Modelling and optimisation of a dual‐control MHz‐level CLLC converter with minimised power losses in battery charging applications

Abstract

In this study, a novel ' f − φ' dual-control modulation is proposed for the MHz-level CLLC converters in battery charging applications. Phase shift between the primary and secondary switches is utilised as an additional control variable to effectively reduce the power losses, especially in light-and medium-load conditions. Compared to other state of the art, a more generalised theoretical model is developed to characterise the converter with higher accuracy based on extended harmonic approximation. Furthermore, a numerical algorithm is utilised to thoroughly examine the converter performance under various operating conditions and systematically search for the optimised design parameters under the proposed modulation scheme. The modelling and optimisation are verified by simulation on a 3.3 kW onboard charger design for electric vehicles, which shows an estimated efficiency enhancement between 1 and 4%. Finally, a laboratory prototype has been developed using gallium nitride semiconductor devices, at the resonant frequency of 1 MHz. The converter measured efficiencies are 96.4, 96.2 and 94% for the selected heavy, medium-and light-load conditions, respectively. This system would allow insights into the practical implementation and evaluation of utilising wide bandgap semiconductors to achieve both high power density and enhanced efficiency for emerging power electronic systems.

Design and Analysis of Reconfigurable Resonant Converter With Ultrawide Output Voltage Range

“…The implementation of Phase Shift Modulation (PSM) in conjunction with PFM enables a more flexible voltage gain performance and narrower switching frequency range albeit at the expense of increase in circulating losses and control complexity [18], [19]. Employing phaseshift for efficiency improvement is further explored in CLLC converters where presence of multiple active bridges allows for a more complex control scheme involving multiple phase shifts [20]- [26]. In RPCs, the output voltage is always linearly dependent on the turns ratio of the isolating transformer.…”

Constant-Current, Constant-Voltage Operation of a Dual-Bridge Resonant Converter: Modulation, Design and Experimental Results

“…In order to avoid the above problems, modified topologies and modulation strategies of FB resonant converters are presented in [18][19][20]. In [21,22], a phase-shifted modulation method is used to increase the efficiency of FB resonant converter under a light load condition.…”

“…However, these methods increase the control complexity. In [20,23,24], higher order resonant tanks are used in the FB resonant converters. Nevertheless, complex topologies create difficulties in terms of optimum design, which will increase the cost of the system as well.…”