Proceedings of International Conference on Mechanical, Electrical and Medical Intelligent System 2017

Transcription

1 on Mechanical, Elecrical and Medical Inelligen Sysem 7 Consan On-ime Conrolled Four-phase Buck Converer via Saw-oohwave Circui and is Elemen Sensiiviy Yi Xiong a, Koyo Asaishi b, Nasuko Miki c, Yifei Sun d Nobukazu Tsukiji e, Yasunori Kobori f, Haruo Kobayashi g Division of Elecronics and Informaics, Faculy of Science and Technology Gunma Universiy, -5- Tenjin-cho Kiryu Gunma, , Japan a <6d6@gunma-u.ac.jp>, b <97@gunma-u.ac.jp>, c <97@gunma-ac.jp>, d <7d@gunma-u.ac.jp>, e <nsukiji@gunma-u.ac.jp>, f <kobori@oyama-c.ac.jp>, g <koba@gunma-ac.jp > Keywords: four-phase buck converer, consan on-ime, saw-ooh-wave, elemen sensiiviy Absrac. This paper proposes a four-phase DC-DC buck converer wih consan on-ime conrol, which can provide large oupu curren wih low volage ripple. We describe here a mehod of sawooh-wave circui, o achieve he four-phase converer. As a resul, he saw-ooh-wave circui well achieves he four-phase conrol, showing sable curren balance and beer ransien response compared o he single-phase converer. Furhermore, he saw-ooh-wave mehod achieves high curren level wih sable curren balance. As for is elemen sensiiviy, he change of he curren balance is measured wihin a cerain componen error range, showing ha he curren balance is sensiive o he on-ime error of he main swich.. Inroducion Muli-phase DC-DC buck converer echnology has been sudied for a long ime. For he operaion of high-performance processors such as PCs and servers, markes demand for fas response and low ripple conrol of heir power supplies []. In addiion, whereas he operaion volage becomes lower, he oupu volage accuracy and low ripple, as well as high speed load response are required []. The convenional muli-phase mehod in swiching power supply uses an exernal clock, and he four-phase PWM signals are generaed by he frequency division of he clock. On he oher hand, in he case of he clock-less power supply, since here is no fixed clock signal, i is necessary for he remaining hree-phase power supply circuis o operae synchronizing wih he reference power supply. As for he conrol mehod of he muli-phase converer, he hyseresis conrol is simple enough o saisfy he demand for high speed load response. However, he swiching frequency will change by he load curren ransien. Aemping o alleviae his problem, anoher mehod called consan on-ime conrol (COT) is considered; i makes he swich on-ime consan, as well as he operaing frequency in he seady sae, regardless of he load curren change []. On he basis of he wo-phase converer echnology [] and he hysereic conrol, his paper proposes an improved four-phase buck converer via saw-ooh-wave circui. In his mehod, he four-phase PWM signals are produced by bleeder circui, and is waveforms are simulaed by SIMPLIS. The resul shows good curren balance, large load curren capabiliy and improvemen in ransien response compared o he single-phase converer. As for he elemen sensiiviy, he change of curren balance is measured wihin a cerain componen error range, resuling ha he curren balance requires exreme precision on he main swich urn-on ime.

