Using Pid Control - Omron VARISPEED G7 Instruction Manual

Using PID Control

PID control is a method of making the feedback value (detection value) match the set target value. By combin-
ing proportional control (P), integral control (I), and derivative control (D), you can even control targets
(machinery) with play time.
The characteristics of the PID control operations are given below.
P control
I control
D control
PID Control Operation
To understand the differences between each PID control operation (P, I, and D, the variation in the amount of
operation (output frequency) is as shown in the following diagram when the deviation (i.e., the difference
between the target value and feedback value) is fixed.
PID Control Applications
The following table shows examples of PID control applications using the Inverter.
Applica-
tion
Speed Con-
trol
Pressure
Control
Flow Rate
Control
Tempera-
ture Con-
trol
-94
6
Outputs the amount of operation proportional to the deviation. You cannot, however, set the
deviation to zero using P control alone.
Outputs the amount of operation that integrates the deviation. Used for matching feedback
value to the target value. I control is not suited, however, to rapid variations.
Outputs the amount of operation derived from the deviation. Can respond promptly to rapid
variations.
Deviation
Amount of operation
Fig 6.59 PID Control Operation
• Feeds back machinery speed information, and matches speed to the target value.
• Inputs speed information from other machinery as the target value, and performs
synchronous control using the actual speed feedback.
Feeds back pressure information, and performs constant pressure control.
Feeds back flow rate information, and controls the flow rate highly accurately.
Feeds back temperature information, and performs temperature adjustment control
by rotating the fan.
D control
Control Details
Time
PID control
I control
P control
Time
Example of Sen-
sor Used
Tachometer genera-
tor
Pressure sensor
Flow rate sensor
• Thermocouple
• Thermistor