Rockwell Automation Allen-Bradley PowerFlex 755T Flux Vector Tuning, Оригинальное руководство пользователя

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Rockwell Automation Publication 750-AT006D-EN-P - January 2022 111
Chapter 7 Applications
PID Gains – The PID gains determine the response of the process PID controller.
9:4 [PID Prop Gain] – The proportional control gain (P) adjusts output proportional to the size of the error. A larger error equates to a
proportionally larger correction. If the error is doubled, then the output of the proportional control is doubled. Conversely, if the error is cut in
half, then the output of the proportional output is cut in half. There is always a nonzero error with proportional only control, so the feedback
and the reference are never equal. 9:4 [PID Prop Gain] is unit-less and defaults to 1.00 for unity gain. With 9:4 [PID Prop Gain] set to 1.00 and
PID error at 1.00%, the PID output is 1.00% of maximum frequency.
9:5 [PID Int Time] – The integral control gain (I) adjusts the output based on the accumulation of error over time. The longer the error is
present, the harder it tries to correct. The integral control by itself is a ramp output correction. This type of control gives a smoothing effect
to the output and continues to integrate until zero error is achieved. By itself, integral control is slower than many applications require and
therefore is combined with proportional control (PI). 9:5 [PID Int Time] is entered in seconds. If 9:5 [PID Int Time] is set to 2.0 seconds and
PI Error is 100.00%, the PI output integrates from 0% to 100.00% in 2.0 seconds.
9:6 [PID Deriv Time] – The derivative control gain (D) adjusts the output based on the rate of change of the error and, by itself, tends to be
unstable. The faster that the error is changing, the larger the change to the output. Derivative control is generally used in Torque Trim mode
and is generally not needed in Speed mode. For example, winders using torque control rely on PD control instead of PI control. Also, 9:10 [PID
LPF BW] is useful in setting the low pass filter bandwidth to remove unwanted signal response in the PID controller.
PID Output Scaling – The output value that is produced by the PID is displayed as ±100% in 9:13 [PID Output Meter]. The following
parameters limit and scale the output.
9:7 [PID Upper Limit] – This parameter sets the output upper limit in units of percent.
9:8 [PID Lower Limit] – This parameter sets the output lower limit in units of percent.
In Exclusive or Speed Trim mode, the limits scale the PID output to a percentage of 10:422 [Maximum Freq]. In Torque Trim mode, they scale
the PID output as a percentage of rated motor torque. After the drive has reached the programmed upper and lower PID limits, the integrator
stops integrating and no further windup is possible.
An example is when the PID upper and lower limits are set to ±10% with the maximum frequency set to 100 Hz. This lets the PID controller
adjust the output of the drive ±10 Hz. 9:7 [PID Upper Limit] must always be greater than 9:8 [PID Lower Limit].
9:15 [PID Output Mult] – This parameter enables additional scaling of the PID controller output.
An example is when the application is a velocity-controlled winder. As the roll builds up, the output gain can be reduced to allow the dancer
signal to be properly reacted to by the PID controller without changing tuning of the PID controller.
Diagrams
Figure 95 on page 112 and Figure 96 on page 113 comprise one extended diagram. The output of the diagram in Figure 95 , PID Output Limited,
is the input for the diagram in Figure 96 .