Delta CT2000 Series, User Manual

Page: 319 / 634

Chapter 12 Description of Parameter Settings

CT2000 Series
12.1-08-2
 Concept of PID control
1. Proportional gain(P):
the output is proportional to input. With only proportional gain control, there will always be
a steady-state error.
2. Integral time(I):
the controller output is proportional to the integral of the controller input. To eliminate the
steady-state error, an “integral part” needs to be added to the controller. The integral time
decides the relation between integral part and error. The integral part will be increased by
time even if the error is small. It gradually increases the controller output to eliminate the
error until it is 0. In this way a system can be stable without steady-state error by proportional
gain control and integral time control.
3. 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. The differential control can be
used to suppress these effects by acting before the error. That is, when the error is near 0,
the differential control should be 0. Proportional gain(P) + differential control(D) can be used
to improve the system state during PID adjustment.
 When PID control is used 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 will send the actual value as PID feedback value. After comparing the PID set point and
PID feedback, there will be an error. Thus, the PID controller needs to calculate the output by
using proportional gain(P), integral time(I) and differential time(D) to control the pump. It controls
the drive to have different pump speed and achieves constant pressure control by using a 4-20mA
signal corresponding to 0-10 bar as feedback to the drive.
pressure
sensor
throttle
R(L1)
S(L2)
T(L3)
R(L1)
S(L2)
T(L3)
U(T1)
V(T2)
W(T3)
IM
3~
ACM
ACI/A VI
- +
DC
(4-20mA /0-10V )
water pump
Feedback 4-20mA
corresponds
0-10bar
analog si gnal common
no fuse breaker
(NFB)
1. Pr.00-04 is set to 10 (Display PID analog feedback signal value (b) (%))
2. Pr.01-12 Acceleration Time will be set as required
3. Pr.01-13 Deceleration Time will be set as required
4. Pr.00-21=0 to operate from the digital keypad
5. Pr.00-20=0, the set point is controlled by the digital keypad
6. Pr.08-00=1 (Negative PID feedback from analog input)
7. ACI analog input Pr. 03-01 set to 5, PID feedback signal.