Different Power Factor Correction Engineering Essay

distinguishable world king figure Correction Engineering EssayDifferent occasion- agent discipline methods argon reviewed, as swell up as the back ground to the forefinger- federal agent in. Problem is arising in modern font electrical distribution transcriptions due to the connexion of cursorily increasing numbers of non-linear electronic loads. The merchantmanonical principles of harmonised generation and limitation in depict outlines atomic number 18 first discussed. The main part presents a critical review of comm single use magnate- calculate discipline techniques that feel been identified in a literature review, and gameylights the advantages and disadvantages of these techniques. After the psycho summary of methods and their working principles, the development of the roughly promising systems such(prenominal) as the boost- role perfluorocarbon convertors is considered. Fin wholey, a project plan is proposed for the next physique of the discourse wo rk. This get out involve investigating the operation, dynamic check and act of the most promising systems by conducting a abstractive study and setting up and running a number of simulation flummoxs utilise the MATLAB/SIMULINK package tools.Key-words Power operator rectification, appealing easing, perfluorocarbon convertorsContentsList of Abbreviations and Principle SymbolsAbbreviationsAC Alternating catameniaAPF Active Power FilterCCM Continuous Conduction ModeDC Direct CurrentDCM noncontinuous Conduction ModeDF torturing FactorFFT Fast-Fourier analysisIGBT Insulated Gate Bipolar TransistorPF Power Factorperfluorocarbon Power Factor CorrectionPWM Pulse Width ModulationRMS Root Mean self-coloredTHD Total Harmonic DistortionTDD Total Demand DistortionPrinciple SymbolsPower FactorDistortion FactorDisplacement Factorh Harmonic contentsRMS foster of the line- underway fundamental comp integrityntRMS lever of the line- topical appealing componentsTotal RMS grade of the line- veritable1. IntroductionIt is now clearly visible from mightiness systems journals and general literatures that military unit- cipher chastisement is now an important investigate topic in the fountain systems area. As non-linear personnel electronic systems are increasingly being connected to power systems in greater quantities as well as capacities for such applications as power quality control, adjustable speed drives, uninterruptible power supplies, renewable energy-source interfacing, and so on 1 2. The power quality regulators of those systems are highly concerned now, because few of their retracebacks, such as kindlys generation and condensed power factor underside spoil their advantages 3. Power electronic systems are effective because their high force and rapidly adjustable product. However, when processing and controlling the gossip electric energy suitable for users 4, power electronic systems oftentimes operate at a number one power-factor, and t hat may cause serious problems to power system operators by reducing distribution component RMS flowing capacity and to separate users on the same ne some(prenominal)rk by distorting the curving yield electric potential seen by early(a) user connected at the same plosive of common coupling as a heavy electronic or power electronic load.. Of all power line disturbances, charitables are probably the most serious one for power users because they exist to a lower place steady state conditions.This literature review considers honourable-hearted generation prediction of power electronic systems and examines the persuasiveness of conformable extenuation methods. The boost- character reference power factor subject field convertors leave be meditaten as the event power factor correction method for future research. The existing publications arising from research in this area and their conclusions have set a good foundation for this report. Results in this report allow be based on a theoretical study and simulation studies using software MATLAB/SIMULINK power-factor correction system models which be developed.2. reachThis character issues discussion on the fundamental principles of power-factor correction, including definitions of power-factor terms and a consideration of the common standards which affect how benevolentals controlled in power system. Also, the harmonic generation prediction of ideal power electronic systems is discussed at the end of this section2.1 Important definitions and objective of power-factor correctionThe power factor (PF) is the ratio of the real power to the apparent power 5 and gives a measure of AC publish utilization on how efficient that the energy is supplied and stand be converted into effective work output. The definition of power factor is as shown below(2.1)In the definition, the value of the power factor is unceasingly between 0 and 1, and stomach be either inductive or capacitive. That means average pow er is always lower than apparent power. The contend is harmonic components and human body-displacement rake,.Hence, the power factor equivalent washbowl be described as below(2.2)is termed the ( period) distortion factor (DF) and cost the harmonic components in the current and relative to wave shape 6. DF is defined as the ratio of the fundamental current component to the RMS current value 4.is termed the displacement factor and defined as the current and voltage wave form phase angle 6. Displacement factor has uniformity value for in-phase current and voltage. The summation of displacement angle will cause hulkingr re expeditious current in the power system 4.Hence, the objective of power-factor correction is to decrease the current distortion or harmonic content and increase the displacement factor or bring the current in phase with the voltage. The closer power factor is to the unity value, the higher efficiency and lower energy loss. And the power system will operate at a lower depict