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Now a days problems regarding power quality is more in large inter connected power systems. There are many method to mitigate these problems but using the latest most efficient compensation method is some what impressive. Here is the brief explanations regarding UPQC using soft computing method(fuzzy logic). This was my academic project along with my friends.

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- 1. POWER QUALITY IMPROVEMENTPOWER QUALITY IMPROVEMENTPOWER QUALITY IMPROVEMENTPOWER QUALITY IMPROVEMENT USING UPQC WITH SOFT COMPUTINGUSING UPQC WITH SOFT COMPUTINGUSING UPQC WITH SOFT COMPUTINGUSING UPQC WITH SOFT COMPUTING METHOD: FUZZY LOGICMETHOD: FUZZY LOGICMETHOD: FUZZY LOGICMETHOD: FUZZY LOGIC POWER QUALITY IMPROVEMENTPOWER QUALITY IMPROVEMENTPOWER QUALITY IMPROVEMENTPOWER QUALITY IMPROVEMENT USING UPQC WITH SOFT COMPUTINGUSING UPQC WITH SOFT COMPUTINGUSING UPQC WITH SOFT COMPUTINGUSING UPQC WITH SOFT COMPUTING METHOD: FUZZY LOGICMETHOD: FUZZY LOGICMETHOD: FUZZY LOGICMETHOD: FUZZY LOGIC By: Sakti Prasanna Muduli Along with R C Muduli A K Mohapatra P C Jena S K Mahallik H Parida POWER QUALITY IMPROVEMENTPOWER QUALITY IMPROVEMENTPOWER QUALITY IMPROVEMENTPOWER QUALITY IMPROVEMENT USING UPQC WITH SOFT COMPUTINGUSING UPQC WITH SOFT COMPUTINGUSING UPQC WITH SOFT COMPUTINGUSING UPQC WITH SOFT COMPUTING METHOD: FUZZY LOGICMETHOD: FUZZY LOGICMETHOD: FUZZY LOGICMETHOD: FUZZY LOGIC Along with: R C Muduli Mohapatra P C Jena S K Mahallik H Parida
- 2. DedicatedDedicatedDedicatedDedicated ToToToTo All my FriendsAll my FriendsAll my FriendsAll my Friends
- 3. CONTENTS Chapter 1: Introduction…………………………………………………………………01 1.1 Overview…………………………………………………………………………..01 1.2 Motivations………………………………………………………………………..02 1.3 Objectives…………………………………………………………………………03 1.4 Organisation of thesis……………………………………………………………03 Chapter 2: Power Quality Problem……………………………………………………04 2.1 Introduction……………………………………………………………………….....04 2.2 Linear and Non-linear Loads……………………………………………………...04 2.2.1 Linear load……………………………………………………………………….04 2.2.2 Non Linear load………………………………………………………………....05 2.3 Major Power Quality problem…………………………………………………...…06 2.3.1 Short Duration Voltage variations…………………………………………..…06 2.3.2 Long Duration Voltage variations…………………………………………...…06 2.3.3 Transients………………………………………………………………………...07 2.3.4 Waveform Distortion……………………………………………………………..08 2.4 Frequency Variation…………………………………………………………………..09 2.5 Harmonics………………………………………………………………………………09 2.7 Power Quality…………………………………………………………………………..09 2.7.1 Voltage dip…………………………………………………………………………10 2.7.2 Voltage dip mitigation……………………………………………………………..10 2.9 Power quality Monitoring……………………………………………………………..13 2.9.1 Asset load monitoring…………………………………………………………….13 2.9.2 Phase Balancing………………………………………………………………….13 2.9.3 Load Balancing……………………………………………………………………14 2.9.4 Distributed Energy Resource management(DER)……………………………14 2.9.5 Direct monitoring and control of DER…………………………………………..14 2.9.6 Shutdown or Islanding verification for DER……………………………………14 2.10 Power Quality controller based on VSC…………………………………………..15 2.11 Voltage Source Converter…………………………………………………………..15 2.12 Distribution Static Compensator……………………………………………………16 2.13 Dynamic Voltage Restorer(DVR)…………………………………………………..17 2.14 UPFC………………………………………………………………………………….18 Chapter 3: Proposed Scheme for Power Quality Improvement………………………19 3.1 Measurement blocks……………………………………………………………….20 3.2 Fuzzy logic Controller………………………………………………………………20 3.2.1 Fuzzy logic Background……………………………………………………….21 3.2.2 Applying truth value……………………………………………………………21 3.2.3 Linguistic Variables…………………………………………………………….22 3.3 PWM Pulse Generator……………………………………………………………...24 3.4 UPQC…………………………………………………………………………………24
- 4. 3.4.1 Series APF………………………………………………………………………26 3.4.2 Shunt APF……………………………………………………………………….26 3.4.3 DC Link Capacitor………………………………………………………………26 3.4.4 Design of UPQC………………………………………………………………...27 3.4.5 configuration of proposed UPQC……………………………………………...29 Chapter 4: System Model and Results…………………………………………………..32 4.1 Simulink Based System model: With UPQC……….…………………………… 32 4.2 Results: Comparison of 3 ph voltage wave forms- with & without UPQC…….34 4.3 Results: Comparison of DC volt Waveforms –with & without UPQC………….34 4.4 Results: Comparison of volt waveforms under transients………………………35 Chapter 5: Conclusion and Future Scope………………………………………………37 5.1 Conclusion……………………………………………………………………………37 5.2 Future Scope………………………………………………………………………...37 Reference………………………………………………………………………………….39
- 5. LIST OF FIGURES Figure No. Title Page No. 2.1 Basic building blocks of D-STATCOM 17 2.2 Standard configuration of DVR 18 2.3 Basic configuration of UPFC 19 3.1 Whole System block diagram 20 3.2 Fuzzy logic 22 3.3 Fuzzy logic system 23 3.4 Simple UPQC scheme 25 3.5 UPQC with Energy storage 30 3.6 Equivalent Circuit diagram for UPQC 30 4.1 Simulink based system model without UPQC 33 4.2 Result without UPQC(Voltage sag) 34 4.3 Result with UPQC(no voltage sag) 34 4.4 DC voltage without UPQC 35 4.5 DC voltage with UPQC 35 4.6 Transients 36 4.7 Compensated system under transients 36
- 6. ABSTRACT In a powers system network there are many problems related to power quality. When the term ‘Power Quality’ comes just after that ‘Voltage Quality’ comes along with. We can say Power Quality is directly referred by voltage quality. So to improve power quality of a system we use different devices such as active power filters. Active power filters are classified into two types those are Shunt Active Power Filter and Series Active Power Filter and combination of both is known as “UPQC (Unified Power Quality Conditioner)”. UPQC is used to mitigate voltage sag and transients due to sudden load variation, fault, capacitor switching etc. Series APF reduces all voltage related problems and shunt APF reduces all current related problems, Harmonics in addition to reactive power support. The control scheme used is based on “Fuzzy logic” as it is a multi- valued logic and simple to understand define a rule.
