Highly Efficient High Step-Up Converter for Fuel-Cell Power Processing Based on Three-State Commutation Cell

The interest toward the application of fuel cells is increasing in the last years mainly due to the possibility of highly efficient decentralized clean energy generation. The output voltage of fuel-cell stacks is generally below 50 V. Consequently, low-power applications with high output voltage require a high gain for proper operation. Several solutions were so far proposed in the literature, ranging from the use of high-frequency transformers to capacitive multipliers. This paper proposes the modification of a boost converter operating with a three-state commutation cell that is already well suited for high current stress in the input due to the current sharing between the active switches. Here, an additional winding is added to the autotransformer to provide not only the required high gain but also to significantly reduce the voltage stress across the active switches. Moreover, by employing the three-state switching cell, the size of the inductor is reduced because the operating frequency is double of the switching frequency. A prototype for the verification of the circuit was built for a 30-45-V input-voltage range, 400-V output voltage, and 250-W output power. The operation is evaluated, and the experimental waveforms and efficiency curves are presented.