A Digital Self-Current-Sharing Method for Modular Parallel High Step-Down LLC System

With an increasing demand for low voltage and large current output, high step-down LLC resonant converters with the parallel modular structure are introduced in high power supplying applications. Nevertheless, it is noticed that current imbalance across parallel modules exists due to mismatches of impedance of resonant tank. Thus, a method applied for stable and accurate current sharing with rapid tracking performance is the vital problem for a modular LLC parallel system. In this paper, a digital self-current-sharing method is proposed for Hybrid-Clamped Three-Level LLC (HCTL-LLC) converters. The current sharing loop for each module, with standalone self-sampling of own current and load current without current-sharing bus interconnected, has been designed with small-signal analysis under wide range voltage input. Stable and consistent current balance performance of each module in both steady status and dynamic load switching is achieved. The validity and performance of proposed method is affirmed utilizing a 5kW system with 200A output current consisting of three independent HCTL-LLC modules.