Capacitor voltage balancing method for uncontrolled precharging stage of modular multilevel converter

The invention relates to a modular multilevel converter, in particularly to a capacitor voltage balancing method especially suitable for an uncontrolled precharging stage of the modular multilevel converter (MMC). A control circuit of an anti-excitation energy power supply is improved, and the control circuit of the improved part structurally includes a control unit, an optocoupler isolation unit,an AND gate unit and a MOS field effect transistor; two input ends of the AND gate unit are connected to an output end of the control unit and an output end of the optocoupler isolation unit respectively; an output end of the AND gate unit is connected to a gate end of the MOS field effect transistor through a resistor R2. By improving the control circuit of the traditional anti-excitation energypower supply and a traditional sub-module capacitor voltage detection method, according to an improved voltage detection method, frequency/voltage conversion circuits in the conventional method are reduced, and frequency volt