International Journal of Scientific & Engineering Research, Volume 7, Issue 8, August ISSN

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1 International Journal of cientific & Enineerin Research, Volume 7, Issue 8, Auust HIGHCONVERIONRATIO BIDIRECTIONAL DC DC CONVERTER WITH COUPLED INDUCTOR K.RINIVA AT.PROF WIT,WARANGAL M.TECH(PE),WIT WARANGAL Abstract In this paper, a hihconversionratio bidirectional dc dc converter with coupled inductor is proposed. In the boost mode, two capacitors are parallel chared and series dischared by the coupled inductor. Thus, hih stepup voltae ain can be achieved with an appropriate duty ratio. The voltae stress on the main switch is reduced by a passive clamp circuit. Therefore, the low resistance RD (ON) of the main switch can be adopted to reduce conduction loss. In the buck mode, two capacitors are series chared and parallel dischared by the coupled inductor. The bidirectional converter can have hih stepdown ain. Aside from that, all of the switches achieve zero voltaeswitchin turnon, and the switchin loss can be improved. Due to two active clamp circuits, the enery of the leakae inductor of the coupled inductor is recycled. The efficiency can be further improved. The operatin principle and the steadystate analyses of the voltae ain are discussed. Index Terms Bidirectional, coupled inductor, hih conversion ratio, switched capacitor. I. INTRODUCTION Renewable enery systems are more and more widely used in the world such as solar and wind enery. However, photovoltaic (PV) solar or wind power cannot provide sufficient power when the load is suddenly increased. Thus, the battery with bidirectional dc dc converter is needed [1] [3]. Conventionally, the batteries are series strins used to provide a hih voltae (HV). However, temperature differences or little mismatches cause chare imbalance, which miht shorten the life of batteries. Althouh the batteries operated in parallel strins alleviate the problems, the output voltae remains low by this connection way [4]. Therefore, a hihefficiency bidirectional dc dc converter with a hih convention ratio is a key component of battery applications [5] Isolated bidirectional dc dc converters such as half [6] [9] and fullbride types [1], [11] can provide hih stepup and stepdown voltae ains by adjustin the turn ratio of the transformer. The hih stepup ain and the hih stepdown voltae ain can be achieved. The number of switches is usually between four and eiht. Also, some isolated bidirectional converters are characterized by a currentfed rectifier on the low voltae (LV) side and a voltaefed rectifier on the HV side [12], [13]. II. OPERATING PRINCIPLE OF THE PROPOED CONVERTER Fi. 1 shows the circuit topoloy of the proposed converter. This converter consists of the dc input voltae V L, the power switch 1 5, the clamp capacitor C 1, two blockin capacitors C 2 and C 3, and the coupled inductors N p and N s. The equivalent model of the coupled inductor includes the manetizin inductor L m, the leakae inductor L k, and an ideal transformer. Fi.1. Circuit confiuration of the bidirectional converter. The switchedcapacitor technique has proposed that parallelchared and seriesdischared capacitors can achieve hih stepup ain. Also, serieschared and paralleldischared capacitors can achieve hih stepdown ain. The character of the coupled inductor is that the secondary side can have opposite polarity when the switch is on and off. In the booststate operation, this character is combined with the switchedcapacitor technique. Two capacitors 216

2 International Journal of cientific & Enineerin Research, Volume 7, Issue 8, Auust C 2 and C 3 are parallel chared when the switch is on and series dischared when the switch is off. In the buckstate operation, the coupled inductor is used as a transformer. Thus, two capacitors C 2 and Fi.2. Key waveforms of the bidirectional converter in the boost state at the CCM. C3 can be series chared by HV side and parallel dischared throuh the secondary side. In addition, the problem of the enery of the leakae inductor is also solved. In the booststate operation, 1 is the main switch, and capacitor C 1 recycles the enery. The voltae across switch 1 can be clamped. ince switch 1 has an LV level, the low conductin resistance R D(ON) of the switch is used to reduce the conduction loss. In the buckstate operation, the main switches are 2 and 5. Two capacitors C 2 and C 3 with Fi.3. Currentflow path of the operatin mode durin one switchin period in the boost state at the CCM. Modes (a) I, (b) II, (c) III, (d) IV, and (e) V. switches 3 and 4 are used as active clamp circuits, recyclin the enery of the leakae inductor on the secondary side of the coupled inductor. Capacitor C 1 with switch 2 is another active clamp circuit that recycled the enery of the leakae inductor on the primary side. Thus, four switches are ZV turned on. The switchin loss is improved; the efficiency can be increased. It is because that the hih stepup converter needs a lare input current, which results that the conduction loss is 216

