Menu 14 − User PID Controller

Mode: Open‑Loop

PID controllers

Two general purpose PID controllers are provided as shown in the diagram below. Both operate in the same way except that PID controller 2 does not include a pre-sleep boost reference or alternative feedback and error selection. In the following sections a description is given for PID controller 1. The descriptions also apply to PID controller 2 except where stated. The sample rate for the PID controllers is always 4ms.


Parameter14.001  PID1 Output
Short descriptionDisplays the output for PID1
ModeOpen‑Loop
Minimum-100.00Maximum100.00
Default Units%
Type16 Bit VolatileUpdate Rate4ms write
Display FormatStandardDecimal Places2
CodingRO, ND, NC, PT

Controller

The controller section for the PID controllers is shown in the introduction. The structure of PID controller 1 shown in the introduction is when PID1 Mode Selector  (14.059) = 0, PID1 Feedback Output Scaling  (14.058) = 1.000, and PID1 Feedback Square Root Enable 2  (14.062) = 0. The additional features provided by these parameters are not available for PID controller 2, and so this controller always has the structure shown. If the combined enable is inactive then all internal states are held at zero and the destination parameter will be defined by PID1 Feed-forwards Reference  (14.019) alone. If the enable is active the PID controller is active even if the destination is not routed to a valid parameter or to 0.000. It should be noted that if either of the enable sources is routed to 0.000 or to a non-valid parameter the source value is taken as 1, therefore with default settings, PID1 Enable Source 1  (14.009) = 0.000 and PID1 Enable Source 2  (14.027) = 0.000, the PID controller can be enabled by simply setting PID1 Enable  (14.008).

PID1 Error  (14.022) is the difference between the reference and feedback produced by the reference and feedback systems described in the previous sections. The PID controller output is defined as follows:

PID1 Output  (14.001) = PID1 Error  (14.022) x [Kp + Ki/s + sKd/(0.064s + 1)]

Kp = PID1 Proportional Gain (14.010)

Ki = PID1 Integral Gain  (14.011)

Kd = PID1 Differential Gain  (14.012)

Therefore:

1. If PID1 Error  (14.022) = 100.00% the proportional term gives a value of 100.00% if PID1 Proportional Gain (14.010) = 1.000.

2. If PID1 Error  (14.022) = 100.00% the integral term gives a value that increases linearly by 100.00% per second if PID1 Integral Gain  (14.011) = 1.000.

3. If PID1 Error  (14.022) increases linearly by 100.00% per second the differential term gives a value of 100.00% if PID1 Differential Gain  (14.012) = 1.000. (A filter with a time constant of 64ms is provided on the differential gain to reduce the noise produced by this term.)

The output may be limited to a range that is less than the maximum range of PID1 Output  (14.001) using PID1 Output Upper Limit  (14.013) and PID1 Output Lower Limit (14.014). If PID1 Output Lower Limit (14.014) > PID1 Output Upper Limit  (14.013) then the output is held at the value defined by PID1 Output Upper Limit  (14.013). If PID1 Symmetrical Limit Enable  (14.018) = 1 then the lower limit = -(PID1 Output Upper Limit  (14.013)). If the output reaches either of these limits the integral term accumulator is frozen until the output moves away from the limit to prevent integral wind-up. The integral hold function can also be enabled by the user by setting PID1 Integral Hold  (14.017) = 1.

PID1 Output Scaling  (14.015) can be used to scale the output, which is limited to a range from -100.00% to 100.00% after this function. The output is then added to PID1 Feed-forwards Reference  (14.019) and is again limited to the range from -100.00% to 100.00% before being routed to the destination defined by PID1 Destination  (14.016).


Parameter14.002  PID1 Feed-forwards Reference Source
Short descriptionDefines the input source for the feed-forwards reference source for PID1
ModeOpen‑Loop
Minimum0.000Maximum59.999
Default0.000Units 
Type16 Bit User SaveUpdate RateDrive reset read
Display FormatStandardDecimal Places3
CodingRW, PT, BU

See PID1 Output  (14.001).


