Abstract : This paper analyzes the energy-saving principle of applying frequency converters to sewage pumps in the sewage treatment process and proposes a design scheme using Vacofi frequency converters produced by Vasa Control Systems GmbH, Finland, as the frequency conversion device for sewage pumps. Practice has proven that after adopting Vacofi frequency converters, the sewage treatment system operates stably, is easy to control, saves energy, and has significant economic and social benefits. Keywords : Vacofi frequency converter, sewage treatment, energy saving 1 Introduction With the continuous improvement of people's requirements for their living environment and the enhancement of their environmental awareness, the country and society are paying more and more attention to the treatment of various types of pollution. Since water is a limited and non-renewable resource, the treatment of water pollution is even more important. Various types of sewage in cities are collected through collection system pipelines to pumping stations, and then pumped to the next level pumping station through sewage pumps, finally reaching the sewage treatment plant. Under normal circumstances, sewage pumps are driven by constant-speed AC motors, but the sewage flow rate varies. In order to ensure the normal discharge of sewage, workers have to frequently adjust the opening of baffles or valves on site to control the sewage discharge. This not only increases the labor intensity of workers, but also wastes a lot of electrical energy on the loss of pump valve resistance. Therefore, sewage pumps need to operate under varying conditions. If a frequency converter is used for speed regulation, replacing the adjustment of baffles or valves by adjusting the motor speed, it can not only reduce the labor intensity of workers but also save energy, which is of great significance for improving the economic efficiency of enterprises. [b]2 Energy-saving principle of frequency converter control for sewage pumps 2.1 Pump characteristic analysis[/b] According to the relevant formulas of the centrifugal pump characteristic curve: [b][align=center]For details, please click: Application of frequency converters in sewage treatment[/align][/b]