3 International Journal of cientific & Enineerin Research, Volume 7, Issue 8, Auust larer than the switchin loss. Thus, reducin the switch voltae stress for alleviatin the conduction loss and the elimination of reverserecovery current is the key point to improve efficiency. imilarly, the main switch of the hih stepup and stepdown converters suffers HV stress and low conductin current. The switchin loss should be reduced to improve efficiency [4]. To simplify the circuit analysis, the followin conditions are assumed. 1) Capacitors C 2 and C 3 are lare enouh that V c2 and V c3 are considered to be constant in one switchin period. 2) The power MOFET and diodes are treated as ideal. 3) The couplin coefficient of the coupled inductor k is equal to L m /(L m + L k ), and the turn ratio of the coupled inductor n is equal to N s /N p. A. Booststate operation: Accordin to the current of the coupled inductor, there are two operation modes; the first is the continuous conduction mode (CCM), and the second is the discontinuous conduction mode (DCM). Fi. 2 shows the typical waveforms in the boost state at the CCM, and Fi. 3 shows the currentflow path of the proposed converter at the CCM. Fi. 4 shows the typical waveforms in the boost state at the DCM, and Fi. 5 shows the currentflow path of the proposed converter at the DCM. There are five operatin modes in one switchin period of the proposed converter in the CCM. witches 2, 3, 4, and 5 are synchronous rectifiers. The main switch is 1 for each modes. The operatin modes at the CCM are described below. 1) Mode I [t, t 1 ]: At t = t, 1 is turned on. 2, 3, and 4 are off, and 5 is on. The currentflow path is shown in Fi. 3(a). The voltae of the primary side is V L = v Lk + V p. Thus, the leakae inductor L k and the manetizin inductor L m are chared by the dc source V L. Due to the leakae inductor L k, the secondaryside current is linearly decreases. The reverserecovery problem of the diode is alleviated. When current i D5 becomes zero at t = t 1, this operatin mode is ended. Fi.4. Key waveforms of bidirectional converter in the boost state at the DCM. 2) Mode II [t 1, t 2 ]: 1 is still on. 2 and 5 are off, and 3 and 4 are turned on at t = t 1. The currentflow path is shown in Fi. 3(b). The dc source VL chares the manetizin inductor L m, as well as the charin capacitors C 2 and C 3 via the coupled inductor. Voltaes V c2 and V c3 are approximately equal to nv L. Two capacitors are chared in parallel. The output capacitor C H provides enery to load R. This operatin mode ends when switch 1 is turned off at t = t