voltage.A nonher commonly used index for measuring the harmonic content of a waveform apply for current distortion direct is total harmonic distortion, THD. THD is the distortion current as a portion of the fundamental current. The equation of THD is given byor (2.3)In AC supply utilizations, power factor,, preserve be expressed in terms of THD and the displacement factor(2.4)With these equations, it is easy to see that high THD leads to low power factor and even damaging of the power network. THD and power factor will be used together in the following work as important index in measuring performance of the harmonic mitigation techniques.2.2 Effects and limitation of harmonic distortion on power systemIn any power conversion process, to get high efficiency and low power loss are important for two reasons the cost of the wasted energy and the difficulty in removing the heat generated due to degenerate energy 4. The performance of power output efficient is defi ned by several factors. The power factor and harmonic distortion are the most important ones.References 8 9 show the main issues of harmonics within the power system include the possibility of them exciting series and line of latitude rapports which cause a further increase of harmonic directs, low efficiency caused in generation, transmission, and utilization of electric energy, increasing thermal losses in the electrical components and shortening their useful life and causing malfunction of motors and other components in the power system.Those effects can be divided into three general categories Thermal stress, Insulation stress and Load disruption 10. Those represent effects on increasing equipment losses and thermal losses, increased value of current unraveln from the power system and insulation stress and failure to action and malfunction of some electrical devices and systems.The IEEE commonplace 519-1992 recommended harmonic current limits with an additional factor, TDD. This is very same as THD except the distortion factor is expressed by load current instead of fundamental current magnitude 11. Hence, the equation of TDD is given by(2.5)Therefore, IEEE Standard 519-1992 limitation for harmonic current in power system expressed with TDD is shown belowMaximum harmonic current distortion in percent ofIndividual harmonic order (Odd harmonics)TDD4.02.01.50.60.35.0207.03.52.51.00.58.05010.04.54.01.50.712.0 one hundred12.05.55.02.01.015.0100015.07.06.02.51.420.0Even harmonics are limited to 25% of the odd harmonics limits above.Table 2.1 IEEE 519-1992 Standard for harmonic current limits 12.Also, in that location are limitations for power system harmonic voltage and power factor regulation, identical IEC 61000-3-2 standard. The methods for power factor correction should not cause disturbances for other aspects of performance.2.3 Harmonics generation in power electronic systemsPower electronic systems may naturally operate at low power-factor due to la rge harmonic generation and phase shifting in controlled devices like controlled rectifiers. Understanding characteristics of the harmonic current is essential for harmonic mitigation research. base on the form on the two sides, converters can be divided into four categories 4 including1. AC to DC (rectifier)2. DC to AC (inverter)3. DC to DC4. AC to ACPower electronic systems always draw high quality of low absolute relative frequency harmonic current from the utility and hence cause problems for other users. Take an ideal single-phase rectifying tube couple rectifier as example, the total harmonic distortion can be up to 48.43% 4 and the 3rd harmonic current can be as large as one third of the fundamental current. If a non-linear load is considered, the displacement factor will fall down from unity value and cause a decrease of power factor. This is surely over the harmonic standards limitation and inescapably to be corrected.Theoretically, Rectifiers and choppers output DC a nd draw a fundamental AC source current and large low frequency harmonic content. On the other hand, inverters output low frequency AC and supply fundamental current and harmonic content usually at higher frequency. Harmonic contents can be reduced by harmonic mitigation techniques and hence increase power factor.Take Fourier analysis result diagram of single-phase diode bridge rectifier and PWM control Buck converter as example.(a) (b) frame of reference 2.1 Fourier analysis diagram for input signal current of (a) single-phase diode bridge rectifier and (b) PWM control Buck converter.2.4 Software tools for harmonic mitigation evaluationTo sifting harmonic current in the power system, the frequency of harmonic contents is essential. However, in practice, the harmonic frequency is not absolutely equal to the theoretical value and that makes analysis of harmonic frequencies very difficult. The reason is stray inductance and capacitance in the system and reverse recovery time and forw ard voltage drop of non-ideal devices 1. To analyze harmonic contents, distinguish software can be helpful. In this project, the software chosen to help analyzing harmonic current drawn by power electronic systems is MATLAB/SIMULINK.Taking the three-phase diode bridge rectifier as an example, a simulation model can be established as shown below. In the model, a three-phase 50Hz AC power supply is used for a resistive load and most devices are not ideal. The model is followed by the diagram of input current waveform and frequency spectrum of AC input current. set of each order harmonic content and total THD are given by Fast-Fourier (FFT) analysis in powergui analysis tools. With the help of Fourier analysis, the performance of harmonic mitigation techniques can be evaluated and compared quickly.Figure 2.2 Simulation model for three-phase diode bridge rectifier.Figure 2.3 Waveform of rectifier input current (phase A).Figure 2.4 Frequency spectra of AC input current of three-phase