The present invention falls within the technical filed of photovoltaic high-voltage converters, and specifically relates to a series-type photovoltaic high-voltage direct-current grid-connected converter topological circuit and a modulation method therefor, wherein same are aimed at solving the problems in the prior art of a complex topological structure, numerous conversion links, poor practicability and a low boosting ratio. The topological circuit in the present invention comprises: a high-frequency transformer for isolating a primary circuit from a secondary circuit, wherein the primary circuit comprises a high-frequency full-bridge inverter circuit, an active-clamping circuit, a C1, a D0 and an L1, and adjusts a boost mode and a buck mode of the topological circuit; the secondary circuit comprises a high-frequency rectifying circuit, a C3 and a C4, and rectifies and filters an output voltage of the high-frequency transformer; and the secondary circuit further comprises a switch transistor Q5, for adjusting the secondary circuit into a voltage multiplication circuit, so as to double the output voltage of the high-frequency transformer. According to the present invention, there is no need to pre-charge an output capacitor, entering a buck mode from zero voltage and gradually transitioning to a boost mode achieves a soft start, and adjusting a topological boosting ratio over a wide range realizes the matching of an input voltage and an output voltage.
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