变频控制系统由电机、VFD 变频器、传感器、PLC组成。传感器采集系统温度 / 压力等过程信号送入 PLC；PLC 将实测值与设定值对比，输出调节指令至 VFD；VFD 改变输出频率，连续调节电机转速，从而改变泵 / 风机输出流量，形成闭环控制，维持系统参数稳定。

The VFD control system consists of a motor, VFD, sensors and PLC. The sensors acquire process signals such as system temperature and pressure and feed them to the PLC. The PLC compares the measured values against the set?points and sends regulating commands to the VFD. The VFD varies its output frequency to continuously adjust the motor speed, which changes the output flow rate of the pump/fan. This forms closed?loop control to keep the system parameters stable.