International Journal of Power Electronics and Drive System (IJPEDS) Vol. 5, No. 2, October 2014, pp. 237~243 ISSN: 2088-8694  237 Journal homepage: http://iaesjournal.com/online/index.php/IJPEDS Modelling of Variable Frequency Synchronous Buck Converter Jeya Selvan Renius A, Vinoth Kumar K, Arnold Fredderics, Raja Guru, Sree Lakshmi Nair Departement of EEE, School of Electrical Sciences, Karunya University, Coimbatore – 641114, Tamil Nadu, India Article Info ABSTRACT Article history: Received Jul 11, 2014 Revised Sep 9, 2014 Accepted Sep 25, 2014 In this paper, novel small-signal averaged models for dc–dc converter operating at variable switching frequency are derived. This is achieved by separately considering the on-time and the off-time of the switching period. The derivation is shown in detail for a synchronous buck converter. The Enhanced Small Signal (ESSA) Model is derived for the synchronous buck converter. The equivalent series inductance (ESL) is also considered in this modelling. The buck converter model is also simulated in MATLAB and the result is also presented. Keyword: DC-DC converter, Enhanced Small Signal Analysis (ESSA), Equivalent Series Inductance (ESL) Copyright © 2014 Institute of Advanced Engineering and Science. All rights reserved. Corresponding Author: Jeya Selvan Renius A, Departement of EEE, School of Electrical Sciences, Karunya University, Coimbatore – 641114, Tamil Nadu, India. Email: renius28@gmail.com 1. INTRODUCTION In the control of dc–dc converters, two control objectives are apparent: performance and efficiency. On the one hand, the research focus in the community has been put on the optimization of the conversion efficiency. For instance, the switching frequency can be reduced at low loads, or the control scheme could be switched between a constant on-time and a constant off-time control scheme depending on the load conditions. On the other hand, a strong interest can be found in the optimization of the dynamic performance. When a variation of the switching period is tolerable during converter operation, this additional degree of freedom offers the opportunity of tight (near optimum) voltage regulation. Nevertheless, to fully exploit the switching period modulation in terms of dynamic transient performance and to ensure stability in all conditions, accurate models, which cover the dynamics of the power conversion system under variable frequency operation, are needed. A frequency-selective averaging is applied such that the switching frequency appears in the dynamic system model. The derivations give an accurate model of the converter dynamics also for situations when the traditional small-ripple conditions are not satisfied, but yield a nonlinear time-varying system formulation. As previous classic control theories largely depend on a linearized representation of the system under exam, the resulting model is of limited interest for the targeted design objective. In this paper, an alternative formulation of the SSA model is presented, which yields a linearized small-signal representation of the power conversion circuit, where the on-time, as well as the off-time of the pulse-width modulation (PWM) signal are treated as distinct control inputs. In this manner, one can study the dynamics under variable switching frequency operation. The correctness of the enhanced converter representation is also discussed in this paper.