Digital implementation and performance evaluation of a time-shift-controlled LLC resonant half-bridge converter

Time-shift control (TSC) is a novel control technique for resonant converters that outperforms the traditional direct frequency control (DFC) method implemented in all of the currently available control ICs. In particular, TSC makes the dynamic behavior of LLC resonant converters closely resembling that of a first-order system. Thus, closing the control loop to meet stability and even demanding dynamic performance specifications becomes a much easier task. This paper, after briefly reviewing the concepts related to TSC, describes its implementation with a digital controller specific for power conversion applications. An LLC resonant half-bridge converter is operated with both TSC and DFC and the dynamic performance achieved with both control methods is compared. This benchmark confirms the superior performance of TSC in terms of load transient response and input ripple rejection. Furthermore, the experiments show that TSC is able to prevent hard-switching of the half-bridge switches at start-up.