A New Buck-Boost D/D onvete of High Efficiency by Soft Switching Technique Dong-Kul Kwak, Seung-Ho Lee, and Do-Young Jung Pofessional Gaduate School of Disaste Pevention, Kangwon National Univesity, 45-711, Koea Abstact-In this pape, we study on a new buck-boost dc/dc convete of high efficiency by soft switching technique. The switching devices in the poposed convete ae opeated by soft switching with a new patial esonant cicuit. The patial esonant cicuit is designed to eplacement of an enegy stoage inducto and a snubbe cicuit used in a conventional buck-boost convete, and then the configuation of the poposed convete is simplified. The switching contol technique of the convete is also simplified fo the switches to dive in a constant switching fequency. The esults ae that the switching powe loss is vey low and system efficiency is high. In addition, the output voltage of the convete is egulated by PWM contol technique, and the discontinuous cuent flowing into the esonant inducto of the convete makes to simplify contol method and contol components. In compaison with the conventional buck-boost dc/dc convete, some simulation esults on compute and expeimental esults ae confimed the validity of analytical esults of the poposed convete. I. INTRODUTION Equipment and machiney which supply dc electicity enegy equies the boost dc-dc convete of high efficiency by active switching modes to make the most use of the povided enegy. The powe convete must be inceased the switching fequency in ode to achieve small size, light weight, and low noise [1]-[3]. Howeve, the switches in the convete ae subjected to high switching powe losses and switching stesses. As a esult, the powe system bings on low efficiency. Recently, to impove the efficiency, a lage numbe of soft switching topologies including esonant cicuits have been poposed [4]-[7]. But these convetes incease the numbe of switches in powe convesion cicuit and complicate the sequence of switching opeation. This pape descibes a new buck-boost dc/dc convete with high efficiency. The switching devices in the poposed convete ae opeated by a soft switching technique with a new patial esonant cicuit. The patial esonant cicuit makes use of a step-up inducto and a loss-less snubbe capacito egeneating accumulated enegy into the input powe souce. The patial esonant opeation makes zeo cuent switching (ZS) and zeo voltage switching (ZS) fo the contol switches without switching powe losses so called soft switching [8], [9]. The esonant opeation of the patial esonant cicuit is patially enfoced at only switching tun-on time o tun-off time. It educes the losses and stesses of the esonant devices. The switching contol technique of the poposed buck-boost dc/dc convete is simplified fo the switches to dive in constant switching fequency [4], [10]. The output voltage of the convete is also egulated by the PWM contol of switches. As a esult, the poposed convete is opeated with high efficiency by the soft switching and the patial esonant opeation.. IRUIT ONFIGURATION Fig. 1 shows a conventional buck-boost dc/dc convete that is geneally used. Thee ae two contol modes fo this convete. One is the continuous conduction mode (M) of dc cuent and anothe is the discontinuous conduction mode (DM) of dc cuent[10]. The output voltage of the convete is also egulated ted by the PWM contol of the switch S. Specially, the tun-on of the switching device in the discontinuous mode is a ZS. On the othe hand, the device must be switched off at a maximum inducto cuent. Theefoe, in ode to elieve tun-off stess of the device, a snubbe cicuit is connected in paallel with the switch of the conventional convete. Howeve, the efficiency of the conventional convete is vey low due to the powe loss of the snubbe cicuit. To impove the efficiency, a new buck-boost dc/dc convete with high efficiency is poposed in this pape and is shown in Fig.. The poposed buck-boost dc/dc convete is composed of contolling devices, a step up-down inducto L, and a snubbe capacito used in simila way fo the conventional convete. It is consideed that the snubbe cicuit in the conventional convete is patly eplaced to a patial esonant cicuit in the poposed convete. The patial esonant cicuit consists of a seies connected switch-diode pai with a esonant capacito, which is opeated to a loss-less snubbe capacito. Fig. 1. onventional buck-boost dc/dc convete. 195
