beautypg.com

Hitachi SJ 300 User Manual

Page 5

background image

SJ100/L100 / PID / 5

(2) I: Integral Control

This is a control to correct the output frequency by integrating the deviation. In the case of

proportional adjustment, a large deviation will result in a large output frequency adjustment, but if the

deviation is small, then the resulting adjustment of output frequency will also be small. However, you

cannot make the deviation zero. Integral performance compensates this problem.

Integral correction of output frequency is performed by accumulating the deviation over time, so that

eventually, the deviation is brought to zero. Integration Gain (K

i

) is a coefficient that determines how

often the deviation is to be integrated. The reciprocal of integration gain is Integration Time Constant

(T

i

: T

i

=1/K

i

).

(3) D : Differential Control

This is a control to correct the output frequency by differentiating the deviation. Since P control is

based on the current deviation and I control is based on the past deviation, there will always be a delay in

the control system. Differential control compensates for this problem.

Differential correction of the output frequency is performed in proportion to the rate of change of the

deviation. Therefore, D control corrects the output frequency rapidly when there is a rapid change in the

deviation. Differentiation Gain (K

d

) is a coefficient to determine how often the deviation is to be

differentiated.

(4) PID Control

PID control is a combined Proportional, Integral and Differential control. You can achieve the best

control by adjusting the three factors, P-gain, I-gain and D-gain. Smooth control may be achieved without

any hunting by P-control; you can correct steady-state deviation by I-control; and by D-control, you can

achieve a quick response to sudden disturbances which can influence the feedback value. A large

deviation can be suppressed by P-control. A small deviation can be corrected by I-control.

(Note)

Since D-control is performed based on the differentiation of

deviation, it is a very sensitive control. Therefore, it may also

react to extraneous signals and noise, and can easily lead to

unstable system control. D-control is not normally required for the

control of processes such as flow, pressure and temperature.

You must set the integration time constant (T

i

) on the SJ100/L100 inverter. You can set the

time between 0.5 second and 150 seconds. When “0.0” seconds is set, NO integral control

will be performed.

You can set Kd between 0 and 100. Gain is (Fmax / 10) * set value of [A74] versus change in
deviation per second.

This manual is related to the following products: