Simulink Control Design™ - MathWorks

Specifying Linearization for Model Components Using

System Identification

This example shows how to specify the linearization for a model component that does not

linearize well using a linear model identified using the System Identification Toolbox™.

This example requires Simscape™ Electrical™ software.

Linearize Hard Drive Model

Open the simulink model for the hard drive.

model = 'scdpwmharddrive';

open_system(model)

In this model, the hard drive plant is driven by a current source. The current source is

implemented by a circuit that is driven by a Pulse Width Modulation (PWM) signal so that

its output can be adjusted by the duty cycle. For details of the hard drive model, see

“Digital Servo Control of a Hard-Disk Drive” (Control System Toolbox).

PWM-driven circuits usually have high frequency switching components, such as the

MOSFET transistor in this model, whose average behavior is not well defined. Thus, exact

linearization of this type of circuit is problematic. When you linearize the model from the

duty cycle input to the position error, the result is zero.

The Simscape solver in this model is configured to run in local solver mode. When

linearizing the model, first turn off the local solver.

SimscapeSolver = [model '/PWM driven converter/Solver Configuration'];

set_param(SimscapeSolver,'UseLocalSolver','off');

Specifying Linearization for Model Components Using System Identification