionswithmechanical,thermal,control,andotherdisciplines.ThisispossiblebecausealltheelectricalpartsofthesimulationinteractwiththeextensiveSimulinkmodelinglibrary.SinceSimulinkusesMATLABasitscomputationalengine,designerscanalsoMATLABtoolboxesandSimulinkblocksets.SimPowerSystemsandSimMechanicsshareaspecialPhysicalModelingblockandconnectionlineinterface.5.2SimPowerSystemsLibraries

WecanrapidlyputSimPowerSystemstowork.Thelibrariescontainmodelsoftypicalpowerequipmentsuchastransformers,lines,machines,andpowerelectronics.Thesemodelsareprovenonescomingfromtextbooks,andtheirvalidityisbasedontheexperienceofthePowerSystemstestingandSimulationLaboratoryofHydroQuebec,alargeNorthAmericanutilitylocatedinCanada,andalsoontheexprienceofEcoledeTechnologiesuprieureandUniversiteLaval.ThecapabilitiesofSimPowerSystemsformodelingtypicalelectricalSystemsareillustratedindemonstrationfiles.AndforuserswhowanttorefreshtheirKnowledgeofpowersystemtheory,therearealsoself-learningcasestudies.Followingaretheblocksusedforthesimulation.5.2.1Three Phasesource5.2.1a.Description:

TheThree-PhaseSourceblockimplementsabalancedthree-phasevoltagesourcewithinternalR-Limpedance.ThethreevoltagesourcesareconnectedinYwithaneutralconnectionthatcanbeinternallygroundedormadeaccessible.YoucanspecifythesourceinternalresistanceandinductanceeitherdirectlybyenteringRandLvaluesorindirectlybyspecifyingthesourceinductiveshort-circuitlevelandX/Rratio.5.2.1b.DialogBoxandParameters

5.2.1c.Phase-to-phasermsvoltageTheinternalphase-to-phasevoltageinvoltsRMS(Vrms).5.2.1d.PhaseangleofphaseAThephaseangleoftheinternalvoltagegeneratedbyphaseA,indegrees.Thethreevoltagesaregeneratedinpositivesequence.Thus,phaseBandphaseCinternalvoltagesarelaggingphaseArespectivelyby120degreesand240degrees.5.2.1e.FrequencyThesourcefrequencyinhertz(Hz).5.2.1f.InternalconnectionTheinternalconnectionofthethreeinternalvoltagesources.Theblockiconisupdatedaccordingtothesourceconnection.Selectoneofthefollowingthreeconnections:Y-ThethreevoltagesourcesareconnectedinYtoaninternalfloatingneutral.Yn-ThethreevoltagesourcesareconnectedinYtoaneutralconnectionwhichismadeaccessiblethroughafourthterminal.Yg-ThethreevoltagesourcesareconnectedinYtoaninternallygroundedneutral.Specifyimpedanceusingshort-circuitlevel:Selecttospecifyinternalimpedanceusingtheinductiveshort-circuitlevelandX/Rratio.3-phaseshort-circuitslevelatbasevoltage:

Thethree-phaseinductiveshort-circuitpower,involts-amperes(VA),atspecifiedbasevoltage,usedtocomputetheinternalinductanceL.ThisparameterisavailableonlyifSpecifyimpedanceusingshort-circuitlevelisselected.TheinternalinductanceL(inH)iscomputedfromtheinductivethree-phases short-circuitspowerPsc(inVA),basevoltageVbase(inVrmsphase-to-phase),andsourcefrequencyf(inHz)asfollows:5.2.1g.BasevoltageThephase-to-phasebasevoltage,involtsRMS,usedtospecifythethree-phaseshort-circuitlevel.Thebasevoltageisusuallythenominalsourcevoltage.ThisparameterisavailableonlyifSpecifyimpedanceusingshort-circuitlevelisselected.5.2.1h.X/Rratio

TheX/Rratioatnominalsourcefrequencyorqualityfactoroftheinternalsourceimpedance.ThisparameterisavailableonlyifSpecifyimpedanceusingshort-circuitlevelisselected.TheinternalresistanceRiscomputedfromthesourcereactanceX(in)atspecifiedfrequency,andX/Rratioasfollows:5.2.1i.SourceresistanceThisparameterisavailableonlyifSpecifyimpedanceusingshort-circuitlevelisnotselected.Thesourceinternalresistanceinohms.5.2.1j.SourceinductanceThisparameterisavailableonlyifSpecifyimpedanceusingshort-circuitlevelisnotselected.Thesourceinternalinductanceinhenries(H).

