Rotation Control of Synchronize Rectifier to Improve Thermal Performance of LLC Converter under Boost Mode Operation

The boost operation mode of the LLC converter can be employed to expand its voltage gain range, thereby broadening the potential applications of the LLC converter. However, it is accompanied by a larger turn off loss for half of the synchronize rectifiers (SR) and imbalanced thermal performance associated with different switching loss. To solve this problem, a rotation control of SR to improve thermal was proposed by changing the roles of SRs periodically so that the average device loss can be balanced. The proposed control method was verified on a 30kW LLC converter with 99% peak efficiency. Adaptive update time of updating compare registers for achieving the rotation control was adopted to avoid duty cycle loss during the mode transition based on TI's TMS320F28388D.