- 7. 1 CHAPTER1 INTRODUCTION 1.1 Overview In today’s world there is great importance of electrical energy as it is the most famous from of energy and all are massively relying on it. Without supply of electricity life cannot be imagined. At the same time the quality and continuousness of the electric power supplied is also very important for the efficient functioning of the end user equipment. Many of the commercial and industrial loads require high quality undisturbed and constant power. Thus maintaining the qualitative power is topmost important in today’s world. Electric power quality (PQ) has become the concern of utilities, end users, manufacturers, and all other customers. Power quality is the set of parameters defining the properties of power supply delivered to the users in normal operating conditions in terms of continuity of supply and characteristics of voltage (magnitude, frequency, symmetry, waveform etc.). Modern electronic equipments and devices, such as microprocessors, microcontrollers, telecommunications equipment and sensitive computerized equipments etc. are susceptible to PQ problems. Poor PQ has become a more important concern of both power suppliers and customers. The global bill for poor power quality is more than 500 billion Euros per year which is 50% of the turnover of the global electricity sector. For many business uses, the cost of poor PQ is higher than the electricity bill and the cost is rising.Due to power electronics devices there is serious effect on quality and continuousness of electric supply. Because of power electronics devices there is uninterrupted power supply, flicker, harmonics, voltage fluctuations etc. There is also PQ problems such as voltage rise/dip due to network faults, lightning, switching of capacitor banks. With the excessive uses of non-linear load (computer, lasers, printers, rectifiers) there is reactive power
- 8. 2 disturbances and harmonics in power distribution system. It is very essential to overcome this type of problems as its effect may increase in future and cause adverse effect. Traditionally passive filters were used for reactive power disturbances and harmonics generation but there is many problems with them like they are large in size, resonance problem, effect of source impedance on performance. Active Power Filters are used for power quality enhancement. Active power filters can be classified according to system configuration. Active power filters are of two types series and shunt. Combining both series APF & shunt APF we get a device known as UPQC. UPQC eliminates the voltage and current based distortions together. A Shunt APF eliminates all kind of current problems like current harmonic compensation, reactive power compensation, power factor enhancement. A Series APF compensates voltage dip/rise so that voltage at load side is perfectly regulated. The Shunt APF is connected in parallel with transmission line and series APF is connected in series with transmission line. UPQC is formed by combining both series APF and shunt APF connected back to back on DC side. In this section, UPQC and fuzzy logic controller is used to mitigate power quality problem efficiently. UPQC is made by combining both shunt APF and series APF. Fuzzy logic is very efficient controller used to eradicate power qualities issues and problems. In this thesis power quality of system was improved by using UPQC and fuzzy logic. First simulation of shunt APF was done after that series APF was done. And after that combining both device simulation of UPQC was done using fuzzy logic controller. 1.2 Motivation At present scenario, one of the serious problems in electrical systems is the increasing number of power electronics devices that are used by industries as well as residences. These devices which need high-quality energy to work properly, at the same time are the most responsible ones for injections of harmonics in the distribution
- 9. 3 system. The goal of this work consists in expand this control strategy of fuzzy logic to deal with the power quality problem issues using UPQC. UPQC is an integration of shunt and series compensation to limit the harmonic contamination. Simulation results on MATLAB can be illustrated in order to verify the accuracy of the expanded control strategy. UPQC is used to solve all problems related to voltage and current harmonics and improve power quality. 1.3 Objective To explore the soft computing techniques fuzzy logic for generating gate pulse for the UPQC. Study the UPQC model for power quality improvement. 1.4 Organization of Thesis Chapters 1 – So far in the chapter1 Basic introduction to our thesis, Motivation, Literature survey and Objective have been discussed. Chapter2–This chapter discusses main theory related to the Power Quality(PQ), mathematical modeling etc. and various method adopted for the improvement in the process based on literature review. Chapter 3- This chapter discusses modeling techniques used, Operations and design principle. The chapter further demonstrates about the basic principles behind the proposed scheme. Chapter 4 –This chapter shows various performances on MATLAB/SIMULINK environment for the adopted scheme.
- 10. 4 Chapter 5 –This chapter shows Concludes with performance analysis methods and results of our adopted technique and further advancement for implementing new innovation in this specific topic. Finally, the thesis ended with references taken for the detailed case study on the topic. CHAPTER2 POWER QUALITY PROBLEM 2.1 Introduction In the day-today life, and in many industries there is very huge use of power electronics devices, Programmable logic circuits (PLC), semiconductor devices, and adjustable speed drives due to this there is power quality problems. There is also many external and internal factors that affect the quantity and quality of power delivered. Many network faults, switching of capacitor banks, voltage sag/swell, lightning, and harmonics also cause power quality problems. Mainly loads work at 50 Hz and 60 Hz frequencies but there are many loads which work at integer multiple of 50 Hz or 60 Hz frequencies. Because of these loads there is harmonics in power system. 2.2 Linear and Non- linear loads 2.2.1 Linear load The loads which have current and voltage waveform sinusoidal are linear loads. The current at any time is proportional to voltage. Linear load only change relative timing (phases) between current and voltage there is no change in shape of current waveform. According to Ohm’s law I(t)= ( ) According to this law if waveform of voltage is sinusoidal then the waveform of current also will be sinusoidal. Linear loads are capacitor and inductor. If capacitor is in load side then the current will lead voltage. If inductor is in load side then voltage will lead. So waveforms in both cases will be out of phase. Power factor defined in case of linear load.
