Design and Performance of a Bidirectional Isolated DC–DC Converter for a Battery Energy Storage System Best Electrical Engineering Projects

 

ABSTRACT:

This paper describes the design and performance of a 6-kW, full-bridge, bidirectional isolated dc–dc converter using a 20-kHz transformer for a 53.2-V, 2-kWh lithium-ion (Li-ion) battery energy storage system. The dc voltage at the high-voltage side is controlled from 305 to 355 V, as the battery voltage at the low voltage side (LVS) varies from 50 to 59 V. The maximal efficiency of the dc–dc converter is measured to be 96.0% during battery charging, and 96.9% during battery discharging. Moreover, this paper analyzes the effect of unavoidable dc-bias currents on the magnetic-flux saturation of the transformer. Finally, it provides the dc–dc converter loss breakdown with more focus on the LVS converter.

 KEYWORDS:

  1. Bidirectional isolated dc–dc converters
  2. Dc-bias currents
  3. Energy storage systems
  4. Lithium-ion (Li-ion) battery

 SOFTWARE: MATLAB/SIMULINK

 CIRCUIT DIAGRAM:


Fig. 1. Li-ion battery bank of 53.2 V, 40 A·h connected to the 6-kW bidirectional isolated dc–dc converter, where LS is the background system impedance (<1%). LAC = 280 μH (1.3%), LF = 44μH (0.2%), RF = 0.2Ω (3%), and CF = 150 μF (33%) on a three-phase 200 V, 6-kW, and 50-Hz base.

EXPECTED SIMULATION RESULTS:

 

 Fig. 2. Experimental waveforms with dc-voltage control at the HVS. (a) Charging mode at PB = 5.9 kW (VD1 = 355 V). (b) Discharging mode at PB = 5.9 kW (VD1 = 305 V).

Fig. 3. Waveforms of vD1, vB , and iB . (a) Battery charging at PB = 5.9 kW.

(b) Battery discharging at PB = 5.9 kW.

Fig. 4. Drain–source and gate–source voltages of a leg in bridge 2 at PB =

5.9 kW, VD1 = 355 V, and VB = 59V

Fig. 5. Effects of the RC-snubber on a MOSFET in bridge 2 during battery charging at PB = 5.9 kW. (a) Drain–source voltage and RC-snubber current. (b) Time-expanded waveform of vDS and iRC .

CONCLUSION:

This paper has presented the experimental results from the combination of a 53.2-V, 40-A·h Li-ion battery bank with a single-phase full-bridge bidirectional isolated dc–dc converter. The results have verified the proper operation of the Li-ion battery energy storage system. Discussions focusing on magnetic flux saturation due to unavoidable dc-bias currents at the high voltage and LVSs have been carried out. The transformer with an air-gap length of 1 mm has been shown experimentally to be robust against magnetic-flux saturation, even in the worst cases. The bidirectional isolated dc–dc converter exhibits high efficiency in the low-voltage and high-current operation. From the estimation of loss distribution in the dc–dc converter, a large portion of the loss at the rated power is caused by the turn off switching loss at the LVS. One of the best methods of improving the efficiency of the dc–dc converter is to operate it at a lower switching frequency. However, this method is accompanied by acoustic noise generation and a bulky transformer.

REFERENCES:

[1] New Energy and Industrial Technology Development Organization (NEDO). (2008). Global warming counter measures: Japanese technologies for energy savings/GHG (greenhouse gases) emissions reduction (Revised ed.), [Online]. Available: http://www.nedo.go.jp

[2] S. C. Smith, P. K. Sen, and B. Kroposki, “Advancement of energy storage devices and applications in electrical power system,” in Proc. IEEE Power Energy Soc. General Meeting, Jul. 2008, pp. 1–8.

[3] P. F. Ribeiro, B. K. Johnson, M. L. Crow, A. Arsoy, and Y. Liu, “Energy storage systems for advanced power applications,” Proc. IEEE, vol. 89, no. 12, pp. 1744–1756, Dec. 2001.

[4] R.W. A. A. De Doncker, D. M. Divan, and M. H. Kheraluwala, “A threephase soft-switched high-power-density dc/dc converter for high power applications,” IEEE Trans. Ind. Appl., vol. 27, no. 1, pp. 63–73, Feb. 1991.

[5] M. H. Kheraluwala, R. W. Gascoigne, D. M. Divan, and E. D. Baumann, “Performance characterization of a high-power dual active bridge dc-todc converter,” IEEE Trans. Ind. Appl., vol. 28, no. 6, pp. 1294–1301, Nov./Dec. 1992.

 

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