Automatic resonant frequency tracking for DCX-LLC based on magnetizing current cancellation

The LLC resonant converter has been widely used as a DC-DC transformer (DCX) to provide a semi-regulated or unregulated bus voltage. However, due to circuit parameter variations, the switching frequency is usually different from the designed resonant frequency, which results in converter efficiency degradation. To achieve the highest efficiency under different scenarios, a novel primary-side regulation (PSR) scheme for LLCs based on magnetizing current cancellation is presented. The transformer magnetizing current component on the sampling resistor can be offset by the compensating current, which is generated by the auxiliary winding and the added compensating inductor. The effect of magnetizing current in the sampled primary resonant current can be effectively eliminated. Thus, the output current can be accurately estimated on the primary side of the LLC resonant converter. Finally, a prototype of a 20-60 V LLC is constructed to validate the theoretical analysis. In the experiment section, various scenarios are tested to assess the efficacy of the solution. It is shown that the LLC converter can always realize resonant frequency tracking with the highest transmission efficiency.