Soft start control method of power electronic transformer

The invention discloses a power electronic transformer soft start control method applied to a 10kV/1kV direct current high-voltage system, a high-voltage side is formed by connecting 10 H-bridge power modules in series, a low-voltage side is formed by connecting 10 H-bridge power modules in parallel, and the high-voltage side and the low-voltage side are connected through a high-frequency isolation transformer; before the system is started, if a direct-current power grid on one side is not electrified, the other end is pre-charged through a power electronic transformer, and at the moment, no matter whether a low-voltage side is charged by a high-voltage side or is reversed, voltage balance control among 10 series modules on the high-voltage side needs to be strictly controlled during pulse opening. According to the soft start control method provided by the invention, the voltage balance of each module in the starting process of the 10kV direct-current power grid is ensured, the voltage of the other end is ens