Delta VFD300C43S-HS User Manual page 409

Concept of PID control
 Proportional gain (P):
The output is proportional to input. With only proportional gain control, there is always a
steady-state error.
Adjustment: Turn off the Ti and Td, or remain Ti and Td in constant value, then adjust the
proportional gain (P).
Increase: Faster status feedback, but excessive adjustment will increase the overshoot.
Decrease: Smaller overshoot, but excessive adjustment will slow down the transient response.
 Integral time (I):
The controller output is proportional to the integral of the controller input. To eliminate the
steady-state error, add an "integral part" to the controller. The integral time controls the relation
between integral part and the error. The integral part increases over time even if the error is small.
It gradually increases the controller output to eliminate the error until it is zero. This stabilizes the
system without a steady-state error by using proportional gain control and integral time control.
Adjustment: The integral time (I) accumulates from the time difference, if the vibration cycle is
longer than the setting for integral time, the integration enhances. Increase the
integral time (I) to reduce the vibration.
Increase: Reduce the overshoot, excessive adjustment causes worse transient response.
Decrease: Faster transient response, but the transient time will be longer, and takes more time to
achieve the steady state. Excessive adjustment causes larger overshoot.
 Differential control (D):
The controller output is proportional to the differential of the controller input. During elimination of
the error, oscillation or instability may occur. Use the differential control to suppress these effects
by acting before the error. That is, when the error is near zero, the differential control should be
zero. Use proportional gain (P) and differential control (D) to improve the system state during PID
adjustment.
Adjustment: When the vibration cycle is shorter and continuous, it means that the differential time
setting is too large, and causes excessive output. Decrease the setting of D gain to
reduce the vibration. If the D gain is set to 0, adjust the PID control again.
Using PID control in a constant pressure pump feedback application:
Set the application's constant pressure value (bar) to be the set point of PID control. The pressure
sensor sends the actual value as the PID feedback value. After comparing the PID set point and
PID feedback, an error displays. The PID controller calculates the output by using proportional gain
(P), integral time (I) and differential time (D) to control the pump. It controls the drive to use a
different pump speed and achieves constant pressure control by using a 4–20mA signal
corresponding to 0–10 bar as feedback to the drive.
Chapter 12 Description of Parameter SettingsC2000-HS
12.1-08-3