LLC series resonant converters for consumer or industrial electronics frequently encounter considerable changes in both input voltage and load current requirements. This paper presents theoretical and practical details involved with the dynamic analysis and control design of LLC series resonant DC-to-DC converters operating with wide input and load variations. The accuracy of dynamic analysis and validity of control design are confirmed with both computer simulations and experimental measurements.

This letter proposes a modified double-dual-boost (DDB) high-conversion-ratio dc–dc converter. The proposed converter is derived from the existing DDB converter by a simple yet effective circuit modification and inherits all the advantages of the existing DDB converter. In addition, the input and output can share a common ground due to the circuit modification, enabling the use of low-side gate drivers for all switching devices. When compared with the existing DDB converter, the proposed converter requires only one more capacitor, and the seemingly two inductors can be integrated into a single inductor. Thus, the overall magnetic volume is the same as the conventional converter. To validate the performance of the proposed converter, a 2-kW prototype was fabricated and tested.

Conventional voltage mode control only offers limited performance for LLC series resonant DC-to-DC converters experiencing wide variations in operational conditions. When the existing voltage mode control is employed, the closed-loop performance of the converter is directly affected by unavoidable changes in power stage dynamics. Thus, a specific control design optimized at one particular operating point could become unacceptable when the operational condition is varied. This paper presents a new current mode control scheme 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 superiority of the proposed current mode control over the conventional voltage mode control is verified using an experimental 150 W LLC series resonant DC-to-DC converter.

This study presents the design and performance evaluation of the digital control adapted to an LLC series resonant dc‐to‐dc converter operating with wide input and load variations. The proposed control design correctly incorporates the wide‐varying power stage dynamics and variable small‐signal gain of a digitally controlled oscillator, thereby offering satisfactory converter performance for all the operational conditions. The proposed digital controller adopts the push–pull mode control scheme, which executes the control action two times in one switching period, to minimise the time delay and enhance the performance. Using a 150 W experimental converter, the performance of the proposed push–pull mode digital control is demonstrated in comparison with that of the conventional complementary mode digital control, which performs the control action only once in one switching period.