Parasitics Assisted Soft-switching and Naturally Commutated Current-fed Bidirectional Push-pull Voltage Doubler

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, L_lk1, Current through series leakage inductance, L_lk2, (d) Current through secondary devices S₃ and S₄, (e) Voltage V_ab, output voltage V_o,Voltage across L_lk1

Fig. 3. Experimental results: (a) Gating signal of switch S₁, V_gs1, current through switch S₁, I_s1, drain-source voltage across switch S₁, V_ds1, (b) Current through boost inductor L, current through series leakage inductance, L_lk1, (c) Current through secondary device S₃, I_s3, Gating pulse of S₃, V_gs3, drain source voltage across switch S₃, V_ds3, (d) Voltage across leakage inductor V_lk1, voltage across transformer primary, V_ab,

  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 storage systems for electric, hybrid electric, fuel cell, and plugin hybrid 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 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.