A New Control Scheme for a Class-D Inverter with Induction Heating Jar Application by Constant Switching Frequency

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1 7 Joual of Powe Electoics, Vol. 5, No. 4, Octobe 5 JPE 544 A New Cotol Scheme fo a ClassD Ivete with Iductio Heatig Ja Applicatio by Costat Switchig Fuecy WoSuk Choi, NamJu Pak *, DogYu ee * ad DogSeok Hyu * * Dept. of Electical Egieeig, HaYag Uivesity, HaegDag Dog, SugDog Gu, 3379, Seoul, Koea ABSTRACT I this pape, a simple powe cotol scheme fo a costat fuecy ClassD ivete with a vaiable duty cycle is poposed. It is moe suitable ad acceptable fo high fuecy iductio heatig (IH) ja applicatios. The poposed cotol scheme has the advatages of ot oly wide powe egulatio age but also ease of cotol output powe. Also it ca achieve a stable ad efficiet ZeoVoltageSwitchig (ZVS) i a whole load age. The cotol piciples of the poposed method ae descibed i detail ad its validity is veified though simulated ad expeimetal esults o 4.8kHz IGBT fo iductio heatig ated o.6kw with costat fuecy vaiable powe. Keywods: IHJa(Iductio HeatigJa), PFM(Pulse Fuecy Modulatio), PWM(Powe Width Modulatio), ClassD Ivete, ZVS(ZeoVoltageSwitchig). Itoductio Recetly with the developmet of powe semicoducto devices, ew cicuit techiques ad cotol schemes, eseach o high fuecy cicuits ad advaced powe devices such as MOSFETs ad IGBTs etc. have bee may pefomed fo high powe applicatios [][5]. The vaious esoat ivetes usig powe devices such as MOSFETs ad IGBTs offe educed switchig loss by usig softswitchig techique ad offe attactive possibilities i developig highe fuecies of opeatio, highe efficiecy, a smalle size ad lighte weight. Iductio heatig (IH) has bee a pat of high powe applicatios ad widely used i idustial fields, office Mauscipt eceived Octobe 8, 4; evised August 5, 5 Coespodig Autho: coffeefull@ihayag.ac.k Tel: 8934, Fax: , Hayag Uiv. * Dept. of Electical ad Electoics Eg., Hayag Uiv. automatio fields ad electic home appliaces. I paticula, IHJa, which is a applicatio of IH is used i home appliaces such as cookes [3][5]. The uiemets fo IH applicatios ae as follows: High fuecy switchig High efficiecy Powe facto close to uity ow cost Wide load age Reliability Highfuecy ClassD ivetes have become vey popula ad become moe ad moe widely used i vaious applicatios. It must be effectively selected accodig to the applicatio i ode to meet the ivete uiemets ude a high fuecy switchig opeatio due to load specificatios. A impotat goal of powe cotol is to achieve a efficiet ad useful poduct. Geeally, most iductio heatig applicatios use a vaiable fuecy scheme to cotol output powe [5][6]. The fuecy modulatio cotol is a basic method that is applied agaist the vaiatio of load o lie fuecy. Copyight (C) 6 NuiMedia Co., td.