4 International Journal of cientific & Enineerin Research, Volume 7, Issue 8, Auust ) Mode III [t 2, t 3 ]: At t = t 2, 1 is turned off, and diode 2 is turned on. Diodes 3 and 4 are still on, and 5 is still off. The currentflow path is shown in Fi. 3(c). The output capacitor CH still provides enery to load R. The eneries of the leakae inductor Lk and the manetizin inductor Lm chare the clamp capacitor C 1. Due to the Leakae inductor of the secondary side of the coupled inductor, currents i D3 and i D4 are linearly decreased. The reverserecovery problem of the diode is alleviated. As 3 and 4 are cut off at t = t 3, this operatin mode ends. 4) Mode IV [t 3, t 4 ]: 1 is still off, and diode D s2 is still on. At t = t 3, diodes 3 and 4 are turned off, and 5 is turned on. The currentflow path is shown in Fi. 3(d). The eneries of the leakae inductor L k and the manetizin inductor Lm are released to the clamp capacitor C 1. ome of the manetic enery is released by the secondary side of the coupled inductor. Voltae Vs of the secondary side is build. At t = t 4, the enery of the leakae inductor is totally recycled by capacitor C 1 ; 2 is cut off. This mode is ended. 5) Mode V [t 4, t 5 ]: 1 is still off and 2 is on, diodes 3 and 4 are still off, and 5 is still on. The currentflow path is shown in Fi. 3(e). The coupled inductor, dc sources VL, and capacitors C 2 and C 3 are connected in series to chare the output capacitor CH and load R. The HV ain is achieved. This operatin mode ends at t = t 5 when switch 2 is turned off and 1 is turned on at the beinnin of the next switchin period. There are three modes at the DCM operation. Fi. 4 shows the waveforms. Fi. 5 shows the currentflow path of the proposed converter for each mode. The operatin modes are described below. 1) Mode I [t, t 1 ]: Durin this time interval, 1 is turned on. The currentflow path is shown in Fi. 5(a). The part enery of the dc source VL chares the manetizin inductor L m. Thus, i Lm is linearly increased. V L also transfers enery to chare capacitors C 2 and C 3 via the coupled inductor. The output capacitor C H is dischared to load R. This mode ends when 1 is turned off at t = t 1. 2) Mode II [t 1, t 2 ]: Durin this time interval, 1 is turned off. The currentflow path is shown in Fi. 5(b). The manetizin inductor Lm is dischared to capacitor C 1. imilarly, C 2, C 3, V L, and Lm are dischared in the series connected to capacitor C H and load R. This mode ends when the enery of Lm is depleted at t = t 2. 3) Mode III [t 2, t 3 ]: Durin this time interval, 1 remains turned off. The currentflow path is shown in Fi. 5(c). ince the enery of L m is depleted, C H is dischared to load R. This mode ends when 1 is turned on at t = t 3. B. Bucktate Operation: In the buckstate operation, there are six operatin modes in one switchin period. witch 1 is the synchronous rectifier. The main switch is 5. witches 2, 3, and 4 are auxiliary switches for achievin ZV turnon. Fi. 6 shows the typical waveforms, and Fi. 7 shows the currentflow path for each mode. The operatin modes are described below. 1) Mode I [t, t 1 ]: At t = t, switch 2 is off. The current flow path is shown in Fi. 7(a). Due to the leakae inductor L k, the current of the secondary side of the coupled inductor flows throuh diode D s5. Capacitors C 1, C 2, and C 3 are also dischared to V H. Then, switch 5 is turned on, and ZV is achieved. Because of the HV V H, current i D1 and i D5 linearly decrease. Meanwhile, the output capacitor C L is chared by the manetizin enery. When current i D5 becomes zero at t = t 1, this operatin mode is ended. 2) Mode II [t 1, t 2 ]: 5 is on. The currentflow path is shown in Fi. 7(b). The output capacitor C L provides enery to load R. Capacitors C 1, C 2, and C 3, and the secondary side coil N s are chared in series by HV V H. Thus, the induced voltae V p on the primaryside coil N p makes current i D1 decrease and chare the manetizin inductor L m. The manetizin current i Lm is increased. At t = t 2, current i D1 is equal to zero. This mode is ended. 216

