Pid - Danfoss VLT AQUA Drive Design Manual

2. Introduction to VLT AQUA Drive

2.9. PID

2.9.1. Closed Loop (PID) Controller
2
The drive's Closed Loop Controller allows the drive to become an integral part of the controlled system. The drive receives a feedback signal from a sensor
in the system. It then compares this feedback to a setpoint reference value and determines the error, if any, between these two signals. It then adjusts
the speed of the motor to correct this error.
For example, consider a pump application where the speed of a pump is to be controlled so that the static pressure in a pipe is constant. The desired
static pressure value is supplied to the drive as the setpoint reference. A static pressure sensor measures the actual static pressure in the pipe and supplies
this to the drive as a feedback signal. If the feedback signal is greater than the setpoint reference, the drive will slow down to reduce the pressure. In a
similar way, if the pipe pressure is lower than the setpoint reference, the drive will automatically speed up to increase the pressure provided by the pump.
NB!
While the default values for the drive's Closed Loop Controller will often provide satisfactory performance, the control of the system
can often be optimized by adjusting some of the Closed Loop Controller's parameters. It is also possible to autotune the PI constants.
The figure is a block diagram of the drive's Closed Loop Controller. The details of the Reference Handling block and Feedback Handling block are described
in their respective sections below.
The following parameters are relevant for a simple PID control application:
22
®
MG.20.N4.02 - VLT is a registered Danfoss trademark
®
VLT AQUA Drive Design Guide