2 A New Cotol Scheme fo a ClassD Ivete with 73 Howeve, pulse fuecy modulatio cotol causes may poblems sice the switchig fuecy has to be vaied ove a wide age to accommodate the wost combiatios of load ad lie. The majo disadvatage of this method is the lage fuecy age uied fo output powe cotol ove a wide age. Fo opeatios below esoace, filte compoets ae lage because they must be desiged fo the low fuecy age. Fo opeatios above esoace, fast switchig devices ae uied to maitai cotol at the uppe fuecy age. It is apt to poduce audible oise whe two o moe ivetes ae opeated at the same time with diffeet switchig fuecy. Besides, the soft switchig opeatig aea of the ZVSPFM high fuecy ivete is elatively aow ude a pulse fuecy modulatio stategy. Keepig the switchig fuecy costat ad cotollig it by pulse width modulatio (PWM) ae obvious ways to avoid the poblems of vaiable fuecy cotol [7][]. Theefoe, ClassD ivete topologies usig a PWM choppe at the iput, phaseshifted PWM cotol, PWM techique, cuet mode cotol ad a vaiable esoat iducto o capacito have bee poposed. Costatswitchig fuecy opeatio supposes that evey ivete i the applicatio is opeatig at the same fuecy, makig it ecessay to cotol powe without fuecy vaiatios. That is highly desied fo optimum desig of the output smoothig ad oise filtes. Howeve these cotol uiemets ad opeatig chaacteistics have a added complexity due to the fixed fuecy of switchig which limits thei pefomace []. Ad if the system has a phaseshift PWM cotol, the ZVS does ot exist at light load [3][4]. This pape deals with a simple powe cotol scheme of costat fuecy vaiable powe (CFVP) fo a ClassD ivete with iductio heatig ja applicatio. Whe the ivete opeates at a fixed switchig fuecy highe tha its esoat fuecy, it ca maitai the ZVS opeatio i the whole load age. Thus switchig losses, EMI, ae deceased. By adjustig the duty cycle of the fixed fuecy, the output powe is simply cotolled i wide load age (%% load). The advatages of this ivete cotol scheme ae simple cofiguatio ad wide powe egulatio age. It ca impove the powe cotol ad elevate cotol espose pefomace. Also the switches always guaatee zeovoltageswitchig (ZVS) fom light to full load ad the filte is easy to desig due to the use of costat switchig fuecy. The poposed powe cotol scheme ad the piciples of the ClassD ivete ae explaied i detail. Theoetical aalysis, simulatio ad expeimetal esults veify the validity of the ClassD ivete with the poposed PWM cotol scheme.. ClassD Seies Resoat Ivete []. Cicuit desciptio The ClassD ivete will be geeally used to eegize the iductio coil to geeate highfuecy magetic iductio betwee the coil ad the cookig vessel, highfuecy eddy cuets ad fially heat i the vessel bottom aea. ClassD ivetes take the eegy fom the mais voltage. The DC voltage is coveted agai ito a highfuecy AC voltage by a ClassD ivete. The the ivete supplies the highfuecy cuet to the iductio coil. S D S C / D C s C s R C / Fig. ClassD ivete system fo IH ja applicatio Fig. shows a ClassD ivete system fo a iductio heatig ja. The ClassD ivete cosists of two switches S, S with atipaallel diodes D, D usig IGBT, two esoat capacitos C / ad a iductio coil that cosists of a seies combiatio of esistace R ad iductace. Oe of the mai advatages of the halfbidge ivete is low voltage acoss the switch that is ual to the supply voltage. Thus, compaed with othe topologies (ClassE, uasiesoat ivete etc.) fo iductio heatig applicatios, it is suited fo highvoltage applicatios []. The utility DC iput voltage of 3V is diectly supplied ito a ivete ad S, D ad S, D ae alteately used to admiiste high fuecy cuet to the iductio coil. Copyight (C) 6 NuiMedia Co., td.

3 74 Joual of Powe Electoics, Vol. 5, No. 4, Octobe 5 I R S D C s C I / S D R C s I R C / C S D C s C / S D C s C / Z Mode (t t ) Mode (t t ) Fig. Equivalet cicuit S C s I R C / S D C s C / I R Fig. epesets the uivalet cicuit model of a ClassD ivete. I paticula, two switches ae opeated at squae wave with suitable dead time betwee the two divig commads. The ClassD ivete is opeated above the esoat fuecy, which meas that the switches ae tuedoff while cayig cuet. S D C s C / S D C s Mode 3 (t t ) Mode 4 (t t ) S D S D C s I R C s C / C / S D C s I R S C s C / C / C / S S Dead Time π π s t s t Mode 5 (t t 3 ) Mode 6 (t 3 t 4 ) Fig. 4 Opeatio modes of the ClassD ivete c V S t t t t t t 3 t 4 I C s, C s D S C s, C s D S Mode Mode Mode 3 Mode 4 s t Fig. 3 Theoetical wavefoms of the ClassD ivete Fig. 3 