Integrated High Frequency Nanocrystalline Based Planar Magnetics Design for a Bidirectional CLLLC Resonant Converter

In a CLLLC bidirectional resonant converter the magnetic part consists of the resonant inductors and the high frequency (HF) transformer. Here, the leakage inductance exists on both primary and secondary windings due to the non-coupled portion of the magnetic flux. This can be utilized to form the series inductors on the two sides of the transformer by use of non-conventional core shapes requiring unique manufacturing process. To integrate substantial value of the series inductors the leakage flux has to be increased. To mitigate this, we propose a method on adjusting the reluctance of the leakage flux path in a controlled manner in the two windings of the HF transformer by introducing additional U-I cores on the windings. These UI cores precisely alter the reluctance to give rise to the necessary resonant inductors without the necessity to increase the leakage flux. Also, by the introduction of air gap among each core, the coupling of mutual magnetic flux between the cores is significantly reduced. This HF planar magnetic arrangements with a nanocrystalline core is designed and developed for a 12 kW AC to DC resonant converter with a 1400 V DC input and 30V-60V DC output voltages. The efficiency at 12 kW and 100 kHz frequency of operation is found as 98.55%.