Novel Zero-Current Switching Current-Fed Half-Bridge Isolated Dc/Dc Converter for Fuel Cell Based Applications

ABSTRACT:

This paper presents a novel zero-current switching (ZCS) current-fed half-bridge isolated dc/dc converter. It is a potential topology for front-end dc/dc power conversion for fuel cell inverters. This proposed converter is unique, not reported in literature and provides a simple solution to switch turn-off problem with ZCS without increase in components count. This will lead to reduced size, lower cost and higher efficiency. Analysis, design and simulation results of the proposed converter are reported in this paper. A comparison with existing active-clamped ZVS current-fed half-bridge converter has been illustrated.

KEYWORDS:

1.      Zero-current switching

2.      Dc/Dc converter

3.      Current-fed

4.      Fuel cells

5.      High efficiency

SOFTWARE: MATLAB/SIMULINK

 BLOCK DIAGRAM:

Fig. 1. Conventional hard-switched current-fed half-bridge dc/dc converter

Fig. 2 Active-clamped ZVS current-fed half-bridge dc/dc converter

Fig. 3. Proposed ZCS current-fed half-bridge dc/dc converter.

 EXPECTED SIMULATION RESULTS:

Fig. 4. Zero-current switching of primary-side switches. The ripple frequency of input current I_in is 200 kHz, which

is same twice the switching frequency f_s. The transformer

Fig. 5. Zero-current turn-on of primary-side switches. V(S1) is voltage across switch S₁ and I(S1) is current through switch S₁. The current waveform is scaled for clarity.

Fig. 6. Current-waveforms through the secondary-side switches.

Fig. 7. Zero-current turn-on of secondary-side switches. V(Sr1) is voltage across switch S_r1 and I(Sr1) is current through switch S_\r1. The current waveform is scaled for clarity.

Fig. 8. Current waveforms through input inductors L₁ and L₂.

Fig. 9. . Input current (I_in) and transformer current I(Ls) waveforms.

REFERENCES:

[1] www.fossil.gov.in

[2] S. K. Mazumder, R. K. Burra, and K. Acharya, “A ripple-mitigating and energy-efficient fuel cell power-conditioning system,” IEEE Transactions on Power Electronics, vol. 22, 2007, pp. 1437-1452.

[3] Jin-Tae Kim, Byoung-Kuk Lee, Tae-Won Lee, Su-Jin Jang, Soo-Seok Kim, and Chung-Yuen Won, “An active clamping current-fed half bridge converter for fuel-cell generation systems,” in Proceedings 2004 IEEE Power Electronics Specialists Conference, pp. 4709-4714.

[4] S. Han, H. Yoon, G. Moon, M. Youn, Y. Kim, and K. Lee, “A new active-clamping zero-voltage switching PWM current-fed half-bridge converter,” IEEE Transactions on Power Electronics, vol. 20, pp 1271- 1279, 2006.

[5] S. J. Jang, C. Y. Won, B. K. Lee and J. Hur, “Fuel cell generation system with a new active clamping current-fed half-bridge converter,” IEEE Trans. on Energy Conversion, vol. 22, pp. 332-340, June 2007.

Study and Implementation of a Current-Fed Full-Bridge Boost DC–DC Converter With Zero-Current Switching for High-Voltage Applications

ABSTRACT:

This paper presents a comprehensive study of a current-fed full-bridge boost dc–dc converter with zero-current switching (ZCS), based on the constant on-time control for high voltage applications. The current-fed full-bridge boost converter can achieve ZCS by utilizing the leakage inductance and parasitic capacitance as the resonant tank. In order to achieve ZCS under a wide load range and with various input voltages, the turn-on time of the boost converter is kept constant, and the output voltage is regulated via frequency modulation. The steady-state analysis and the ZCS operation conditions under various load and input voltage conditions are discussed. Finally, a laboratory prototype converter with a 22–27-V input voltage and 1-kV/1-kW output is implemented to verify the performance. The experimental results show that the converter can achieve high output voltage gains, and the highest efficiency of the converter is 92% at full-load condition with an input voltage of 27 V.

