B5: Pid Control - YASKAWA CIMR-VU BA0001 Technical Manual

5.2 b: Application
Multi-function Contact
Input: Timer Function
Multi-function Contact
Output: Timer Function
u

b5: PID Control

The drive has a built in PID (Proportional + Integral + Derivative) controller that can be used for closed loop control of system
variables such as pressure, temperature etc. The difference between the target and the feedback value (deviation) is fed into
the PID controller. The PID controller adjusts the drive output frequency in order to minimize the deviation, providing an
accurate control of the system variables.
n P Control
The output of P control is the product of the deviation and the P gain so that it follows the deviation directly and linearly. With
P control only an offset between the target and feedback remains.
n I Control
The output of I control is the integral of the deviation. It minimizes the offset between target and feedback value that typically
remains when pure P control is used. The integral time (I-time) constant determines how fast the offset is eliminated.
n
D Control
D control predicts the deviation signal by multiplying its derivative (slope of the deviation) with a time constant and adding
this to the PID input. This way the D portion of a PID controller provides a braking action to the controller response and can
reduce the tendency of oscillations and overshoot.
Be aware that D control tends to amplify noise on the deviation signal, which can result in control instability. D control should
therefore only be used when necessary.
n
PID Operation
To better demonstrate how PID works, the diagram below shows how the PID output changes when the PID input (deviation)
jumps from 0 to a constant level.
n Using PID Control
Applications for PID control are listed in the table below.
Application
Machinery speed is fed back and adjusted to meet the target value. Synchronous control is
Speed Control
performed using speed data from other machinery as the target value
Pressure Maintains constant pressure using pressure feedback.
Fluid Control Keeps flow at a constant level by feeding back flow data.
Temperature
Maintains a constant temperature by controlling a fan with a thermostat.
Control
136
ON
ON
b4-01 b4-02
Figure 5.15 Timer Operation
PID input
D control
PID Output
Figure 5.16 PID Operation
Description
YASKAWA ELECTRIC SIEP C710606 18F YASKAWA AC Drive – V1000 Technical Manual
ON
ON
b4-01 b4-02
Time
PID output
I control
P control
Time
On (Closed)
Off (Open)
On (Closed)
Off (Open)
Sensors Used
Tachometer
Pressure sensor
Flow rate sensor
Thermocoupler,
Thermistor