descibed the opeatio mode icludig switchig sigals ad ivete output voltage V s ad cuet I wavefoms. As show i Fig. 3, if the switches ae opeated above esoat fuecy, the seies esoat cicuit epesets a iductive load ad the load cuet I lags behid the output voltage V s, Theefoe, load cuet I flows i the ode of C s,c s D S C s,c s D S. At this time, the switchig losses do ot occu at tuo because the switches ae tued o at zeo voltage. The ClassD ivete with the PWM cotol scheme is explaied i detail whe it is applied to the IHja. Fig. 3 ad Fig. 4 illustates the steadystate theoetical wavefoms ad opeatio modes of the ClassD ivete. The steadystate aalysis of the ClassD ivete is based o the followig assumptios. All compoets ae ideal. Iput voltage of the DC lik is costat i oe switchig cycle. Effects of the paasitic capacitaces of the switch ae eglected. oad cuet is ealy siusoidal because the lage load quality facto () is high eough.. Cicuit Opeatio ad Aalysis of Mode,, 3 At tt, C s ad C s begi to esoate with eegy i the iducto. The load cuet i is tasfeed fom S to capacito C s ad C s. At tt, the load cuet, i flows though D R, thus switch S is tued o ude the ZVS coditio at t. These modes ae cotiuous i cicuit opeatio ad povide the same cicuit coectio with its actual diectio of cuet flow show i Mode, Mode ad Mode 3 of Fig. 4. At this poit, accodig to the Thevei shotope cicuit method, the Thevei impedace Z TH /(πfc) ad Thevei voltage V TH / ca be obtaied. Next, the eegy is deliveed fom iput to load side though switch S voltage ad the cuet uatios of the uivalet cicuit ae epeseted by Eq. ad Eq. at tuo. Copyight (C) 6 NuiMedia Co., td.

4 A New Cotol Scheme fo a ClassD Ivete with 75 di ± Vd / Ri idt dt C () i Whee β e ( R R t / 4 I cos Vd V R βt ± I si β β β β () t ) (/ C ) V, I : Iitial Voltage acoss C ad cuet though i the RC uivalet cicuit : fo Modes, ; ad : fo Mode 3, 4.3 Cicuit Opeatio ad Aalysis of Mode 4, 5, 6 The aalysis pocedues i these two modes ae the same as i the pevious oes. The two modes of cicuit opeatio ae also cotiuous ad povide the cicuit coectio as show i Mode 4, Mode 5 ad Mode 6 of Fig. 4. The Thevei impedace Z /( fc TH π ) ad V / Thevei voltage TH ae also obtaied. Paametes fo aalysis iclude the followig. a) The esoat fuecy C The omalized switchig fuecy s (3) (4) Degee s Pout Z P o Vd R (a) Chaacteistic impedace..5 s.5 (b) Output powe P out..5.5 Fig. 5 Theedimesioal epesetatio of the, P out as fuctio of ad / Z R j s C R j s (7) Fig. 5(a). illustates (5) i a theedimesioal space as a fuctio of (4), (6) The chaacteistic impedace z R (8) Z C C The quality facto (5) The cuet phase agle is Φ o ta (9) R R C Z R The iput impedace of the esoat tak cicuit i Fig. (6) The iput voltage of esoat tak cicuit V s is V d fo Vs fo < t π π < t π s s () Copyight (C) 6 NuiMedia Co., td.

5 76 Joual of Powe Electoics, Vol. 5, No. 4, Octobe 5 The fudametal wave of the alteatig compoet of Vs ca be foud by Fouie aalysis: Vs Vm sist, Whee fo < s t π () The desied output powe ca be egulated by vaiatios of the powe cotol duty atio, D powe. Fig. 6 shows the output powe is i popotio to the switchig duty cycle i low fuecy..6 V V Vd π () d m. 637 The load cuet though the esoat tak cicuit is deived by Output powe : Pout (kw) i Whee I si( t Φ) m s (3) Powe cotol Ivete duty cycle Switchig of low fuecy:d duty cycle powe Fig. 6 Output powe vesus powe cotol duty cycle I m Vm Vd Vd cosφ Z π Z π R π R V d (4) Fig. 5 (b). illustates (5) i a theedimesioal space as a fuctio of (4), (6) The covetioal output powe is give by usig Eq (4). P If out R Vd cos φ I m π R π R ated s ated Vd (5) is the switchig fuecy at full load powe,, P out P ated at full load powe. We defie D powe as a atio of output powe ad it ca be obtai at the low fuecy duty atio D powe as a fuctio of P desied / P ated. Theefoe, the desied powe ca be obtaied by usig Eq (5). P desied D powe P ated R Vd cos φ I m Dpowe D π R powe (6) Fig. 7 shows the fuecy chaacteistics of the seies loaded esoat cicuit. The xaxis descibes the atio of the switchig fuecy to the esoat fuecy, ad the yaxis descibes the omalized powe. Switchig fuecy opeates above esoat fuecy to esue a zeovoltageswitchig coditio. Fig. 8 shows the output powe vesus the switchig fuecy with PFM cotol. Powe / s Fig. 7 The fuecy chaacteistics of the seies loaded esoat cicuit Output powe : Pout (kw) Ivete Switchig Fuecy : Fs(kHz) Fig. 8 Output powe vesus switchig fuecy Copyight (C) 6 NuiMedia Co., td.