5 International Journal of cientific & Enineerin Research, Volume 7, Issue 8, Auust Fi5. Currentflow path of the operatin mode durin one switchin period in the boost state at the DCM. Modes (a) I, (b) II, and (c) III. 3) Mode III [t 2, t 3 ]: 5 is on. The currentflow path is shown in Fi. 7(c). At t = t 2, current i D1 is equal to zero. The leakae inductor L k is chared by the primaryside coil N p. The chare current flows throuh the anti parallel dioded s2 of switch 2. Then, 2 is turned on, and ZV is achieved. Capacitors C 1, C 2, and C 3, and the secondary side coil N s are still chared in series by HV V H, and the manetizin inductor L m is also chared. The output capacitor C L provides the enery to load R. At t = t 3, i D2 is equal to zero. This mode is ended. 4) Mode IV [t 3, t 4 ]: 2 and 5 are on. The currentflow path is shown in Fi. 7(d). At t = t 3, capacitor C 1 starts to chare the manetizin inductor L m. The output capacitor C L dischares to load R. Because two capacitors C 2 and C 3, and the coupled inductor are chared in series by the HV side V H, the hih stepdown voltae ain can be achieved. At t = t 4, switches 2 and 5 are turned off. This mode is ended. 5) Mode V [t 4, t 5 ]: At t = t 4, switches 2 and 5 are turned off. The currentflow path is shown in Fi. 7(e). The current of the leakae inductor flows throuh the anti parallel diodes D s1, D s3, and D s4 of switches 1, 3, and 4. Then, switches 3 and 4 are turned on, and ZV turn on is achieved. The enery of the manetizin inductor Lm dischares to capacitor CL and load R. At t = t 5, currents i D3 and i D4 are zero. This mode is ended. 6) Mode VI [t 5, t 6 ]: 3 and 4 are on. The currentflow path is shown in Fi. 7(f). At t = t 5, the enery of capacitors C 2 and C 3 dischares to the output capacitor C L and load R throuh the coupled inductor. The manetizin inductor L m also dischares to the output. This mode is ended at t = t 6 when 3 and 4 are off. Fi.6. Key waveforms of the bidirectional converter in the buck state operation. 216

6 i 2 International Journal of cientific & Enineerin Research, Volume 7, Issue 8, Auust Fi.7. Currentflow path of the operatin mode durin one switchin period in the buck state. Modes (a) I, (b) II, (c) III, (d) IV, (e) V, and (f) VI. III. IMULATION MODEL AND REULT To demonstrate the performance and the functions of the proposed converter, a prototype circuit is implemented in the laboratory. The specifications are: 1) DC voltae V L and V H : 24 and 4 V, respectively; 2) rated power: 2 W; 3) witchin frequency: 5 khz; 4) Boundary condition: 1 W; 5) MOFETs 1 and 2 : IRFP4568PBF; 3 4 : IXFK64N5P; 5 : IXFK64N6P; 6) Coupled inductor: ETD59, core pc4; N p : N s = 1: 5 L m = 6μH; L k =.16μH; 7) Capacitors C 1 : 47μF/1 V; C 2 /C 3 : 23.5μF. Vd1 Vd3 Discre te, Convert G_134 s = 5e8 s Id1 Id3 i_out NOT G_25 G_134 Vd2 Vd5 D Id2 Id5 Id1 G_134 G_25 Id2 Id5 G_25 For P=2W i + D + i R=(4*4)/2 D But keep approx. of R=(4*4)/215 Vd2 v + Vd5 v + i_out For P=4W R=(4*4)/4 G_134 Id3 Vd1 + i D + v + v <> Vd3 + + v Fi 8: imulation model for boost 216

7 5 4 3 International Journal of cientific & Enineerin Research, Volume 7, Issue 8, Auust Id2 Vd2 Id1 Vd Fi. 9. imulation results in the boost mode under full load Po = 2 W. 5 Id3 Vd3 Vd Id Fi. 1. imulation results in the boost mode under full load Po = 4 W P_out Fi.11. ZV in the boost mode under 2 W. 216

8 International Journal of cientific & Enineerin Research, Volume 7, Issue 8, Auust Discre te, s = 5e8 s Convert Vd2 Vd3 G_134 Id2 Id3 NOT G_25 G_134 Vd1 Vd5 D Id1 Id5 2 1 i_out For P=2W R=(24*24)/2 But keep approx. of R=(24*24)/22 + v Id1 G_134 Id2 Id5 G_25 + i D + i D Vd2 + v ivd5 v + G_134 Id3 Vd1 + i D + For P=4W R=(24*24)/44 + i_out D + v + v <> Vd3 Vd Fi 12: imulation model for buck Id Vd Id Fi.13. imulation results in the buck mode under full load P o = 2 W. 216

