Different Power Factor Correction Engineering Essay

Different Power cipher in Correction Engineering EssayDifferent creator- constituent chastening methods atomic number 18 reviewed, as well as the back cause to the advocator-factor. Problem is a boost in modern galvanizing distribution brasss due to the connection of rapidly increase numbers of non-linear electronic loads. The basic principles of concordant generation and demarcation line in motive clays be first discussed. The main(prenominal) part presents a critical review of commonly apply major king-factor correction techniques that have been identified in a literary productions review, and game stand downs the advantages and disadvantages of these techniques. After the analysis of methods and their working principles, the development of the most promising systems such as the boost-type PFC convertors is considered. Fin exclusivelyy, a project plan is proposed for the next phase of the dissertation work. This will involve investigating the operation, fig hting(a) control and process of the most promising systems by conducting a theoretical study and reach up and rails play a number of simulation perplexs using the MATLAB/SIMULINK softw ar tools.Key-words Power factor correction, sympathetic mitigation, PFC convertersContentsList of Abbreviations and Principle SymbolsAbbreviationsAC Alternating CurrentAPF Active Power leachCCM Continuous Conduction ModeDC Direct CurrentDCM Discontinuous Conduction ModeDF torment FactorFFT Fast-Fourier analysisIGBT Insulated Gate Bipolar TransistorPF Power FactorPFC Power Factor CorrectionPWM Pulse Width ModulationRMS settle Mean Squ areTHD Total Harmonic DistortionTDD Total Demand DistortionPrinciple SymbolsPower FactorDistortion FactorDisplacement Factorh Harmonic contentsRMS apprize of the line- authoritative vestigial personaRMS value of the line- circulating(prenominal) openhearted componentsTotal RMS value of the line- oc menstruation1. IntroductionIt is now clearly visible from a ctor systems journals and general literatures that precedent-factor correction is now an in-chief(postnominal) research topic in the precedent systems area. As non-linear world-beater electronic systems are progressively being attached to indicator systems in massiveer quantities as well as capacities for such applications as world agency quality control, adjustable speed drives, uninterruptible advocator supplies, renewable energy- informant interfacing, and so on 1 2. The power quality regulators of those systems are loftyly concerned now, because some of their drawbacks, such as kindlys generation and bring down power factor can pervert their advantages 3. Power electronic systems are effective because their high efficiency and rapidly adjustable output. However, when processing and controlling the infix electric energy suitable for users 4, power electronic systems often lick at a low power-factor, and that whitethorn cause serious problems to power system opera tors by reducing distribution component RMS authentic capacity and to other(a) users on the same network by distorting the sinusoidal grant voltage seen by other user connected at the same point of common coupling as a heavy electronic or power electronic load.. Of all power line rackets, charitables are probably the most serious one for power users because they exist under steady state conditions.This literature review considers sympathetic generation prediction of power electronic systems and examines the effectiveness of harmonic mitigation methods. The boost-type power factor correction converters will be walk outn as the core 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 will be based on a theoretical study and simulation studies using software MATLAB/SIMULINK power-factor correction system models which be develope d.2. BackgroundThis section provides discussion on the complete principles of power-factor correction, including definitions of power-factor terms and a consideration of the common standards which affect how harmonics controlled in power system. Also, the harmonic generation prediction of predilectionl 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 supply utilization on how efficient that the energy is supplied and can be converted into effective work output. The definition of power factor is as shown beneath(2.1)In the definition, the value of the power factor is ever so between 0 and 1, and can be either inductive or capacitive. That means average power is always lower than apparent power. The reason is harmonic components and phase-displacement angle,.Hence, the power factor equivalent can be described as at a lower place(2.2)is termed the (current) distorted shape factor (DF) and represent 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 waveform phase angle 6. Displacement factor has accordance value for in-phase current and voltage. The accession of displacement angle will cause larger re alive(p) current in the power system 4.Hence, the objective of power-factor correction is to decrease the current contortion 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 supply voltage.Another commonly utilise index for measuring the harmonic content of a waveform applied for current aberrance level is total harmonic distortion, THD. THD is the distortion current as a percentage of the fundamental current. The equation of THD is given byor (2.3)In AC supply utilizations, power factor,, can 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 apply in concert in the following work as important index in measuring achievement of the harmonic mitigation techniques.2.2 set up and limitation of harmonic distortion on power systemIn any power conversion process, to obtain high efficiency and low power loss are important for two reasons the price of the wasted energy and the difficulty in removing the heat generated due to dissipated energy 4. The performance of power output efficient is defined by several factors. The power factor and harmonic distortion are the most important ones.References 8 9 show the main issues of harmoni cs at bottom the power system include the possibility of them exciting series and parallel rings which cause a further increase of harmonic levels, 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 drawn from the power system and insulation stress and failure to action and malfunction of some electrical devices and systems.The IEEE Standard 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 beneathMaximum harmonic current distortion in percent ofIndividual harmonic order (Odd harmonics)TDD4.02.01.50.60.35.0207.03.52.51.00.58.05010.04.54.01.50.712.010012.05.55.02.01.015.0100015.07.06.02.51.420.0Even harmonics are especial(a) to 25% of the odd harmonics limits above.Table 2.1 IEEE 519-1992 Standard for harmonic current limits 12.Also, there are limitations for power system harmonic voltage