Traditional constant pressure water supply methods utilize water towers, elevated water tanks, and pressure tanks. With the development of variable frequency drive (VFD) technology and the increasing demands for drinking water quality, VFD constant pressure water supply systems have gradually replaced traditional methods. This system primarily utilizes the PID function of the VFD to regulate the pump flow rate, achieving constant pressure water supply. It features low investment, high efficiency, powerful functionality, flexible configuration, and a high degree of automation. It not only eliminates water hammer effects but also has a low failure rate and significant energy savings, achieving 20%–40% energy savings. Composition of a VFD Constant Pressure Water Supply System The VFD constant pressure water supply system mainly consists of a VFD, a PID controller (or one built into the VFD), pressure sensors, hydraulic sensors, power control circuitry, and a water pump. The VFD is the core component of the entire system. The system block diagram is shown in Figure 1. [align=center] Figure 1. Block Diagram of a Variable Frequency Drive (VFD) Constant Pressure Water Supply System [/align] The system uses a pressure sensor installed on the outlet water pipe network to convert the outlet pressure signal into a standard 4-20mA signal, which is then sent to a PID controller. After calculation and comparison with the given pressure parameter, an adjustment parameter is obtained and sent to the VFD. The VFD controls the pump speed, adjusting the system's water supply to maintain the pressure in the water supply network at the given pressure. When the water supply load changes, the changing signal is transmitted to the PID controller, which adjusts the VFD's frequency to control the pump speed, achieving closed-loop control. If the VFD itself has PID control functionality, an external PID controller is not required. If the water consumption exceeds the supply capacity of one pump, additional pumps are added via the PID controller. The number of working pumps and the VFD's speed adjustment are controlled by a relay control circuit or PLC based on the water consumption, achieving constant pressure water supply. [b][align=center]For more details, please click: Application of VFDs in Constant Pressure Water Supply Systems[/align][/b]