Lead-Lag Controller
- Gary Cane
Operator Menu Location: Controller Blocks
Operator Bitmap:
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Functional Description:
The Lead-Lag Controller block implements a lead-lag compensator with transfer function:
where 
and 
are compensator time constants, and K is the compensator gain. The corresponding discrete-time implementation is
where y is the compensator output (OUT), x is the compensator input (IN), and (delta)t is the schema loop sampling time.
In addition to the analog signal input (IN) and compensator coefficient inputs (K, 
, and 
), the lead-lag controller block has an Enable input. When the Enable input is HIGH, the output is computed as indicated above; when the Enable input is LOW, the compensator is disabled and the output simply passes the input, i.e., y(t) = x(t).
The value of output y is limited by user-defined parameters, 
and 
. Even if the input value is outside of the range 
, the output will never fall outside of that range.
User-Defined Properties:
Object Name. A string label that identifies the operator
Initial Condition. The output value at startup (at time t=0)
Minimum Output. The minimum output value
Maximum Output. The maximum output value
Comments:
• Design Pad will issue an error on processing if the IN input pin is not connected
•The coefficients 
and 
are expressed in minutes
•The lag coefficient must be at least 60 milliseconds, i.e., 
min
See Also: PID Controller, PID Controller with External Feedback