Streamlining Power Electronics Teaching

Transcription

1 Sreamlining Power Elecronics Teaching Clovis Anonio Pery, Joabel Moia, Fernando Sanana Pacheco Elecronics Deparmen, Campus Florianópolis Federal Insiue of Sana Caarina Av. Mauro Ramos, 950, Florianópolis SC, Brasil Absrac This work inends o inroduce he use of remoe laboraories for power elecronics eaching, by means of VISIR Virual Insrumen Sysem in Realiy). The sysem is applied for he analysis of wo simple circuis, a RC filer and an AC measuring nework. The proposed mehodology inroduces remoe aciviies afer heoreical lessons, pen and pencil exercises, circui simulaions, and on-sie laboraory experimenaion. This sraegy has been validaed by professors and a pilo group of sudens a he Elecronics Deparmen of he Federal Insiue of Sana Caarina. As a general conclusion, remoe labs conribue o learning, bu canno subsiue compleely on-sie laboraories. Keywords remoe laboraory, power elecronics, VISIR. I. INTRODUCTION Teaching of power elecronics is commonly accomplished by means of lecures, problem solving, circui simulaion, and laboraory aciviies [1]. Thus, he mehodology for eaching power elecronics is no differen han he widespread analog elecronics eaching approaches [2, 3]. In boh conexs, some phenomena concerning he operaion of power elecronics componens are discerned only by means of laboraory experimens, which reinforce he imporance of hands-on aciviies for elecronics learning [1 5]. Throughou he world, effors have been made in order o spark he ineres of sudens o hemes relaed o power elecronics. Problem based approaches allow he inegraion of inerdisciplinary knowledge and learning of differen skills, and consiue an ineresing alernaive as discussed in [1 3, 6 8]. Besides problem based learning PBL), he use of remoe laboraories seems o sreamline he learning process of sudens, accompanied or no wih hands-on aciviies and circui simulaion [9 16]. Comparaive sudies beween remoe, virual, and hands-on laboraories applied in echnical areas are presened in [9 10]. In he same way, professors of he Deparmen of Elecronics a he Federal Insiue of Sana Caarina have been assessing sraegies o make educaion more aracive and dynamic. Some of he iniiaives o urn power elecronics more aracive o sudens are discussed in his work. Therefore, his work inends o inroduce he use of remoe laboraories for power elecronics eaching wih he aid of a ool called Virual Insrumen Sysem in Realiy VISIR) [12]. In our sudy, we show he assessmen of wo circuis wih small degree of difficuly eiher by sudens and by professors. Gusavo Ribeiro Alves, Manuel Carlos Felgueiras Deparmen of Elecrical Engineering Polyechnic of Poro School of Engineering Rua Dr. Anónio Bernardino de Almeida, Poro, Porugal This paper is organized as follows. We presen he challenges in eaching power elecronics in Secion II. In Secion III, we presen our proposal o inroduce VISIR in power elecronics classes. Secion IV describes he assessmen of VISIR by sudens and professors. Conclusions and suggesions for fuure work are presened in Secion V. II. TEACHING POWER ELECTRONICS Power elecronics is a mulidisciplinary area inside he elecrical engineering domain. Thus, eaching of power elecronics implies, for he eacher, knowledge of diverse fields, among which elecrical circuis, magneic elemens, power sysems, signal processing, and conrol sysems [19, 20]. On his basis, disciplines relaed o power elecronics are placed a he end of elecronics courses. In his conex, he eaching of power elecronics is a he same ime rewarding and challenging, since he sudens have already accumulaed knowledge o develop more comprehensive and deeper sudies. On he oher hand, a he end of a four or five-year course, sudens have acquired mauriy o discern beween convenional sraegies and inspiring eaching approaches. Many research groups in power elecronics have conduced sudies and aemps o make he eaching of his subjec more aracive and dynamic for sudens a he end of he course or even for freshmen [1 3, 8, 17]. Over he years, we carried ou various aemps o improve he eaching of power elecronics for elecronics echnicians. Noe ha, in his level of formal educaion, sudens are eenagers and power elecronics is a he final phase of he course. Our firs inspiraion was he solar climber [3], projec carried ou in he Power Elecronic Sysems Laboraory of ETH Zurich Fig. 1). Their plan comprises a phoovolaic panel, power saic converers, and moors, allowing he inegraion beween he energy source, he load, and he processing circuiry. In his regard, our firs aemp o he final erm projec of power elecronics was an elecric car, based on a oy vehicle plaform Fig. 2), commercially available. This projec was carried ou in The main goal was o apply phoovolaic cells o sore energy in ulra capaciors, emulaing a recharge saion, and hen perform a race wih he cars, emphasizing he opimizaion of energy processing circuis saic converers). Over he following semesers, he proposals were modified o ease he developmen of he projecs by sudens. Fig. 3 shows one projec using he Arduino plaform [21] conneced

