* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download 10 kV High Voltage Generator with LLC Resonant Circuit for
Stepper motor wikipedia , lookup
Spark-gap transmitter wikipedia , lookup
Mercury-arc valve wikipedia , lookup
Wireless power transfer wikipedia , lookup
Power engineering wikipedia , lookup
Transformer wikipedia , lookup
Pulse-width modulation wikipedia , lookup
Electrical ballast wikipedia , lookup
Three-phase electric power wikipedia , lookup
Power inverter wikipedia , lookup
History of electric power transmission wikipedia , lookup
Variable-frequency drive wikipedia , lookup
Electrical substation wikipedia , lookup
Amtrak's 25 Hz traction power system wikipedia , lookup
Current source wikipedia , lookup
Schmitt trigger wikipedia , lookup
Integrating ADC wikipedia , lookup
Resistive opto-isolator wikipedia , lookup
Stray voltage wikipedia , lookup
Transformer types wikipedia , lookup
Surge protector wikipedia , lookup
Distribution management system wikipedia , lookup
Voltage regulator wikipedia , lookup
Voltage optimisation wikipedia , lookup
Alternating current wikipedia , lookup
Mains electricity wikipedia , lookup
Opto-isolator wikipedia , lookup
Switched-mode power supply wikipedia , lookup
10 kV High Voltage Generator with LLC Resonant Circuit for Sterilizing Microbe Applications S.-Y. Tseng H.-C. Lin # Y.-D. Chang ## S.-T. Peng S.-Y. Fan GreenPower Evolution Applied Research Lab. #Department of Electrical Engineering ##Linear Motor Research Laboratory (G-PEARL) National Chung Cheng University Department of Electrical Engineering Department of Electrical Engineering Wufeng Institute of Technology Chang Gung University Ming-Hsiung, Chia-Yi, Taiwan Kwei-Shan, Tao-Yuan, Taiwan, R.O.C E-mail: [email protected] E-mail: [email protected] TEL: +886-5-2267125 Tel: 886-3-2118800 FAX: +886-3-2118026 Fax:886-3-2118026 Abstract-This paper proposes a high step-up voltage ratio of full-bridge converter associated with LLC resonant circuit for sterilizing microbe applications. The proposed circuit structure adopts full-bridge converter to generate a high DC voltage, while the LLC resonant circuit is used to recover the energy trapped in leakage inductance of transformer and to reach zero-voltage switching feature increasing conversion efficiency. Moreover, the LLC one can also avoid generating a large resonant current which occurs in between the large leakage inductance and the large equivalent capacitor of primary winding in transformer due to transformer with a high turns ratio. As compared with a conventional full-bridge converter with hard-switching circuit or phase-shift control method, the proposed converter can reduce voltage and current stresses of switches and increase conversion efficiency with soft-switching features. Finally, a prototype of high voltage generator under output voltage of 10 kV and maximum output power of 1 kW has been implemented to prove the feasibility of the proposed high voltage generator. I. INTRODUCTION Due to the advanced development of semiconductor technology, design and implementation of high output voltage generator become more facility. It will expand applications of pulsed electric field (PEF) technology, such as food sterilization, waste treatment, pollution control, and medical diagnosis and treatment [1]-[10]. In particular, when PEFs are used to sterilize microbes of liquid food, they only cause a little increase in temperature. As compared with conventional thermal processing, the PEF method can provide consumers with safe and nutritious food, and with fresh quality. It can replace or complement conventional thermal processing methods. For food sterilization using PEF processing, researchers have proposed various processing waveforms, which can be divided into two groups: wide pulse and narrow pulse. Since effectiveness of food sterilization using wide pulses is higher than that using narrow pulses, wide pulses are usually used in a great deal of liquid food sterilization. In recent years, it is widely used in fruit juice and milk sterilization. When a wide pulse with high enough electric intensity is applied to the suspension, as illustrated in Fig. 1, and creates a voltage higher then 1 V across the cell membrane, it will induce irreversible