Abstract : This paper focuses on the application of variable frequency speed control technology in the in-boiler chemical dosing system of Jingmen Power Plant, and provides a relatively systematic explanation of the basic principles of variable frequency speed control technology. It also demonstrates significant applicability and practical value in improving in-boiler water quality and reducing chemical consumption. Keywords: Variable frequency speed control; frequency converter; thermal power plant; in-boiler chemical dosing. With the continuous improvement of automation in China's power industry, variable frequency speed control technology has been widely applied in thermal power plants. Due to its advantages such as low failure rate, high speed control accuracy, multiple protection functions, and significant energy-saving effect, it has become the ideal choice for technical transformation of DC speed control and electromagnetic slip speed control. For AC motors, which account for 2/3 of the country's total electricity consumption, a 0-50Hz AC-DC-AC frequency converter is needed, with an energy-saving frequency range of 5-45Hz, achieving an energy-saving rate of approximately 20%-60%. Currently, most of these motors operate under full voltage, rated frequency, and constant speed conditions, with an operating efficiency of only about 60% and a power factor of only 0.7. Therefore, the state listed speed regulation technology as one of the ten demonstration projects for comprehensive resource conservation and utilization technology transformation during the Ninth Five-Year Plan period. Previously, Jingmen Power Plant had successfully completed the transformation of its steam turbine drain pumps, boiler fuel oil (light diesel) ignition pumps, and chemical domestic water pumps using variable frequency speed regulation technology. The plant also implemented technical transformation of the in-boiler chemical dosing system for the two 200MW units in Phase II. 1. Variable Frequency Speed ​​Regulation Technology and the Working Principle of Variable Frequency Speed ​​Controllers The working principle of an asynchronous motor using a variable frequency speed controller is as follows: it converts AC to DC, smooths and filters it, and then through an inverter circuit, converts the DC to AC of different frequencies, enabling the motor to obtain the voltage, current, and frequency required for stepless speed regulation. According to motor theory, the motor speed n = 6of/p, where p is the power supply frequency and P is the number of pole pairs. When the number of pole pairs remains constant, the speed n is directly proportional to the power supply frequency. For example, if the number of pole pairs is two, and the power supply frequency is 50Hz... The electric motor's speed is 1500 r/min. When the power supply frequency is 20 Hz, the motor's speed correspondingly changes to 600 r/min. Continuously changing the power supply frequency allows for smooth adjustment of the motor's speed; this is the working principle of variable frequency speed control. The key equipment in variable frequency speed control is the frequency converter, which determines the performance, function, and reliability of the entire speed control system. A frequency converter is a power supply device that rectifies and inverts grid power into AC power with variable frequency and voltage for a three-phase AC motor. It mainly consists of power modules and ultra-large-scale dedicated microcontrollers. Different brands of frequency converters, due to the use of different power modules, microcontrollers, and control methods, have different performance and functions suitable for different applications. [b][align=center]For more details, please click: Application of Variable Frequency Speed ​​Control Technology in Power Plant Boiler Chemical Dosing Systems[/align][/b]