5.2.2Three-PhaseV-IMeasurement:5.2.2a.Description:

TheThree-PhaseV-IMeasurementblockisusedtomeasurethree-phasevoltagesandcurrentsinacircuit.Whenconnectedinserieswiththree-phaseelements,itreturnsthethreephase-to-groundorphase-to-phasevoltagesandthethreelinecurrents.Theblockcanoutputthevoltagesandcurrentsinperunit(p.u.)valuesorinvoltsandamperes.Ifyouchoosetomeasurethevoltagesandcurrentsinp.u.,theThree-PhaseV-IMeasurementblockdoesthefollowingconversions:

Whereisthebaseline-to-linevoltageinvoltsRMSandisthethree-phasebasepowerinvolts-amperes.ThetwobasevaluesandarespecifiedintheThree-PhaseMeasurementblockmenu.Thesteady-statevoltageandcurrentphasesmeasuredbytheThree-PhaseV-IMeasurementblockcanbeobtainedfromthePowerguiblockbyselectingSteady-StateVoltagesandCurrents.ThephasormagnitudesdisplayedinthePowerguistayinpeakorRMSvalueseveniftheoutputsignalsareconvertedtop.u.

5.2.2b.DialogBoxandParameters

5.2.2c. Voltage measurementSelectnoif you do not want to measure three-phase voltage. Selectphase-to-groundif you want to measure the phase-to-ground voltages. Selectphase-to-phaseif you want to measure the phase-to-phase voltages. Use a labelIf selected, the voltage measurements are sent to a labeled signal. Use a From block to read the voltages. The Goto tag of the From block must correspond to the label specified by theSignal labelparameter. If not selected, the voltage measurements are available via the output of the block. Signal labelSpecifies a label tag for the voltage measurements.Voltages in pu, based on peak value of nominal phase-to-ground voltage .If selected, the measured phase-to-ground voltages are converted in pu.Voltages in Pu, based on peak value of nominal phase-to-phase voltageIf selected, the measured phase-to-phase voltages are converted in pu. This parameter is not visible in the dialog box ifVoltage measurementparameter is set tophase-to-groundorno.Nominal voltage used for pu measurement (Vrms phase-phase)The nominal voltage, in volts RMS, used to convert the measured voltages in pu. This parameter is not visible in the dialog box ifVoltage measurementparameter is set tono.5.2.2d. Current measurementSelectyesif you want to measure the three-phase currents that flow through the block.Use a labelIf selected, the current measurements are sent to a labeled signal. Use a From block to read the currents. The Goto tag of the From block must correspond to the label specified by theSignal labelparameter. If not selected, the current measurements are available via the output of the block.Signal labelSpecifies a label tag for the current measurements.Currents in puIf selected, the three-phase currents are measured in pu. Otherwise they are measured in amperes.5.2.2e. Base power (VA 3 phase)The three-phase base power, in volt-ampere (VA), used to convert the measured currents in pu. TheBase power (VA 3 phase)parameter is not visible in the dialog box ifCurrents in puis not selected.5.2.2f. Output signalSpecifies the format of the measured signals when the block is used in a phasor simulation. TheOutput signal parameter is disabled when the block is not used in a phasor simulation. The phasor simulation is activated by a Powergui block placed in the model.Set toComplexto output the measured voltages and currents as complex values. The outputs are complex signals.Set toReal-Imagto output the real and imaginary parts of the measured voltages and currents.Set toMagnitude-Angleto output the magnitudes and angles of the measured voltages and currents.Set toMagnitudeto output the magnitudes of the measured voltages and currents. The output is a scalar value.5.2.2g. Inputs and Outputs

. The three measured phase-to-ground or phase-to-phase voltages. The output disappears when theUse a labelparameter is selected or when theVoltage measurementmenu is set tono.