pore changes and kill microbes with a mechanism of rupturing cell membrane [9]-[10]. This process is called electroporation and is illustrated in Fig. 2, which was digested from [10]. Before PEFs are applied to cell, they will create permeable pores over the membrane and water molecules will 978-1-422-2812-0/09/$25.00 ©2009 IEEE flow into the cell through the pores. If PEFs are continuously across the cell membrane, they will cause water influx. When the repetitive rate and pulse width are large enough, the cell membrane will be ruptured and cytoplasm will flow outside the cell. Finally, the cell is destructed. Outer Membrane R S1 R S1 E field E field Cm Suspension Cell R C2 C S RS2 R C1 Cn Cn Rn C S RS2 R C1 Cm R S1 R S1 Intracelluar Membrane Nucleus Fig. 1. Equivalent model of a cell insidesuspension. Initial State EF Excitation Legend: Water Influx Electric Field Membrane Rupture Cell Destruction Water Cytoplasm Fig. 2. Illustration of electroporation processing of a cell. In PEF application with wide pulses, electric intensity varies from ten to tens of kV/cm, pulse width ranges from several to hundreds of μs and repetitive rate changes from 0.1 Hz to 100 Hz. To realize the above specifications, many PEF generators (PEFGs) adopt a high voltage generator (HVG) combined with switch sets with high voltage ratings (SSHVR) to generate pulse voltage waveforms, as shown in Fig. 3. Since HVG must generate an extremely high output voltage (≈10 kV), it needs a converter with a high step-up voltage ratio. Moreover, the one with high powering capability is also required to achieve effectiveness of liquid food sterilization. As mentioned above, a full-bridge converter associated with a transformer with high turns ratio is adopted, [11]-[13], as shown in Fig. 4(a). Due to transformer with high turns ratio, a 1641 large leakage inductance and a large equivalent capacitance, which is reflected from secondary winding to primary winding of transformer, will be induced in the primary winding. As a result, a large resonant current is generated when switches are within the turn-on transition interval. To solve this problem, a resonant circuit is introduced into the full-bride converter [14]-[18], as shown in Fig. 4(b). II. ANALYSIS OF THE PROPOSED HVG In order to analysis of LLC resonant circuit, a single full-bridge converter with one is shown in Fig. 4(c). Its equivalent circuit can be depicted in Fig. 5. where Rac is the equivalent load resistance of primary side in the transformer Tr and Vab is applied to the LLC one. According to equivalent circuit of LLC resonant circuit, the equivalent resistance Re(ac) can be determined as Re ( ac ) = Fig. 3. Block diagram of a wide pulse PEF generator for liquid food sterilization. Although full-bridge converter with the resonant circuit can avoid generating a large resonant current, it requires a output inductor to generate dc voltage output, as shown in Fig. 4(b). When the output inductor is placed on output side, it will suffer a high voltage stress, resulting in a higher cost for attaining high enough isolation and a larger volume. To resolve this problem, full-bridge converter with LLC resonant circuit is adopted. Moreover, the one can help switches to operate at zero-voltage switching (ZVS) and aid secondary rectifier diodes to communicate with zero-current switching (ZCS), as shown in Fig. 4(c). With this circuit structure, the proposed HVG which adopts LLC resonant circuit can avoid a large resonant current, reduce weight, size and volume, and increase conversion efficiency significantly. 8R L , (1) (nπ )2 where RL is load resistance and n is turns ratio of transformer Tr. To analyze the LLC resonant topology, the resonant frequency fr1 of Cr and Lr in series is derived by 1 . (2) f = r1 2π Lr C r Similarly, the resonant frequency fr2 of Cr and (Lr + Lm) in series is expressed as follows: 1 . (3) f = r2 (Lr + Lm )Cr 2π Additionally, according to the Fourier theorem, the square wave, which is applied to LLC resonant circuit, can be approximated by the fundamental component Vab, and its maximum value Vab(max) can be derived by Vab(max) = 4 π Vi , (4) where Vi is input voltage of full-bridge converter. Therefore, rms value of Vab can be determined as Vab ( rms ) = 2 2 π Vi . (5) According to analysis of LLC resonant circuit shown in Fig. 4(c), input to output transfer ratio M of full-bridge converter is derived by . (6) (sLm // Re(ac ) ) VDC M= (a) nVi sL + 1 + (sL // R ) r m e ( ac ) sCr From (6), it can be seen that when the proposed converter is operated at different loads, its transfer ratio M will be varied. In order to attain a constant transfer ratio M for generating constant voltage output, the proposed one must regulate switching frequency. Thus, transfer ratio M can be rewritten as , (7) M= (b) M1 M2 Cr Vi D3 Lr IDC CO Lm RL VDC 1:N M3 D5 M4 D6 n2 (c) Q= Fig. 4. Schematic diagram of full-bridge converter (a) with hard-switching circuit (b) with resonant circuit, and (c) with LLC resonant circuit for generating high output voltage. 978-1-422-2812-0/09/$25.00 ©2009 IEEE 1 1 2 2 Lr Lr C r ⎛ ω s ⎞ ⎡ π 2 ⎛ ω s ω r 1 ⎞ ⎤ ⎟ + ⎢ Q⎜ ⎜ ⎟ ⎥ − Lm ω s 2 ⎜⎝ ω r22 ⎟⎠ ⎢ 8 ⎜⎝ ω r1 ω s ⎟⎠ ⎥ ⎣ ⎦ where ωs (=2πfs) is the angular frequency of switching frequency fs, ωr1 (=2πfr1) is that of frequency fr1, ωr2 (=2πfr2) is that of frequency fr2 and Q is quality factor. In (7), quality factor Q can be expressed by D4 Tr VDC nVi 1642 Lr Cr . RL (8) When ratio α (=Lm / Lr) and frequency gain γ (=fs / fr1) are defined, transfer ratio M can be further rewritten as . (9) M= V DC nVi 1 ⎛1 1 ⎜⎜ + 1 − αγ 2 ⎝α 2 ⎞ ⎞ π 4 2⎛ 1 ⎟⎟ + Q ⎜⎜ − γ ⎟⎟ 64 ⎠ ⎝γ ⎠ 2 According to (7), the DC characteristic of the LLC resonant converter can be illustrated in Fig. 6. From Fig. 6, it can be observed that operational regions of LLC resonant circuit can be divided into three regions: region I, region II and region III. According to different operation region, the proposed converter has different operational features. In the following, features of each operational region are briefly described. output diodes can not be operated with ZCS, resulting in voltage spike across output diodes. B. Region II (fr2 < fs < fr1) When fr2 < fs < fr1, operational region of the proposed one is on between frequency fr1 and fr2. The converter can be operated at a higher gain and with ZVS feature. Additionally, the proposed one can operated in two different resonant periods. When switches are communicated, resonant inductor Lr and capacitor Cr will start to resonate. The resonant period enters the first resonant period. Within this time period, inductor Lm is clamped to output voltage and is linearly increased. When resonant current iLr is equal to current iLm, the second resonant will occur, which is the resonant between Cr and Lm in series with Lr. This resonant period will last till the primary switches have been turned on again. During the second resonant time period, the current of secondary side in transformer remains zero. As a result, secondary output diodes are operated with ZCS. C. Region III (fs < fr2) When fs < fr2, operational region of the proposed one is on the left hand side of fr2. The proposed converter is operated with ZCS. It is not suitable for power MOSFET applications. As mentioned above, the proposed converter is designed in region II to increase conversion efficiency. Fig. 5. Equivalent circuit of LLC resonant circuit. Fig. 6. Plots of characteristic of the LLC resonant converter. A. Region I (fs < fr1) When fs < fr1, operational region of LLC resonant converter is on the right hand side of frequency fr1, operational principle of the proposed converter is similar to traditional series resonant converter. Therefore, it can reach ZVS feature. In this operational region, resonant components Lr and Cr act as series resonant, while Lm is clamped by output voltage and does not participate in the resonant process. As a result, III. OPERATIONAL PRINCIPLE OF THE PROPOSED PVG In the liquid food sterilization system, the PEFG shown in Fig. 7 consists of two circuits: a high voltage generator (HVG) and a switch set with high voltage ratings (SSHVR). They can process power from input voltage Vac to treatment chamber (TC) for sterilizing microbes. The HVG adopts two full-bridge converters connected in parallel to generate a high dc-link voltage VDC, and its soft-switching features which include ZVS in switches and ZVS in output diodes are achieved with LLC resonant technology. The SSHVR is composed of four sets of high-voltage switch, in which each of the high-voltage switches is formed with 15 MOSFETs in series, to chop a DC voltage to pulse voltage. Fig. 4(c) shows schematic diagram of single full-bridge converter with LLC resonant circuit. According to operational principle of the proposed one, its operational modes can be divided into 6 modes over one switching cycle, as shown in Fig. 8, while its key waveforms are shown in Fig. 9. In the following, each operational mode is described briefly. Fig. 7. Schematic diagram of a complete PEF generator. 