A low-cost single-stage isolated differential ĈCuk inverter for fuel-cell application

Several inverter configurations have been proposed in literature to achieve fuel-cell power conversion at significantly lower cost, which is one of the most critical constrains to make such alternative energy systems viable. A single-stage isolated dc/ac Cuk inverter would potentially be a better alternative with reduced system complexity, costs, improved reliability, and high efficiency because it achieves direct dc/ac power conversion using only four main switches. Simple drive circuit (owing to all low-side power devices), possibility for integrated magnetics, and less turns ratio requirement for transformer lead to a low-cost, high-power-density energy-conversion system. This paper investigates the possibility of using and performance of this inverter for low power (< 3 kW) fuel-cell applications. The operational principle for isolated dc/ac Cuk inverter, which has not appeared in the literature, is presented. Key design issues of a 1 kW prototype for the application are addressed. In order to achieve higher efficiency, the turns ratio of the transformer needs to be selected to achieve a trade off between output voltage distortion and duty ratio range. Switching losses due to the leakage of the transformer and high reverse current during device turn off can be reduced by implementing active lossless clamp circuit, which has been presented in this paper.