For grid-connected power system based on photovoltaic（PV） source and fuel cells, high step-up and high-efficiency DC–DC converters are needed, due to the bus voltage of the grid-connected inverter is much higher than the output voltage of PV and fuel cells. In this paper, a novel high step-up converter is proposed. An auxiliary capacitor is introduced into the boost converter, which serves as a voltage source. It is in series with the input voltage source with the same voltage polarities. Thus, the input voltage is increased equivalently and the voltage gain is increased accordingly. To reduce the voltage stresses of the switch and the diode, multiple output capacitors are introduced. The voltage of each output capacitor is degraded leading to the reduced voltage stress. To replenish energy for the multiple output capacitors, a coupled inductor is adopted. Based on this, high step-up converter adopting auxiliary capacitor and coupled inductor is derived. The operating principles and voltage gain of the proposed converters are analyzed in this paper. In theend, experiment results are given to verify the theoretical analysis.
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