Z-domain modeling and control design of single-switch bridgeless SEPIC PFC converter with damping circuit

This paper presents a comprehensive digital control strategy for a single-switch bridgeless SEPIC PFC converter which employs the damping circuit to improve the stability of the converter. To do this, first, the 5^th order control-to-inductor current model and control-to-output model are derived mathematically in both the s- and the z-domains, in where the digital delay effects are included. After that, it is confirmed that the damping circuit assists to stabilize the control loops from the loop-gain analysis of the derived models. The design procedures of the digital voltage and the current feedback controllers and the current feed-forward controller are explained in detail. The experimental results show that the designed controller is very well adopted for a 150 W LED drive application. The experimental results show that the input current THD meets EC61000 standard as well as verifying the designed digital controller under the given specification.