- 11. 5 Power factor = = cos∅ Table 2.1 Linear load 2.2.2 Non-Linear loads In non-linear loads the shape of current waveform changes its shape from original shape. Non-linear loads produce harmonics with original fundamental component of AC current. Non-linear loads examples are power electronics devices like BJT,MOSFET. Given in table 2.2. Table 2.2
- 12. 6 2.3 Major power quality problems 2.3.1 Short duration voltage variation Due to faults there is voltage rise (swells), voltage dip (sag), or complete loss of voltages (interruptions) which are temporary for certain interval of time depending upon the type of fault occurred and location of fault. The duration is around 1 min for short voltage variation. Also if duration of fault is for few millisecond then it is short duration voltage variation. (i)Voltage sag:- Voltage sag is also called voltage dip . The rms line voltage decreases to 10 % to 90 % of nominal line voltage. The time interval for voltage dip is about 0.5 cycle to 1 min. The equipment which causes voltage dip are induction motor starting etc. Voltage dip is shown in figure below. (ii)Voltage swell:- Voltage swell is also called voltage rise. The rms line voltage increases from 1.1 % to 1.8% of nominal line voltage. The duration for voltage rise is around 0.5 cycles to 1 min. The voltage swell is caused due to energizing the large capacitor bank and shutting down the large loads. Voltage swell is shown in fig 2.2 (iii) Interruption:- Interruption is degradation in current or line voltage up to 0.1 pu of the nominal value. It is for the time period of 60 seconds and not going beyond it. The causes of interruption are failures in equipment, faults in power systems, control malfunctions. 2.3.2. Long- Duration voltage variation The long duration voltage variations are caused because of sustained interruptions, under voltages and over voltages. (i)Sustained interruptions:- When there is zero supply voltage for a interval of time more than 60 sec, it is considered as sustained interruption in case of long duration voltage variation.
- 13. 7 ii) Under voltages:- It is the reduction in rms ac voltage to lower than 90 % at power frequency for a time interval 60 sec or may be greater than it. The switching off of capacitor banks and switching on of loads cause under voltage as far as voltage regulation device on the system bring back the voltage to the given tolerance limits. The under voltage is also caused due circuits which are overloaded. (iii) Over voltages:- It is the rise in rms ac voltage to more than 110 % at power frequency for a time interval of more than 60 sec. Over voltages are caused due to the wrong tap settings of transformers and switching of loads. 2.3.3 Voltage fluctuations Fluctuations in voltage are irregular or repeated variations in magnitude of source voltage due to sudden change in real and reactive power drawn by the load. The characteristics of voltage fluctuation depend upon type of loads. The magnitude of voltage fluctuation does not rise above 12 10% of nominal supply voltages. The Lamp flicker is the effect of voltage fluctuations. Loads that cause fluctuations in voltages are arc furnaces, arc welders, air conditioner units, rolling mills, cyclo-converters, and equipment with excessive motor speed changes. 2.3.4 Voltage Unbalance Voltage unbalances occur when there is difference in magnitude of phases or line voltages and phase angle is different from balanced conditions. Voltage unbalance is due to different loads in the phases causing drops in voltages at phase – line impedance. 2.3.5 Transients Transients are sudden & small change in current and voltage signals for a very less period of time.
- 14. 8 (i) Impulsive transients:- Impulsive transient are variation in current, voltage or both on power line in one direction (unidirectional). The causes of impulsive transients are switching in power distribution systems, inductive loads switching, lightning. The impulsive transients can be removed with help of zener diode which suppresses the transient voltage. (ii)Oscillatory transients:- Oscillatory transients are transients which have swing (bidirectional) i.e. rapid change of polarity of current , voltage or both on power line. Capacitors switching which help in power factor correction. 2.3.6 Waveform Distortion A power system network tries to generate a sinusoidal voltage and current waveform but due to certain problem it is not able to generate the sinusoidal nature waveform and distortions occurs. There are many causes of waveform distortion:- (i)DC Offset:- A DC offset is a presence of DC voltage or current in a AC power system. Due to DC offset the signal shifts from its actual reference position. (ii) Noise:- Noise is unwanted electrical signals. It is caused due to interference in communication network. The unwanted signals are superimposed in powers system current or voltages which are in phase or in neutral conductors. (iii) Notching:- Notching is voltage disturbances caused periodically due to transfer of current from one phase to another when power electronics equipment are commutated.
- 15. 9 (iii)Harmonics:- The harmonics are sinusoidal currents and voltages which operate at frequencies that are integer multiple of fundamental frequency. The 50 Hz and 60 Hz are fundamental frequency. The harmonics are caused due to non- linear loads. (iv) Inter harmonics:- Inter harmonics are harmonics which are not at the frequencies that are integer multiple of fundamental frequency (50 Hz or 60 Hz). That are caused due to induction furnaces, cyclo-converters, arc furnaces, static frequency converters. 2.4 Frequency variations In a power system many equipment and devices are made to operate at fundamental frequency. But there is variation in frequency due sudden disturbances in supply or demand. Frequency variations are mainly caused due to failure of generators and switching of loads. 2.5 Harmonics Harmonics are sinusoidal voltage & current which operate at integer multiple of fundamental frequency. In power Quality Corporation some index values has been developed to determine the service quality and distortions caused due to harmonics. 2.7 Power Quality The term power quality is not universally agreed upon but the concept has become a very important aspect of power delivery. Other terminology in use is quality of power supply and voltage quality. Interest in power quality has recently increased mainly due to the following factors: • Equipment has become more sensitive to voltage disturbances. • Equipment causes voltage disturbances. The number of loads fed via power electronic converters has recently increased. These present a challenge in ensuring power quality. • There is a growing need for standardization and performance criteria.
