Adaptive Control - Introduction

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Adaptive control is a control methodology where the controller can adapt itself to new circumstances, that is it can adjust its characteristics for the changing environment so that the overall system performance is not affected.

Need for Adaptive Control
  • The main reason for switching to adaptive control is that, most of process are non linear by nature. In conventional control system, the output is made to follow the set-point by compensating the errors. This is possible only up till a linear range of the process, once the process exceeds the linear range, the conventional control system fails to control.
  • The disturbance that occur can be unpredictable and its magnitude may vary with time.
These effects cannot be controlled by a normal control system, hence we go for an adaptive control.

For example, let us consider a flight control system, the control dynamics change with speed, altitude, angle of flight, effect of gravity, surrounding weather, etc..
As we know that the effect of gravity changes as altitude changes and the surrounding weather, wind speed may also change with time and location. 
The controller must be capable to overcome these changes and produce desired output. This cannot be done with linear feedback control with constant coefficients. 
Hence we go for an adaptive control.

Generally an adaptive controller has 2 loops,
  • Loop 1 is for the normal feedback of the process.
  • Loop 2 is for the parameter adjustment.

Block Diagram of an Adaptive Control System
Block Diagram of an Adaptive Control System

As shown in the block diagram, the controller has 3 inputs, 
  • the set-point
  • the output fed back to the controller (like in normal feed back control)
  • the controlled parameter
The control parameter is estimated by parameter adjustment block and it is based on the set-point, control signal and the output. 
As discussed in the previous example, the output varies with surrounding changes, this can be over come by modifying the control parameter accordingly.
 
There are various schemes introduced for adaptive control, these include
  • Gain Scheduling
  • Model Reference Adaptive Control
  • Self Tuning Regulator
  • Dual Control
Location: Chennai, Tamil Nadu, India

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