A Secondary-Side Phase-Shift-Controlled <italic>LLC</italic> Resonant Converter With Reduced Conduction Loss at Normal Operation for Hold-Up Time Compensation Application

Abstract

A novel secondary-side phase-shift-controlled (SS-PSC) LLC resonant converter is proposed for applications requiring hold-up time operation such as distributed power systems and server power supplies. High efficiency at the normal input voltage is achieved because the proposed SS-PSC LLC converter always operates at the series-resonant frequency of the resonant tank. What's more, the magnetizing inductor of the proposed converter doesn't need to be reduced to provide desired voltage boost ratio for the hold-up time operation, which results in reduced conduction losses and improved efficiency. Sufficient voltage boost ratio for the hold-up time operation is provided by using secondary-side phase-shift control strategy. In comparison with the conventional variable-frequency-controlled LLC resonant converter, the main advantages are that the circulating current caused by the magnetizing inductor is effectively suppressed and the efficiency of normal operation is significantly improved. The operation principles, output characteristics and design considerations of the proposed converter are presented in detail. Experimental results are given to verify the effectiveness and the advantages of the proposed solutions.

Highly Efficient and Reliable SiC-Based DC–DC Converter for Smart Transformer

“…Generally, the converter is designed to operate at the resonant frequency ( f s = f o ) [25], reaching then the maximum efficiency point. To do so, the pair L r and C r have to satisfy the condition imposed in (1).…”

Latest Advances of LLC Converters in High Current, Fast Dynamic Response, and Wide Voltage Range Applications

“…To charge the resonant tank more, the secondary windings are short circuit for a certain period in every switching cycle. Based on [37], a few improving methods have been proposed to adopt either Boost PWM discontinuous current mode (DCM) control [38] or phase shift control on LLC topology [39], [40]. These methods share the similar intrinsic principle with [37], but optimize the LLC converter for different specifications with respective topologies, circuits and control.…”

LCLC resonant converter for hold up mode operation

“…To reach the peak gain at 1.6 for 250V input, the equivalent L m should be 70 H according to FHA analysis. Based on this, the parallel current can be calculated in (7), so that minimum parallel capacitance can be calculated in (8), considering the maximum voltage ratings in (9).…”

“…More recently, a few methods are proposed to add switches on either primary side or secondary side to adopt Boost PWM discontinuous current mode (DCM) control scheme on a LLC topology [6]- [9]. For those methods, the positive aspect is that normal efficiency remains uninfluenced compared with a conventional LLC which is optimized for 400V input voltage.…”