- 16. 10 • The power quality can be measured. Harmonic currents and voltage dips are no longer difficult to measure. The quality of electrical power supply is a set of parameters which describe the process of electric power delivery to the user under normal operating conditions, determine the continuity of supply (short and long supply interruptions) and characterize the supply voltage (magnitude, asymmetry, frequency, and waveform shape). Power quality phenomena can be divided into two types. • A characteristic of voltage or current (e.g., frequency or power factor) is never exactly equal to its nominal and desired value. The small deviations are called voltage variations or current variations. • Occasionally the voltage or current deviates significantly from its normal or ideal wave shape. These sudden deviations are called events. Power quality events are the phenomena which can lead to tripping of equipment, to interruption of the production or of plant operation, or endanger power system operation. This includes interruptions, under voltages, overvoltage, phase angle jumps and three phase unbalance. 2.7.1 Voltage Dip: A voltage dip is a short time (10 ms to 1 minute) event during which a reduction in r.m.s voltage magnitude occurs. It is often set only by two parameters, depth/magnitude and duration. The voltage dip magnitude is ranged from 10% to 90% of nominal voltage (which corresponds to 90% to 10% remaining voltage) and with a duration from half a cycle to 1 min. Voltage dip in a three phase system affects both phase to phase(line voltage) and phase to ground(phase voltage). 2.7.2 Voltage Dip Mitigation: Voltage dips in transmission and distribution systems can be mitigated in different ways. At present, a wide range of very flexible controllers, which capitalize on newly available power electronics components, are emerging for custom power applications . These devices are used to control and stabilize voltage in the Power System. These devices consist of static VAR generator or absorber and a suitable controlling power
- 17. 11 electronic device. These devices provide fast-acting reactive power compensation to power system networks. These devices are connected on transmission systems to improve voltage profile and system stability during both normal and contingency system conditions. The use of these devices helps to increase transmission capacity and stabilizes voltage in different buses over a wide range of loads. These devices also compensate the reactive power demand of the widely varying loads. If the load in the system is very high, the demand of reactive power is also very high, so there will be high amount of reactive power flow in the system and it causes the voltage drop in the line. Therefore, the voltage at the receiving end will decrease. Similarly, if the load in the system is very low, voltage at the receiving end of the line increases due to charging current (Ferranti effect). It means that if the generated reactive power is less than the consumed reactive power in the system, the voltage drops and vice versa. Therefore, the variation of voltage is because of imbalance in generation and consumption of reactive power in the system. As the power quality problems are originated from utility and customer side, the solutions should come from both and are named as utility based solutions and customer based solutions respectively. The best examples for those two types of solutions are FACTS devices (Flexible AC Transmission Systems) and Custom power devices. FACTS devices are those controlled by the utility, whereas the Custom power devices are operated, maintained and controlled by the customer itself and installed at the customer premises. Both the FACTS devices and Custom power devices are based on solid state power electronic components. As the new technologies emerged, the manufacturing cost and the reliability of those solid state devices are improved; hence the protection devices which incorporate such solid state devices can be purchased at a reasonable price with better performance than the other electrical or pneumatic devices available in the market. Some of these Custom Power Devices are: Series-connected compensator like DVR (Dynamic Voltage Restorer), shunt-connected compensator like DSTATCOM (Distribution Static compensator), Series and shunt compensator like UPQC (Unified Power Quality Conditioner) and SSTS (Solid State Transfer Switch). Among these, the UPQC is an effective custom power solution which consists of two
- 18. 12 back to back connected IGBT based voltage sourced bidirectional converters with a common DC bus. Unified Power Quality Conditioner (UPQC) is an integration of shunt active power filter and series active power filter. The series portion compensates for supply voltage harmonics and voltage unbalances, acts as a harmonic blocking filter and damps power system oscillations. The shunt portion compensates load current harmonics, reactive power and load current unbalances. In addition, it regulates the DC link capacitor voltage. The power supplied or absorbed by the shunt portion is the power required by the series compensator and the power required to cover losses. A Unified Power Quality Conditioner that operates in simultaneous voltage and current control modes. UPQC combines the operations of a Distribution Static Compensator (DSTATCOM) and Dynamic Voltage Restorer (DVR) together. In the voltage control mode it can make bus voltage at load terminal sinusoidal against any unbalance, harmonic or flicker in the source voltage or unbalance or harmonic in the load current. In the current control mode, it draws a balanced sinusoidal current from the utility bus irrespective of unbalance and harmonic in either source voltage or load current. General configuration of UPQC In present case UPQC with right shunt topology is considered. In right shunt topology, shunt active power filter will come right side of series active power filter that is near to load so that the currents flowing through the series transformers will be balanced sinusoidal. UPQC voltage references are calculated based on Fourier series, extraction of fundamental sequence components using half cycle running (moving) averaging, current references are calculated using the instantaneous symmetrical component theory. At the PCC of shunt active power filter, the voltage is load voltage which is balanced sinusoidal after compensating the source voltages by series active power filter. So we can use the instantaneous symmetrical component theory for calculating the source reference currents, which will be in phase with the load voltage, so that source will supply only average active power, remaining part of oscillating active power and total reactive power will be supplied by the UPQC. A mathematical model for UPQC with right shunt topology considering non-linearity in load is derived.
- 19. 13 2.9 Power Quality Monitoring Today for some larger customers and at select locations on the grid we are able to monitor harmonics, wave form, phase angles and other power quality indicators. The need continues to grow as large screen televisions and other consumer electronics devices are increasingly adding harmonics to the system. With the newest metering technology some power quality monitoring is built into the meter and more is on the way. While not every house needs to monitor power quality, a percentage of the meters deployed should probably have this advanced capability. 2.9.1 Asset Load Monitoring With Connectivity Verification and Geo-Location information it is possible to group the devices in a tree structure that correctly shows connection points in the grid. With the ability to read intervals from the meters it is then possible to build a picture of the load that each asset (e.g. transformers, conductors, etc.) are subjected to. This allows an operator to monitor heavily loaded assets and look for ways to off load some of the demand from that asset. It also allows a maintenance planner to prioritize what maintenance should be done to maximize the reliability of the grid, as part of a reliability centered maintenance program. 2.9.2 Phase Balancing One of the least talked about issues with losses in the distribution grid today is single phase load and the imbalance it can cause between the phases. These losses have seldom been measured in the grid and little study has been done of the amount of phase imbalance on the grid today. In early studies the chronic phase imbalance in several circuits that were monitored averaged over 10 percent. While correction is hard when the circuit is run as single phase laterals, in many cases there is enough load on the feeder portion of the circuit to allow rebalancing of the circuit to eliminate more than half of the chronic phase imbalance.
- 20. 14 2.9.3 Load Balancing Where there is an option to move a portion of the load from one circuit to another, the instrumentation is not always available to make good choices or to be able to forecast the load in a way that makes the movement pro-active instead of reactive. Automated feeder switches, and segmentation devices are becoming more and more common in the grid. The ability to use metering data to support the operation of these devices will only increase their value to the grid operator. Today with information only at the substation end of the circuit, it is tough to determine where on the circuit the load really is and where to position segmentation and when to activate a segmentation device when more than one is available. Operators today typically learn the right way by trial and error on the system. 2.9.4 Distributed Energy Resource (DER) Management In the future, more and more of the resources on the grid will be connected to the distribution network and will complicate the operation of the grid for the future. Failure to integrate these resources into the grid and understand their impact will only degrade the operation of the grid and its reliability. It is no longer an option to deal with distributed resources, the time for refusing to allow them has passed. The only choice is to either embrace them and manage their impact or ignore them and suffer the consequences. 2.9.5 Direct Monitoring and Control of DER Some DER units at customer sites could be monitored in “near-real-time” and possibly directly controlled by the utility or a third party (e.g. an aggregator) via the AMI system, in an equivalent manner to load control. 2.9.6 Shut-Down or Islanding Verification for DER Each time an outage occurs that affect the power grid with DER, the DER should either shut down or island itself from the rest of the grid, only feeding the “microgrid” that is directly attached to. In many cases the shut-down or islanding equipment in smaller installations is poorly installed or poorly maintained. This leads to leakage of the power into the rest of the grid and potential problems for the field crews.
