Research Of A Novel Wide Input LLC Resonant Converter

The conventional full/half-bridge LLC resonant converter is not suitable for wide input voltage range and its input current is discontinuous. Therefore, it is not a good candidate for renewable energy generation(REG) system. This paper proposes a novel full-bridge LLC resonant converter that is able to achieve high efficiency over a wide input voltage range. Not only the gain range is extended, but also the input current ripple is significantly minimized by integrating two interleaved Boost inductors. The proposed novel LLC resonant converter is a preferable candidate for REG systems. In addition, compared with cascaded interleaved Boost+LLC converter, the interleaved Boost circuit and LLC converter share the same switching unit, leading to reduced amount of switches and diodes. All primary power switches operate with zero voltage switching(ZVS) ON over full operating range, leading to reduced switching losses and increased efficiency.Firstly, the operation principle is introduced. The two Boost converters operate with interleaving and are phase-shifted with 180°. Instead of conventional pulse frequency modulation(PFM), the fixed frequency pulse width modulation(PWM) control is adopted, facilitating the optimization of magnetic components and filter circuits. The equivalent circuits and the expression of the current and the voltage of the resonant thank are shown with time-domain analysis.Secondly, the main characteristics regarding gain, input current ripple, and zero voltage switching considering the nonlinear output capacitance of MOSFET, are investigated and compared with conventional solutions. The expression of the minimum current to achieve ZVS for primary power switches is given. Compared with conventional full-bridge LLC converter, the gain characteristic is improved in terms of both gain range and optimal operation area, and the input current ripple is minimized as well.And then, in order to further increase the efficiency, the influence of the parameters on the losses of the converter is analyzed. The thesis proposes an optimization solution, and the design procedure for some key parameters is presented.Finally, the feasibility of the proposed topology and the correctness of theoretical analysis are verified by experimental results of a prototype converter with 120~240 V input and 24 V/25 A output.