6 A New Cotol Scheme fo a ClassD Ivete with 77 As show i Fig. 8, the switchig fuecy is adjusted to geeate the desied output powe. To obtai maximum powe, the switchig fuecy is vey close to the esoat fuecy, wheeas whe low output powe is desied fo the same load, the switchig fuecy is fathe fom the esoat fuecy. That is to say, the switchig fuecy eeded fo light loads is vey high. This iceases the magetic coe loss ad poses poblems i the desig of the cotol cicuit ad this cotol scheme uies a wide switchig fuecy to obtai wide powe cotol age. Theefoe the soft switchig aea is elatively aow ude the PFM stategy. 3. Poposed Cotol Stategy 3.. The Oveall Block Diagam The vaiable output powe is the mai value i the ClassD ivete fo iductio heatig ja. We poposed a ew simple powe cotol scheme by adjustig the vaiable duty cycle of the costat low fuecy that is combied with a fixed high powe fuecy. The oveall block diagam of the poposed scheme is show i Fig. 9. Iput Souce ClassD ivete Output Stage R is fo cotollig the powe duty cycle at low fuecy, D powe, ad the othe oe is fo sychoizatio ad sythesis of the fixed low ad high fuecy sigals. The load cuet, I is compaed with the desied powe, P desied to decide, D powe though the compaato. If D powe is deceased, the ms load cuet, I is also deceased. Theefoe, output powe ca be cotolled by adjustig the D powe. The D powe is sychoized ad sythesized with the fixed high fuecy. Accodig to the poposed powe cotol scheme, output powe is simply cotolled by adjustig the D powe. Sice the switches opeate at fixed fuecy, which is above esoat fuecy, switches of this ivete always esues zeovoltage switchig (ZVS) fom light to full load. Theefoe tu o losses, EMI ad oises i the switches ae low i the ivete with this poposed cotol scheme. 3. The Cotol Scheme of Sychoizig ad Sythesis To elimiate the cuet ad voltage spikes i ooff times of the low fuecy sigal, the powe cotol low fuecy ad costat high fuecy sigals must be simultaeously cossed zeo. The switches S ad S ae alteately opeated afte dead time settig. Fig. shows the cotol scheme of the sychoizatio ad sythesis logic block. Gate sigal Gate Dive ciduit Dsw Dpowe of low fuecy Delay Fixed High fuecy J CK K Dead time Settig Switchig Sigal S S Fixed high fuecy Sychoizatio & Sythesis Powe cotol duty cycle ogic Pdesied Dpowe Fig. 9 Poposed Cotol Block diagam of the ClassD Ivete The poposed cotol scheme cosists of two pats. Oe I Fig. Cotol Scheme of the Sychoizatio ad Sythesis ogic Block The high fuecy sigal is fixed to a specific value above the detemied esoat fuecy fo zeovoltageswitchig. D powe is modulated by the feedback load cuet. These sigals have to be sychoized at ooff time by the logic block. The flipflop is used fo sychoizatio betwee the fixed low ad high fuecy sigals. As show i Fig., the two sigals ae sychoized though the logic ad leads to the switchig sigal D sw, which keeps them sychoized. Copyight (C) 6 NuiMedia Co., td.

