Simulink 7.4

Designing an Aircraft Elevator Control System -- Overview

In this case study, we use Model-Based Design with Simulink, Stateflow, and Simulink Verification and Validation to design a fault detection, isolation, and recovery (FDIR) application for a pair of aircraft elevators with redundant actuators. The system is modeled from a set of requirements. We then use requirements-based testing in order to verify that these requirements have been met. A similar design and testing methodology could be applied to any event-driven, or complex logic-based controller.

This case study has four parts:

• 1) Controller Design Design mode logic for redundant actuator switching
• 2) Fault Detection and Isolation Detect faults in system and isolate appropriate actuators if necessary
• 3) Recovery Recover subsystems when faults are no longer present
• 4) Verification and Validation Produce a coverage report. Then verify and validate that requirements are met.

Contents

Description of an Elevator Control System

A typical aircraft has two elevators attached on the horizontal tails (one on each side of the fuselage). There are a number of redundant parts in the system to ensure safety.

For example, as shown in Figure 1, there are:

Figure 1: Components of the elevator redundancy system. Click on image to see enlarged view.

In this example, we limit each PFCU to have only one control law, and to control only one set of actuators to reduce the complexity of the case study. Here, the outer actuators run the full control law, and the inner actuators run the reduced-range control law. Each outer actuator has a dedicated hydraulic circuit, whereas the inner actuators share one hydraulic circuit. By default, the outer actuators are on, and the inner actuators are on standby. If a fault is detected in the outer actuators or in the hydraulic circuits that are connected to them, we want the system to respond accordingly to maintain stability by turning the outer actuators off and activating the inner actuators.

This case study focuses on the fault detection, isolation, and recovery logic that causes the actuators to switch from one mode to another. We have created simple yet representative models of the hydraulic actuators and elevators, as well as the feedback control laws, to illustrate the behavior of this logic.

Additional Information

Learn more about the key products used in this demo:

From these product pages you can request a free 30-day trial, read the documentation, read user stories, request more information, and get pricing.

A recorded webinar based on this demo is also available on the MATLAB Central File Exchange Web site: Using Stateflow in Mode Logic and Fault Detection Applications.

Visit The MathWorks Web site to read more about Model-Based Design, including user stories:

References