Parameter14.003  PID1 Reference Source
Short descriptionDefines the input source for the reference for PID1
ModeOpen‑Loop
Minimum0.000Maximum59.999
Default0.000Units 
Type16 Bit User SaveUpdate RateDrive reset read
Display FormatStandardDecimal Places3
CodingRW, PT, BU

The reference section for the PID controllers is shown in the introduction. The pre-sleep boost control is only included in PID controller 1. The reference sections are always active even if the PID controller itself is disabled or the reference sources are not routed to valid parameters. If a reference source is not a valid parameter or is 0.000 then the value is taken as zero.

The reference is the sum of the reference source, the PID1 Digital Reference  (14.025) and the PID1 Pre-sleep Boost Level  (14.028) when it is active. The result is multiplied by PID1 Reference Scaling  (14.023) and then limited to +/-100.00%. The reference can then be inverted if required (PID1 Reference Invert (14.005) = 1) and then a slew rate limit is applied with PID1 Reference Slew Rate  (14.007). This limits the maximum rate of change so that a change from 0.00 to 100.00% takes the time given in PID1 Reference Slew Rate  (14.007).

Sleep mode is used to stop the motor if the frequency or speed reference falls below a specified level so that the system does not run inefficiently at low speeds (see Sleep / Wake Threshold (06.053)). If the frequency or speed reference is controlled by PID controller 1 then the PID controller feedback will fall when sleep mode becomes active because the motor has stopped. The PID controller output will rise again above the sleep/wake threshold and the motor will restart. To minimise the number of transitions into and out of sleep mode the sleep condition can be delayed and an increased reference applied during this period by setting PID1 Pre-sleep Boost Level  (14.028) to a non-zero value. When Sleep Required (06.056) = 1 the PID1 Pre-sleep Boost Level  (14.028) is added to the reference until PID1 Error  (14.022) is reduced below zero or until this additional reference has been applied for PID1 Maximum Boost Time  (14.029). This system is only intended for applications where PID controller 1 alone is used to control the motor frequency or speed via the Menu 1 reference system and the motor rotates in the positive direction under normal conditions. When the PID output first falls below the Sleep / Wake Threshold (06.053) it is possible for PID1 Error  (14.022) to be negative because of a positive value remaining in the integral accumulator. To allow the error to become positive so that the boost period is not terminated immediately, the PID1 Pre-sleep Boost Level  (14.028) is applied for a minimum of 100ms before the end of the boost period can be terminated because PID1 Error  (14.022) is greater than or equal to zero.


Parameter14.004  PID1 Feedback Source
Short descriptionDefines the input source for the feedback for PID1
ModeOpen‑Loop
Minimum0.000Maximum59.999
Default0.000Units 
Type16 Bit User SaveUpdate RateDrive reset read
Display FormatStandardDecimal Places3
CodingRW, PT, BU

Feedback

The feedback section for the PID controllers is shown in the introduction. The feedback sections are always active even if the PID controller itself is disabled or the feedback sources are not routed to valid parameters. If a reference source is not a valid parameter or is 0.000 then the value is taken as zero.

The feedback is the sum of the feedback source and the PID1 Digital Feedback  (14.026). The result is multiplied by PID1 Feedback Scaling  (14.024) and then limited to +/-100.00%. A square root function can be applied (PID1 Feedback Square Root Enable 1 (14.060) = 1) and the feedback can then be inverted if required (PID1 Feedback Invert  (14.006) = 1). The square root function is defined as follows.

Square root function output = Sign(Input) x 100.00% x √(|Input| / 100.00%)

where Sign(Input) = 1 if Input ≥ 0 or -1 otherwise

The square root function is useful in applications where the PID controller is operating with air flow as its reference and feedback and the motor is controlling a fan. It is easier to use a pressure transducer than a flow transducer, and so the feedback from the transducer needs to be converted from pressure to flow. As flow = Constant x √Pressure the square root function can be used in the conversion.


