Design Methodology of Bidirectional CLLC Resonant Converter for High-Frequency Isolation of DC Distribution Systems

TLDR

The paper proposes a bidirectional full‑bridge CLLC resonant converter with a symmetric LLC resonant network and intelligent digital control algorithms to enable high‑frequency galvanic isolation of 380‑V DC buses and bidirectional power conversion. The converter uses a symmetric LLC resonant network that provides zero‑voltage switching for primary switches and soft commutation for output rectifiers, eliminates snubber circuits, and is controlled by digital algorithms implemented on a DSP in a 5‑kW prototype. Experimental results show the converter can smoothly reverse power flow and achieves a maximum bidirectional efficiency of 97.8 %, with equal efficiency in both directions.

Abstract

A bidirectional full-bridge CLLC resonant converter using a new symmetric LLC-type resonant network is proposed for a low-voltage direct current power distribution system. This converter can operate under high power conversion efficiency because 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 snubber circuits to reduce the voltage stress of the switching devices because the switch voltage of the primary and secondary power stage is confined by the input and output voltage, respectively. In addition, the power conversion efficiency of any directions is exactly same as each other. Using digital control schemes, a 5-kW prototype converter designed for a high-frequency galvanic isolation of 380-V dc buses was developed with a commercial digital signal processor. Intelligent digital control algorithms are also proposed to regulate output voltage and to control bidirectional power conversions. Using the prototype converter, experimental results were obtained to verify the performance of the proposed topology and control algorithms. The converter could softly change the power flow directions and its maximum power conversion efficiency was 97.8% during the bidirectional operation.