Averaged switch model of single-ended primary inductor converter in discontinuous conduction mode

This paper proposes a new averaged switch model for pulse-width modulated (PWM) single-ended primary-inductor converter (SEPIC) operating in discontinuous conduction mode (DCM). The equivalent series resistance (ESR) of each energy component is considered to achieve a more precise model. The model, which is modification of the conventional averaging equation, accurately reflects both the remaining current and the actual charge on each capacitor in DCM. The proposed model utilizes a new duty ratio constraint and predicts better than previous models at high frequencies. The dependent sources of the switch components are derived from the modified averaged equation, and an implementation of the model in LTspice XVII is provided to facilitate the frequency response analysis. The frequency response of a prototype SEPIC in DCM, with an input voltage of 5 V, an output voltage of 13.5 V, and a switching frequency of 100 kHz, was experimentally measured to verify the proposed model. Simulation and experimental results demonstrate that the proposed averaged switch model solves the discrepancies at high frequencies, which was a limitation of previous models.