2 o elecronic circuis for energy processing and o drive a DC moor. Fig. 4 shows anoher projec wih Arduino, o conrol he brighness of a ligh bulb. Fig. 1. Solar Climber of ETH Zurich [3]. Fig. 2. Final erm projec employing oy cars. Fig. 5. Sudens using componens of he final erm projec for aciviies developed during he classes. Over he semesers in which he final erm projecs were carried ou from 2010 unil 2013), we noiced a higher degree of involvemen from sudens, and greaer inegraion of differen subjecs learned hroughou he semeser. Our conclusion is ha he use of a plaform like Arduino allowed faser and easier work by sudens, increasing moivaion, as well as enabled flexibiliy o applicaions in command and conrol of power elecronics circuis. The biannual organizaion of he projec aciviies allows he diluion of heoreical classes, simulaion aciviies, and hands-on experimens hroughou he semeser. Pracical aciviies, as shown in Fig. 5, le sudens increase heir problem solving experience. Afer our experience wih final erm projecs, we began o discuss how sudens could use es equipmens ouside he labs. Some research works [9 10, 24] discuss key poins regarding eaching of elecronics or oher echnical areas using compuer simulaions, on-sie lab aciviies, and remoe laboraories. Currenly, here is no consensus abou wha form is beer for eaching opics relaed o engineering. Fig. 3. Final erm projec wih Arduino and DC moor drive. The use of remoe laboraories are usually associaed o cos reducions of laboraories faciliies [17] or o make he experimens available a any ime and a any place [11 16]. This way, remoe labs become anoher ool o sreamline power elecronics eaching, joining o he lis of resources: heoreical classes, resoluion of exercises, simulaion of circuis, and on-sie laboraory aciviies. Virual Insrumen Sysem in Realiy VISIR) is discussed in [11 16] as a resource for carrying ou differen aciviies of a elecronics laboraory. These research works focus on general elecronics, addressing aciviies relaed o circui analysis, filers, and operaional amplifiers, among ohers. In [18], he use of VISIR is exended for differen applicaions, including circuis for power elecronics, as shown in Fig. 6. These circuis were implemened as par of he main plaform, i.e., hey are currenly no available for parner insiuions hrough sandard modules. Fig. 4. Final erm projec in which Arduino conrols he brighness of ligh bulbs. The circuis shown in Fig. 6 are: a) and b) second order filer; c) full wave recifier wih capaciive filer; d) linear

