This paper presents an isolated LLC series
resonant DC/DC converter with novel frequency adaptive phase shift modulation
control, which suitable for wide input voltage (200-400V) applications. The
proposed topology integrates two half-bridge in series on the primary side to
reduce the switching stress to half of the input voltage. Unlike the
conventional converter, this control strategy increases the voltage gain range
with ZVS to all switches under all operating voltage and load variations.
Adaptive frequency control is used to secure ZVS in the primary bridge with
regards to load change. To do so, the voltage gain becomes independent of the
loaded quality factor. In addition, the phase shift control is used to regulate
the output voltage as constant under all possible inputs. The control of these
two variables also significantly minimizes the circulating current, especially
from the low voltage side, which increases the efficiency as compared to a
conventional converter. Experimental results of a 1Kw prototype converter with
200-400V input and 48V output are presented to verify all theoretical analysis
and characteristics.
KEYWORDS:
1. LLC
2. Resonant converter
3. Frequency adaptive phase shift modulation control
(FAPSM)
4. Zero-Voltage-Switching (ZVS)
5. Wide gain range.
SOFTWARE: MATLAB/SIMULINK
CIRCUIT
DIAGRAM:
Fig. 1. Proposed LLC resonant
converter.
EXPECTED SIMULATION RESULTS:
Fig. 2(a). Simulation waveforms of
proposed converter under 400V input, 48V output and full load condition.
Fig. 2(b). Simulation waveforms of
proposed converter under 200V input, 48V output and full load condition.
Fig. 2(c). Simulation waveforms of
proposed converter under 400V input, 48V output and 20% load condition.
Fig. 2(d). Simulation waveforms of
proposed converter under 200V input, 48V output and 20% load condition.
CONCLUSION
In this paper, a
variable frequency phase shift modulation control for a DAB LLC resonant
converter has been incorporated. This control strategy makes the converter
operating at a wide gain range with ZVS over all load conditions. The
combination of two half bridge connected in series on the inverter side reduces
the voltage stress across each switch, which also makes the converter capable
of operating at high-voltage applications. The voltage stresses remain half of
the input voltage over all load variations. With the proposed control, the
voltage gain becomes independent of Q and K values. Thus, the process of
parameter design can be simplified. The magnetizing inductance has been calculated
as high to reduce the conduction loss. It also reduced the circulating current
(or, reactive power) from the secondary side even at light load condition,
which increased the efficiency as compared to conventional DAB LLC resonant
converter. The performance of the proposed LLC resonant converter is
experimentally verified with 200-400V input and 48V output converter prototype.
Therefore, the proposed converter becomes a good candidate for variable input
and constant output voltage applications.
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