Disclosed is a neutral point clamp (NPC) three-level inner tube lossless voltage-sharing clamp circuit, comprising a power frequency first half period and a power frequency second half period consisting of an IGBT (Q1-Q4), a diode (D1-D10), a capacitor (C1-C4) and a resistor (R1-R2) with a symmetrical structure; the IGBT comprises a first IGBT (Q1), a second IGBT (Q2), a third IGBT (Q3) and a fourth IGBT (Q4), wherein the first IGBT and the second IGBT are in the power frequency first half period, the third IGBT and the fourth IGBT are in the power frequency second half period, and the first IGBT and the fourth IGBT are connected to a bus respectively; when the second IGBT is conductive, the first IGBT is in an instant switched on state, the third IGBT is switched off, and the third IGBT and the fourth IGBT bear a full bus voltage (Vin); when the second IGBT is conductive, the first IGBT is in a switched off state; and one diode and one IGBT are conductive in each of the power frequency first half period and/or the power frequency second half period to form zero level. The clamp circuit can dynamically clamp two inner tubes to enable the voltage thereof not to exceed +10 percent of half of a bus voltage, so as to achieve the purpose of restraining a switched off voltage peak of the inner tubes in a lossless manner.
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