Extended Describing Function Modeling and Closed-Loop Control of LLC Converter in Battery Charging Applications

The variable switching frequency control of LLC converters makes the modeling and compensator design rather a difficult task. In this paper, an extended describing function modeling that can represent the beat frequency successfully has been examined in detail. The small signal model of the converter dynamics has been extracted for output current and voltage. Two compensators have been designed to close the loop for constant-current and constant-voltage operations considering main operating regions. The performances of the designed compensators have been verified under different load conditions. It has been shown that the designed controller successfully tracks the reference output current and voltage appropriately by adjusting the switching frequency.