The system has two operating mode: manually or automatically. In the first mode, an operator can start or stop any individual pumps manually, and all the pumps are to run at power frequency, i.e. 60Hz. The manual mode can be used to test whether the pumps work properly. In the second mode, the system can work automatically without any human interruption. The system can supply water as any user demands without wasting electric power by the means of a PLC and a VFD. The changeover of the two operating modes is implemented by a HOA (Hand, Off, Auto) switch.
After the main power to the system is on, an operator can choose the needed operating mode by the HOA switch. When choosing the manual mode, an operator should start one or more pumps according to the need. While an operator closes the HOA switch to automatic mode, which will put the VFD and the PLC into operation. The system will control the four pumps to run according to the water pressure. If the water pressure is low and the water demand goes high, the PLC coordinates with the VFD to put one or more of the four pumps into operation. When any pump or pumps cannot meet the demand of water even running at full speed, the next pump will be put into use until all the four pumps operate at power frequency. If the water pressure becomes high, the PLC coordinates with the VFD to remove one or more pumps until the water pressure goes normal. During the hours of the least water consumption, only one pump runs at variable speed which is enough to satisfy the demand of water.
Proportional term is where the controller provides an output number that is proportional to the error value. The response of the proportional value can be changed by multiplying the error by a constant K. This value is the proportional gain constant.
The proportional gain should never be too high because it will result in a change too big in the output for the error that the system will become unstable. The proportional gain should never be too small either or the system will respond with a large error and less responsive/sensitive controller. And if the gain is way too low the system may not even respond to the gain.