Parameter14.005  PID1 Reference Invert
Short descriptionSet to 1 to invert PID1 reference
ModeOpen‑Loop
Minimum0Maximum1
Default0Units 
Type1 Bit User SaveUpdate Rate4ms read
Display FormatStandardDecimal Places0
CodingRW

See PID1 Reference Source (14.003).


Parameter14.006  PID1 Feedback Invert
Short descriptionSet to 1 to invert the PID1 feedback
ModeOpen‑Loop
Minimum0Maximum1
Default0Units 
Type1 Bit User SaveUpdate Rate4ms read
Display FormatStandardDecimal Places0
CodingRW

See PID1 Feedback Source  (14.004).


Parameter14.007  PID1 Reference Slew Rate
Short descriptionDefines the rate in change of output for PID1
ModeOpen‑Loop
Minimum0.0Maximum3200.0
Default0.0Unitss
Type16 Bit User SaveUpdate RateBackground read
Display FormatStandardDecimal Places1
CodingRW

See PID1 Reference Source (14.003).


Parameter14.008  PID1 Enable
Short descriptionEnables the use of PID1
ModeOpen‑Loop
Minimum0Maximum1
Default0Units 
Type1 Bit User SaveUpdate Rate4ms read
Display FormatStandardDecimal Places0
CodingRW

See PID1 Output  (14.001).


Parameter14.009  PID1 Enable Source 1
Short descriptionDefines the input source for enabling PID1
ModeOpen‑Loop
Minimum0.000Maximum59.999
Default0.000Units 
Type16 Bit User SaveUpdate RateDrive reset read
Display FormatStandardDecimal Places3
CodingRW, PT, BU

See PID1 Output  (14.001).


Parameter14.010  PID1 Proportional Gain
Short descriptionDefines the Kp gain used for PID1
ModeOpen‑Loop
Minimum0.000Maximum4.000
Default1.000Units 
Type16 Bit User SaveUpdate RateBackground read
Display FormatStandardDecimal Places3
CodingRW

See PID1 Output  (14.001).


Parameter14.011  PID1 Integral Gain
Short descriptionDefines the Ki gain used for PID1
ModeOpen‑Loop
Minimum0.000Maximum4.000
Default0.500Units 
Type16 Bit User SaveUpdate RateBackground read
Display FormatStandardDecimal Places3
CodingRW

See PID1 Output  (14.001).


Parameter14.012  PID1 Differential Gain
Short descriptionDefines the Kd gain used for PID1
ModeOpen‑Loop
Minimum0.000Maximum4.000
Default0.000Units 
Type16 Bit User SaveUpdate RateBackground read
Display FormatStandardDecimal Places3
CodingRW

See PID1 Output  (14.001).


Parameter14.013  PID1 Output Upper Limit
Short descriptionDefines the maximum value of the output for PID1
ModeOpen‑Loop
Minimum0.00Maximum100.00
Default100.00Units%
Type16 Bit User SaveUpdate Rate4ms read
Display FormatStandardDecimal Places2
CodingRW

See PID1 Output  (14.001).


Parameter14.014  PID1 Output Lower Limit
Short descriptionDefines the minimum value of the output for PID1
ModeOpen‑Loop
Minimum-100.00Maximum100.00
Default-100.00Units%
Type16 Bit User SaveUpdate Rate4ms read
Display FormatStandardDecimal Places2
CodingRW

See PID1 Output  (14.001).


Parameter14.015  PID1 Output Scaling
Short descriptionDefines the scaling factor of the output for PID1
ModeOpen‑Loop
Minimum0.000Maximum4.000
Default1.000Units 
Type16 Bit User SaveUpdate Rate4ms read
Display FormatStandardDecimal Places3
CodingRW

See PID1 Output  (14.001).


Parameter14.016  PID1 Destination
Short descriptionDefines the output parameter for PID1
ModeOpen‑Loop
Minimum0.000Maximum59.999
Default0.000Units 
Type16 Bit User SaveUpdate RateDrive reset read
Display FormatStandardDecimal Places3
CodingRW, DE, PT, BU

See PID1 Output  (14.001).


