Programmed or Gain Scheduled Adaptive Control

Programmed or Gain Scheduled Adaptive Control

The Programmed Adaptive Control is one of the major and important adaptive control mechanisms. The Programmed Adaptive Control adjusts the controller parameters based on the measurement of an auxiliary variable
that affects the control loop gain in a predictable manner or by the known nonlinear behavior of the process for various operating conditions. The Gain Scheduling gives the rough controller parameters and adaptive control does the tuning of controller parameters.

Block Diagram of Programmed or Gain Scheduled Adaptive Control

If the process exhibits predictable variations, then the adaptation of controller parameters can be programmed or scheduled. The variations in the process are identified by the measurement of auxiliary variables. The auxiliary variables are to be selected in such a way that it correlates well with the process dynamics changes. The appropriate values of controller parameters are mapped to the values of the auxiliary process variable.

The programmed adaptive control system is composed of two loops. One is the normal feedback control loop. The other one is the parameter adjustment loop that adjusts the controller parameters using the values of gain programmed into the adjustment mechanism. The parameter adjustment loop is slower than the normal feedback loop.

An advantage of Gain Scheduling

The advantage of gain scheduling is that the controller parameters are changed quickly in response to the changes in process dynamics. It requires no estimation as the values of controller parameters are programmed in advance.

Limitations of Gain Scheduling 

1. The design of programmed adaptive control system is time-consuming because the controller parameters have to be determined for all possible operating conditions and have to be checked by simulations.

2. There is no feedback to compensate for an incorrect adaptation making it comparable to feedforward or open-loop compensation.

Example

Programmed Adaptive Control for a Combustion System

Ratio Control for a Combustion System (Left) and Adaptive Ratio Control Mechanism for a Combustion System (Right)

The air-fuel ratio is to be kept at an optimal value in a combustion system to attain high efficiency. A ratio control mechanism can be used to maintain the air-fuel ratio. The need for adaptive control arises because the optimal value of the air-fuel ratio depends on the temperature of the air. The temperature of the air is a variable that changes at any time (non-stationary process) in the process. The programmed adaptive control can be implemented by determining the optimal value of the air-fuel ratio for different air temperatures through experiments. The air temperature is measured (auxiliary measurement) and it used to adjust the value of the air-fuel ratio. It is to be noted that a ratio control mechanism is a form of feedforward compensation.


Also read other control schemes

Inferential Control 

Self-Adaptive Control

Adaptive Control - An Introduction

Override Control

Feedforward Control

Feedback Control

Cascade Control

Ratio Control

Feedforward control vs Feedback control