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In order to deal with mismatched voltage levels between parallel-connected low-voltage photovoltaic (PV) arrays and the required higher voltage of the grid, a novel hybrid boost three-level dc-dc converter is proposed based on the traditional single-phase diode-clamped three-level inverter. Only one inductor, two capacitors in series, and those power switches and diodes, which are easy to be integrated, are adopted to establish the topology with transformerless high voltage gain. The operation principle of the proposed topology is analyzed, and then the pulsewidth modulation (PWM) control method is obtained according to the switching functions about the output pulse voltages of both half-bridges. Therefore, the proposed converter cannot only operate with high voltage gain, but also make the duty cycles of power switches closer to 0.5. Moreover, voltages across the capacitors in series are well balanced in both steady and dynamic states, and the blocking voltages of the power switches are half of the output dc voltage. Finally, a 1-kW prototype is set up in our laboratory, and the measured maximum efficiency of the proposed converter is about 93.1%. All experimental results verify the feasibility of the proposed topology and validity of the PWM control method.