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Design of Integrated Transformer and Inductor for a High-Power High-Frequency Resonant Converter

Topology circuit
Fig. 1. Serial Half Bridge Topology
  LLC Resonant Converters are widely used for DC-DC Converters and a resonant inductance embedded transformer is a critical component as it provides the required isolation between primary and secondary side and takes a large portion of the total volume of the whole converter. This paper presents a comprehensive design procedure of a 100 kHz, medium voltage trans-former for a 30 kW Serial Half Bridge Converter with 45 kW overload condition. The design method of a high-power high frequency integrated transformer and inductor with perfect current sharing is presented in this paper.

  The transformer structure is as shown in in Figure 2. Fig. 2 gives some cases with different leakage inductance and current sharing waveform. The leakage inductance between the winding on the same leg is more important for current sharing. 13% difference on leakage inductance between Lk_pri1sec2 and Lk_pri2sec1 only causes 2% current difference. But 30% difference between Lk_pri1sec1 and Lk_pri2sec2 causes 31% current difference. However, the structure in Fig. 2(b) can be avoided using bobbin and Fig. 2(c) is not mechanical stable, so both cases can be avoided.
winding structure
Fig. 2. Current sharing for difference in winding structure

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