(a) (b) Fig.. Poposed buck-boost dc/dc convete. The switching devices in the poposed convete ae opeated with the soft switching by patial esonance and with constant switching fequency. When the switching devices, S 1 and S, ae tuned off, the inducto L cuent chages the capacito by the patial esonant opeation. Theefoe, the tun-off of the S 1 and S is ZS. Since the cuent pulses in DM convete always begin at zeo, the tun-on of the S 1 and S is ZS. Futhemoe, at the tun-on of the S 1 and S, it is fo an accumulated enegy in the snubbe capacito to egeneate into the input powe souce by patial esonant opeation without the powe loss of snubbe cicuit, which is geneally poduced in the conventional buckboost dc/dc convete. As a esult, the poposed convete using a patial esonant cicuit achieves the soft switching (the ZS at tun-on and the ZS at tun-off). The powe losses of the switching devices ae dastically deceased, and then the poposed convete is opeated with high efficiency.. OPERATION PRINIPLE OF PROPOSED ONERTER Fig. 3 shows fou equivalent cicuits of each opeational mode in one cycle switching of the poposed convete. At initial condition, the cuent flowing though inducto L is zeo, Main switches S 1 and S ae off-state, and the capacito is chaged to sum of the input voltage d and the output dc voltage cd. 1) Mode 1 ( T 1 : t 0 t< t 1 ) : Mode 1 begins by tuning on both S 1 and S at the same time. The input voltage d and the capacito voltage v c ae added and applied to the inducto L. Then this mode takes the fom of a seies L esonance cicuit. The capacito dischages its electic chage though the inducto L. The tun-on of the switching devices occus at zeo cuent state. Hence this is ZS. The capacito voltage v c is expessed in (1) and the inducto cuent i inceases accoding to (). v = ( + )cosω t (1) i c d cd d d + cd = sinωt () X whee ω = 1 L, X = L. This mode ends when v c = 0. The time duation T 1 of this mode can be obtained by the following. (c) Fig. 3. Equivalent cicuits of each opeational mode in one cycle switching: (a) mode 1, (b) mode, (c) mode 3, and (d) mode 4. d T1 = cos d + cd The inducto cuent I 1 at the end of this mode is 1 I1 = ( d + cd) d (4) X ) Mode ( T : t 1 t< t ) : Mode begins when the voltage acoss becomes zeo. Then the diodes D 1 and D stat conducting. The inducto cuent is divided into two paths of S 1 -D 1 and D -S. The inducto cuent linealy inceases as the following until the switches ae tuned off. d i t I1 (d) (3) = + (5) This mode ends when both S 1 and S ae tuned off simultaneously. Then the time duation T of this mode is expessed as T = T T (6) on 1 whee T on is the tun-on peiod of the switches S 1 and S, and the inducto cuent I at the end of this mode can be obtained by the following. d d I = I1 + Ton cos L + d cd 3) Mode 3 ( T 3 : t t< t 3 ) : Mode 3 begins by tuning off both S 1 and S at the same time. The cuent flowing though L takes a oute of D - -D 1 and chages. Then this mode takes the fom of a seies L esonance cicuit. The tun-off of S 1 and S occus at ZS because the voltage of is zeo. In this mode, the voltage of and the cuent of L ae expessed as follows. (7) 196
whee vc = d + Ia sin ( ωt+ θ) (8) i = I cos( ω t+ θ) (9) a = +, θ = sin ( d ). L + I d Ia d I When the capacito voltage v c becomes equal to d + cd and the diode D 3 stats conducting, this mode ends. The time duation T 3 of this mode is expessed as (10) and the inducto cuent I 3 at the end of this mode is given by (11). TABLE I IRUIT PARAMETERS Input voltage, d 100 Output voltage, cd 00 Resonant inducto, L Resonant capacito, Snubbe esisto, R s Snubbe capacito, s 100H Smoothing capacito, d 000F 50nF Load esisto, R L 100 50 Switching fequency, f c 40kHz 0.47F Duty facto, D 40% T3 = L { sin ( cd ) θ} (10) L I + d I = I (11) 3 ( cd d ) 4) Mode 4 ( T 4 : t 3 t< t 4 ) : By the conducting of the diode D 3, the inducto cuent i flows though the load side. The cuent linealy deceases as the next equation. = + (1) cd i t I3 This mode ends when i = 0. The time duation T 4 of this mode is obtained by the following. L T = I (13) 4 3 cd At the tun-on of both S 1 and S simultaneously, anothe cycle stats.. OMPUTER SIMULATION AND EXPERIMENTAL RESULTS The poposed convete was analyzed by PSpice simulation pogam. The cicuit paametes fo the simulation ae listed in Table I. The output voltage cd of the simulation cicuit is egulated at about dc 00. The diodes ae ideal, and evey switch is eplaced by an equivalent cicuit consisting of a vaiable esistance and an ideal diode. Fig. 4 shows the wavefoms of each pat in one cycle switching fo the poposed convete, in ode to veify the patial esonant opeation and the soft switching opeation of the contol devices. In Fig. 4, the contolling switches, S 1 and S, of duty facto 40% ae simultaneously tuned on at t 0, and the capacito begins to dischage. The capacito voltage v c becomes zeo at t 1. At t, the contolling switches ae simultaneously tuned off and the capacito is chaged by the inducto cuent i. The voltage of becomes equal to d + cd at t 3. At t 4, the cuent i of the inducto eaches zeo and the switches ae kept off till the next cycle. Fig. 4. Simulation wavefoms in switching one cycle. The indicated T c is the peiod of one cycle of switching opeation. In addition, as the cuent flowing though switches is zeo at t 0, the switches ae tuned on at ZS. As the voltage acoss switches is also zeo at t, the switches ae tuned off at ZS. The simulated esults confim the validity of theoetical esults fo each mode peviously stated. In ode to confim the feasibility, the poposed convete was built in the maximum output powe of 1.0kW. The pincipal cicuit devices in the poposed convete wee designed on the basis of Table 1. Specifically, the output load was composed of a vaiable wiing esisto within the ange of 10 to 1000 of 1.0kW ating. The used powe switches wee implemented by Fuji IGBT seies 1MBH-60 ( E =600, I =40A, and T off =640ns ated fo 0kHz switching fequency opeation). Additionally, the powe diodes wee used to FRD (fast ecovey diode) type. The contol cicuit of the convete was built in a Micom. package of Intel s 80c196kc pocesso. 197