978-1-422-2812-0/09/$25.00 ©2009 IEEE 1643 (a) (b) Fig. 9. Key waveforms of full-bridge converter with LLC resonant circuit over one switching cycle. Mode 1 [Fig. 8(a); t0 ≤ t < t0]: Before t0, switches M1 and M3 are in the on state, while M2 and M4 are in the off state. Within this time interval, magnetizing inductor Lm, leakage inductor Lr and capacitor Cr form a resonant network and they are in the resonant state. In addition, output diodes D1 ~ D4 are in reversely bias, and the energy stored in output capacitor CO is supplied to load RL. When t = t0, switches M2 and M3 are turned off. Resonant inductor Lr, capacitor Cr and parasitic capacitors CM1 ~ CM4 connect in series and they will start to resonate. Within this time interval, since resonant current iLr is greater than iLm, current of secondary side of transformer is not equal to zero. Therefore, diodes D1 and D4 are forced to forwardly conduct. As a result, magnetizing inductor of secondary side is clamped to output voltage VDC. The current iLm of primary side linearly increases. Additionally, resonant current iLr increases with the resonant mode. Since resonant current iLr increases, voltages across body diodes CM1 and CM4 are released from Vi to 0. Those across CM2 and CM3 are charged from 0 to Vi. (c) DM1 M1 CM1 M2 IDS2 ID DM2 CM2 Cr ir D1 Lr D2 Tr im Lm Vi M3 IDS3 DM3 CM3 M4 1:N DM4 CM4 D3 IC IDC CO RL VDC D4 (d) Mode 2 [Fig. 8(b); t1 ≤ t < t2]: At t1, since energies stored in CM1 and CM4 are discharged to 0, body diodes DM1 and DM4 are in forwardly bias. At the moment, switches M1 and M4 are turned on. They are operated with ZVS at turn-on transition. Moreover, resonant inductor Lr and capacitor Cr form a resonant network and they will start to resonate. Therefore, resonant current iLr increases with the resonant manner. Within this time interval, diodes D1 and D4 still keep in the forwardly bias state. Thus, current iLm also increases with the linear manner. Additionally, energies are transferred from input voltage Vi to load through transformer and diodes D1 and D4. (e) (f) Fig. 8. Equivalent circuit of full-bridge converter with LLC resonant circuit operated in region II for each operational mode over one switching cycle. 978-1-422-2812-0/09/$25.00 ©2009 IEEE Mode 3 [Fig. 8(c); t2 ≤ t < t3]: When t = t2, resonant current iLr is equal to current iLm. At the moment, current of secondary side in transformer decreases to 0. As a result, diodes D1 and D4 are reversely biased. Resonant inductor Lr, magnetizing inductor Lm and capacitor Cr form a resonant network and they will begin to resonate. During this time interval, currents iLr and iLm decrease with the resonant manner. Additionally, energy stored in output capacitor CO supplies power to load. 1644 Mode 4 [Fig. 8(d); t3 ≤ t < t4]: When t = t3, switches M1 and M4 are turned off. Resonant inductor Lr, capacitor Cr and parasitic capacitors CM1 ~ CM4 form a resonant network and they will start to resonate. Since resonant current iLr is greater than iLm, current of secondary side is not equal to 0. As a result, diodes D2 and D3 are in forwardly bias and secondary winding is clamped to output voltage VDC. Therefore, current iLm linearly decreases. Moreover, resonant current iLr increases with the resonant mode. Since resonant current iLr increases, voltages across CM2 and CM3 are discharged from Vi to 0, while those across CM1 and CM4 are charged from 0 to Vi. Mode 5 [Fig. 8(e); t4 ≤ t < t5]: When t = t4, voltages across CM2 and CM3 are clamped to 0 and body diodes DM2 and DM3 are in forwardly bias. At the same time, switches M2 and M3 are turned on. Thus, switches M2 and M3 are operated with ZVS at turn-on transition. In addition, resonant