- 21. 15 Each time an outage occurs, meters that are designed to monitor net power can tell if the islanding occurred correctly, if they are installed at the right point in the system. This reporting can minimize crew safety and allow the utility to let the customer know that maintenance is required on their DER system. In most cases when the islanding fails, other problems also exist that reduce the efficiency of the DER system, costing the customer the power that they expected to get from the 2.10 Power Quality Controllers based on VSC Power quality control will be one of the issues addressed in smart grids. Power electronics is expected to be the main enabling technology in this area. The most widely used active power quality controllers based on power electronics are FACTS devices FACTS (Flexible AC Transmission System) are a power electronic based system and other static equipment that provide control of one or more AC transmission system parameters to enhance controllability and increase power transfer capability. The FACTS devices like Unified Power Flow Controller , Unified Power Quality Conditioner, Distribution Synchronous Compensator, Dynamic Voltage Restorer are expected to gain widespread use in smart distribution networks for power quality control. Power quality controllers which are based on voltage source converter are explained in the following topics. These controllers are DSTATCOM, DVR and UPFC. The emphasis in this paper is on the capability of these devices in mitigating voltage dips in a distribution system. 2.11 Voltage Source Converter: A voltage-source converter is a power electronic device, which can generate a sinusoidal voltage with any required magnitude, frequency and phase angle. The converter is normally based on an energy storage device, which will supply the converter with a DC voltage. The solid-state electronics in the converter is then switched to get the desired output voltage. The controller generates the required switching pattern. The VSC is a basic component of devices used for mitigation of voltage dips and harmonic distortion. In VSC based HVDC transmission schemes
- 22. 16 described herein, the switching of IGBT valves follows a pulse width modulation pattern. This switching control allows simultaneous adjustment of amplitude and phase angle of the converter ac output voltage with constant dc voltage even with a two level converter. With these two independent control variables, separate active and reactive power control loops can be used for regulation. 2.12 Distribution Static Compensator When the STATCOM is applied in distribution system is called DSTACOM (Distribution-STACOM) and its configuration is the same, or with small modifications, oriented to a possible future amplification of its possibilities in the distribution network at low and medium voltage, implementing the function so that we can describe as flicker damping, harmonic filtering and short interruption compensation. Distribution STATCOM (DSTATCOM) exhibits high speed control of reactive power to provide voltage stabilization, flicker suppression, and other types of system control. The dstatcom utilizes a design consisting of a GTO- or IGBT-based voltage sourced converter connected to the power system via a multi-stage converter transformer. The dstatcom protects the utility transmission or distribution system from voltage sags and/or flicker caused by rapidly varying reactive current demand. In utility applications, a dstatcom provides leading or lagging reactive power to achieve system stability during transient conditions. The dstatcom can also be applied to industrial facilities to compensate for voltage sag and flicker caused by non-linear dynamic loads, enabling such problem loads to co-exist on the same feeder as more sensitive loads. The dstatcom instantaneously exchanges reactive power with the distribution system without the use of bulky capacitors or reactors. In most applications, a dstatcom can use its significant short-term transient overload capabilities to reduce the size of the compensation system needed to handle transient events. The short-term overload capability is up to 325% for periods of 1 to 3 seconds, which allows applications such as wind farms and utility voltage stabilization to optimize the system’s cost and performance. The dstatcom controls traditional mechanically switched capacitors to provide optimal compensation on a both a transient and steady state basis.
- 23. 17 Figure 2.1 Basic Building Blocks of The DSTATCOM 2.13 Dynamic Voltage Restorer: Dynamic Voltage Restorer (DVR) is a voltage controller having the same building blocks as a DSTATCOM but its coupling transformer is connected in series with the ac system .The resulting voltage at the load bus bar equals the sum of the grid voltage and the injected voltage from the DVR. The converter generates the reactive power needed while the active power is taken from the energy storage. The energy storage can be different depending on the needs of compensation. If the injected voltage V DVR is kept in quadrature with IL, no active power injection by the DVR is required to correct the voltage. It requires only the injection of reactive power which is generated by the DVR itself. DVR can be kept in quadrature with IL only up to a certain value of voltage dip and beyond which the quadrature relationship cannot be maintained to correct the voltage dip. For such a case, injection of active power into the system is essential which must be provided by the energy storage system of the DVR.
- 24. 18 Figure 2.2 Standard Configuration Of A DVR 2.14 Unified Power Flow Controller The Unified Power Flow Controller (UPFC) is used to control the power flow in a transmission system by controlling the impedance, voltage magnitude and phase angle. The basic structure of the UPFC consists of two voltage source converters (VSCs); where one converter is connected in parallel to the transmission line through a shunt transformer while the other is in series with the transmission line through a series transformer. Both VSCs are connected to each other by a common dc link including a storage capacitor. The shunt inverter is used for voltage regulation at the point of connection injecting reactive power into the line and to balance the real power flow exchanged between the series inverter and the transmission line. The series inverter can be used to control the real and reactive line power flow inserting voltage with controllable magnitude and phase in series with the transmission line. Thereby, the UPFC can fulfill functions of reactive shunt compensation, active and reactive series compensation and phase shifting.
- 25. 19 Figure 2.3 Basic Configuration Of UPFC CHAPTER3 PROPOSED SCHEME UPQC DESIGN FOR POWER QUALITY IMPROVEMENT In this proposed scheme we have introduced UPQU as compensator with Fuzzy logic controller as control element which provides gate pulses to SCRs used in the active filters in the UPQC. The figure below describes the whole system for voltage compensation and hence to improve the power quality.
- 26. 20 The main subsystems of the above given scheme are described in detail below 3.1 Measurement Block: This block consists of some Voltmeters and Ammeters connected to the system through PTs and CTs. These meters collect the line parameters (volt and current), compare with the predefined values and create the error signals. These error signals are fed to the controller block for further processing. 3.2 Fuzzy Logic Controller: The FACTS device used in the system requires proper gate pulse for operation. PWM generator generates pulse for SCRs used in UPQC and it requires a reference wave for generating the reference signal. This reference signal is obtained from Fuzzy Logic Controller. Actually Fuzzy logic controller is a soft computing method used for generating desired output signal using predefined rules. Figure 3.1 Whole System Block Diagram
- 27. 21 3.2.1 Fuzzy logic background Fuzzy logic is a form of many-valued logic in which the truth values of variables may be any real number between 0 and 1, considered to be "fuzzy". By contrast, in Boolean logic, the truth values of variables may only be 0 or 1, often called "crisp" values. Fuzzy logic has been extended to handle the concept of partial truth, where the truth value may range between completely true and completely false. Furthermore, when linguistic variables are used, these degrees may be managed by specific (membership) functions. The term fuzzy logic was introduced with the 1965 proposal of fuzzy set theory by Lotfi Zadeh. Fuzzy logic has been applied to many fields, from control theory to artificial intelligence. Fuzzy logic had however been studied since the 1920s, as infinite-valued logic—notably by Łukasiewicz and Tarski. Humans and animals often operate using fuzzy evaluations in many everyday situations. In the case where someone is tossing an object into a container from a distance, the person does not compute exact values for the object weight, density, distance, direction, container height and width, and air resistance to determine the force and angle to toss the object. Instead the person instinctively applies quick “fuzzy” estimates, based upon previous experience, to determine what output values of force, direction and vertical angle to use to make the toss. 3.2.2 Applying truth values: A basic application might characterize various sub-ranges of a continuous variable. For instance, a temperature measurement for anti-lock brakes might have several separate membership functions defining particular temperature ranges needed to control the brakes properly. Each function maps the same temperature value to a truth value in the 0 to 1 range. These truth values can then be used to determine how the brakes should be controlled.
