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.
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[1]
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