On-line auto-tuning technique of switching frequency for resonant converter considering resonant components tolerance and variation

A simple on-line auto-tuning technique for a resonant converter to achieve output voltage regulation while tuning the switching frequency to the resonant frequency is proposed in this paper. The proposed method can deal with resonant frequency variation caused by the resonant components tolerance and variation. The proposed technique is developed by detecting the zero-crossing point and peak point of resonant current. Moreover, the correction term of DC-bus voltage reference is generated based upon the error between switching period (frequency) and resonant period (frequency). The voltage reference of PFC output voltage is thus tuned to achieve both switching frequency tracking and output voltage regulation of resonant converter. The proposed method is simple and no knowledge of resonant frequency is required in prior. The proposed method is realized in software using DSP. Test results derived from a digital-controlled server power shows that switching frequency can track the resonant frequency well even with large variation of resonant components. These measured results fully support the effectiveness of the proposed technique.