LLC Resonant Converter as a Current Source Using Simple Trajectory Control

Abstract

This paper discusses a simple method for controlling an LLC resonant DC-DC converter using a state space trajectory based on a linear combination of the voltage across the capacitor and the current through the inductance in the series resonant tank. An analysis of the converter using the state plane technique for the continuous current operation mode is proposed. The output, control and load characteristics of the converter, required for its design and application, are built for the different inductance ratios. They specify the limitations in the control range of the LLC resonant converter which result from the use of the control method. It is shown that under this control, the converter possesses linear control characteristics and has current source behavior. Therefore, the converter can successfully be used as a battery-charging device. Simulations of the converter’s operation, both in steady state and when the control parameter is changed significantly, are implemented. Studies using the model confirm that the considered simple trajectory control provides a fast dynamic response and stable operation of the LLC resonant converter, even in cases of a significant change in the control.