2 on Mechanical, Elecrical and Medical Inelligen Sysem 7. Conrol of Consan On-ime. Circui Configuraion and Operaion Principle The configuraion of he buck converer wih he consan on-ime conrol is shown in Fig.. The operaion principle waveforms hereof are shown in Fig.. The circui configuraion of his sysem consiss of he convenional power sage and he COT conroller including an S flip-flop. f, Cf are used, as a ripple injecion circui creaes riangular wave and injecs i ino o, which resuls o r hereby. r and he reference volage ref are direcly compared by he comparaor, and he oupu pulse is used o se he S flip-flop, in which here is a Ton imer o achieve he consan on- ime. Sae ~ A, he ripple volage r reaches o he ref, he comparaor oupus a high level, so does Q por of he S flip-flop, resuling ino he urning on of swich SW. The on-ime of SW is se o a consan ime by he Ton imer. When he fixed on-ime is over a, he Ton imer oupus a high level o he por, and Q becomes low level hereby, resuling in he urning off of he swich SW. Then r sars o decrease from peak, so does he inducor curren IL. Sae ~ From, he SW keeps urning off unil, during which r and IL coninue decreasing. When i comes o, r becomes lower han ref again, causing he high level oupu from he comparaor. Then he SW urns on again in nex cycle. SW I o I L r ref comp T on COT Conroller Fig. Buck converer wih COT conrol PWM Fig. Waveforms during COT operaion. Simulaion esuls Fig. shows he simulaion resuls wih he parameers in Table I. The operaing frequency is khz and he on-ime is 87.7 ns. The seady sae simulaion waveforms are consisen wih he operaion principle waveforms.

3 on Mechanical, Elecrical and Medical Inelligen Sysem 7 PWM / A [/] r.. ref PWM [I/A] 5. Io 5 IL usecs/div Fig. Simulaed waveforms in seady sae Table I. Parameers of COT conrol circui in o L C f C f L [] [] [uh] [uf] [K] [nf].9 [kω] 7[kΩ].6 [Ω]. Four-phase Converer wih COT Conrol Fig. shows he configuraion of he four-phase converer wih COT conrol. Besides he main converer, here are hree oher sub-converers below. Each sub-converer receives he same inpu volage in and includes he same componens as he main converer, bu hey are conrolled by differen PWM signals whose phase posiions differ by 9 from each oher, so do heir inducor currens IL, IL, IL. Fig.5 shows he waveforms of he four-phase PWM signals generaed by he fourphase generaor. The oher hree signals PWM, PWM, PWM are keeping heir paces in he main signal PWM, and keeping he phase difference of 9 exacly wih each oher. L o Sub-Converer Sub-Converer Sub-Converer Fig. Four-phase converer wih COT conrol Fig.5 Four-phase PWM signals. Four-phase Converer via Saw-ooh-wave Circui. Peak-hold Circui of Saw-ooh-wave The proposed peak-hold circui is shown in Fig.6. comp in Fig. is picked up o generae he sampling pulse and a rigger pulse wih lile delay. The inpu volage of he saw-ooh goes o he swich hrough a volage follower which provides high inpu impedance and low oupu impedance, making he capacior C segregaed. When i is abou o reach he peak volage, he sampling pulse comes o make he swich urn on and he capacior C is charged o he peak volage hereby. Once he

4 on Mechanical, Elecrical and Medical Inelligen Sysem 7 sampling pulse is over, he swich urns off immediaely, and he volage on he capacior says a he previous peak value, meanwhile he rigger pulse follows on o rese he saw-ooh-wave. The pracical simulaion resul is shown in Fig.7. Trigger Pulse Differeniaor comp Buffer Curren Source Sampling Pulse olage Follower olage Follower C Peak Hold olage [/] 8 6 Peak-hold Fig.6 Configuraion of he peak-hold circui usecs/div Fig.7 Simulaion resul of he peak-hold circui. olage Divider for Generaion of Four Phases I is easy o know ha he saw-ooh-wave made by comp has he same phase posiion as PWM in Fig.. There we use a volage divider o divide he peak volage of he saw-ooh ino quarered four pars, and hrough he comparison beween each divided volage and he peak-hold volage, he oher hree pulses are generaed. The simulaion resul is shown in Fig.9, and we can see ha he generaed hree oher pulses are following he main pulse, keeping he phase difference regularly. Peak Hold olage Saw-ooh olage [/] 5 Comp COT Circui PWM comp PUL PUL PUL Comp COT Circui PWM PWM / PWM Comp COT Circui Fig.8 Four-phase pulse generaor PWM PWM / PWM PWM PWM Fig.9 Simulaion resul of four-phase PWMs 5nSecs/div. Characerisics Simulaion of Four-phase Converer via Saw-ooh-wave Mehod. Four-Phase Curren Balance As shown in Fig., in he case of Io =5.6A, he inducor currens in each phase are almos he same as.6a, which shows good curren balance in he case of four-phase converer.

