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Conventional voltage mode control only offers limited performance for LLC series resonant dc-to-dc converters experiencing wide variations in operating conditions. This paper presents average current mode control which could consistently provide good closed-loop performance for LLC resonant converters for the entire operational range. The proposed control scheme employs an additional feedback from the current of the resonant tank network to overcome the limitation of the existing voltage mode control. The principles, implementation and performance of the average current mode control scheme are investigated to identify their respective merits and limitations compared with conventional control schemes. The accuracy of dynamic analysis and validity of control design are confirmed with both computer simulations and experimental measurements using 150W prototype converter.