Synchronous Rectification for LCLC Resonant Converter

The synchronous rectifiers are implemented to enhance the converter efficiency and its power density. A Synchronous rectification scheme for LCLC resonant converter is proposed in this paper. Several synchronous rectification methods for LLC resonant converters are discussed in literature such as on state drain-source voltage (vdson) sensing, current transformers (CT's) based methods to sense the rectifier current, adaptive technique, and other alternative methods. Resonant Capacitor Voltage (RCV) sensing method is one of the attractive methods discussed in the literature for LLC resonant converter. This method eliminates the requirement of CT's and it is least affected by the noise injected by parasitic components unlike vdson sensing technique. The typical RCV method cannot be used for LCLC resonant converter due to resonant tank equivalent parallel branch inductance (Lpeq) variation with switching frequency. A control technique for the synchronous rectification of the LCLC resonant converter is proposed to compensate for the change in Lpeq value. The proposed estimation block in the control technique improves the control performance and facilitates digital implementation. Detailed analysis is carried out for the proposed control scheme and the performance is evaluated in simulations for a LCLC resonant converter.