5 on Mechanical, Elecrical and Medical Inelligen Sysem 7 A [I/A] Fig. Currens of each phase in he four-phase converer I o=5.6a I Lmean=I Lmean=I Lmean=I Lmean=.6A usecs/div. Comparison of Oupu olage ipple and Transien esponse beween Single-phase and Four-phase Converers As Fig. and Fig. show, he oupu volage ripple of he four-phase converer decreased by 57% compared o ha of he single-phase converer. As for he load flucuaion, when he load curren changes by A, he four-phase converer decreases by 7% in overload and by 59% in under load, and he recovery ime is jus abou one-fifh of he single-phase converer. o / o / [/] p-p =.8m Single-phase Converer p-p =.m Four-phase Converer Fig. Comparison of he oupu volage usecs/div ripples o / o / Io / A [/] [I/A] 6 6m 5A m Single-phase Converer Four-phase Converer 5A 89m 699m 5uSecs/div Fig. Comparison of he load flucuaions 5A. Large Load Curren Tes Fig. shows he simulaion resul of he large load curren es. The load curren successfully reaches o a high level of 55A, and he curren balance among he curren of he four phases remains sable. [I/A] 6 5 Io A I L, I L, I L, I L Fig. Simulaion resul of he large load curren 5uSecs/div

6 I/A I/A Proceedings of Inernaional Conference on Mechanical, Elecrical and Medical Inelligen Sysem 7 5. Elemen Sensiiviy for Curren Balance As shown in Fig. and Fig. 5, he curren balance changes wih he error of various parameers, such as he on-ime of PWM and he resisance of main inducor L. In Fig., when he on-ime of PWM increases by only %, IL increases by more han %, showing high sensiiviy. As for sensiiviy o L, wih he increase of L, IL decreases linearly while IL IL, IL increases linearly. Bu he change is no obvious as a whole I L.8 I L %.6.5 I L I L I L.%.5 % I L~I L. % /ns /mω Fig. Curren balance via Ton of PWM Fig.5 Curren balance via L 6. Conclusion In his paper, we have proposed a consan on-ime conrol and applied i o a four-phase buck converer via saw-ooh-wave circui which does no need an exernal clock. The consan on-ime conrol makes he frequency of he PWM signal fixed even when he load curren changes, so ha he four-phase buck converer is achieved wihou an exernal clock. The saw-ooh-wave circui mehod obains good curren balance, and i also ges much improvemen in he oupu volage ripple and ransien response compared o he case of he single-phase converer. I successfully achieves large load curren wih a sable curren balance, reflecing pracical applicaion value. On he oher hand, he es resul of elemen sensiiviy shows ha he curren balance is sensiive o he on-ime of PWM, meaning ha he on-ime of PWM mus be se o ns precisely o guaranee he seady operaion of he four-phase buck converer. eferences [] H. Kobayashi, T. Nabeshima (ediors), Handbook of Power Managemen Circuis, Pan Sanford Publishers 6. [] P. Xu, J. Wei, F. C. Lee, "Muliphase Coupled-Buck Converer A Novel High Efficien olage egulaor Module", IEEE Transacions on Power Elecronics, vol. 8, no., Jan.. [] K. Asaishi, N. Tsukiji, Y. Kobori, Y. Sunaga, N. Takai, H. Kobayashi, "Hyseresis Conrol Power Supply wih Swiching Frequency Insensiive o Inpu/Oupu olage aio", IEEE h Inernaional Conference on Solid-Sae and Inegraed Circui Technology, Hangzhou, China, Oc. 6. [] Y. Xiong, Y. Sun, N. Tsukiji, Y. Kobori, H. Kobayashi, "Two-phase Sof-swiching DC-DC Converer wih olage-mode esonan Swich", IEEE Inernaional Symposium on Inelligen Signal Processing and Communicaion Sysems 7, Xiamen, China, Nov. 7.