Modular multilever converter (MMC) module topological structure applicable for flexible direct current transmission

The invention provides a module topology which is applied to a modular multilever converter (MMC) type flexible direct current transmission system and has improved power density. The module topology comprises four insulated gate bipolar translators (IGBTs) VT1, VT2, VT3 and VT4, wherein the four IGBTs are respectively and reversely connected in parallel with diodes VD1, VD2, VD3 and VD4; a direct-current capacitor C is input or removed by controlling the switch-on or switch-off of the two IGBTs VT1 and VT2 in a first H half-bridge structure so as to generate a required alternating-current voltage; and an extra LC circuit is controlled by the two IGBTs VT3 and VT4 in a second H half-bridge structure to absorb a fundamental frequency on the direct-current capacitor and the frequency fluctuation of a second harmonic frequency, so that the frequency fluctuation is reduced, the capacitance and the volume of the direct-current capacitor are reduced. The capacitance of the direct-current capacitor can be reduced through the introduction of an auxiliary circuit, thus, the module volume is reduced, and the power density is improved.