ABSTRACT:
A snubberless current-fed push-pull dc/dc voltage doubler
is proposed with zero voltage switching (ZVS) turn-on of low voltage
current-fed devices by using the parasitic resonance between the drain-source
capacitance of MOSFETs and the leakage inductance of the high frequency
transformer. \Secondary modulation helps reduce switching losses further by obtaining
zero current switching (ZCS) turn-off of primary devices and ZVS turn-on of
secondary devices. Realizing ZCS of current-fed devices introduces natural zero
current commutation and eliminates the traditional requirement of active-clamp
or passive snubbers in current-fed topologies. Push-pull topology has low
device and driver requirement. Voltage doubler offers 2x voltage gain reducing
the device count by half on secondary that simplifies the transformer and control
design and efficiently reduce the low frequency dc current harmonics. The
proposed topology with novel modulation is suitable for interfacing energy storage
and/or fuel cell stack with dc bus in FCVs or as frontend dc/dc converter in
fuel cell inverters or connecting fuel cells to dc grid. Steady-state operation
and analysis of proposed topology with proposed modulation has been studied.
Design of a 1kW prototype is explained. Simulation results using PSIM 9.3 and
experimental results of a 1 kW prototype have been demonstrated to verify the
operation, proposed mathematical analysis, design, and the proposed claims.
KEYWORDS:
1.
Current-fed
converter
2.
Push-pull
3.
Natural
commutation
4.
Soft-switching
SOFTWARE: MATLAB/SIMULINK
BLOCK DIAGRAM:
Fig.1.
Architecture of a dc microgrid
Fig.
2. Architecture of a fuel cell car.
EXPECTED SIMULATION RESULTS:
Fig.2.
Simulation results: (a) Gating signal of switch S1, current
through switch S1, voltage across switch S1,(b)
Gating signal of switch S2, current through switch S2,
voltage across switch S2, (c) Current through boost inductor L,
Current through series leakage inductance, Llk1,
Current through series leakage inductance, Llk2, (d)
Current through secondary devices S3 and S4,
(e) Voltage Vab, output voltage Vo,Voltage
across Llk1
Fig.
3. Experimental results: (a) Gating signal of switch S1, Vgs1,
current through switch S1, Is1,
drain-source voltage across switch S1, Vds1,
(b) Current through boost inductor L, current through series leakage
inductance, Llk1, (c) Current through secondary
device S3, Is3, Gating pulse of S3,
Vgs3, drain source voltage across switch S3,
Vds3, (d) Voltage across leakage inductor Vlk1,
voltage across transformer primary, Vab,
CONCLUSION:
A
truly snubberless current-fed push-pull dc/dc converter is proposed with zero
current commutation and natural device voltage clamping. Push-pull
configuration and voltage doubler circuit reduces the active device and driver
count. It leads to a simple control design and implementation. Voltage doubler
improves the gain by 2x and reduce transformer size. Traditionally, current-fed
converters are hard-switching with device voltage spike at turn-off and require
snubber circuits. In this paper, an innovative modulation is proposed to
utilize circuit parasitics and introduce soft-switching of all devices. Zero
current commutation and device voltage clamping are obtained without additional
snubber making it a truly snubberless topology. The proposed modulation solves
the classical problem in current-fed converters and makes a novel contribution.
Furthermore, the proposed converter topology can efficiently eliminate the low
frequency current ripples on the source (fuel cell stack) side. Low frequency
dc current harmonics coming from power electronics have a negative impact on
the lifetime and the performance of fuel cell power generation systems. The
elimination of such low frequency current ripples may also simplify the control
of fuel cell system ancillaries, such as air compressor. Thus, it is suitable for
low voltage high current applications requiring high voltage gain, low ripple
dc current, and precise operating point control. Major applications include
interfacing energy storage with dc link in FCVs due to bidirectional nature and
also as a front end dc-dc converter in case of fuel cell inverters. Switching
losses are reduced significantly owing to soft-switching of all the devices. Synchronous
rectification may be employed to obtain high efficiency. Steady state operation,
analysis and circuit design have been explained in detail. Simulation results
are presented to verify the concept and experimental results are demonstrated
to show the performance and the claims.
REFERENCES:
[1]
F. A. Farret, M. G. Simoes, “Integration of Alternative Sources of Energy,” 1st
ed. New Jersey: Wiley, 2006.
[2]
A. Khaligh and Z. Li, “Battery, ultracapacitor, fuel cell, and hybrid energy
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electric vehicles: State of the art,” IEEE Trans. Veh. Technol.,
vol. 59, no. 6, pp. 2806–2814, Oct. 2009.
[3]
A. Emadi and S. S. Williamson, “Fuel cell vehicles: Opportunities and challenges,”
in Proc. IEEE Power Eng. Soc., 2004, pp. 1640–1645.
[4]
K. Rajashekhara, “Power conversion and control strategies for fuel cell vehicles,”
in Proc. IEEE Annu. Conf. Ind. Electron. Soc., 2003, pp. 2865– 2870.
[5]
A. Emadi, S. S. Williamson, and A. Khaligh, “Power electronics intensive
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systems,” IEEE Trans. Power Electron., vol. 21, no. 3, pp. 567– 577, May
2006.