KEYWORDS:

1.      Current fed

2.       High voltage

3.       Zero-current switching (ZCS)

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Conventional full-bridge ZCS PWM converter circuit.

EXPECTED SIMULATION RESULTS:

Fig. 2. Experimental waveforms of VO at a full-load condition.

Fig. 3. Experimental waveforms of Vgs1, Vgs2, VAB, and iLk at (a) full-load

condition and (b) 20%-load condition.

Fig. 4. Switching waveforms of V_gs1, V_ds1, and i_S1 at (a) full-load condition

and (b) 20%-load condition.

                      

CONCLUSION:

This paper has presented a study of the current-fed full bridge boost converter with ZCS, based on the constant on-time control for high-voltage dc–dc applications. The turn-on time of the full-bridge boost converter is designed as a constant in order to achieve ZCS, and the output voltage is regulated by varying the switching frequency. The parasitic components of the high-voltage transformer can also be incorporated with the resonant tank for ZCS operation. The steady-state analysis and the ZCS operation conditions are also discussed in this paper. By carefully designing the circuit parameters, the converter can be operated with ZCS at various load and input-voltage conditions. Furthermore, the presented converter can achieve high efficiency and high output voltage gain.

REFERENCES:

[1] A. I. Pressman, Switching Power Supply Design, 2nd ed. New York: McGraw-Hill, 2008.

[2] E. T. Calkin and B. H. Hamilton, “A conceptually new approach for regulated DC to DC converters employing transistor switches and pulse width control,” IEEE Trans. Ind. Appl., vol. 12, no. 4, pp. 369–377, Jul. 1976.

[3] B. P. Israelsen, J. R. Martin, C. R. Reeve, and V. S. Scown, “A 2.5 Kv high-reliability TWT power supply: Design techniques for high efficiency and low ripple,” in Proc. IEEE PESC, 1977, pp. 212–222.

[4] R. Redl and N. O. Sokal, “Push–pull current-fed multiple-output DC/DC power converter with only one inductor and with 0 to 100% switch duty ratio,” in Proc. IEEE PESC, 1980, pp. 341–345.

[5] S. Ohtsu, T. Yamashita, K. Yamamoto, and T. Sugiura, “Stability in high-output-voltage push-pull current-fed converters,” IEEE Trans. Power Electron., vol. 8, no. 2, pp. 135–139, Apr. 1993.

Naturally Clamped Zero Current Commutated Soft-switching Current-fed Push-Pull DC/DC Converter: Analysis, Design, and Experimental Results

ABSTRACT:

The proposed converter has the following features: 1) zero current commutation (ZCC) and natural voltage clamping (NVC) eliminate the need for active-clamp circuits or passive snubbers required to absorb surge voltage in conventional current-fed topologies; 2) Switching losses are reduced significantly owing to zero-current switching (ZCS) of primary side devices and zero-voltage switching (ZVS) of secondary side devices. Turn-on switching transition loss of primary devices is also negligible. 3) Soft-switching and NVC are inherent and load independent. 4) The voltage across primary side device is independent of duty cycle with varying input voltage and output power and clamped at rather low reflected output voltage enabling the use of low voltage semiconductor devices. These merits make the converter good candidate for interfacing low voltage dc bus with high voltage dc bus for higher current applications. Steady state, analysis, design, simulation and experimental results are presented.

KEYWORDS:

1.      Current-fed converter

2.       DC/DC converter

3.      Natural clamping

4.       Soft-switching

5.       Zero-current commutation

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Diagram of a FCV propulsion system.

CIRCUIT DIAGRAM:

Fig.2. Proposed ZCS current-fed push-pull dc/dc converter.