inductor Lr and capacitor Cr form a resonant network and they will start to resonate. Therefore, resonant current iLr increases with the resonant manner. During this time interval, diodes D2 and D3 are still in forwardly bias. Thus, current iLm linearly increases. Moreover, energies are transferred from input voltage Vi to load through transformer and diodes D2 and D3. Mode 6 [Fig. 7(f); t5 ≤ t < t6]: At t5, resonant current iLr is equal to current iLm. As a result, current of secondary side decreases to 0 and diodes D2 and D3 are reversely biased. Therefore, D2 and D3 can reach ZCS feature. Within this time interval, resonant inductor Lr, magnetizing inductor Lm and capacitor Cr form a resonant network and they will keep in the resonant state. Therefore, currents iLr and iLm decrease with the resonant manner. Additionally, energy stored in output capacitor Co supplies power to load. When t = t6, switches M2 and M3 are turned off. Operational modes of one switching cycle are complete. IV. EXPERIMENTAL RESULTS To verify the analysis and feasibility, a prototype of the proposed HVG was implemented with the following specifications. ●input voltage: AC 110 V (with voltage double); ●switching frequency fS: 30 kHz ~ 50 kHz, ●output voltage VDC: 10 kV, ●output current IDC: 0.1 A, and ●output power PO: 1 kW. To consider high step-up ratios and isolation requirement, the proposed HVG adopts two sets of full-bridge converter and two sets of transformer to generate output voltage of 10 kV, as shown in Fig. 5.That is, each transformer will boost up a 5 kV dc-link voltage. Additionally, the components of the proposed HVG are determined as follows: ● switches M1 ~ M4: IRFP 460, ● turns ratio of transformer Tr1, Tr2: 10, ● magnetizing inductance Lm1 or Lm2: 3 mH, ● resonant inductance (include leakage inductance) Lr1 or Lr2: 1 mH, ● resonant capacitor Cr1 or Cr2: 15 nF, and ● diodeD1~ D4: UF 1010 (7 diodes connected in series). high equivalent capacitance appearing at the primary side of the transformers, and there is no ZVS feature. Figs. 11, 12 show the measured voltage VDS and current IDS of switches M1 and M2 when the proposed HVG is respectively operated at 10 % and 50 % of full load. From Figs. 11, 12, it can be observed that switches M1 and M2 can be operated with ZVS at turn-on transition. Measured voltage VD and current ID waveforms of output diode is illustrated in Fig. 13, from which it can be seen that output diode can reach ZCS feature. Fig. 14 shows efficiency measurements of the proposed HVG, from which it can be seen that the maximum efficiency can reach as high as 93 % at 90 % of full load, and around 91 % under full load. The output voltage VDC and current IDC is shown in Fig. 15, illustrating that output voltage ripple is very low within 1 %. As mentioned above, the proposed HVG is relatively feasible in high output voltage applications, which has been verified by the experimental results. (VDS : 100 V/div, IDS: 5A/div, 5 μs/div) Fig. 10. Measured voltage VDS and current IDS waveforms of switch in full-bridge converter with phase-shift control method. (VDS : 200 V/div, IDS: 1A/div, 5 μs/div) (a) (VDS : 200 V/div, IDS: 1A/div, 5 μs/div) (b) Fig. 11. Measured voltage VDS and current IDS waveforms of switches (a) M1 and (b) M2 in the proposed HVG under 10% of full load. The measured waveforms of voltage VDS and IDS of switch M1 show in Fig. 10 when full-bridge converter with the conventional phase-shift control method is adopted. From Fig. 10, it can be seen that high spike current occurs due to the 978-1-422-2812-0/09/$25.00 ©2009 IEEE 1645 V. CONCLUSIONS This paper has proposed a full-bridge converter with LLC resonant circuit to form a high voltage generator. The proposed HVG can use resonant technology and transformer with high turns ratio to reach a high step-up voltage ratio. By adopting the LLC resonant circuit, energy trapped in the leakage inductor can be recovered, ZVS features can be achieved and current spike can be suppressed effectively. In the paper, analysis of the generator has been presented in detail, from which design equations and circuit parameters are derived. Experimental results have verified that the proposed HVG can achieve high efficiency over a wide load range. It