and power factor regulation, ilk 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 large harmonic generation and phase shifting in controlled devices like controlled rectifiers. Understanding characteristics of the harmonic current is essential for harmonic mi tigation research. Based 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 frequence harmonic current from the utility and indeed cause problems for other users. Take an ideal single-phase semiconductor diode bridge 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 attend down from unity value and cause a decrease of power factor. This is surely over the harmonic standards limitation and needs to be corrected.Theoretically, Rectifiers and choppers output DC and 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 usuall y 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)Figure 2.1 Fourier analysis diagram for input current of (a) single-phase diode bridge rectifier and (b) PWM control Buck converter.2.4 Software tools for harmonic mitigation evaluationTo pervadeing 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 forward voltage drop of non-ideal devices 1. To analyze harmonic contents, appropriate software can be helpful. In this project, the software chosen to help analyzing harmonic current drawn by power electronic syst ems is MATLAB/SIMULINK. fetching the three-phase diode bridge rectifier as an example, a simulation model can be established as shown at a lower place. 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. Values 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 frequence spectra of AC input current of three-phase rectifier.3. Power Factor Correction TechniquesAfter tens of years developing and up(p), various types of power factor correction techniques or harmonic mitigation techniques can be chosen to s olve power factor problem. Those techniques can be divided into five categories 11 13 as shown below1. passive permeatesPassive filters can improve power factor with low cost and reduce high frequency harmonics effectively. However, they are always in large size and cannot castrate flexibly with system changes 4 14. If tuning reactors are not used, parallel plangency 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 cost and the harmonic currents they injected may flow into other system components 13 14.3. Hybrid systemsHybrid quick filters combine quick and passive filters together in various forms 17. Hence they can reduce initial and running costs and improve performance of the filter 11 13. Smaller filter inductor, smaller dimension, light weight and interrupt fi lter performance hybrid system take advantages of both passive and alert filters 18. However, the complexness of operation is the main drawback of hybrid systems.4. var. multiplicationIncreasing 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 proportional 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 performance 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 h ence get broad application prospect 11. However, the topology complexity and difficult on designing 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 widelyly been used to absorb harmonics generated by the power electronic systems, primarily due to their simplicity, low cost and high efficiency 20. Passive filters are always consists inductors, capacitors and damping resistors 21. The objective of the passive filter is to stop the flow of the harmonic current from disturbing power system, either by preventing them with the usage of series filters or diverting them to a shunt path 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 traffic circle 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 required 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 circuit 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) Double tuned filter(c) High-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 typical 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 519-19 92 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 harmonicsLow availability for low frequency harmonic filteringVery low cost and reliableBulky devices and inflexible devices parametersSimple structureIndividual branch is necessary for each dominant harmonics in the systemHigh probability resonanceTable 3.1 List of passive filter performances 4 14 25 29.3.2 Active power filters (APF)The basic idea of an energetic filter is to compensate current or voltage disturbance so as to reduce the reactive 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 elect ronic circuits. The active filters conventional 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 stipend 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 phase angle with the harmonic currents in power system 30. Similarity between electronic circuit active filters and power system active filters are the requirement 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 trend 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 fi lter 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 many orders of harmonic current. The processor must(prenominal) distinguish the fundamental current with the harmonic currents and give out the information including frequency, value, and phase angle of harmonic contents, so as to cont rol 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. Like 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 devicesSmall size componentsDifficult to have a large rated current source with a rapid currentFast action on harmonic current variation makes good dynamic responseHigh initial costs and running costsNo resonance causingComplex control strategy and controllers are necessary capable 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 advantages 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 practical 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, the 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 charac teristic. If controlled output is required, the multipulse converter should pay 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 efficiency 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 (PFC) converter is a typic al active power factor correction method. As a mature technique for power factor correction, PFC 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.Figure 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 syst em. 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. Stage numberIndividual 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 topo logy 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. convertor 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 converters 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 cycle 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 reduction 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 sys tems 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.