Nonisolated high step-up DC–DC converters are widely employed in uninterruptible power supplies and renewable energy systems. In such applications, a high step-up converter is used to generate a high-voltage DC bus for the next stage inverter. The main objective of this research is to study and improve nonisolated high step-up DC–DC converters regarding their voltage gain and energy efficiency as well as their dynamic responses. Existence of a right-half-plane (RHP) zero in the control-to-output transfer functions of boost converters is known as the main limiting factor of their frequency responses. In this research, the use of forward-type coupled inductors is suggested as a new method to improve the dynamic responses of high step-up converters by eliminating their RHP zeros. Moreover, two new nonisolated high step-up converters are proposed based on the impedance-source and quasi-impedance-source structures and using forward-type coupled inductors. Although the first proposed converter offers ultra-high voltage gain and high efficiency, it cannot achieve fast dynamics. However, the second proposed converter meets all the desired features such as large voltage gain, high efficiency, a small number of components, continuous input current, and fast dynamics. Key Words: Nonisolated high step-up DC–DC converters, improvement of dynamic response, state-space modeling, soft-switching techniques.
