The DC-DC converter is a converter where we are regulating the input voltage to obtain the desired output voltage which is greater or equal to or less than the input voltage with positive or negative polarity. A large number of dc-dc converters are available in the world of which SEPIC (single-ended primary inductor converter) converter is one of them. To analyze the converter, there are many techniques available. The state space technique is applied to this higher-order converter and becomes a transfer function. The reduced order technique is applied to the system and compared to the higher order system which provides approximate results for all types of analyzes. A lot of dc-dc converter has been designed for different application purposes such as buck converter, boost converter, buck-boost converter, flyback converter, push-pull converter, forward converter etc. The converters are designed on the basis Of the switching operation helping To transfer the power from the load to the source. The SEPIC converter is one of the dcdc converters that gives greater or lesser output voltage as compared to the input voltage with the aid of the switching operation and energy storage elements as inductor and capacitor.
The mode of operation of the converter depends on the flow of the charge current which may be continuous or discontinuous. Therefore, the inverter can operate as a continuous drive mode (CCM) or a discontinuous drive mode (DCM) depending on whether the load is heavy or light. The switching operation takes place at a higher frequency which increases the system response. When designing any converter, we have to consider the source, switching elements, filter elements and loads. The filter elements are mainly the energy storage elements that decide the order of the system. For lower order converters, it is easier to design converters that can operate in stable mode and the design of the controller is also simple. For higher order converters, it is very difficult to design the controller that can operate the converter in stable mode. The SEPIC converter is a 4th order converter where two inductors and two capacitors are used. Since the system is non-linear, the design of the controller is very difficult. To analyze the behavior of the system, the order of the system must be reduced using well-defined methods. In this work, we are using small signal analysis including equivalent series resistance for inductor and capacitor. The average model is designed and with the help of state space analysis, the system becomes the transfer function form. The theory of stability has been used to verify the mode of operation. Depending on the energy state of each state variable, the order of the system is reduced which helps to analyze the system better.