Research on Control Strategy of Three-Level Half-Bridge LLC Resonant Converter with Wide Output Voltage Range

Abstract

Three-level(TL) converter is received extensive attention and research in some applications with high voltage and high power, such as DC-DC supplies and electrical vehicles, because voltage stress of each switch in TL converter is half of input voltage.In order to achieve a wide range of output voltage, and to overcome the shortcoming of variable frequency(VF) modulation that the voltage range is small, this paper introduces phase-shift(PS) modulation to Three-level Half-bridge(TL HB) LLC converter.It analyzes the working process, voltage adjustment range and soft switching condition of PS modulation.Besides, it deduces the demarcation point at working state of soft switching, thus proposes a hybrid modulation strategy of TL HB LLC converter.According to the soft switching state, this strategy can achieve soft-switching during the whole control process and wide range of output voltage from switching PS mode and VF mode.The experiment can verify the correctness of theoretical analysis results, the feasibility and effectiveness of the proposed modulation strategy.