7 78 Joual of Powe Electoics, Vol. 5, No. 4, Octobe 5 Dpowe Fixed high Fuecy cotol fuecy, f p fo 5.4Hz to avoid acoustic oise. Fig (a) ad (b) show the sychoizatio betwee S ad S. To elimiate the switchig cuet spike, it must be sychoized betwee S ad S though a flipflop at ooff time. Sychoizatio Dpowe Dpowe S S S S Sythesis D sw S (a). O time of D powe (b) Off time of D powe S Fig. Wavefoms of the Sychoized ad Sythesized Sigals 4. Simulatio Ad Expeimetal Results To veify the validity of the ClassD ivete system with the poposed cotol scheme, a simulatio ad a expeimet wee pefomed ually ude the coditios of Table. I additio, Table shows that the switchig fuecy is geate tha the esoat fuecy, which meas ZVS is achieved. Fig. Sychoized Switchig Sigal S, S, (V/div., time: s) As show i Fig (a), (b), the powe cotol low fuecy, D powe ad costat high fuecy sigals simultaeously coss zeo at ooff time. Fig. 3(a) shows the simulated ad expeimet esults of the load cuet I at full load. Dpowe I Table Paametes of the ClassD ivete COMPONENTS PARAMETERS V s Iput voltage 3 V DC P ated Rated output powe.6kw f s Switchig fuecy 4.8kHz f p Powe cotol fuecy 5.4Hz f Resoat fuecy 34.6kHz Equivalet iducto 66 µ H R Equivalet esisto 6.4Ω C Resoat capacito 3 F S, S Switch IGBT F9N6UFD I (a) (A/div., time: 5ms) oad cuet I at % load As show i Fig 3(a), the load cuet I flows cotiuously due to % D powe. Fig. 3(b) shows the simulated ad expeimet esults of the load cuet I at % load. Dpowe I The simulatio ad expeimet esults of the ClassD ivete usig the poposed scheme ae pefomed i case the system is opeated at a vaiatio of load (%%). The costat switchig fuecy, f s is chose as 4.8kHz to geeate.6kw at full load ad we chose the powe I (b) (A/div., time:.s) oad cuet I at % load Copyight (C) 6 NuiMedia Co., td.

8 A New Cotol Scheme fo a ClassD Ivete with 79 As show i Fig. 3(b), accodig to % D powe, the aaveage load cuet is lowe due to the discotiuous flow of I, so this meas the aveage output powe is deceased. Thee ae o cuet spikes because switchig sigals betwee the high fuecy, 4.8kHz ad the powe cotol low fuecy, D powe, 5.4Hz ae sychoized at ooff time. Fig. 3(c) shows the simulated esult of the switch voltage ad cuet at a % load. Dpowe I (a) (A/div., time:.s) Output powe P out ad oad cuet I.(fom. to duty cycle) (Simulatio esult (ight) : A/div., time:.s D powe : khz) Pout I Is Vs Is Vs Fom this esult, it is show that the output powe of the poposed ivete is pecisely egulated i a whole load age by adjustig D powe. Also, all the expeimetal esults ae i accodace with the simulated esults. (c) (V/div., A/div., time:.5s) Switch voltage ad cuet at % load Dpowe Pout As show i Fig. 3(c), zeo voltage switchig (ZVS) of the switch is safely achieved at tuo i the case of a light load. I additio, we kow the ZVS opeatio of the ClassD ivete with the poposed cotol scheme is guaateed i a whole age of vaiable output powe. Fig. 3(d) ad (e) idicate wavefoms of the aveage output powe with the poposed cotol scheme i the case of % ad % loads. I (b) (A/div., time:.s) Output powe P out ad oad cuet I.(fom to. duty cycle) (Simulatio esult (ight) A/div., time:.s D powe : khz) I Fig. 4 Wavefoms at vaiatios of D powe. Covetioal PFM Poposed PWM Pout 9 8 (d) Output powe P out at % load (e) Output powe P out at % load Pout Efficiecy (%) Fig. 3 The simulated ad expeimet esult of Poposed ClassD ivete Fig. 4(a) idicates wavefoms of the aveage output powe ad load cuet, I by vaiatio of the duty cycle (fom % to % load) ad Fig. 4(b) idicates wavefoms of the aveage output powe ad load cuet, I by vaiatio of the duty cycle (fom % to % load) Output Powe(%) Fig. 5 Ivete efficiecy compaiso betwee the poposed PWM ad the covetioal PFM cotol scheme Fig. 5 is the ivete efficiecy cuve i load age. As show i Fig. 5, at full load, the efficiecy of the ClassD ivete is the same betwee the covetioal PFM ad Copyight (C) 6 NuiMedia Co., td.

