Abstract : This paper introduces the design and application of Dongfang-Hitachi Inverter and its power frequency auto bypass in wind-draught device speed regulation. Key words : Dongfang-Hitachi Inverter, Switch between power frequency and adjusted frequency 1 Introduction With the increasing popularity of energy conservation and the construction of an energy-saving society, high-voltage and high-power variable frequency speed regulation technology has become increasingly mature, and variable frequency speed regulation technology has been widely used in thermal power plants. In recent years, its application in forced and induced draft fans has been relatively common. However , in order to ensure reliability, manual power frequency bypass systems are often selected. Practice has proven that although this method has a certain effect, it has a major drawback. The main problem is that the fan must be stopped during switching. Stopping the fan will reduce the boiler output by 30% to 40%, directly affecting the power generation and causing power loss. It is essential to ensure that the fan can smoothly and seamlessly switch from variable frequency speed control to mains frequency speed control and vice versa. This function is necessary for routine maintenance and troubleshooting. [b][align=center]For details, please click: Design and Application of Hitachi Inverters and Automatic Mains Frequency Bypass in Exhaust Fan Speed ​​Control[/align][/b]