5-6 Operation Functions
5
PID Function
This function enables process control of such elements as flow rate, air volume, and pressure.
To use this function, set A071 to "01: Enabled" or "02: Reverse output enabled."
You can disable the PID operation in progress using an external signal.
To use this function, allocate "23: PID disabled" to any of the multi-function inputs. While the
PID terminal is turned ON, the Inverter disables the PID function and outputs normally.
You can limit the PID output under various conditions.
Refer to "Maximum Frequency" on page 5-28, "Frequency Limit" on page 5-60 and PID
Variable Range Limit (A078).
Parameter
No.
A071
A072
A073
A074
A075
A076
A077
A078
A079
A156
Function name Data
PID Selection
PID P Gain
PID I Gain
PID D Gain
PID Scale
PID Feedback
Selection
PID Deviation
Reverse Output
PID Variable Range
Limit
PID Feedforward
Selection
PID Sleep Function
Operation Level
00: Disabled
01: Enabled
02: Reverse output enabled
0.00 to 25.00
Proportional gain
0.0 to 3600.
Integral gain
0.00 to 100.
Differential gain
0.01 to 99.99
For unit conversion of PID Feedback
Value Monitor (d004)
00: FI (current)
4 to 20 mA
01: FV (voltage)
0 to 10V
02: Modbus communication (Modbus-
RTU)
03: Pulse train frequency
10: Operation function output
*1
00: Disabled
01: Enabled (reversing of deviation polarity)
0.0 to 100.0
Variable range with reference to the target value
00: Disabled
01: FV (voltage)
*2
0 to 10V
02: FI (current)
*2
4 to 20 mA
0.0 to 400.0(1000.)
Operation stops once the PID output drops to below the operation level.
Default setting
00
1.00
1.0
0.00
1.00
00
00
0.0
00
0.00
Unit
−
− s s
−
−
−
%
−
Hz
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5-6 Operation Functions
Parameter
No.
Function name Data
A157
C044
C052
C053
C001 to C007
PID Sleep Operation
Delay Time
PID Deviation
Excessive Level
Feedback Comparison
Signal Off Level
Feedback Comparison
Signal On Level
Multi-function Input
Selection
C021 to C022
C026
Multi-function Output
Terminal Selection
Multi-function
Relay Output
Function Selection
Related functions
0.0 to 25.5
Set the delay time until sleep operation is started.
0.0 to 100.0
OD signal output judgment level
0.0 to 100.0
FBV signal output judgment level
0.0 to 100.0
FBV signal output judgment level
23: PID (PID disabled)
24: PIDC (PID integral reset)
04: OD (PID excessive deviation)
31: FBV (PID FB status output)
A001, A005, d004
*1. Refer to "Frequency Operation Function" on page 5-70.
*2. Refer to "Analog Input (FV, FI)" on page 5-37.
Default setting
0.0
3.0
100.0
0.0
−
−
Unit
s
−
−
%
%
%
5
Reference
When the PID function is used, do not set the Analog Input Filter to 500 ms (A016 = 31).
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5-6 Operation Functions
5
Basic Structure of PID Control
Feedforward Disabled
0 to 10 V
4 to 20 mA
Target value
+
0 to 10 V
4 to 20 mA
−
Deviation
ε
Kp
1
1
+
Ti
· s
+
Td
Feedback 0 to 10 V
4 to 20 mA
· s
+
+
Manipulated value fs
Normal control of the Inverter
M =
Transducer
Sensor
Kp: Proportional gain Ti: Integral time Td: Differential time s: Operator
ε: Deviation
PID Operation
(1) P operation
Operation where the manipulated value is proportional to the deviation (target value
− current value).
Changes in steps Changes in lamps
Target value
Large
Large
A072
Manipulated value
Small
A072
Small
(2) I operation
Operation where the mainpulated value is proportional to the time-integrated value of deviations. As the current value becomes closer to the target value, the deviation decreases and thus the effect of P operation is reduced, and consequently the time needed to achieve the target value increases. I operation compensates for this condition.
Target value
Manipulated value
Small
A073
Large
Small
A073
Small
(3) D operation
Operation where the mainpulated value is proportional to the ratio of change in deviation.
Although use of PI operations alone require a response time, D operation has the effect of compensating for the response.
Target value
Manipulated value
Large
A074
Small
Large
A074
Small
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5-6 Operation Functions
PID scale
When PID Scale (A075) is set, the following parameters undergo scale conversion.
(Value after conversion) = (Value before conversion) × (A075) d004
A023
A031
F001
A024
A032
A011
A025
A033
A012
A026
A034
A020
A027
A035
A220
A028
A101
A021
A029
A102
A022
A030
A145
Feedback Selection
Select a terminal used for the feedback signal in PID feedback selection A076.