rectifier.3. Power Factor Correction TechniquesAfter tens of years developing and improving, respective(a) types of power factor correction techniques or harmonic mitigation techniques can be chosen to solve power factor problem. Those techniques can be divided into basketball team categories 11 13 as shown below1. excreteive voice dripsPassive filters can purify power factor with low cost and reduce high frequency harmonics effectively. However, they are always in large size and cannot vary flexibly with system changes 4 14. If tuning reactors are not used, parallel resonance may occur in operation 15.2. Active filtersActive filters improve power factor and provide stable output even under varying supply condition, and reduce harmonics in the output current effectively and efficiently 4 16. These, however, always requires much higher costs and the harmonic currents they injected may flow into other system components 13 14.3. Hybrid systemsHybrid dynamic filters combine brisk and unresisting filters together in various forms 17. Hence they can reduce initial and running costs and improve performance of the filter 11 13. little filter inductor, smaller dimension, light weight and better filter performance hybrid system take advantages of both nonoperational and active filters 18. However, the complexity of operation is the main drawback of hybrid systems.4. Phase multiplication change magnitude the pulse number of power converters can raise the lowest harmonic order generated by the converter 2. Typically, 6-pulse converter has the lowest harmonic order of 5 1. When rising pulse number to 12, the lowest harmonic order can increase to 11. As value of harmonic current are ideally comparative to fundamental current value 4, the amount distortion of the power system can de reduce to a low level. On the other hand, the effectiveness of this technique is based on balanced load 13 which rarely happens in practice.5. PWMPWM converters have much better perf ormance compared to traditional converters like diode rectifiers and square-wave control inverters 4. As a control strategy improvement, PWM harmonic mitigation technique can even used with some devices for traditional converters and hence get broad application prospect 11. However, the topology complexity and difficult on be aftering controllers 19 makes the use of PWM is limited.The objective of these techniques is to make the input current nearly a pure sinusoidal waveform and hence to improve the power factor in electrical supply system. All these five techniques are discussed separately in the following work.3.1 Passive filtersPassive filters have widely been used to assume harmonics generated by the power electronic systems, primarily due to their simplicity, low cost and high efficiency 20. Passive filters are always consists inductors, electrical capacitys and damping resistors 21. The objective of the passive filter is to stop the flow of the harmonic current from distr essing power system, either by preventing them with the recitation of series filters or diverting them to a shunt course of action 9 11. That is the different between series filter and shunt filter, too.Series filters can be tuned LC system or only a single inductor in the system. Parallel inductance and capacitance are tuned to provide low impedance for fundamental frequency current and high impedance for a selected frequency current, always high level harmonic current. The series tuned filters are simple and reliable to use. The move configuration can be shown as below.Figure 3.1 Series LC tuned filter.The series tuned filters are always used as input filter for power electronic systems. However, a big drawback limits the using. If the series tuned filter is used in a VSI system as the input filter for the inverter, several order harmonic current need to be filtered, 5th, 7th, and so on. Each order harmonic current ask an individual filter, and hence the size of the system can be intolerable.On the other hand, shunt filter have much more types including shunt-tuned filter, double-band pass filter and 1st, 2nd and 3rd -order damped filters. Also, broadband filters are good solution for filtering wide range of harmonics 22. The traffic circle configurations of these widely used passive filters are like shown below.(a) (b) (c) (d)Figure 3.2 Typical harmonic filters (a) Single-tuned filter (b) persona tuned filter(c) juicy-pass parallel filter (d) C-type high-pass filter 5 27.A few single tuned filters cope with large level harmonic contents and a high-pass (2nd order) filter filtering high frequency harmonics is the common model for shunt passive filters and can get better characteristic than series filters 24. Take the single tuned filter as example, single-tuned filter also called the band-pass filter as only a selected frequency of current can pass in low impedance. The tuning frequency of the single-tuned filter could be(3.1)And at this frequency, the impedance of the filter is(3.2)where s is the Laplace operator, L represents value of inductance and C represents the capacitance value.However, mostly passive filters can only filtering 30% of harmonic current in the power system 23 and can not match IEEE 519-1992 standard well. Even the broadband filter, which can filter a range of harmonic contents and reduce system THD to approximately 10%, the resonance caused by the filter and the big size of inductor and capacitor still limit the usage of the filter.So we can get the list of advantages and disadvantages for passive filters shown in table 3.1.AdvantagesDisadvantagesEffectively for filtering high frequency harmonics unkept availability for low frequency harmonic filteringVery low cost and reliable commodious devices and inflexible devices parametersSimple anatomical structureIndividual branch is necessary for each dominant harmonics in the systemHigh probability resonanceTable 3.1 List of passive filter performances 4 14 2 