9 8 Joual of Powe Electoics, Vol. 5, No. 4, Octobe 5 the poposed PWM cotol scheme. But efficiecy of the ClassD ivete with the poposed PWM cotol scheme is emakably highe tha covetioal PFM ClassD ivetes at light load because the ZVS is boke i cases of ClassD ivetes with a covetioal PFM cotol scheme. Theefoe, the ClassD ivete with the poposed PWM cotol scheme has a bette pefomace i total efficiecy tha those with the covetioal PFM cotol scheme. 5. Coclusio I this pape, we poposed a simple powe cotol scheme fo a ClassD ivete with CFVP (Costat Fuecy Vaiable Powe) fo a iductio heatig ja which supplies cuet to a iductio heatig coil ad explaied the piciples of the poposed cotol scheme i detail. The mai advatage of this cotol scheme is the fuecy does ot have to vay because the output powe simply ca be cotolled by D powe i a whole load age. Evidece that this powe cotol is stable is pove i simulated ad expeimet esults. It ca be cocluded that the poposed cotol scheme has the followig advatages: It is moe appopiate fo wide powe egulated ages tha covetioal cotol of the ClassD ivete. The ZVS opeatio is guaateed i a whole load age This cotol scheme has a simple cofiguatio. ow switchig losses, EMI ad stesses ae achieved It has bette pefomace i efficiecy i compaiso to ClassD ivetes with a covetioal PFM cotol scheme. Theefoe, the poposed cotol scheme ca be applied to othe ivete topologies uiig well egulated output powe. Refeeces [] K. Kazimieczuk, et al. "ClassD Voltageswitchig MOSFET powe Amplifie", Poc. Ist. Elect. Eg., Nov, 99. Vol. 38, No. 6, pp [] M. K. Kazimieczuk, et al. "ClassD Zeo VoltageSwitchig Ivete with oly Oe shut Capacito", Poc. Ist. Elect. Eg., Sep, 99. Vol. 39, No. 5, pp [3] D. W. Tebb, "A iductio heatig powe supply usig high voltage MOSFET", i PIC Poceedigs., 987, pp [4] DogYu ee, DogSeok Hyu, "A New Hybid Cotol Scheme Usig ActiveClamped ClassE Ivete with Iductio Heatig Ja fo High Powe Applicatios", Joual of Powe Electoics, 5989, Vol., No, pp.4, [5] Hey W. Koetze, Jacobus D. va Wyk ad Ja A. Feeia. "Desig of the HalfBidge Seies Resoat Covete fo Iductio Cookig", i Poceedigs of the995 Powe Electoics Specialist cofeece, 95CH3588, pp [6] M. K. Kazimieczuk, T. Nadakuma ad Shag Wag,. "Alysis of seiespaallel esoat covete", IEEE Tasactio of AES, Vol. 9, No, Ja 99, pp [7] Izaki, Y. Hiota, H. Yamashita, M. Kamli, H. Omoi ad M. Nakaoka,. "New Costat Fuecy vaiable poweed quasiesoat ivete topology usig soft switched type IGBTs fo iductioheated cookig appliace with active powe filte", i Poceedigs of the995 Euopea Powe Electoics cofeece, pp.934. [8] F.S Tsai, P.Mateu, F.C ee, "Costat Fuecyclamped Mode Resoat Covetes", i Poceedigs of PESC'87 Recod, Jue 987, pp [9] Hisayuki Sugimua, Hidekazu Muaoka, Taek Ahmed; Sawouth Chadhaket, Eiji Hiaki, Mutsuo Nakaoka, ad HyuWoo ee, "Dual Mode PhaseShifted ZVSPWM Seies oad Resoat HighFuecy Ivete fo Iductio Heatig Supe Heated Steame Joual of Powe Electoics", 5989, Vol.4, No.3, pp.385, 4 [] YougSup Kwo, ByougKuk ee, SagBog Yoo ad DogSeok Hyu, "HalfBidge Seies Resoat Ivete fo Iductio Cookig Applicatios with oadadaptive PFM Cotol Stategy", Poceedigs ICPE 98, 988 Iteatioal Cofeece o Powe Elctoics, pp.83, 998 [] Powe Electoics Vol.3, No.4, Oct 988, pp [] J.H. Cheg ad A. F. Witulski, "A Geealized DC Model ad ow Fuecy Dyamic Aalysis fo the ClassD covete at Fixed Fuecy", IEEE Powe Electoic Specialist Cofeece Recod, 997, pp.73. [3] A.K.S Bhat, "Fixed Fuecy PWM seiespaallel esoat covete", IEEE Tas. Idustial Applicatio, Vol. 8, No. 5, 99, pp:9. [4] K.D.T. Ngo, "Aalysis of a seies esoat covete pulsewidth modulated o cuet cotolled fo low Copyight (C) 6 NuiMedia Co., td.