(a) Fig. 6. Powe losses of main devices in the poposed convete. (b) Fig. 5. Expeimental wavefoms of each pat fo switching contol signal [1]: (a) Inducto cuent i [] and capacito voltage v c [3], (b) Switch cuent i s [] and voltage v s [3]. The switching signal was contolled with a pogammed PWM data function table and a designed voltage-feedback cicuit boad though the A/D (analog/digital) conveting pot of the Micom. Fig. 5 shows the wavefoms of each pat in one cycle switching fo the poposed convete, in ode to veify the patial esonant and soft switching opeation of the contol devices. Expeimental values ae obtained fo the case of the load esisto R L = 100, duty facto D c = 40%. In Fig. 5, the switches used in the convete wee opeated with the soft switching, namely tun-on at zeo cuent and tun-off at zeo voltage, accoding to patial esonant opeation. Paticulaly, the esonant opeation of the patial esonant cicuit was patially enfoced at only switching tun-on time and tun-off time. It educes the losses and stesses of the esonant devices. The above expeimental esults agee well with theoetical studies and compute simulation esults peviously stated. The powe losses of the main devices in the poposed convete ae shown in Fig. 6, espectively. Fig. 7 shows the elation between a system efficiency and an output powe. The output powe was measued in the adjusted ange of the vaiable esisto with PWM switching contol fo a fixed output voltage of dc 00. Fig. 7. Relationship between efficiency and output powe. The snubbe cicuit in the conventional convete was also composed of a snubbe esisto of 50 and a snubbe capacito of 0.47F, which was geneally used in vaiable had switching convetes. The efficiency of the poposed buck-boost convete opeated to soft switching was inceased moe than that of the conventional had switching convete.. ONLUSION A new buck-boost dc-dc convete with high efficiency has been pesented in this pape. To achieve the soft switching of the contolling switches, the poposed convete applied a patial esonant cicuit using a step-up inducto and a loss-less snubbe capacito. That is, the patial esonant cicuit was designed to eplacement of an enegy stoage inducto and a snubbe cicuit which have been used in a conventional buck-boost convete, and then the configuation of the poposed convete was simplified. The accumulated enegy in the loss-less snubbe capacito was egeneated into the input powe souce by the patial esonant opeation. The patial esonant opeation also conduced to the eduction of the losses and stesses of the esonant devices. The switching contol technique and contol components of the poposed convete wee simplified fo the switches to dive in a constant switching fequency with PWM and DM. As a esult, the poposed buck-boost dc/dc convete was that the switching powe losses wee vey low and the 198
system efficiency was high in compaison with the conventional buck-boost dc/dc convete. REFERENES [1] O. Gacia, J. A. obos, et al., Single phase powe facto coection : A suvey, IEEE Tans. on PE, ol. 18, No. 3, pp. 749-755, May 003. [] E. R.. Silva, M.. avalcanti, and. B. Jacobina, ompaative study of pulsed dc-link voltage convetes, IEEE Tans. on PE, ol.18, No. 4, pp. 108-1033, July 003. [3] H.. Shin, and. H. Lee, Opeation mode based high level switching activity analysis fo powe estimation of digital cicuits, IEIE Tans. ommun., ol. E90-B, No. 7, pp. 186-1834, July 007. [4] IEEJ: Recent development on soft switching, IEEJ Technical Repot, No. 899, pp. 4-8, Sept. 00 (in Japanese). [5] W. Guo, and P. K. Jain, A low fequency ac to high fequency ac invete with build-in powe facto coection and soft-switching, IEEE Tans. on PE, ol. 19, No., pp. 430-44, Mach 004. [6] Y. Tsuuta, and A. Kawamua, A high efficiency and high powe choppe cicuit QRAS using soft switching unde test evaluation at 8KW, Jounal of Powe Electonics, ol. 6, No. 1, pp. 1-7, Jan. 006. [7] W. J. Lee, S. W. hoi,. E. kim, and G. W. Moon, A new PWM-contolled quasi-esonant convete fo a high efficiency PDP sustaining powe module, Jounal of Powe Electonics, ol. 7, No. 1, pp. 8-37, Jan. 007. [8] S. K. hung, and J. G. Lim, Design of bootstap powe supply fo halfbidge cicuits using snubbe enegy egeneation, Jounal of Powe Electonics, ol. 7, No. 4, pp. 94-300, Oct. 007. [9] T. Ahmed, S. Nagai, M. Nakaoka, and T. Tanaka, Utility-inteactive fouswitch thee-phase soft-switching invete with single esonant dc-link snubbe and boost choppe, Jounal of Powe Electonics, ol. 7, No., pp. 109-117, Apil 007. [10] D. Sadanac, W. Abida, and. Kaimi, The double discontinuous mode opeation of a convete : A method fo soft switching, IEEE Tans. on PE, ol. 19, No., pp. 453-460, Mach 004. 199