In Fangkou Lead-Zinc Mine, the mine ventilators are driven by high-voltage synchronous motor or high-voltage asynchronous motor. By adopting direct high-voltage frequency converter and three-potential high-voltage frequency converter, the frequency-conversion seep regulation of the operation of mine ventilators has been achieved, resulting in remarket power economization. This paper expounds the principle of economizing power by seep regulation for ventilation, describes the structure and operating principle of the high-voltage frequency converters.