Abstract : This paper introduces a method for technically transforming the soft water supply system of a steel plant using a microcontroller and frequency converter. After the transformation, the system has significant energy-saving effect, reliable operation, and convenient operation. Keywords : Microcontroller; Frequency converter; Water supply system; Transformation scheme 0 Introduction In the production process, the steel plant in this city needs to replenish soft water as industrial cooling water at any time according to the production process requirements. The original design installed three centrifugal water pumps, equipped with 150kW motors, and implemented a main pipe water supply system: two pumps were in operation and one was on standby. The electrical control system used logic circuits composed of discrete components, which frequently failed during operation. In addition, with the improvement of production process and the improvement of filtered water quality, the amount of soft water used has decreased year by year. When using it, the flow rate is adjusted by changing the opening of the outlet valve, resulting in a large energy loss. Therefore, the original system was technically transformed. [b]1 Transformation Scheme Architecture 1.1 System Architecture Diagram is shown in Figure 1. [align=center] Figure 1 System Architecture Diagram [/align] This system consists of a microcontroller, frequency converter, motor soft starter, three-phase AC centrifugal water pump, pressure sensor, relay group, etc. [b][align=center]For details, please click: Water Supply System Retrofit Scheme Based on Microcontroller Control[/align][/b]