Zero-sequence fault transmission suppression method for medium-voltage flexible looped network controller of uncoupled transformer

The invention discloses a zero-sequence fault transmission suppression method for a medium-voltage flexible looped network controller of a coupling-free transformer, two ends of a power grid of MMC topology at two ends of the controller are connected by adopting back-to-back flexible direct current converter stations, each phase of the converter stations at the two ends is connected in series with 2N half-bridge sub-modules, the voltage is equalized, and the direct current side is connected in series with a coupling inductance coil. A full-bridge sub-module is prevented from being adopted, a series compensation circuit is arranged on the direct-current side, and the direct-current side is connected through a coupling inductor, so that voltage fluctuation of the direct-current side during a fault is restrained, and transmission of a zero-sequence component of the alternating-current side is prevented. According to the topological structure, the occupied area is reduced, the loss is reduced, the economical effi