utilization of a transformer and passive snubbers in isolated converters increases the losses, volume, and cost. The second category is nonisolated converters, which are used for low or medium power levels. These have simple structure, low weight and high efficiency. Most of nonisolated converters are obtained by development of the boost and buckboost topologies. 7,8 It should be noticed that the boost and buck-boost converters are an unsuitable choice for DC/DC energy conversion, because of the pulsating output current. 9 Furthermore, the single-ended primary-inductor converter (SEPIC) normally presents an unbalanced output current. This deteriorated current may be undesirable for electronic systems. To overcome this drawback, Zeta converter has been introduced in many studies. 9-11 It produces a continuous output current. But, the input current of the Zeta converter is discontinuous, resulting in high losses and efficiency reduction. Hence, Ćuk converter has been proposed for industrial applications such as photovoltaic plants, 12 wind energy, 13 electrical vehicles, 14 compressor, 15 and fuel cell systems. 16 This converter can operate in a wide range of the output voltage, input voltage, and load. 17 The first goal of this paper is to show that a Ćuk converter can be well employed in battery charger applications as a soft starter to prevent the system from large current oscillations.So far, many researches have been focused on modelling and control of DC/DC converters. Small signal analysis of power converters is performed in a previous study 18 by considering the effects of parametric resistances and double-loop proportional-integral (PI) controller based on classical methods is proposed in another study. 19 Generally, traditional proportional-integral-derivative (PID)-type or PI-type controllers are common control methods in industrial systems, because of the unsophisticated design, simple control scheme, and effortless implementation. 20,21 The design theory of classical controllers is based on local linearization of the plant model to predict the system response in the frequency domain. However, these are inappropriate for large-signal models, which are subjected to significant variations. Also, it is necessary that the gains of classical methods is repeatedly adjusted to guarantee a favorable performance, because of the changes of controlled system parameters and the effects of uncertainties. In an existing work, 22 an automatic procedure is applied for optimal design of PI and PID controllers. Although this strategy brings more flexibility in design and provides a better response, the proposed control scheme looks to be more complicated as compared with nonadaptive design methods. Contrary to the aforementioned traditional approaches, some nonlinear control techniques have been offered for DC/DC converters in last decades. In the other research, 23 a particular linearized method around the equilibrium point of power converters is utilized to estimate the complete nonlinear system. Moreover, the analogue...