The three measured line currents. The output disappears when theUse a labelparameter is selected or when theCurrent measurementmenu is set tono.

CHAPTER 66.1: SIMULATION RESULTSMatlab simulink toolboxes are used to develop the modelsto execute both the SDM and p-q theory calculations. Thesimulink models are shown in figures 4.2.3& 4.4.According to the load currents the SAPF generates compensationcurrents in each phase. These currents for SDM and p-qtheory are shown in figure 6.6 and 6.4 respectively. The resultantsinusoidal supply currents for both the methods are shown infigures 8 and 5. The implication of SAPF results the supplyphase currents to become sinusoidal, balanced and in phase with the supply phase voltages. Moreover SAPF has also madecurrent through the neutral wire to zero.Table 6.1 Shows values of total harmonic distortion (THD)for the phase and neutral currents and displacement powerfactor (DPF), power factor (PF) for each of the phases of the power source before and after applying SAPF. Results showthat SAPF can compensate the power factor to one and theharmonic currents to zero at the source end.

Figure 6.1:The three phase load currents for load set A (a) (a)and (a)

Figure 6.2:The three phase load currents for load set B (a) (a)and (a)

Figure 6.3:The three phase source currents before compensation for load (P-q-SAPF) (a)(b)and (c)

Figure 6.4: The three phase compensation currents for load (p-q SAPF) (a)(b) (C)

Figure 6.5:The three phase source currents after compensation for load (p-q -SAPF) (a)(b)and (c)

Figure 6.6:The three phase compensation currents for load (SDM- SAPF) (a)(b) (C)

Figure 6.7:The three phase source currents before compensation for load (SDM-SAPF) (a)(b)and (c)

Figure 6.8:The three phase source currents after compensation for load (SDM-SAPF) (a)(b)and (c)

6.2: CONCLUSION& FUTURE SCOPE

Faster power quality improvement is a prerequisite forindustrial and consumer equipment and SAPF offers betterperformance than other state-of-the-art compensation methods.It improves power quality by significantly reducing the harmoniccomponents in currents and correcting the power factor.The results of simulations performed in this work shows thatdigital control of SAPF based on p-q theory provide fasterpower quality improvement than SDM technique. In summing,digital control of SAPF should be the preferred choice forpower quality improvement.Comparing the performance of the two methods it is realizedthat digital control based on p-q theory is much fasterthan compensation using SDM. The resultant source currentwaveforms show that p-q theory compensates the undesirablecurrent components within 1st cycle whereas SDM takes about14 cycles (approximately 0:23 seconds for 50 Hz source).So for faster power quality improvement digital control ispreferable to SDM.

Reactive power compensation and harmonic compensation are essentially twodifferent requirements from the frequency of operation of inverter perspective. Harmonic compensation requires a high frequency low power inverter whereas reactive power requires low frequency high power operation. Therefore, itis important to develop a suitable methodology such that these tasks aredecoupled and compensation can be done by two different invertersTo meet higher power requirements multi-level inverter would be used, anSAPF using such inverter and control strategies suitable for such invertershould be taken up.

BIBILOGRAPHY

[1] E. W. J. M. Joo Afonso, Maurcio Aredes, Shunt active filter for power quality improvement, International Conference UIE 2000 Electricityfor a Sustainable Urban Development Lisboa, Portugal, Nov. 2000.[2] M. Najafi, M. Hoseynpoor, M. Davoodi, T. KarimiBushehr Branch, Islamic Azad University, bushehr, Iran A Simple Control of Shunt Active Power Filter to Enhancing Current Quality. Australian Journal of Basic and Applied Sciences, 5(7): 678-683, 2011 ISSN 1991-8178. [3] Ahmad Jamshidi, S. Masoud Barakati, and M. Moradi Ghahderijani. Impact of Distributed Power Flow Controller to Improve Power Quality Based on Synchronous Reference Frame Method. IACSIT International Journal of Engineering and Technology, Vol. 4, No. 5, October 2012.[4] Mr.B.Dastagiri Reddy, 2V.Naga Bhaskar Reddy, 3 Mr.K.Rajasekhara Reddy, Control of Shunt Active Filters for Power Quality Improvement. DRDO Sponsored Eighth Control Instrumentation System Conference, CISCON-2011(An International Conference).[5] Ginnes K John1, Sindhu M R2, and Manjula G Nair3. DSP Based Digital Controller for Shunt Active Power Filter to Improve Power Quality. International Journal of Recent Trends in Engineering, Vol 2, No. 7, November 2009.[6] Sangu Ravindra#1, Dr.V.C.Veera Reddy#2, Dr.S.Sivanagaraju. Design of Shunt Active Power Filter to eliminate the harmonic currents and to compensate the reactive power under distorted and or imbalanced source voltages in steady state. International Journal of Engineering Trends and Technology- Volume2Issue3- 2011 .[7] Vedat M. KarslMehmet Tmay Berrin Sslolu An evaluation of time domain techniques for compensating currents of shunt active power filters.[8]Luis A. Morn(1) Juan W. Dixon(2) Jos R. Espinoza(1) Rogel R. Wallace(1) Using active power filters to improve power quality.

[9]Janko Nastran, Member, IEEE, Rafael Cajhen Matija Seliger, and Peter Jereb, Active power filter for nonlinear ac loads .Member, IEEE transactionson power electronics, vol. 9, no. 1, january 1994[10]Mauricio Aredes1,2,a, Student Member, IEEE and Edson H. Watanabel, Member, IEEENEW CONTROL ALGORITHMS FOR SERIES AND SHUNT THREEPHASE FOUR-WIRE ACTIVE POWER FILTERS EEE Transactions on Power Delivery, Vol. 10, No. 3, July 1995[11]Moleykutty George and 2Kartik Prasad Basu Three-Phase Shunt Active Power Filter.63100 Cyberjaya, Malaysia American Journal of Applied Sciences 5 (8): 909-916, 2008ISSN 1546-9239[12]Emlio F. Couto, Jlio S. Martins, Joo L. Afonso Simulation Results of a Shunt Active Power Filter withControl Based on p-q Theory. Department of Industrial Electronic University of Minho Campus de Azurm 4800-058 Guimares (Portugal)[13]Moinuddin k Syed, 2dr. BV Sanker ram Instantaneous power theory based activepower filter: a matlab/ simulink approach.[14] Control of Shunt Active Filters for Power Quality Improvement.Mr.B.Dastagiri Reddy, V.Naga Bhaskar Reddy, Mr.K.Rajasekhara Reddy, DRDO Sponsored Eighth Control Instrumentation System Conference, CISCON-2011(An International Conference).[15] Joo L. Afonso, M. J. Seplveda Freitas, and Jlio S. Martins, p-q Theory Power Components Calculations.ISIE2003 - IEEE International Symposium on Industrial Electronics Rio de Janeiro, Brasil, 9-11 Junho de 2003, ISBN: 0-7803-7912-8[16] Joo L. Afonso, Member IEEE, H. J. Ribeiro da Silva and Jlio. S. Martins, Member IEEE Active Filters for Power Quality Improvement. 2001 IEEE Porto PowerTech, 10-13 Set. 2001, Porto, Portugal, ISBN: 0 7803 7139 9.

BIODATA

NAME: Mahesh C Giriyappanavar

USN: 4AI12EPS05

DATE OF BIRTH: 4TH December 1990

MAIL ID: Maheshgiriyappanavar@gmail.com

ADDRESS:M.C. GiriyappanavarNear S.R.S High School, GuttalTq/dst: Haveri (581108)

ACADEMIC QULIFICATION: Electrical and Electronics EngineeringS.T.J.I.T College Ranebennure Visvesvaraya UniversityFirst Class (64.63%)

Dept of E&E ,AIT ChikmaglurePage 23