Novel Multi-Element Resonant Converters (2007)
LLC resonant converters are adopted gradually due to high efficiency and high frequency operation capability. However, to make practical use of this converter, there are still some issues to be solved. The purpose of over current protection is to limit the current stress in the system during over load or short circuit condition, also to limit the inrush current during start up when output voltage is zero so that the power converter can be protected from destructive damage under those conditions. On the other hand, most of resonant converters developed so far include some inherent problems, such as reduced power conversion efficiency due to circulating energy generation. LLC resonant converters will generate more circulating energy than PWM counterparts. In order to overcome all these involving issues of conventional PWM and resonant converters, novel multi-element resonant converters are proposed. The novel multi-element resonant converters can achieve natural inherent over load, startup and short output protection. The circulating energy will be significantly reduced. In addition, the proposed new topology can achieve zero voltage switching (ZVS) over all load range. The secondary side rectifiers can achieve zero current switching (ZCS). Therefore, extremely low switching loss will be obtained. Voltage gain can be designed high to achieve hold up time operation without scarifying efficiency at nominal conditions.