Cuk-Based Universal Converters in Discontinuous Conduction Mode of Operation

This paper introduces an open-loop control scheme for uk-based universal converters that have recently been proposed by the author. Cuk-based universal converters extend the principles of the operation a dc-dc Cuk converter to systems with single-phase or multi-phase ac sources and/or loads. These power converters can provide galvanic isolation by adding a single-phase high frequency transformer to the link. This eliminates the need for low frequency transformers that have large volume and weight. Being single-stage, the Cuk-based universal converters do not require decoupling components, and a small capacitor is used for transferring the power from input towards output. This eliminates the need for large electrolytic capacitors that have high failure rates. In prior works, a closed-loop control system was used for the Cuk-based universal converters. These converters were controlled such that they always operate at the boundary of continuous and discontinuous conduction modes, which leads to a variable switching frequency and a large voltage ripple across the link capacitor. The closed-loop operation along with variable switching frequency result in a complex control algorithm, which can limit the maximum switching frequency of the converter. This paper proposes an open-loop control scheme that allows the converter operate in discontinuous conduction mode and with a fixed switching frequency. Implementation of the proposed control scheme is simpler than the closed-loop control method. This paper presents details of the proposed method and evaluates its effectiveness.