  

  EXPECTED SIMULATION RESULTS:

Fig. 3. Operating waveforms of proposed ZCS current-fed push-pull converter

in the buck mode.

 Fig. 4. Simulation results for output power of 250W at 300V. (a) Current through input inductor i_L and voltage V_AB. (b) Primary switches currents i_S1 and i_S2 and secondary switches currents i_S3 and i_S4.

Fig. 5. Experimental results for output power of 250W at 300V(x-axis: 2μs/div): (a) Boost inductor current i_L (5A/div), (b) Voltage v_AB (100V/div) and voltage across secondary of transformer v_sec (500 V/div), (c-d) Gate-to-source voltage V_gs (10V/div) and drain-to-source voltage V_ds (50V/div) across the primary side MOSFETs and currents through them (10A/div). (e-f) Gate-to-source voltage V_gs (10V/div) and drain-to-source voltage V_ds (200V/div) across the secondary side MOSFETs and currents through them (2A/div).

Fig. 6. Experimental results for output power of 100W at 300V(x-axis: 2μs/div): (a) Boost inductor current iL (5A/div), (b) Voltage vAB (100V/div) and voltage across secondary of transformer vsec (500 V/div), (c-d) Gate-to-source voltage Vgs (10V/div) and drain-to-source voltage Vds (50V/div) across the primary side MOSFETs and currents through them (10A/div). (e-f) Gate-to-source voltage Vgs (10V/div) and drain-to-source voltage Vds (200V/div) across the secondary side MOSFETs and currents through them (2A/div).

CONCLUSION:

This paper presents a novel soft-switching snubberless bidirectional current-fed isolated push-pull dc/dc converter for application of the ESS in FCVs. A novel secondary side modulation method is proposed to eliminate the problem of voltage spike across the semiconductor devices at turn-off. The above claimed ZCC and NVC of primary devices without any snubber are demonstrated and confirmed by the simulation and experimental results. ZCS of primary side devices and ZVS of secondary side devices are achieved, which reduces the switching losses significantly. Soft-switching is inherent and is maintained independent of load. Once ZCC, NVC, and soft-switching are designed to be obtained at rated power, it is guaranteed to happen at reduced load unlike voltage-fed converters. Turn-on switching transition loss of primary devices is also shown to be negligible. Hence maintaining soft-switching of all devices substantially reduces the switching loss and allows higher switching frequency operation for the converter to achieve a more compact and higher power density system. Proposed secondary modulation achieves natural commutation of primary devices and clamps the voltage across them at low voltage (reflected output voltage) independent of duty cycle. It therefore eliminates requirement of active-clamp or passive snubber. Usage of low voltage devices results in low conduction losses in primary devices, which is significant due to higher currents on primary side. The proposed modulation method is simple and easy to implement. These merits make the converter promising for interfacing low voltage dc bus with high voltage dc bus for higher current applications such as FCVs, front-end dc/dc power conversion for renewable (fuel cells/PV) inverters, UPS, microgrid, V2G, and energy storage. The specifications are taken for FCV but the proposed modulation, design, and the demonstrated results are suitable for any general application of current-fed converter (high step-up). Similar merits and performance will be achieved.

REFERENCES:

[1] A. Khaligh and Z. Li, “Battery, ultracapacitor, fuel cell, and hybrid energy storage systems for electric, hybrid electric, fuel cell, and plug-in hybrid electric vehicles: State of the art”, IEEE Trans. on Vehicular Technology, vol. 59, no. 6, pp. 2806- 2814, Oct. 2009.

[2] A. Emadi, and S. S. Williamson, “Fuel cell vehicles: opportunities and challenges,” in Proc. IEEE PES, 2004, pp. 1640-1645.

[3] K. Rajashekhara, “Power conversion and control strategies for fuel cell vehicles,” in Proc. IEEE IECON, 2003, pp. 2865-2870.

