Simulink

Simulink

The MATLAB Control System Toolbox offers functions for finding the transfer functions from a given block diagram. However, as we shall shortly see, the simulation environment provided by MATLAB’s Simulink Toolkit obviates the need for block diagram reduction. The Simulink model mimics the block diagram of a feedback control system and is used to evaluate the response of controlled variable to any test input. It also provides the response of any internal variable of the control system (output variable of a subsystem block) without the need for block diagram reduction.

Let us reiterate the fact we have emphasized earlier: a good plant/process model is the backbone of any realistic control design. A Simulink model based on the structure and parameters of the system model is constructed. The responses of the actual system and its Simulink model are obtained using a set of test inputs. If the actual responses to the test inputs were significantly different from the Simulink responses, certain model parameters would have to be revised, and/or the model structure would have to be refined to better reflect the actual system behavior. Once satisfactory model performance has been achieved, various control schemes can be designed and implemented.

In practice, it is best to test a control scheme off-line by evaluating the system performance in the “safety” of the Simulink environment. The key components of a control system include actuators, sensors, and the plant/process itself. A decision to include all aspects such as amplifier saturation, friction in the motor, backlash in gears, dynamics of all the devices, etc., may improve the model, but the complexity of the model may result in a more complicated controller design, which will ultimately increase the cost and sophistication of the system. The design is usually carried out using an approximated model; the evaluation of the design is done on the “true” model, which includes nonlinearities, and other aspects neglected in the approximate model. Simulink is an excellent tool for this evaluation.

SIMULINK (SIMUlation LINK) is an extension of MATLAB for modeling, simulating, and analyzing dynamic, linear/nonlinear, complex control systems. Graphical User Interface (GUI) and visual representation of simulation process by simulation block diagrams are two key features which make SIMULINK one of the most successful software packages, particularly suitable for control system design and analysis.

Simulation block diagrams are nothing but the same block diagrams we are using to describe control system structures and signal flow graphs. SIMULINK offers a large variety of ready-to-use building blocks to build the mathematical models and system structures in terms of block diagrams. Block parameters should be supplied by the user. Once the system structure is defined, some additional simulation parameters must also be set to govern how the numerical computation will be carried out and how the output data will be displayed.

Because SIMULINK is graphical and interactive, we encourage you to jump right in and try it. To help you start using SIMULINK quickly, we describe here the simulation process through a demonstration example with MATLAB version 7.0, SIMULINK version 6.0.