Function Application
‑512‑
Figure 3‑18 Simple PLC as the main frequency source
Step 3: Set FC‑16 to select the simple PLC operation mode.
Step 4: Set FC‑17 to determine whether to retain the PLC operation stage and
operating frequency upon power failure or stop.
3.1.2.7 Setting the Main Frequency Through PID
PID control is a common process control method, which calculates the proportion,
integral, and derivative of the difference between feedback signals and target signals
of the controlled variable, and adjusts the output frequency of the AC drive
accordingly to create a closed‑loop system to stabilize the controlled variable at the
target value. Generally, PID output can be used as the running frequency for on‑site
closed‑loop process control applications, such as closed‑loop pressure control and
closed‑loop tension control.
● Proportional gain Kp: When there is a deviation between the PID input and output,
the PID regulator adjusts the output to reduce the deviation of the controlled
variable. The deviation reduction speed depends on the proportionality coefficient
Kp. A greater Kp value means faster deviation reduction. However, a large Kp value
often causes oscillation, especially in the case of long hysteresis. A smaller Kp
value means lower probability of oscillation. However, a small Kp value leads to
slow adjustment. (Proportional gain of 100.0 means that the PID regulator adjusts
the output frequency reference at an amplitude of the maximum frequency when
the deviation between the PID feedback value and preset value is 100.0%.)
● Integral time Ti: Ti determines the intensity of integral adjustment by the PID
regulator. A shorter integral time means stronger integral adjustment by the PID
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