3 volage regulaor, and e) swiched regulaor. These circuis cover a broad range of opics sudied in power elecronics, from AC-DC converers o DC-DC converers, passive filers, and pulse-widh modulaion PWM), among ohers. Oher research works [22 24] also discuss power elecronics eaching, wih a focus on online simulaions and apples. An imporan comparaive sudy beween he main eaching echniques for power elecronics is shown in [24]. A ha ime 2002), auhors classified eaching ools ino he following ypes: Slideshow A sandard ool for eaching, in he mos diverse areas of knowledge and also in indusry. A pracical, easy, and flexible sysem. The passiveness of he suden is poined ou as a disadvanage as well as he fac ha usually slides are no prepared for selfsudy. Slideshows are adequae for presening conen quickly and in a focused manner. Slideshow wih movies, ex and audio The inclusion of mulimedia conen increases he possibiliy of using slideshows for self-sudy. Numerical Simulaion Compuer simulaions for circui design are commonplace boh in academia or in indusry. Numerical simulaions enable cos reducion, increase flexibiliy, and preven he risk of misakes made by sudens in real experimens. However, simulaions only become effecive ools for learning when associaed wih he familiariy wih physical elemens obained in lab aciviies. Web-Based Simulaion For an adminisraive poin of view, i is beer han convenional simulaion packages, since i dispenses he purchase of sofware, and usually permis operaion under differen operaing sysems. The dependency on a reliable inerne connecion, and he difficuly simulaion resuls are poined ou as disadvanages. Simulaion combined wih ex Here, i presens he conen direcly on he websie, incorporaing simulaions in Java, videos, exercises, among oher resources. Ineracive Animaions wih he ipes Auhors discuss a sysem developed and used a ETH Zurich, which has an emphasis on conen ineraciviy, reducing he focus on simulaion. I has as a main advanage he quick response, since sudens can change any parameer and examine he resul immediaely, because i operaes as an animaion and no as a simulaion. Flexibiliy is no a key poin; sudens mus follow exacly wha is expeced in a se of predeermined circuis. As a conclusion, any ool has advanages and disadvanages, and none of he previously shown can replace compleely he ohers. I is he main responsibiliy of professors and adminisraive saff ake ino accoun he characerisics of he conen, analyze he previous experience of sudens, and he environmen in which he suden is, o selec he bes opion. Especially in power elecronics, some opics are beer undersood during he experimenaion in he laboraory; for example, semiconducors under swiching operaion, he performance of elemens wih hea sinks, and he analysis of speed variaion of an engine. Oher conens may be exploied by numerical simulaion; for insance, modulaion circuis, signal filering and condiioning. Some issues require repeiion of exercises and circui modificaions o assure sudens undersand how elemens work. As an example, driver circuis for power ransisors. Finally, learning wih error is imporan in some opics, where sudens should hink how o obain he expeced resuls. For example, he generaion of command signals for ransisors from sinusoidal PWM modulaion requires his king of hinking. Thereby, his work proposes he inclusion of remoe lab aciviies o he usual oolbox for power elecronics eaching. This way, opics are inroduced wih heoreical lessons, and are advanced hrough exercises for fixing he conen, numerical simulaion of circuis, on-sie laboraory experimenaion and aciviies in remoe labs. Fig. 7 shows briefly hese differen seps for eaching elecronics and power elecronics. III. PROPOSAL OF A NEW METHODOLOGY Power elecronics circuis usually exhibi wo sages: energy processing, and signal processing. The energy processing sage consiss of passive componens and high volage and/or high curren power semiconducors. Signal processing circuis drive such power semiconducors, apply a closed-loop conrol for power converers, are responsible for sysem proecion, and operaion supervision [1]. Among signal processing circuis, circuis for measuring elecrical quaniies are usual in power elecronics applicaions. Moreover, passive filers and resisive neworks are commonly employed o reduce he ampliude of he signals under analysis [19 20]. Power circuis, on he oher hand, are usually classified in he following caegories: AC-DC, AC-AC, DC- DC, and DC-AC converers [19]. Among AC-DC converers, i is common pracice o begin he sudy by simpler circuis wih diodes and sinusoidal signals [19]. Afer a firs conac wih power semiconducor devices, sudens are inroduced o recifiers and filers by lecures. Pen and pencil exercises and sofware simulaions are he nex aciviies. The las sage is he pracical implemenaion, where sudens assemble he circuis on a breadboard and perform he measuremens. Remoe laboraories are a complemen here, giving he opporuniy o sudens repea he laboraory aciviies, reinforcing he knowledge acquired and exploring some advanced opics beer. The main conceps of he subjec being sudied will be addressed boh in he lecures, during he simulaions, and wih he laboraory classes. This way, sudens have hree disinc momens o absorb and o undersand he conens. The eaching mehodology for power elecronics proposed in his work have been implemened in hree sages. In he firs one, professors evaluae he mehodology, making some

4 experimens wih he remoe lab plaform VISIR. In he second sage, all proposed seps are developed, checking for improvemen poins and rying o predic some difficulies ha sudens could find in heir developmen. This validaion phase was implemened wih a pilo group of sudens in he beginning of This paper repors resuls from his wo phases, collecing opinions from professors and sudens. The final sage is he applicaion of his mehodology for differen classes of elecronics echnician sudens, hrough a cooperaive projec beween IFSC and he Poro Superior Insiue of Engineering ISEP). L e a r n i n g V e r i f i c a i o n Remoe Laboraory Experimenaion Laboraory Experimenaion Elecronics Conen Conen Exposiion Exercises Numerical Simulaion Theoreical Par Simulaion Phase Experimenal Phases Fig. 7. Aciviies carried ou by he suden for sudies in power elecronics. IV. EXPERIMENTS USING VISIR In his pilo sudy, he proposed experimens wih VISIR Virual Insrumen Sysem in Realiy) comprise wo simple circuis wih passive elemens resisors and capaciors). These circuis can be implemened using a gues accoun in he virual experimenaion environmen. Boh experimens require o measure an oupu volage considering a variaion of frequency in he inpu signal. Experimens were carried ou by professors and sudens as specified in Secion III. Sudens' learning pah followed all he seps shown in Fig. 7. A. Experimen 1 RC Filer The firs experimen is a firs order lowpass filer, wih only a resisor and a capacior, as shown in Fig. 8. The inpu and oupu volage waveforms are also shown in his Figure. A ypical applicaion for his circui is in filering a pulse widh modulaion PWM) signal generaed by a microconroller for an analog circui applicaion. R kω + v i v i v o C 1 56 nf v o - - Fig. 8. Lowpass filer circui, and inpu and oupu volage waveforms. Three differen professors and eigh sudens have implemened his circui using VISIR. Fig. 9 shows one session of such an experimen, wih he circui elemens, and he connecions o he funcion generaor and oscilloscope. Fig. 6. Power elecronic circuis implemened in [18] using he VISIR. The inpu volage is a square signal wih ampliude of 2 V and 2 V of mean value, as shown in Fig. 10. Professors measured he ripple in he oupu volage signal and filled Table I, for he firs sage. For he pilo group of sudens, we modified he inpu signal. Since heir class assignmen involved sinusoidal