[4] A. Emadi, S. S. Williamson, and A. Khaligh, “Power electronics intensive solutions for advanced electric, hybrid electric, and fuel cell vehicular power systems,” IEEE Trans. Power Electron., vol. 21, no. 3, pp. 567–577, May. 2006.

[5] A. Emadi, K. Rajashekara, S. S. Williamson, and S. M. Lukic, “Topological overview of hybrid electric and fuel cell vehicular power system architectures and configurations” IEEE Trans. on Vehicular

Technology, vol. 54, no. 3, pp. 763–770, May. 2005.

Extended Range ZVS Active-Clamped Current-Fed Full-Bridge Isolated DC/DC Converter for Fuel Cell Applications: Analysis, Design, and Experimental Results

ABSTRACT:

This paper presents analysis and design of zero voltage switching (ZVS) active-clamped current-fed full-bridge isolated dc/dc converter for fuel cell applications. The designed converter maintains ZVS of all switches from full load down to very light load condition over wide input voltage variation. Detailed operation, analysis, design, simulation, and experimental results for the proposed design are presented. The additional auxiliary active clamping circuit absorbs the turn-off voltage spike limiting the peak voltage across the devices allowing the selection and use of low-voltage devices with low on-state resistance. In addition, it also assists in achieving ZVS of semiconductor devices. The converter utilizes the energy stored in the transformer leakage inductance aided by its magnetizing inductance to maintain ZVS. ZVS range depends upon the design, in particular the ratio of leakage and magnetizing inductances of the transformer. Rectifier diodes operate with zero-current switching. An experimental converter prototype rated at 500 W has been designed, built, and tested in the laboratory to verify the analysis, design, and performance for wide variations in input voltage and load.

KEYWORDS:

1.      Fuel cells

2.      High-frequency (HF) dc/dc converter

3.      Renewable energy systems

4.      Zero voltage switching (ZVS)

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Active-clamped ZVS current-fed full-bridge dc-dc converter.

EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation waveforms at V_in = 22 V and full load: (a) voltage v_AB, leakage inductance current i_lk, and magnetizing inductance current i_Lm (b) main switches’ currents i_S1 and i_S2, auxiliary switch’s current i_Sax and voltage across auxiliary capacitor V_Ca.

Fig. 3. Simulation waveforms at V_in = 41 V and 10% load: (a) voltage v_AB, leakage inductance current i_lk, and magnetizing inductance current i_Lm (b) main switches’ currents i_S1 and i_S2, auxiliary switch’s current i_Sax and voltage across auxiliary capacitor V_Ca.

Fig. 4. Experimental waveforms at V_in = 22 V and full load: (a) Voltage v_AB (100 V/div) and leakage inductance current i_lk (50 A/div), (b) main switch voltage v_DS (50 V/div) and gate voltage v_GS (10 V/div), (c) auxiliary switch voltage v_DS (50 V/div) and gate voltage v_GS (20 V/div), (d) main switch current i_S1 (20 A/div), (e) auxiliary switch current i_Sax (20 A/div) and (f) magnetizing inductance current i_Lm (0.5 A/div).

Fig. 5. Experimental waveforms at V_in = 41 V and full load: (a) Voltage v_AB (50 V/div) and leakage inductance current i_lk (50 A/div), (b) main switch voltage v_DS (50 V/div) and gate voltage v_GS (10 V/div), (c) auxiliary switch voltage v_DS (50 V/div) and gate voltage v_GS (20 V/div), (d) main switch current i_S1 (20 A/div), (e) auxiliary switch current i_Sax (10 A/div) and (f) magnetizing inductance current i_Lm (1 A/div).

Fig. 6. Experimental waveforms at V_in = 22 V and 20% load: (a) Voltage v_AB (50 V/div) and leakage inductance current i_lk (10 A/div), (b) main switch voltage v_DS (50 V/div), gate voltage v_GS (20 V/div) and current i_S1 (10 A/div), (c) auxiliary switch voltage v_DS (50 V/div) and gate voltage V_gs (10 V/div), (d) auxiliary switch current i_Sax (5 A/div) and (e) magnetizing inductance current i_Lm (0.5 A/div).