Parameter14.017  PID1 Integral Hold
Short descriptionEnables the integral hold function for PID1
ModeOpen‑Loop
Minimum0Maximum1
Default0Units 
Type1 Bit VolatileUpdate Rate4ms read
Display FormatStandardDecimal Places0
CodingRW

See PID1 Output  (14.001).


Parameter14.018  PID1 Symmetrical Limit Enable
Short descriptionEnables the symmetrical limit for PID1
ModeOpen‑Loop
Minimum0Maximum1
Default0Units 
Type1 Bit User SaveUpdate RateBackground read
Display FormatStandardDecimal Places0
CodingRW

See PID1 Output  (14.001).


Parameter14.019  PID1 Feed-forwards Reference
Short descriptionDisplays the value of the feed-forwards reference for PID1
ModeOpen‑Loop
Minimum-100.00Maximum100.00
Default Units%
Type16 Bit VolatileUpdate Rate4ms write
Display FormatStandardDecimal Places2
CodingRO, ND, NC, PT

See PID1 Output  (14.001).


Parameter14.020  PID1 Reference
Short descriptionDisplays the value of the reference for PID1
ModeOpen‑Loop
Minimum-100.00Maximum100.00
Default Units%
Type16 Bit VolatileUpdate Rate4ms write
Display FormatStandardDecimal Places2
CodingRO, ND, NC, PT

See PID1 Reference Source (14.003).


Parameter14.021  PID1 Feedback
Short descriptionDisplays the value of the feedback for PID1
ModeOpen‑Loop
Minimum-100.00Maximum100.00
Default Units%
Type16 Bit VolatileUpdate Rate4ms write
Display FormatStandardDecimal Places2
CodingRO, ND, NC, PT

See PID1 Feedback Source  (14.004).


Parameter14.022  PID1 Error
Short descriptionDisplays the value of the error for PID1
ModeOpen‑Loop
Minimum-100.00Maximum100.00
Default Units%
Type16 Bit VolatileUpdate Rate4ms write
Display FormatStandardDecimal Places2
CodingRO, ND, NC, PT

See PID1 Output  (14.001).


Parameter14.023  PID1 Reference Scaling
Short descriptionDefines the scaling factor for the reference for PID1
ModeOpen‑Loop
Minimum0.000Maximum4.000
Default1.000Units 
Type16 Bit User SaveUpdate Rate4ms read
Display FormatStandardDecimal Places3
CodingRW

See PID1 Reference Source (14.003).


Parameter14.024  PID1 Feedback Scaling
Short descriptionDefines the scaling factor of the feedback for PID1
ModeOpen‑Loop
Minimum0.000Maximum4.000
Default1.000Units 
Type16 Bit User SaveUpdate Rate4ms read
Display FormatStandardDecimal Places3
CodingRW

See PID1 Feedback Source  (14.004).


Parameter14.025  PID1 Digital Reference
Short descriptionDefines the value of the digital reference for PID1
ModeOpen‑Loop
Minimum-100.00Maximum100.00
Default0.00Units%
Type16 Bit User SaveUpdate Rate4ms read
Display FormatStandardDecimal Places2
CodingRW

See PID1 Reference Source (14.003).


Parameter14.026  PID1 Digital Feedback
Short descriptionDefines the value of the digital feedback for PID1
ModeOpen‑Loop
Minimum-100.00Maximum100.00
Default0.00Units%
Type16 Bit User SaveUpdate Rate4ms read
Display FormatStandardDecimal Places2
CodingRW

See PID1 Feedback Source  (14.004).


Parameter14.027  PID1 Enable Source 2
Short descriptionDefines the input source for enabling PID1
ModeOpen‑Loop
Minimum0.000Maximum59.999
Default0.000Units 
Type16 Bit User SaveUpdate RateDrive reset read
Display FormatStandardDecimal Places3
CodingRW, PT, BU

See PID1 Output  (14.001).