High Efficiency Bidirectional LLC Resonant Converter for 380V DC Power Distribution System Using Digital Control Scheme

Abstract

A bidirectional full-bridge LLC resonant converter with a new symmetric LLC-type resonant network using a digital control scheme is proposed for a 380V dc power distribution system. This converter can operate under high power conversion efficiency since the symmetric LLC resonant network has zero voltage switching capability for primary power switches and soft commutation capability for output rectifiers. In addition, the proposed topology does not require any clamp circuits to reduce the voltage stress of the switches because the switch voltage of the primary inverting stage is confined by the input voltage, and that of the secondary rectifying stage is limited by the output voltage. Therefore, the power conversion efficiency of any directions is exactly the same as each other. In addition, intelligent digital control schemes such as dead-band control and switch transition control are proposed to regulate output voltage for any power flow directions. A prototype converter designed for a high-frequency galvanic isolation of 380V dc buses was developed with a rated power rating of 5kW using a digital signal processor to verify the performance of the proposed topology and algorithms. The maximum power conversion efficiency was 97.8% during bidirectional operations.