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Multimode Hybrid Control Strategy of LLC Resonant Converter in Applications with Wide Input Voltage Range
Yan LiĘ”, Kun Zhang*, and Shuaifei Yang*
Abstract This study proposes a multimode hybrid control strategy that can achieve zero-voltage switching of primary switches and zero-current switching of secondary rectifier diodes in a wide input voltage range for full-bridge LLC resonant converters. When the input voltage is lower than the rated voltage, the converter operates in Mode 1 through the variable-frequency (VF) control strategy. When the input voltage is higher than the rated voltage, the converter operates in Mode 2 through the VF and phase-shift control strategy until the switching frequency reaches the upper limit. Then, the converter operates in Mode 3 through the constant-frequency and phase-shift control strategy. The secondary-side diode current will operate in the discontinuous current mode in Modes 1 and 3 and in the boundary current mode in Mode 2. The current RMS value and conduction loss can be reduced in Mode 2. A detailed theoretical analysis of the operation principle, the voltage gain characteristics, and the realization method is presented in this paper. Finally, a 500 W prototype with a 100?200 V input voltage and a 40 V output voltage is built for verifying the feasibility of the multimode hybrid control strategy.
Keyword multimode hybrid control, LLC resonant converter, wide input voltage, BCM
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