Seamless operation of bi-directional LLC resonant converter for PV system

This paper proposes the simple and seamless operation technique for bi-directional LLC converter. Generally, bi-directional operation of LLC converter is complicated and difficult to control. Because, the switching frequency has to be changed across fsr (series resonant frequency) and the switching sequences has to be also changed due to resonant characteristics. In order to simplify the switching scheme, the switching frequency is moved to higher frequency than fsr where ZVS condition is maintained and simple switching sequence is achieved for both direction. The experimental results for 400Vin, 48Vo, 300W board achieves 93% efficiency and validated this method is useful practically.