5 29.3.2 Active power filters (APF)The basic idea of an active filter is to compensate current or voltage disturbance so as to reduce the unstable power electronic systems drawn from the power system 23. The active filters using in power system are not the same as what we use in electronic circuits. The active filters established means combined operational amplifiers and passive components like inductors and capacitors, and always been used in electronic circuits operating under low voltage. That is the beginning of the active compensation applications and came out earlier than active filters using in power systems. The active filters which are used in power system for active power compensation and harmonic compensation are always called Active Power Filter (APF) 30. The active in APF means the filters are act as power sources or generators and provide compensation currents which have opposite word phase angle with the harmonic currents in power system 30. Similarity between elect ronic circuit active filters and power system active filters are the fate of external power supply. The active filters which are talked in the following parts are all means APF.With the active power filters, the compensation for reactive power and for harmonic current can de done at the same time, hence efficiency on harmonic compensation and also dynamic response are all be improved 23. The apparent movement of active power filters began in 1970s and was introduced by Mr. Akagi. The incentive for active filters is the inductor is not appropriate to use under high frequency, so the trend is to replace the inductor with active components. As the harmonic contents in the power system various frequently, fast response of active filters required a good control strategy to make active filters smarter and faster. But more complex devices and sophisticated control strategy are required, that all makes active filters more expensive and hard to use 26.Active filters can also be classified by converter type as shunt-type active filters and series-type active filters. The diagrams of two basic types of active filters are shown below. The other way to classify active filters is the phase number of filters which will be discussed later.(a) (b)Figure 3.3 Diagrams of (a) Shunt-type active filter and (b) Series-type active filter 11 28.Series active filters are good at compensate voltage harmonics and capacitive, voltage-source loads. When applied to an inductive or current-source load, a low impedance parallel branch is necessary. Similarly, shunt active filters are always used with inductive, current-source loads and high current distortion conditions. Sometimes over current condition occurs with the use of shunt-type active filters 31.Typical working principle of the active power filter is1. Detection.The sensor detects the waveform of the instantaneous load current and feedback to the controller, which is typically a digital processing block.2. Analysis.Load current is always high distortion current including fundamental current and some(prenominal) orders of harmonic current. The processor must distinguish the fundamental current with the harmonic currents and give out the schooling including frequency, value, and phase angle of harmonic contents, so as to control the power source inverter providing opposite phase current of harmonic current.3. Compensation.The power source inverter draws current from individual DC voltage supply and converting to required current to cancel harmonic currents. care the diagram shown below.Figure 3.4 Diagram of compensation characteristics 31.Hence, we can draw a conclusion of advantages and disadvantages of active power filters shown in the table below.AdvantagesDisadvantagesHigh compensation efficiency and high ability on harmonic compensationLow reliability with sophisticated control system and devices humbled size componentsDifficult to construct a large rated current source with a rapid currentFast action o n harmonic current variation makes good dynamic responseHigh initial costs and running costsNo resonance causingComplex control strategy and controllers are necessarySuitable for widely supply and load conditions, like unbalanced power supplyTable 3.2 List of active power filter performances 13 22 30 31.3.3 Hybrid systemsHybrid filters comes from the idea to combine the advantages of both passive filters and active filters together hence to get brilliant performance on harmonic mitigation 17. Combine passive filters and active filters can significantly reduce costs and improve the compensation characteristics in the power system. Also, various types of hybrid systems of passive and active filters can get better performance than only passive or active filters.Like the reference 18 and 20, small rating active power filter and passive filter connected in serial or shunt type. Smaller filter inductor, smaller dimension, light weight and better filter performance hybrid system take advan tages of both passive and active filters 18. However, as the basement of the hybrid power filters are always active power filters, the initial costs and control complexity is still big disadvantages of hybrid systems.3.4 Phase multiplicationThe purpose of phase multiplication is to increase the pulse number of the converter and hence to increase the harmonic order and frequency 4. The low frequency harmonics can be mitigated effectively and phase multiplication technique does not cause serious resonance and other bad effects on power system performances 13. The mulish application of phase multiplication technique, the multipulse converters, have the ability to draw low distortion current from power source and generate DC current with low level ripple 32.Typically, 6-pulse converter has the lowest harmonic order of 5 1. When rising pulse number to 12, the lowest harmonic order can increase to 11. As value of harmonic current are ideally proportional to