Pulse frequency modulation and unilateral dual-phase-shift hybrid control strategy for bidirectional full-bridge LLC resonant converter

Abstract

Bidirectional LLC resonant converter has been popular in applications such as electric vehicle, energy storage system and uninterruptible power supply for its good soft-switching characteristics. A novel control strategy combined pulse frequency modulation (PFM) with unilateral dual-phase-shift (DPS) control is proposed in this work. By controlling the switches in the converter, the forward buck mode operation can be realised under PFM control, as well as the backward boost mode operation can be realised under unilateral DPS control; therefore, the bidirectional power flow and zero-voltage-switching of all switches can be realised; thus, the efficiency of the converter is improved. The detailed operation principle, control strategies, voltage gain expression, soft-switching characteristics and design of parameters are analysed. The feasibility of PFM-DPS control is finally verified by PSIM simulation and prototype experimental results.

Keywords

• zero voltage switching
• resonant power convertors
• switching convertors
• pulse frequency modulation
• PWM power convertors
• zero current switching
• discrete systems
• continuous systems
• bidirectional full-bridge LLC resonant converter
• PSIM simulation
• soft-switching characteristics
• voltage gain expression
• combined pulse frequency modulation
• unilateral dual-phase-shift hybrid control strategy
• PFM-DPS control
• zero-voltage-switching
• bidirectional power flow
• unilateral DPS control
• backward boost mode operation
• PFM control
• forward buck mode operation
• unilateral dual-phase-shift control
• uninterruptible power supply
• energy storage system
• electric vehicle