Submerged arc furnace is a necessary equipment for smelting ferrosilicon, ferronickel, ferrochromium and calcium carbide in ferroalloy industry. According to incomplete statistics, there are more than 30000 submerged arc furnaces in China. For a long time, domestic submerged arc furnaces mostly use AC power supply, resulting in low power factor, difficult control and balance of three-phase power grid, low efficiency and high operation cost.