Fig. 7. Experimental waveforms at V_in = 41 V and 10% load. (a) Voltage v_AB (50 V/div) and leakage inductance current i_lk (10 A/div), (b) main  switch voltage v_DS (50 V/div) and gate voltage v_GS (10 V/div), (c) auxiliary  switch voltage v_DS (50 V/div) and gate voltage v_GS (10 V/div), (d) main switch current i_S1 (10 A/div), (e) auxiliary switch current i_Sax (5 A/div) and (f) magnetizing inductance current i_Lm (1 A/div).

CONCLUSION:

 To achieve ZVS for wide source voltage variation and varying output power/load while maintaining high efficiency has been a challenge, particularly for low-voltage higher current input applications. A ZVS active-clamped current-fed full bridge isolated converter has been restudied in this paper. The magnetizing inductance increases the leakage inductance current value at light load and therefore the energy stored in leakage inductance to maintain ZVS of main switches as well as auxiliary switch.

Detailed steady-state operation and analysis of current-fed full-bridge converter have been presented. Design to attain soft switching over an extended range of input voltage and load i.e., output power has been presented. Simulation results using PSIM 9.0.4 have been presented. An  experimental prototype of. the converter rated at 500Whas been designed, built, and tested for variations in input voltage and load in order to validate the analysis. Experimental results verify the accuracy of the analysis and show that the proposed configuration is able to maintain ZVS of all switches over a wide range of load and input voltage variation due to the variation in fuel flow and stack temperature. Theoretically, the converter is able to maintain ZVS till 20% load at 22 V and 5% load 41 V.

In a practical fuel cell application, when the load current drops due to reduced fuel flow, the light or reduced power below rated power is transferred at higher fuel cell voltage. It can be clearly seen and understood also from the fuel cell V –I characteristic. If the load current or power is around 10% of the rated power, then the fuel cell stack voltage increases nearly to 41 V. Hence, the possibility of the condition Vin = 22 V at 10% load is only during transition period when load is suddenly changed from full load to 10% due to fuel flow adjustment. Hence, it is justifiable to have ZVS range of 20% load at low input voltage and below 10% at higher input voltage will cover the operating range at steady state. Rated converter efficiency of 94% is obtained for the developed lab prototype rated at 500 W. The converter has limitation that duty cycle of the main switch should be greater than 50%.

REFERENCES:

[1] S. Jain and V. Agarwal, “An integrated hybrid power supply for distributed generation applications fed by nonconventional energy sources,” IEEE Trans. Energy Convers., vol. 23, no. 2, pp. 622–631, Jun. 2008.

[2] Y. Lembeye, V. D. Bang, G. Lefevre, and J. P. Ferrieux, “Novel half-bridge inductive dc-dc isolated converters for fuel cell applications,” IEEE Trans. Energy Convers., vol. 24, no. 1, pp. 203–210, Mar. 2009.

[3] J. Mazumdar, I. Batarseh, N. Kutkut, and O. Demirci, “High frequency low cost dc-ac inverter design with fuel cell source home applications,” in Conf. Rec. IEEE IAS Annu. Meeting, Oct. 2002, vol. 2, pp. 789–794.

[4] J. Wang, F. Z. Peng, J. Anderson, A. Joseph, and R. Buffenbarger, “Low cost fuel cell converter system for residential power generation,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1315–1322, Sep. 2004.

[5] R. Gopinath, S. Kim, J.-H. Hahn, P. N. Enjeti, M. B. Yeary, and J. W. Howze, “Development of a low cost fuel cell inverter system with DSP control,” IEEE Trans. Power Electron., vol. 19, no. 5, pp. 1256–1262, Sep. 2004.