- 28. Figure In this image, the meanings of the expressions represented by functions mapping a temperature scale. A point on that scale has three "truth values" — one for each of the three functions. T represents a particular temperature that the three arrows (truth values) gauge. Since the red arrow points to zero, this temperature may be interpreted as "not hot". The orange arrow (pointing at 0.2) may describe it as "sligh 0.8) "fairly cold". 3.2.3 Linguistic variables: While variables in mathematics usually take numerical values, in fuzzy logic applications, the non-numeric are often used to facilitate the expression of facts. A linguistic variable is variables is that they can be modified via linguistic hedges applied to primary terms. These linguistic hedges can be associated with certain functions. Fuzzification operations can map mathematical input values into fuzzy membership functions. And the opposite de-fuzzifying operations can be used to map a fuzzy output functions into a “crisp” output value that can be then used for decision or control purposes. Fuzzy logic is a logic having many values. Unlike the binary logic system, here the reasoning is not crisp ,rather it is approximate and having a vague The variables in fuzzy logic system may have any value in between 0 and 1 and hence 22 Figure 3.2 Fuzzy logic temperature control In this image, the meanings of the expressions cold, represented by functions mapping a temperature scale. A point on that scale has three one for each of the three functions. The vertical line in the image represents a particular temperature that the three arrows (truth values) gauge. Since the red arrow points to zero, this temperature may be interpreted as "not hot". The orange arrow (pointing at 0.2) may describe it as "slightly warm" and the blue arrow (pointing at While variables in mathematics usually take numerical values, in fuzzy logic numeric are often used to facilitate the expression of facts. A linguistic variable is young or its antonym old. However, the value of linguistic variables is that they can be modified via linguistic hedges applied to primary terms. can be associated with certain functions. Fuzzification operations can map mathematical input values into fuzzy membership functions. And fuzzifying operations can be used to map a fuzzy output functions into a “crisp” output value that can be then used for decision or control Fuzzy logic is a logic having many values. Unlike the binary logic system, here the reasoning is not crisp ,rather it is approximate and having a vague The variables in fuzzy logic system may have any value in between 0 and 1 and hence cold, warm, and hot are represented by functions mapping a temperature scale. A point on that scale has three he vertical line in the image represents a particular temperature that the three arrows (truth values) gauge. Since the red arrow points to zero, this temperature may be interpreted as "not hot". The orange tly warm" and the blue arrow (pointing at While variables in mathematics usually take numerical values, in fuzzy logic numeric are often used to facilitate the expression of rules and old. However, the value of linguistic variables is that they can be modified via linguistic hedges applied to primary terms. can be associated with certain functions. Fuzzification operations can map mathematical input values into fuzzy membership functions. And fuzzifying operations can be used to map a fuzzy output membership functions into a “crisp” output value that can be then used for decision or control Fuzzy logic is a logic having many values. Unlike the binary logic system, here the reasoning is not crisp ,rather it is approximate and having a vague boundary. The variables in fuzzy logic system may have any value in between 0 and 1 and hence
- 29. 23 this type of logic system is able to address the values of the variables those lie between completely truth and completely false. The variables are called linguistic variables and each linguistic variable is described by a membership function which has a certain degree of membership at a particular instance. System based on fuzzy logic carries out the process of decision making by incorporation of human knowledge into the system. Fuzzy inference system is the major unit of a fuzzy logic system. The decision making is an important part of the entire system. The fuzzy inference system formulates suitable rules and based on these rules the decisions are made. This whole process of decision making is mainly the combination of concepts of fuzzy set thoery, fuzzy IF-THEN rules and fuzzy reasoning. The fuzzy inference system makes use of the IF-THEN statements and with the help of connectors present (such as OR and AND), necessary decision rules are constructed. The basic Fuzzy inference system may take fuzzy inputs or crisp inputs depending upon the process and its outputs, in most of the cases, are fuzzy sets. Fuzzy sets in X Fuzzy sets in Y. Figure. 3.3 A pure fuzzy system
- 30. 24 The fuzzy inference system can be called as a pure fuzzy system due to the fact that it takes fuzzy sets as input and produces output that are fuzzy sets. The fuzzy rule base is the partresponsible for storing all the rules of the system and hence it can also be called as the knowledge base of the fuzzy system. Fuzzy inference system is responsible for necessary decision making for producing a required output. In most of the practical applications where the system is used as a controller, it is desired to have crisp values of the output rather than fuzzy set values. Therefore a method of defuzzification is required in such cases which converts the fuzzy values into corresponding crisp values. In general there are three main types of fuzzy infernece systems such as :- Mamdani model, Sugeno model and Tsukamoto model. Out of these three, Mamdani model is the most popular. 3.3 PWM Pulse generator: Pulse-width modulation (PWM), or pulse-duration modulation (PDM), is a modulation technique used to encode a message into a pulsing signal. Many digital circuits can generate PWM signals (e.g., many microcontrollers have PWM outputs). They normally use a counter that increments periodically (it is connected directly or indirectly to the clock of the circuit) and is reset at the end of every period of the PWM. When the counter value is more than the reference value, the PWM output changes state from high to low (or low to high). This technique is referred to as time proportioning, particularly as time-proportioning control– which proportion of a fixed cycle time is spent in the high state. 3.4 UPQC(Unified Power Quality Conditionor): Basically UPQC (Unified Power Quality conditioner) is a equipment which is used for compensate for voltage distortion and voltage unbalance in a power system so that the voltage at load side is completely balance and sinusoidal & perfectly regulated and also it is used to compensate for load current harmonics so that the current at the source side is perfectly sinusoidal and free from distortions and harmonics. UPQC is a
- 31. 25 combination of a Shunt Active power filter and Series Active power filter. Here Shunt Active power filter (APF) is used to compensate for load current harmonics and make the source current completely sinusoidal and free from harmonics and distortions. Shunt APF is connected parallel to transmission line. Here Series APF is used to mitigate for voltage distortions and unbalance which is present in supply side and make the voltage at load side perfectly balanced, regulated and sinusoidal. Series APF is connected in series with transmission line. UPQC consists of two voltage source inverters connected back to back through a DC link capacitor in a single phase, three phase-three wire, three phase-four wire configuration. The inverter in shunt APF is controlled as a variable current source inverter and in series APF is controlled as a variable voltage source inverter. Earlier passive filters where also used for compensation of harmonics and voltage distortion but due to their many disadvantages they are not used nowadays. Figure 3.4 Simple UPQC Scheme
