SHENZHEN INVT ELECTRIC CO., LTD. CHV160 Operation Manual
74
Code
Value
P9.04
Proportional gain (Kp)
0.00
100.00
0.00
100.00
0.10
P9.05
Integrating time (Ti)
0.01
10.00s
0.01
10.00
0.10s
P9.06
Derivative time (Td)
0.00
10.00s
0.00
10.00
0.00s
Proportional gain (Kp): determines the adjusting strength of PID adjustor. The bigger the
P, the bigger the adjusting strength is. This parameter being 100 means that when the
difference between the PID feedback value and the assigned value is 100%, the adjusting
range of PID adjustor to the output frequency command is the maximum frequency (ignore
integral action and derivative action).
Integrating time (Ti): determines the speed at which PID adjustor performs integral
regulation to the discrepancy between the PID feedback value and the assigned value. The Ti
is indicating the period of time that integral controller (ignore proportional action and derivative
action), when the discrepancy between the PID feedback value and the assigned value is
100%, continuously regulates to make the regulating amount to reach the maximum frequency
(P0.07). The shorter the integrating time, the stronger the adjusting strength is.
Differential time (Td): determines the controlling strength at which PID adjustor performs
adjustment to the variance ratio of discrepancy between the PID feedback value and the
assigned value. The Td is indicating the period of time within which if the feedback value is
changed 100%, the regulating amount of integral controller is the maximum frequency (P0.07)
(ignore proportional action and integral action). The longer the Td, the bigger the controlling
strength is.
PID is the most popularly used control mode in process control, with each part playing
different role. Following simply introduces the operational principle and the controlling method:
Proportion control (P): when there is discrepancy between feedback and the assignment,
output the regulating amount in proportion to the discrepancy. If the discrepancy is constant,
the regulating amount keeps constant. Proportion control can response quickly to the feedback
variation, but only using proportion control is unable to perform noncorresponding control. The
bigger the proportional gain, the faster the system regulating speed, but being too big may
cause oscillation. The control method is first to set a long integrating time and a zero
differential time, and then run the system only by using proportion control. Change the
assigned value, and watch the stable discrepancy (steady-state error) of feedback signal and
assigned value. If the steady-state error is at the varying direction of assigned value (for
instance, increase the assigned value, the feedback value after the system is steady is always
less than the assigned value), continue to increase the proportional gain, otherwise decrease it.
Repeat the above until the steady-state error is relatively small (it is very difficult to do no
steady-state error).
Integral time (I): when there is a discrepancy between the feedback and assignment,
continuously accumulate the output regulation amount. If the discrepancy still exists, continue
to increase the regulation amount until there is no discrepancy. Integral controller can
effectively eliminate the steady-state error. Integral controller being too strong can cause
repeated overshooting, system unstable and up till oscillating. The characteristic of oscillation
caused by too strong integral action is that the feedback signal is swinging up and down
around the assigned value, and the amplitude of swing increases gradually till the oscillation