9 2 International Journal of cientific & Enineerin Research, Volume 7, Issue 8, Auust Id3 Vd Vd Id Fi.14. imulation results in the buck mode under full load Po = 4 W P_out Fi. 15. ZV in the buck mode under 2 W. V. CONCLUION This paper has proposed a novel, hihefficiency, and hih stepup/stepdown bidirectional dc dc converter. By usin the capacitor chared in parallel and dischared in series by the coupled inductor, hih conversion ratio and hih efficiency have been achieved. The steadystate analyses of the proposed converter have been discussed in detail. The voltae ain and the utility rate of the manetic core have been increased by usin a coupled inductor with a low turn ratio. The enery of the leakae inductor has been recycled with the clamp circuit. A prototype circuit has been built in the laboratory. imulation results show that the maximum efficiency is 97.33% at the boost mode and 96.23% at buck mode. This topoloy provides efficient conversion of various power sources. This technique can be also applied in different power conversion systems easily. 216

10 International Journal of cientific & Enineerin Research, Volume 7, Issue 8, Auust REFERENCE [1] R. Gules, J. D. P. Pacheco, H. L. Hey, and J. Imhoff, A maximum power point trackin system with parallel connection for PV standalone applications, IEEE Trans. Ind. Electron., vol. 55, no. 7, pp , Jul. 28. [2] R. J. Wai, R. Y. Duan, and K. H. Jhen, Hihefficiency bidirectional dc dc converter with hihvoltae ain, IET Power Electron., vol. 5, no. 2, pp , Feb [3] R. Y. Duan and J. D. Lee, Hihefficiency bidirectional dc dc converter with coupled inductor, IET Power Electron., vol. 5, no. 1, pp , Jan [4] R. J. Wai and R. Y. Duan, Hihefficiency bidirectional converter for power sources with reat voltae diversity, IEEE Trans. Power Electron., vol. 22, no. 5, pp , ep. 27. [5] M. Jan and V. G. Aelidis, A minimum powerprocessinstae fuelcell enery system based on a boostinverter with a bidirectional backup battery storae, IEEE Trans. Power Electron., vol. 26, no. 5, pp , May 211. [6] G. Ma, W. Qu, G. Yu, Y. Liu, N. Lian, and W. Li, A zerovoltaeswitchin bidirectional dc dc converter with state analysis and softswitchin oriented desin consideration, IEEE Trans. Ind. Electron., vol. 56, no. 6, pp , Jun. 29. [7] F. Z. Pen, H. Li, G. J. u, and J.. Lawler, A new ZV bidirectional dc dc converter for fuel cell and battery application, IEEE Trans. Power Electron., vol. 19, no. 1, pp , Jan. 24. [8] H. Li, F. Z. Pen, and J.. Lawler, A natural ZV mediumpower bidirectional dc dc converter with minimum number of devices, IEEE Trans. Ind. Appl., vol. 39, no. 2, pp , Mar./Apr. 23. [9] B. R. Lin, C. L. Huan, and Y. E. Lee, Asymmetrical pulsewidth modulation bidirectional dc dc converter, IET Power Electron., vol. 1, no. 3, pp , ep. 28. [1] K. Wu, C. W. de ilva, and W. G. Dunford, tability analysis of isolated bidirectional dual active full bride dc dc converter with triple phaseshift control, IEEE Trans. Power Electron., vol. 27, no. 4, pp , Apr [11] Z.Wan and H. Li, A soft switchin threephase currentfed bidirectional dc dc converter with hih efficiency over a wide input voltae rane, IEEE Trans. Ind. Electron., vol. 27, no. 2, pp , Feb [12] F. Zhan and Y. Yan, Novel forwardflyback hybrid bidirectional dc dc converter, IEEE Trans. Ind. Electron., vol. 56, no. 5, pp , May 29. [13]. Jalbrzykowski, A. Bodan, and T. Citko, A dual fullbride resonant classe bidirectional dc dc converter, IEEE Trans. Ind. Electron.,vol. 58, no. 9, pp , ep KARATLAPELLI RINIVA COMPLETED M.TECH UNDER THE KAKATIYA UNIVERITY WARANGAL WITH DITICTION. PREENT WORKING A A AT.PROF IN WIT,WARANGAL srinivaskaratlapelli@mail.com 2. M.TECH( PE) UNDER THE KAKATIYA UNIVERITY WARANGAL 216