- 32. 26 3.4.1 Series APF: In a transmission line series APF is generally connected in series. It is connected to the transmission line with the transformer. Series APF is a voltage source inverter connected in series with transmission line. It is used to compensate or mitigate the problems which come due to voltage distortions and voltage unbalances. The series APF injects a compensating voltage so that load voltage will be perfectly balanced and regulated. Controlling of series inverter is done by PWM (pulse width modulation) techniques. Here we used Hysteresis band PWM techniques as it implementation is easy. Also its response is fast. Its details are explained in subsequent sections. 3.4.2 Shunt APF: In a transmission line shunt APF is generally connected in parallel. Shunt APF is used to compensate for distortions & harmonics which are produced due to current. Due to non- linear load there is harmonics in load current, so to keep source current completely sinusoidal and distortion free we uses Shunt APF. Shunt APF injects compensating current so that the source current is completely sinusoidal and free from distortions. Controlling of Shunt APF is done by hysteresis band PWM techniques. In hysteresis band PWM techniques output current follows the reference and current and is within the fixed hysteresis band. 3.4.3 DC link capacitor: The two voltage source inverters are connected back to back through a DC capacitor. DC capacitor is provides a DC voltage for working of both the inverter. The DC capacitor also provides a real power difference between source and load during the transient period and also acts as a energy storage elements. During steady state real power supplied by source should be equal to the sum real power demand of load & a small amount of power which compensates for active filter. DC capacitor voltage should be equal to reference value but due to disturbance in real power balance between source and load due to change in load conditions the DC capacitor value is changed from reference value.
- 33. 27 3.4.4 Design Of Upqc Controller: The control algorithm for series APF is based on unit vector template generation scheme where as the control strategy for shunt APF is discussed in this section. Based on the load on the 3P4W system, the current drawn from the utility can be unbalanced. In this paper, the concept of single phase P-Q theory. According to this theory, a single phase system can be defined as a pseudo two-phase system by giving π/2 lead or π /2 lag that is each phase voltage and current of the original three phase systems. These resultant two phase systems can be represented in α-β coordinates, and thus P-Q theory applied for balanced three phase system can also be used for each phase of unbalanced system independently. The actual load voltages and load currents are considered as α-axis quantities, whereas the π/2 lead load or π/2 lag voltages and π/2 lead or π/2 lag load currents are considered as β-axis quantities. In this paper, π/2 lead is considered to achieve a two-phase system for each phase. The major disadvantage of p–q theory is that it gives poor results under distorted and/or unbalanced input/utility voltages. In order to eliminate these limitations, the reference load voltage signals extracted for series APF are used instead of actual load voltage unbalanced input/utility voltages. In order to eliminate these limitations, the reference load voltage signals extracted for series APF are used instead of actual load voltage The electric power industry in the 21st century will see dramatic changes in both its control and communication infrastructure. These changes are the result of mainly three factors: 1) the push toward a deregulated industry, 2) the development of more efficient and/or less polluting energy resources that are cost competi-tive with traditional power generation sources, and 3) the continued electrification and integration of infor- mation technology into most facets of our everyday lives has resulted in a need for a better reliability and improved power quality than the existing power grid can supply. In this context and with the progress of electronics component technology some efficient solu-tions as the unified power quality conditioner (UPQC) are used. It consists of combined series and shunt active filters for simultaneous compensation of voltage and current.
- 34. 28 The UPQC can compensate not only harmonic currents and unbalances of a non-linear load, but also voltage harmonics and unbalances of the power sup-ply, which improves the power quality offered for other harmonic sensitive loads. There are also different custom power devices such as dynamic voltage restorer (DVR), which improves the quality of power supply, distribution static compensator (DSTATCOM), which compensates current unbalance and harmonics of non-linear loads, and combined SVC with DSTATCOM, which generates reactive power and compensates load current simultaneously. The main objective of this work is the improvement of the performances of UPQC with respect to the variation of the frequency. In order to achieve this goal, we present in this paper, a new method based on GA which allows the determination of the optimized parameters and consequently an optimal operating point of the system, a wide pass band with a unity gain of both the ratio of the compensating voltage to the voltage generated by the series PWM converter and the ratio of the compensating current to the current generated by the shunt PWM converter, and a no load normal total impedance, in other words without resonance. The results given by the GA method is com-pared with the results given by the classical method, which uses iterative calculations under certain conditions to find the optimal parameters that satisfy all constraints. The GA method seems to be more efficient and gives better results. Therefore, the following presented results are interesting and confirm the efficiency of the proposed new method. The equivalent circuit of UPQC that has been considered in this study is presented in Figure 1. In this figure the primary side is the network side and the secondary side is the PWM converter side.
- 35. 29 3.4.5 Configuration of proposed UPQC: The UPQC is utilized for simultaneous compensation of the load current and the voltage disturbance at the source side. Normally the UPQC has two voltage-source inverters of three-phase four-wire or three-phase three-wire configuration. One inverter, called the series inverter is connected through transformers between the source and the common connection point. The other inverter, called the shunt inverter is connected in parallel through the transformers. The series inverter operates as a voltage source, while the shunt inverter operates as a currentsource. The UPQC has compensation capabilities for the harmonic current, the reactive power compensation, the voltage disturbances, and the power flow control. However, it has nocompensation capability for voltage interruption because no energy is stored. This paper proposes a new configuration for the UPQC that has the super-capacitors for energy storage connected to the dc link through the DC/DC converter. The proposed UPQC can compensate the voltage interruption in thefundamental component of the A- B transformed current, iα′ = sin(ω1t) and iβ′ = cos(ω1t) . The calculated active power S p′ and reactive power S q′ includes the positive sequence fundamental component of the source voltage vs .