10 A New Cotol Scheme fo a ClassD Ivete with 8 switchig loss", IEEE Tas. Powe Electoics, Vol. 3, 988, pp:5563. [5] Wu, T.F.; Yag, H.P.; Pa, C.M, "Aalysis ad desig of vaiable fuecy ad phaseshift cotolled seies esoat covete applied fo electic ac weldig machies", Poceedigs of the 995 IEEE IECON st Iteatioal Cofeece, Vol, 995, pp: Wosuk Choi was bo i Seoul, Koea i 977. He eceived a B.S. i electical egieeig fom Soogsil Uivesity, Seoul, Koea, i 3 ad a M.S. degee i electical egieeig fom Hayag Uivesity, Seoul, Koea, i 5. He is cuetly wokig at Faichild Semicoducto as a Applicatio Egiee. His eseach iteests ae i iductio heatig applicatio developmet, soft switched powe supply topologies, powe facto collectio cicuits ad its cotol cicuits. NamJu Pak was bo i Gyeogam, Koea, i 973. He eceived a M.S. degee i cotol ad istumetatio egieeig. fom Gyeogsag Natioal Uivesity, Jiju, Koea, i, whee he is cuetly wokig towads a Ph.D. degee i electical egieeig. of Hayag Uivesity, Seoul, Koea. His pimay aeas of eseach iteest iclude highfuecy esoat ivetes, high fuecy PWM DCDC covete topology ad its cotol cicuit, soft switchig techiques such as ZVS, ZCS, powe facto coectio cicuits ad electoic ballast. Dogseok Hyu(S 79M 83SM 9) eceived his B.E. ad M.E. degees i electical egieeig fom Hayag Uivesity, Seoul, Koea, i 973 ad 978, espectively, ad his Ph.D. degee i electical egieeig fom Seoul Natioal Uivesity, Seoul, Koea, i 986. Fom 976 to 979, he was with the Agecy of Defese Developmet, Koea, as a eseache. He was a eseach associate i the depatmet of Electical Egieeig, Uivesity of Toledo, Toledo, OH, duig , ad a visitig pofesso i Electical Egieeig at the Techical Uivesity of Muich, Gemay, duig Sice 979, he has bee with Hayag Uivesity, whee he is cuetly a pofesso i the Depatmet of Electical Egieeig ad Diecto of the Advaced Istitute of Electical Egieeig ad Electoics (AIEE). He is the autho of moe the 9 publicatios coceig electic machie desig, highpowe egieeig, powe electoics, ad moto dives. His eseach iteests iclude powe electoics, digital sigal pocessig, tactio, ad thei cotol systems. D. Hyu is a fellow membe of IEEE Powe Electoics, IEEE Idustial Elctoics, IEEE Idustial Appicatios, ad IEEE Electo Device Societies, the Istitutio of Electical Egiees(U.K.), the Koea Istitutio of Electical Egiees, ad the Cicuit Cotol Society. DogYu ee was bo i Chobuk, Koea, i 968. He eceived his M.S. ad Ph.D. degees i electical egieeig fom Hayag Uivesity, Seoul, Koea, i 998, ad 3. He has also woked fo the Koea Istitute of Sciece Techology (KIST), Seoul, Koea, as a eseache. He is cuetly wokig at Samsug SDI as a Seio Reseache. His pimay aeas of eseach iteest icludes highfuecy PWM DCDC covete topologies ad its cotol cicuits, soft switchig techiques such as ZVS, ZCS, powe facto collectio cicuits ad electoic ballast. Copyight (C) 6 NuiMedia Co., td.