is relatively suitable for PEFG applications. VDS1 IDS1 (VDS : 200 V/div, IDS: 1A/div, 5 μs/div) (a) VDS2 [1] IDS2 [2] [3] (VDS : 200 V/div, IDS: 1A/div, 5 μs/div) (b) Fig. 12. Measured voltage VDS and current IDS waveforms of switches (a) M1 and (b) M2 in the proposed HVG under 50% of full load. [4] [5] [6] [7] [8] (VDS : 2 k V/div, IDS: 100 mA/div, 10 μs/div) Fig. 13. Measured voltage VD and current ID waveforms of output diode. [9] Efficiency(% ) 100 90 80 70 60 50 40 30 20 10 0 [10] [11] [12] 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% LLC resonant circuit Hand-switching circuit [13] Load (% ) Fig. 14. Comparison of converter efficiency between full-bridge converter with hard-switching circuit and with the proposed LLC resonant circuit. [14] [15] [16] [17] (Vo: 5 kV/div, Io: 100 mA/div, 5μs/div) Fig. 15. Measured output voltage VDC and output current IDC under full load condition. 978-1-422-2812-0/09/$25.00 ©2009 IEEE [18] 1646 REFERENCE X. Qiu, L. Tuhela and H. Zhang, “Application of Pulsed Power Technology in Nonthermal Food Processing and System Optimization,” Proceedings of Pulsed Power Conf., 1997, pp. 85-90. J. E. dunn and J. S. Pearlman, “Methods and Apparatus of Extending the Shelf Life of Fluid Food Products,” US patent 4,695,472, 1987. U.-R. Pothakamury, et al., “Effect of Growth Stage and Processing Temp. on the Inactivation of E. Coli by PEF,” Journal. Food Protect. Vol. 59, 1996, pp. 1167-1171. Jia, M., Zhang, Q. H. and Min, D. B., “Pulsed electric field processing effects on flavor compounds and microorganisms of orange juice,” Food Chemistry 65, 1999, pp. 445-451. Lado, B. H., et al., “Alternative food-preservation technologies efficacy and mechanisms,” Microbesand Infection 4, 2002, pp.433440. H. S. Karl, et al., “Bioelectrics-New Applications for Pulsed Power Technology,” IEEE Transactions on Plasma science, Vol.30, No.1, 2002. R. Redl, N. O. Sokal, L Balogh, “A Novel Soft switching Full Bridge DC/DC Converter: Analysis, Design considerations, and Experimental Result at 1,5 kW, 100 kHz,” IEEE PESC `90, 1990, pp.162-172. S. J. Beebe, et al., “Nanosecond pulsed electric field (nsPEF) application effects on human cells: intracellular membrane disruption and apoptosis induction,” IEEE Transactions on Pulsed Power Plasma Science, 2001, pp.251 T. S. Zheng and R. A. Flavell, “Apoptosis: All’s Well that Ends Dead,” Nature, Vol. 400, 1999, pp. 410-411. Daniel A. Crowl and Joseph F. Louvar, 1990; “Chemical Process Safety : Fundamentals with Applications,” ISBN 0-13-129701-5, Prentice-Hall Inc., Englewood Cliffs, New Jersey, USA. Ji, Z., Kennedy, S. M., Booske, J. H., Hagness, S. C., “Experimental Studies of Persistent Poration Dynamics of Cell Membranes Induced by Electric Pulses,” IEEE Trans. On Plasma Science, vol. 34, Issue 4, Aug. 2006, pp. 1416-1424. Zhang, R., Cheng, L., Wang, L., Guan, Z., “Inactivation Effects of PEF on Horseradish Peroxidase (HRP) and Pectinesterase (PE),” IEEE Trans. On Plasma Science, vol. 34, Issue 6, Aug. 2006, pp. 2630-2636. Min, S., Evrendilek, G. A., Zhang, H. Q., “Pulsed Electric Fields: Processing System, Microbial and Enzyme Inhibition, and Shelf Life Extension of Foods,” IEEE Trans. On Plasma Science, vol. 35, Issue 1, Feb. 2007, pp. 59-73. L. Zhu, “A Novel Soft-Commutating Isolated Boost Full-Bridge ZVS-PWM DC–DC Converter for Bidirectional High Power Applications,” IEEE Trans on Power Electronics,vol. 21, Issue 2, 2006, pp.422-429. Y. Zhongming, J.C.W. Lam, P.K. Jain and P.C. Sen, “A Robust One-Cycle Controlled Full-Bridge Series-Parallel Resonant Inverter for a High-Frequency AC (HFAC) Distribution System,” IEEE Trans. on Power Electronics, vol. 22, Issue 6, 2007, pp. 2331-2343. C. Cavallaro, et al. “A Phase-Shift Full Bridge Converter for the Energy Management of Electrolyzer Systems,” IEEE Trans. on International Symposium,2007, pp. 2649-2654. Y. Zhongming, P.K. Jain and P.C.Sen, “A Full-Bridge Resonant Inverter With Modified Phase-Shift Modulation for High-Frequency AC Power Distribution Systems,” IEEE Trans. on Industrial Electronics, vol. 54, Issue 5, 2007, pp. 2831-2845. W. Chen, X. Ruan, and R. Zhang “A Novel Zero-Voltage-Switching PWM Full Bridge Converter,” IEEE Trans. on Power Electronics, vol. 23, Issue 2, 2008, pp.793-801.