Abstract : This paper introduces the composition and control principle of a towerless constant pressure water supply system in a residential area, as well as the application of frequency converter technology in industrial control systems. Keywords : Frequency converter; constant pressure water supply; PID controller; soft start 1 Introduction With the improvement of industrial automatic control, the technology of frequency converter constant pressure water supply devices has become relatively mature and has received a good market response. Its energy-saving operation and system stability and reliability have been widely recognized. This system has also been continuously updated and developed along with the development of controller and frequency converter technology. Regarding controllers, the evolution has progressed from relay logic, microcontrollers, PLCs, to dedicated controllers. Regarding frequency converter speed regulation, its development has gone through multi-segment speed control, analog signal control, and dedicated controllers. Each step of development means replacing traditional methods with newer and better devices. This system uses a relatively advanced programmable logic controller (PLC) as the controller to complete the frequency converter constant pressure water supply. Based on different water consumption levels, the system receives signals from remote pressure transmitters on the pipeline network, which are input to the PLC to achieve automatic PID regulation, controlling the water pump's operating status to maintain the pipeline water supply pressure. The application of variable frequency technology (VFD) systems is quite extensive, applicable to many aspects such as domestic, industrial, and fire-fighting water supply. Below, we take a residential community constant pressure water supply system as an example to introduce the application of VFD technology in industrial control systems. 2. Process Flow Introduction Previously, most water supply systems used traditional water towers, elevated water tanks, or pressure tank-type booster equipment. However, these all required pumps to increase the water volume at a pressure higher than the actual water usage level, resulting in increased pump shaft power and energy loss. Furthermore, since the user water pressure is constant, the pressure tank needed periodic inflation, increasing the equipment's safety risks. The current VFD towerless constant pressure water supply technology overcomes these shortcomings. The VFD constant pressure water supply control system measures the network pressure, and after calculation by the PLC's built-in PID controller, adjusts the output frequency of the VFD to achieve constant pressure water supply in the network. As shown in process flow diagram 1, purified water from the water company flows into the community's water storage tank, and then two motors and two industrial frequency pumps controlled by one VFD deliver the water to each user's home in the community. The operation of the four pumps is controlled according to the water pressure in the user's network. When water consumption is low, only one variable frequency pump operates to ensure constant pressure within the pipes. When water consumption is high, the system automatically starts the remaining pumps to maintain a constant water pressure supplied to the community. Motors A and B are controlled by a single frequency converter, collectively referred to as variable frequency motors. Under low water consumption conditions, the two variable frequency pumps switch between each other according to a time controller to extend their lifespan. To prevent overflow from the storage tank due to excessively high water levels when water consumption is low, a level interlock alarm control is added to improve system safety. A vent valve is added to the bottom of the tank for periodic cleaning to ensure the cleanliness of the water supplied to users. [b][align=center]For more details, please click: Fully Automatic Variable Frequency Tankless Constant Pressure Water Supply System[/align][/b]