Input Power Proportional Control of LLC Resonant Converter

This paper introduces a new approach to controlling resonant converters that modulates the switching frequency by comparing the input power to a control signal. This means that the input power is directly controlled by the feedback loop that regulates the output voltage or current, making this loop relatively insensitive to the parameters and tolerances of the power stage. Two more advantages result from the fact that the control variable is proportional to the input power: first, the converter’s power output is limited because the control signal is also limited within a range; second, the control signal can be utilized as a load monitor regardless of variations in the input/output voltage of the resonant converter, making it as a viable solution in case of a wide input/output voltage applications, ex: battery chargers, LED drivers. Lastly, this innovative approach offers excellent dynamic response as well. A theoretical analysis of the new method will be presented in the paper, including the steady-state equations and the operating principle. Lastly, the novel method’s viability and advantages will be shown with the help of simulations and the hardware results.