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A Combined Topology With Coupled LLC Resonance for Wide-Range Operation

This paper proposes a topology combination scheme to achieve wide-range operation for LLC resonant converters. Instead of directly adding an auxiliary current injection circuit for each individual LLC converter, the proposed scheme combines two LLC converters through coupled resonance. Then, one LLC circuit can be utilized to adjust the equivalent resonant parameters of the other LLC circuit. By only controlling the phase delay between the mosfet bridges, output voltage regulation is properly maintained without changing the switching frequency. Since the total power rating does not change and each converter can share the load, it does not have any extra cost of power components. The advantages of this design include higher power efficiency, smaller size, and optimized utilization of each converter at different load, since both converters can fulfill isolated power conversion with independent control. Also, by taking the benefit of suppressed frequency variation, a smaller leakage inductance and a lower ratio between the leakage inductance and the magnetizing inductance are allowed, so that the coupling of transformer windings and transformer efficiency just improve. In addition to detailed theoretical analysis, experimental results verify the feasibility and effectiveness of the proposed concept.