- 36. 30 Figure 3.5 Upqc System Inter Connected With Energy Storage 3.4.5 Circuit Description Figure 3.6 Euivalent Circuit Diagram For Upqc Taking the load voltage, VL as a reference phasor and suppose the lagging power factor of the load is CosφL we can write
- 37. 31 Where factor k represents the fluctuation of source voltage, defined as, The UPQC is assumed to be lossless and therefore, the active power demanded by the load is equal to the active power input at PCC. The UPQC provides a nearly unity power factor source current, therefore, for a given load condition the input active power at PCC can be expressed by the following equations, The above figure shows the whole system which we developed using MATLAB Simulink as tool.
- 38. 32 Table 4.1 Whole system Parameter values Serial No. Parameter Measurement Value 1 System Voltage 800V 2 Coupling Transformer 100:1 3 DC link Capacitor 1000 micro F 4 Volt measurement Components As Required 5 Current measurement components As Required 6 System Frequency 50Hz CHAPTER4 SYSTEM MODEL & RESULTS 4.1 Simulink based system model: with UPQC We have designed a simple model showing three phase transmission line with line voltage measuring instruments and wave form viewer. A fault block is introduced in order to examine the effect of fault on the system voltage. Here is the Simulink model showing all the required parts of the power system. At end of the transmission line ac voltage is converted to dc form only for better observation.
- 39. 33 Figure 4.1 Simulink based syetm model: with upqc
- 40. 34 4.2 Results: Comparison of Three phase voltage waveforms-with& without UPQC These are the result wave forms from an uncompensated line and compensated line. Voltage sag is introduced in line by the fault box, effect of which is shown in fig 4.2 and in fig 4.3 the compensated voltage waveform is shown which is fully compensated(i.e.,100% compensated) in three phase waveform presentation. Figure 4.2 Result without UPQC(Voltage sag) Figure 4.3 Result with UPQC(No voltage sag) 4.3 Results: Comparison of dc voltage waveforms-with& without UPQC Fig 4.4 and in Fig 4.5 the compensated and uncompensated voltage waveform in reference to DC analysis respectively. Voltage Volt age Time Time
- 41. 35 Figure 4.4 DC voltage without UPQC Figure 4.5 DC voltage with UPQC 4.4 Results: Comparison of Voltage waveforms under transients With significant change in fault box it produces transient, and this transient is introduced in the system line. Then in fig 4.6 and 4.7 the three phase voltage waveforms under transients compensated and uncompensated is compared respectively. Time(ms) DC volt DC volt Time(ms)
- 42. 36 Figure 4.6 Transients without UPQC controller Figure 4.7 Transients with UPQC controller
- 43. 37 Individual analyzing and comparison of different results under different conditions like voltage sags and transients, reveals that system is fully compensated (or 100% compensated). Hence we can say that the system as a whole performed satisfactorily (as expected). CHAPTER-5 CONCLUSION & FUTURE SCOPE In this chapter the general conclusions of this thesis and suggestions for future work have been listed. The following conclusions have been drawn from this thesis. 5.1 Conclusion Unified quality conditioner was studied and investigated in this thesis for power quality improvement. UPQC is a type of advance hybrid filter which uses series APF for removal of voltage related problems like voltage dip/rise, fluctutaion, imbalance and shunt APF for removal of harmonics in current harmonics. What type of problems are there in power quality was studied and discussed. UPQC system is developed and discussed in detail. The simulink models of Shunt APF, Series APF, UPQC are developed. UPQC model was developed by joining Shunt APF and series APF back to back using DC capacitor. The controlling techniques used here are Fuzzy logic controller. The simulation is done and voltage sag, transients are eliminated.
- 44. 38 5.2 Future Scope This model can be enhanced and enriched to terminate the power quality problems in a power system. The various ways for doing that – The prototype of this UPQC model can be established in laboratory. Other soft computing techniques like Neural Network(NN), Genetic Algorithm(GA), etc can also be used. We can connect wind turbines, solar energy system that is renewable source of energy to UPQC to get improved power in consumer ends during serious conditions
- 45. 39 REFERENCES [1] N. G. Hingorani and L. Gyugyi, “Understanding FACTS Concepts and Technology of Flexible ACTransmission Systems”. New York: IEEE Press, 2000. [2] I.J. Nagrath and M.Gopal “ Control System Engineering” Fifth Edition, New Age International Publisher, New Delhi [3] Roger C. Ducan, Mark F. McGranghan, Surya Santoso and H. Wayne Beaty “Electrical Power Quality” Third Edition, Mc Graw Hill Education [4] Fuzzy Logic Tool box For Use with MATLAB®, User’s Guide Version 2, The Math Works [5] Sriram Rengarajan and Shumuganathan Loganathan “Power Theft Prevention and Power Quality Improvement using Fuzzy Logic” IJEEE-ISSN (PRINT): 2231 – 5284, Vol-1, Iss-3, 2012 [6] Dipen A. Mistry, Bhupelly Dheeraj, Ravit Gautam, Manmohan Singh Meena, Suresh Mikkili “Power Quality Improvement Using PI and Fuzzy Logic Controllers Based Shunt Active Filter” International Journal of Electrical, Computer, Energetic, Electronic and Communication Engineering Vol:8, No:4, 2014 [7] Mr.R.V.D.Rama Rao and Dr.Subhransu Sekhar Dash, “Design of UPQC with Minimization of DC Link voltage for the Improvement of Power Quality by Fuzzy Logic Controller”, ACEEE Int. J. on Electrical and Power Engineering, Vol. 02, No. 01, Feb 2011. [8] Puranik Sahu, Ghanshyam Vishwakarma, “Power Quality Improvement using FC- TCR (SVC) with Fuzzy Logic Controller”, International Journal of Engineering Sciences & Research Technology. [9] N.Karpagam , D.Devaraj, “Fuzzy Logic Control of Static Var Compensator for Power System Damping”, World Academy of Science, Engineering and Technology Vol:3 2009-04-22.
- 46. 40 [10] H. Akagi, “Trends in active line conditioner”, IEEE Transactions On Power Electronics, vol.9, no.3, 1994. [11] H. Fujita and H. Akagi, “ The Unified Power Quality Conditioner : The integration of series and shunt active filters” IEEE Transactions on Power Electronics, vol.13, no.2 March 1998. [12] N. Hingorani, “Introducing Custom Power,” IEEE Spectrum, Vol.32, Issue: 6, June 1995,pp 41-48. [13] Rajiv Ku. Sinku, “Study Of Unified Power Quality Conditioner For Power Quality Improvement”, NIT, Rourkela, EE, May 2015

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