5 signals, he inpu signal was modified o a sinusoidal one wih ampliude of 1 V and variable frequency as shown in Table II. Since values obained by he eigh sudens are similar, Table II shows only he resuls from one of hem. Sudens were inroduced o he circui opology and wih pencil and pen calculaions, filled he columns gain and Calculaed oupu volage. Afer ha, using a simulaion sofware Proeus from Labcener Elecronics), hey obained he values in he column Simulaed oupu volage. An onsie laboraory was se up and wih esing equipmens oscilloscope being he main one) hey obained values in he column Experimenal oupu volage. Finally, hey had heir firs conac wih VISIR Figs. 6 and 7) and filled he column VISIR oupu volage. Afer he experimens, users professors and sudens) answered a form poining ou heir opinion abou he virual experimenaion plaform. TABLE I. MEASURED VALUES FOR THE FIRST EXPERIMENT MADE BY PROFESSORS User 1 User 2 User 3 Frequency [khz] TABLE II. Frequency [khz] Gain [V/V] MEASURED VALUES FOR THE FIRST EXPERIMENT MADE BY STUDENTS Calculaed Simulaed Experimenal VISIR 1 0,273!"#$% 0,270 0,280 0, ,140!"&'! 0,135 0,140 0, ,094!"!' 0,094 0,100 0, ,071!"!$& 0,070 0,080 0, ,057!"!)$ 0,050 0,060 0, ,028!"!#* 0,028 0,040 0,060 Fig. 10. Oscilloscope view inside VISIR wih inpu upper signal) and oupu lower signal) volage waveforms for he firs experimen. B. Experimen 2 AC measuring circui The following circui comprises a resisive nework wih a capaciive filer Fig. 11). This circui is commonly employed for measuring sinusoidal signals. The resisive nework reduces he ampliude of he signal while he RC filer fades high frequency noise. + v i - R 1 R 2 1 kω 1 kω C 1 56 nf Fig. 11. Circui for he second experimen, wih applicaions in sinusoidal signal measuring. Here we followed he same mehodology of he firs experimen. Three professors and a pilo group of eigh sudens ake par in he ess. One session of VISIR for his experimen is shown in Fig. 12. The inpu volage is a sinusoidal signal wih ampliude of 1 V and 2 V of mean value, as shown in Fig. 13. Professors should measure he ripple in he oupu volage signal and fill Table III. Wih he same procedure described for he firs experimen, sudens filled Table IV. For heir session, inpu signal was sinusoidal, wih null mean value and ampliude of 1 V. + v o - v i v o TABLE III. MEASURED VALUES FOR THE SECOND EXPERIMENT MADE BY PROFESSORS Fig. 9. A session of VISIR wih he firs circui lowpass filer). User 1 User 2 User 3 Frequency [khz]