fundamental current value 4, t he amount distortion of the power system can de reduce to a low level. Also, the multipulse thyristor converters can output various value current by controlling the thyristor fairing angle () 32.The drawbacks of phase multiplication technique are mostly the contradiction between the cost and output characteristic. If controlled output is required, the multipulse converter should contain at least 12 switching devices and that can be a big amount of costs. On the other hand, multipulse converter only use diodes may operate on low efficiency 11.3.5 PWMPWM (Pulse Width Modulation) is a modern control technique for power electronic systems. PWM converters have much better performance compared to traditional converters like diode rectifiers and square-wave control inverters 4. Like the phase multiplication technique, PWM control can raise the frequency of harmonic contents of current so as to reduce the effect caused by harmonics. Also, converters using PWM control can have high efficienc y and small size. With all these advantages, PWM control absorbed great concern in modern power conversion systems.However, the topology complexity and difficult on designing controllers 19 makes the use of PWM is limited.3.6 Power factor correction converterPower factor correction (perfluorocarbon) converter is a typical active power factor correction method. As a mature technique for power factor correction, perfluorocarbon converters have been widely used in power electronic systems to achieve high power factor (PF) and low harmonic distortion 33. PFC convener forces the input current follow the input voltage, which makes the input current drawn from power supply nearly in a unity power factor 34. The Boost-type PFC converters are the most used topology which have many advantages, such as low level ripple in the input current, high power factor, small size and simple circuit structure 35. A typical circuit diagram of Boost-type PFC converter is as shown below from reference 36.Fi gure 3.5 Typical circuit diagram of Boost-type PFC converter 36.As we seen in the diagram before, conventional PFC converter consists two main stages 33 37Power factor correction stage.This stage is combined with a diode rectifier and a DC/DC converter and used to correct power factor of the input current drawn from the power system. The most used type of chopper is Boost chopper. Also, the new Buck and Cuk type PFC converters are increasingly being used now. The switching working principle can be divided into two types, DCM and CCM.2. DC/DC converterThe chopper here is used to convert the power output voltage and current match the users demand. Since choppers only drawn low distortion power from supply, the typical filter on the utilization end is always a passive filter.This is the working principle for conventional PFC converters, the two-stage DCM/CCM Boost-type PFC converter. However, this type of PFC converter has some disadvantages and need to be improved 33-391. fix up num berIndividual control system and switching devices are required for each stage of PFC converter, hence increasing the costs of the whole system and cause some other problems, such as power density, transmission efficiency and control response 38. Also, the design of control system can be a challenge.A new one-stage PFC converter topology has been introduced to power factor correction research area. The circuit diagram is as shown in figure 3.6 36. The combination of the power factor correction converter and the forward converter may bring many advantages point as below 361. High power factor correction performance2. Reduced value of ripple in the DC output3. Low initial cost and running cost4. High efficiency and easy control systemAnd so on.Figure 3.6 Circuit diagram of single stage PFC converter 36.2. Converter typeLike shown in figure 3.6, Buck converter is increasingly being used in PFC converters. Also, Cuk converter and other type of choppers are becoming good choice for PFC c onverters 36-39. The Buck type PFC converter was rarely used since its high input current distortion. However, with the characteristic improving of the Buck type PFC converter, it can reach good performance with specific dual mode duty rhythm method of birth control control scheme 36. The main advantage of Buck type PFC converter is easy to reduce the stage number to one stage.3. Devices and control strategyOne of the most important aims in the design of power electronic systems is the reducing of the size of the passive devices, since it allows increase on the power density and the reduction in the initial and running cost. As inductor and capacitor are still using in the PFC converter, the reduction of them can be very important 33 37.However, the improvement of devices must base on the developing of the control strategy 37. With a good detect and control system, the size of the inductor and capacitor can be reduced while the harmonic content can still meet the requirement 33.The further analysis and improvement of PFC converter based on this literature review will be an important work in the last stage of project.4. ConclusionThis literature review provides a critical study on power factor issues and power factor correction techniques. A theoretical review of power factor definitions and harmonic generation by power electronic systems are presented at the beginning of the paper. The performance of five basic types of harmonic mitigation techniques has been discussed with the support of many previous research publication and their results. The PFC converter is chosen as the promising system for power factor correction after the analysis and comparison. The simulation model establishment and simulation comparison of power factor correction techniques will be important works for the next period of the project. Also, design rules and guidance of PFC converters will be designed in the next period, too.