The target value depends on the terminal selected in frequency reference A001 other than that in A076. Also note that when A001 is set to "01: Control circuit terminal block," the setting of
FV/FI Selection (A005) is disabled.
To specify "02: Modbus communication (Modbus-RTU)" for PID Feedback Selection (A076), transfer the data as follows.
Write the data in holding register address 0006h based on 100% representing 10,000.
Register
Number
Function name
Parameter
No.
R/W
Monitor and setting parameters
Data
Resolutio n
0006h
PID Feedback
Selection
−
R/W 0 to 10000 0.01 [%]
Note: You can read and write data. However, you can read data only when Modbus-RTU is selected for the PID feedback.
Data cannot be read under other settings.
If "03: Pulse train input" is set for PID Feedback Selection (A076), the Inverter obtains a percent conversion result (100% at maximum frequency) of the input pulse train frequency (Hz) as a feedback value.
For details on pulse train input frequency, refer to "Pulse Train Frequency Input" on page 5-82.
5
Feedforward Selection
Select a terminal used for feedforward signals in PID Feedforward Selection A079.
The A079 setting is enabled even if the terminal selected in A079 is duplicated with the terminal selected for target value or feedback value input.
If A079 is set to "disabled", feedforward control is disabled.
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5
5-6 Operation Functions
PID Deviation Reverse Output
Depending on the sensor characteristics, etc. the polarity of deviation between the target value feedback values may not match the Inverter's command. In this case, the deviation polarity can be reversed by using the PID Deviation Reverse Output (A077 = 01).
Example) Controlling a refrigerator compressor
The temperature sensor specification is 0 to 100 °C: 0 to 10 (V) and the target value is 5 °C.
If the current temperature is 10 °C, "(Feedback value) > (Target value)" is satisfied and therefore the Inverter frequency drops under normal PID control.
→ Set A077 to "01" so that the Inverter increases the frequency.
A077
PID target value
PID operation
−1
PID feedback
PID Variable Range Limit
This function limits PID output within a variable range relative to the target value.
To use this function, set PID Variable Range Limit (A078). The output frequency is limited within a range of "target value
± (A078)", with the maximum frequency defined as 100%.
With A078 set to 0.0, this function is disabled.
PID output (%)
PID output range
PID target value
PID Variable Range Limit (A078)
PID Variable Range Limit (A078)
Time (s)
PID Reverse Output
If the PID operation result is a negative value under normal PID control, the frequency reference given to the Inverter is limited by 0 Hz. When PID Selection (A071) is set to "02:
Reverse output enabled," a reverse output can be output to the Inverter even when the PID operation result is a negative value.
If A071 = 02: Reverse output enabled, PID Variable Range Limit (A078) explained above is disabled.
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5-6 Operation Functions
PID Gain Adjustment
If a stable response cannot be obtained in PID function operation, adjust each gain as follows according to the situation.
The feedback value changes slowly when the target value is changed. → Raise P Gain A072.
The PID feedback value changes fast but isn't stable.
The PID feedback value fluctuates unstably.
→ Lower P Gain A072.
The target and the PID feedback values wouldn't match smoothly. → Lower I Gain A073.
Response is slow even with P gain raised.
→ Raise I Gain A073.
→ Raise D Gain A074.
With P gain raised, the PID feedback value fluctuates and isn't stable. → Lower D Gain A074.
PID Excessive Deviation (OD)
You can set PID excessive deviation level C044 during PID control. A signal can be output to a multi-function output terminal when the PID deviation
ε reaches the level set in C044 or above.
Allocate "04: OD" to any Multi-function Output Terminal Selections (C021 to C022) or Relay
Output Function Selection (C026).
C044 can be set from 0 to 100. The setting corresponds to the range of 0 to the maximum target value.
Feedback Comparison Signal
A signal can be output to a multi-function output terminal when the PID feedback is out of the specified range.
Allocate "31: FBV" to any Multi-function Output Terminal Selections (C021 to C022) or Relay
Output Function Selection (C026).
5
PID feedback
C052 (OFF level)
C053 (ON level)
Time
FW input
ON
OFF
FBV output
ON
OFF
PID Feedback Value Monitor (d004)
You can monitor the PID feedback value.
The monitor value is displayed as the product of PID Scale (A075).
"d004 display" = "Feedback value [%]"
× "PID Scale (A075)"
PID Integral Reset (PIDC)
Clears the integral value of PID operation.
Allocate "24: PIDC" to any Multi-function Input Selections (C001 to C007).
Clears the integral value every time the PIDC terminal is turned on.
Do not turn on the PIDC terminal during PID operation to avoid a possible overcurrent trip. Turn
ON the PIDC terminal after turning OFF PID operation.
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