6 TABLE IV. MEASURED VALUES FOR THE SECOND EXPERIMENT MADE BY STUDENTS Frequency [khz] Gain [V/V] ,492 0,408 0,289 0,247 0,136 0,093 Calculaed!"'#!"'!*!"#*!"#'$!"&%+!"!% Simulaed 0,490 0,398 0,282 0,236 0,138 0,089 Experimenal 0,480 0,412 0,304 0,264 0,150 0,116 VISIR 0,450 0,400 0,280 0,260 0,120 0,090 3) Measuring elecrical insrumenaion was? ) Easy ) Inermediae ) Hard quaniies using VISIR 4) Time spen for virual experimens, when compared wih real experimens? ) Small ) Medium ) Large 5) Your general impression abou he use of VISIR for hese aciviies was? ) Bad ) Good ) Very good 6) Considering hese experimens, he poenial for using VISIR in classes is? ) Small ) Medium ) Large Fig. 12. A session of VISIR wih he second circui resisive nework for measuring sinusoidal signals). Fig. 13. Oscilloscope view inside VISIR wih inpu upper signal) and oupu lower signal) volage waveforms for he second experimen. Users' answers are shown from Fig. 14 unil Fig. 19. Fig. 14. Answers for quesion 1. C. Discussion abou users' answers Afer he experimens, users answered some quesions regarding he use of he virual insrumenaion environmen. The form is he following: 1) Circui implemenaion using VISIR was? ) Easy ) Inermediae ) Hard 2) Equipmen adjusmens inside VISIR were? ) Easy ) Inermediae ) Hard Fig. 15. Answers for quesion 2.

7 Fig. 16. Answers for quesion 3. Fig. 17. Answers for quesion 4. Fig. 19. Answers for quesion 6. Equipmen adjusmen inside VISIR was considered easy and of inermediae difficuly, wha is probably associaed wih previous experience wih similar equipmen; Measuremen using VISIR equipmen were considered easy and of inermediae difficuly, maybe expressing he difficuly wih he firs use of he sysem; Regarding ime spen wih he experimens, users considered he aciviies quicker han convenional experimens, ha are usually slow; The general percepion of he users regarding VISIR was beween good and very good, wha is posiive and indicaes a good accepance of he plaform; The poenial for he use of VISIR in eaching environmens was considered beween medium and large, wha indicaes is prospecive use for power elecronics classes. Fig. 18. Answers for quesion 5. Opinions from professors and sudens are convergen, wih some differences abou equipmen adjusmen and he overall impression abou VISIR. As he firs general conclusion, he inroducion of he remoe lab wih VISIR had a posiive effec. From professors' answers, we can infer ha: Users considered he implemenaion wih VISIR easy, wha is also expeced from sudens; Oherwise, from sudens' answers, we can infer ha: VISIR is an adequae choice for circui verificaion. However, sudens consider on-sie laboraory experimens indispensable; Sudens also poined ou he agreemen in resuls from VISIR and on-sie experimens. However, hey again sressed he imporance of hands-on experience; VISIR user inerface is considered enjoyable and easy o use. I is a good complemen o classes, and o reinforce some opics, mainly because one can access from home; As a general opinion, sudens hink remoe labs conribue o learning, bu canno subsiue on-sie laboraories. In shor, we can conclude ha VISIR has a good poenial of applicaion in some opics of elecronics, especially in power elecronics when combined wih radiional eaching.

8 V. CONCLUSIONS AND FUTURE WORK The use of remoe laboraories o eaching has been promising, and seems o be an effecive way o spark suden's ineres. From our firs experience and from he lieraure, we can conclude ha remoe experimenaion plaforms like VISIR are very promising for elecronics eaching. Two simple experimens were done in his work using he gues accoun, wihou any modificaion in VISIR hardware. This way, he hree professors could be in he role of sudens, giving heir opinion abou he use of he plaform, as well as eigh sudens evaluaed he use of his new ool. Our users in his work professors and sudens) judged he poenial of remoe laboraories for elecronics as very high, combining differen sraegies like lecures, problem solving, simulaion, and experimens in sandard laboraories. This way, he effecive use of VISIR, even for simple circuis, allows sudens o reproduce experimens many imes, giving confidence and improving he success rae. Moreover, VISIR gives flexibiliy regarding he ime schedule and number of simulaneous users. Finally, we can conclude ha VISIR is appropriae for power elecronics eaching, firsly wih simple circuis like he ones presened here. Thus, sudens and professors can learn how o use he plaform, and, afer some ime, hey can develop more complex aciviies. In a fuure work, we plan o exend hese aciviies o a larger group of sudens and also o inroduce new circui opologies like modulaion circuis. ACKNOWLEDGMENT Auhors would like o hank sudens of Elecronics a IFSC for heir conribuion in his research. REFERENCES [1] P. Bauer, J. W. Kolar, Teaching Power Elecronics in he 21s Cenury. 15h European Conference on Power Elecronics and Applicaions, EPE Journal, Vol.13 n o 4, Lille, France, November [2] Jiang W., Yu, F., Mo, Y., A problem oriened model for eaching power elecronic circuis. IEEE 10h Inernaional Conference on Power Elecronics and Drive Sysems PEDS 2013), Kiakyushu, Japan, pp: [3] T. 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