A Frequency Adaptive Phase Shift Modulation Control Based LLC Series Resonant Converter for Wide Input Voltage Applications

ABSTRACT

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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