High Step-Up Buck–Boost Converter with Coupled Inductors

This paper presents an in-depth analysis of a non-isolated buck–boost DC–DC converter which uses coupled inductors. The converter is designed to achieve a high static conversion ratio while using a moderate number of semiconductor devices. The proposed topology, originally introduced in a former paper of the authors, under ideal operating conditions, is now evaluated taking into account non-ideal components, modeling the conduction losses of the semiconductor devices and the equivalent series resistance of the output capacitor. In order to get a regulated output voltage, closed-loop behavior is also investigated. By using the state-space modeling approach, the calculation of the converter static conversion ratio and control-to-output transfer functions is performed. Because the topology is of fourth order, a procedure for controller design is provided. A type III error amplifier is chosen, and the pole-zero placement technique is used for its design, demonstrating that the classical control strategy still works even with this fourth-order converter. Thus, a good phase margin of 62.3 degrees is achieved. The theoretical results are validated both on open-loop and closed-loop operation, in the presence of conduction losses. Furthermore, a laboratory prototype is implemented, and it validates the theoretical and simulation results. The study demonstrates that the proposed coupled inductors buck–boost converter is a good choice for step-up applications that need a large difference between input and output voltages.