An Adaptive Frequency Optimization Scheme for LLC Converter With Adjustable Energy Transferring Time

This letter proposes a new frequency optimization scheme for LLC converters with adjustable energy transferring time. The output voltage is regulated by simultaneous adjustment of the resonant time and the switching frequency. Meanwhile, the concept of adaptive current injection is borrowed to solve the problem of difficult control regulation when only a narrow frequency range is allowed. Therefore, in comparison to a scheme that keeps the switching frequency constant, the new scheme does not add any additional circuit. The advantage is that higher power efficiency is achievable, since the conduction loss is significantly reduced by actively controlling the switching cycle with respect to the variation of resonant time. In addition, since the frequency range is narrow, a lower ratio between the leakage inductance and the magnetizing inductance is still allowed. In addition to detailed theoretical analysis, experimental results verify the feasibility and effectiveness of the proposed concept.