A Feedforward-Enhanced Feedback Hybrid Hysteretic Charge Control for LLC Converters

Power supplies for server and data center applications have stringent requirements for output voltage regulation and transient response, given by the Modular Hardware System - Common Redundant Power Supply (M-CRPS) specifications. These requirements introduce additional challenges for the design and control of LLC resonant DC-DC converters, commonly used for these applications, using conventional control architectures. Many of these design employ large output filters to meet these transient requirements. This paper introduces a novel feedforward-enhanced feedback hybrid hysteretic charge (HHC) control for LLC resonant dc-dc converters. This methodology enables fast and robust control of the output voltage during rapid load transients across wide variations in load capacitance, and allows for a reduction in the size and volume of output filters. A 400-12V 1-kW LLC dcv-dc converter-based prototype is utilized to validate the effectiveness for the proposed control approach. Experimental results confirm that the proposed feedforward-enhanced feedback control ensures stable output voltage regulation, meeting the stringent transient requirements.