Self-excitation soft start method for chain-type converter valve

The invention discloses a self-excitation soft start method for a chain-type converter valve. The soft start system comprises a grid-connected circuit breaker, an electric reactor and a starting circuit which correspond to each phase and are connected in series with one another. The soft start method comprises the following steps: controlling to close the grid-connected circuit breaker, so that direct current capacitors of power units of the chain-type converter valve are charged for the first time by a power grid by virtue of a current-limiting resistor; controlling to switch on a by-pass switch, bypassing the current-limiting resistor, selecting at least one power unit from various power units of the converter valve, and bypassing the selected power units, so that the non-bypassed direct current capacitors of power units are charged by the power grid; unlocking the chain-type converter valve, and allowing the chain-type converter valve to enter a direct current voltage closed loop to control the operation; and judging that the direct current voltage of each power unit is stabilized at a value needed by normal operation, and transferring into a closed loop of a control target to control the operation. According to the method, the direct current voltage of each unit can be effectively improved before the converter valve is started, the start impact current of the converter valve is effectively reduced, the direct current voltage balancing control of the converter valve is promoted, and the safety operation of a power device is guaranteed.