1 A BEHAVIORAL AVERAGE MODEL OF SEPIC CONVERTERS WITH COUPLED INDUCTORS D. Adar, G. Rahav and S. Ben-Yaakov Power Electronics Laboratory Dept. of Electrical and Computer Engineering Ben-Gurion University of the Negev Beer-Sheva 84105 ISRAEL Tel.: + (972) (7)461-561; Fax: + (972) (7)472 949; Email: sby@bguee.bgu.ac.il Abstract An average model of SEPIC converters with coupled inductors was developed and verified against cycle-by-cycle simulations. The model can be used as-is by any modern circuit simulator to run steady state (DC), large signal (Transient) and small signal (AC) analyses. The inductors coupling coefficient, incorporated as a parameter in the model, can be varied from zero to almost unity. Zero coupling coefficient represents the case of a SEPIC converter with uncoupled inductors. Introduction Practical SEPIC converters are usually built with coupled inductors (L s and L p , Fig. 1) to lower production costs. Yet, the SEPIC dynamic behavior is still poorly understood and the single simulation model proposed hitherto for this topology is valid only for the uncoupled inductors situation [1]. The coupled inductors case appears to represent a still open simulation issue. It involves two coupled inductors acting as a transformer, in the sense that current flows on both sides at the same time, while both sides are loaded by capacitors (C fi , C s and C p , Fig. 1). Assuming that the capacitors are large enough so that there voltages do not vary appreciably during one cycle, they can be replaced by voltage sources. Therefore, we have in fact a transformer connected to voltage sources at the input and output at the same time (Fig. 2). Consequently, the leakage inductances (L sp and L pp , Fig. 2) cannot be neglected in this case. The voltages of the two terminals (V 1 and V 2 , Fig. 2) have different values during the 'on' and 'off' times, but can be considered almost constant within the 'on' and 'off' intervals. The magnitude of the voltages, assuming ideal diode and switch, are as follows: