Light direct current converter and modulation method thereof

The invention discloses a light direct current converter and a modulation method thereof, the light direct current converter comprises six bridge arms, and each bridge arm comprises m A type sub-modules, n B type sub-modules, r C type sub-modules and an electric reactor. The capacitance voltage of the B-type sub-module is two times that of the A-type sub-module, and the capacitance voltage of the C-type sub-module is three times that of the A-type sub-module. According to the voltage reference value of each bridge arm and the current direction of the bridge arm, various sub-modules which specifically need to be input can be calculated and determined. The method has the following advantages that the number of sub-modules required for construction of the direct current converter can be reduced, the construction cost is remarkably reduced, and the investment cost is reduced; therefore, the capacitance value of the sub-module capacitor can be reduced, the occupied area of the converter is reduced, the weight of t