Fault Detection and Fault Tolerant Control

Ref-Nr: TDO0193

Technology abstract

A Portuguese space company has developed a system to enable performance improvement and reduction of Operation & Maintenance costs of dynamic systems based on advanced, proven Fault Detection & Isolation (FDI) methods and Fault Tolerant Control (FTC) methods. They are interested in commercial/manufacturing agreements with power plant and smart grid operators; wind turbine/electronic system manufacturers; control system developers for power plants or other of dynamic systems.

Technology Description

Autonomy-enabling technologies play a major role especially in dynamic systems where Operation & Maintenance (O&M) costs are significant (Fig. 1). Examples of such systems include offshore wind turbines – recognized as the most promising type of wind power generators, given that, as described in the Strategic Energy Technologies Information System of the European Commission, the “trend for offshore wind farms is to build them further away from shore and in deeper water” –, but also solar power plants, and smart grids.
This offer provides a Condition Monitoring and Control System (CMCS) and service for dynamic systems that takes advantage of state-of-the-art Fault Detection and Isolation (FDI) and Fault Tolerant Control (FTC) technologies, providing early warnings and self-adaption if there are deviations from nominal operation, intensively used in aerospace.
In the fields of FDI and FTC, the company has considerable experience in conveying these types of techniques from academia to industry, including the application of such systems in projects with a high Technology Readiness Level (TRL). In particular, the company is leading an ongoing FP7 project (RECONFIGURE) where FDI and FTC have been identified as key enablers for moving towards this new paradigm of enhanced autonomy.
The offer described herein is an off-the-shelf solution, without any stringent requirements in terms of infrastructure or human resources. From the customer’s perspective, the effort required to implement the proposed solution in future infrastructures, or upgrade current ones, is minimal. The system comprises three main types of modules: 
Central Data Processing module (CDP): This module is composed of a computer and  associated software,  with  a  Graphical  User  Interface  (GUI),  allowing  the dynamic system to be monitored in a user-friendly way. Not only does it receive and display the information from the several CMS modules, but it also merges the data with that from other relevant sources (e.g., meteorological data).
Condition Monitoring System module (CMS): The CMS modules are placed locally in the dynamic system and collect the relevant data available. Based on the model of the dynamics of the plant, each CMS module monitors the health of typically a sub-part of the overall system, gathering all the relevant information to be sent to the CDP module.
Control System module (CS): The (usually) distributed CS modules receive data both from the associated CMS module and the CDP unit, to automatically compensate for faults, fully reconfiguring the local controller when required. 
In addition to the aforementioned modules, the company provides two services: 
Installation service: The determination of the dynamic model of the system is a key step in the installation of the system. As a consequence of the flexibility of the FDI and FTC algorithms adopted, the CDP, CMS, and CS modules can handle different types and combinations of sensors/actuators. 
CMS add-on for exogenous data sources:  As a complementary (and optional) service, the company can provide their customers with the seamless integration of additional sources of data, including weather conditions and forecasts, with the FDI data coming from the CMS modules.

Innovations & Advantages

The current offer is based on state-of-the-art FDI and FTC technologies that rely on a computational model of the system to evaluate the consistency between the measured outputs and the control input, and automatically compensate for off-nominal deviations. 
One of the main strengths of this type of method stems from the fact that no changes are typically required to the system itself, nor to the sensor/actuator set attached to it. From the point of view of FDI, a possible interpretation for this type of approach is that the model of the system behaves as a virtual sensor, thus providing redundant measurements. Therefore, this offer increases the reliability and robustness of the operations, without installing any additional sensor modules. Compared with reference approaches, it has reduced costs of installation and operation, while avoiding installing additional modules that are themselves also prone to failure.
Overview of the advantages associated to the offered solution: reduction of O&M costs; avoidance of premature breakdowns; remote diagnosis; improvement of the capacity factor of power plants; support for future developments, due to the collection of data over long periods of operation, allowing for the optimization of the system design.

Further Information

As the dynamics of the plant get degraded, the ability of a fixed controller (or Passive Fault Tolerant Controller - PFTC) to stabilize the system and yield superior levels of performance is diminished. As a consequence, controller reconfiguration is necessary at a certain degree of fault severity (Active Fault Tolerant Control - AFTC). In certain plants, a complete restructuring may be possible. For example, shutting down the entire system may be a solution in cases like wind turbines. 
In case of reduced fault severity, the accommodation of the faults is, in general, preferable, as it allows for a smooth compensation. If, however, reconfiguration is necessary to attain the required levels of performance, it may be advantageous to switch to a low-performance high-robustness controller when a fault is detected and until it is isolated and identified. From that moment onwards, a high-performance reconfigurable controller is used. This leads to performance profiles where the detection of the fault and the switching to a high-robustness controller avoids severe performance degradation, while the isolation (or diagnosis) of the fault helps retrieve performance levels close to those of nominal operation. The rule of thumb adopted is that a controller can only be connected to the plant if it is guaranteed to render the closed-loop stable.

Current and Potential Domains of Application

The system and service described in this offer are directed to any non-space markets where O&M costs are significant and/or that are safety critical. The system & service offered aims to address these issues, by conveying well-established space technology to other industries, namely FDI and FTC technology that has been implemented, in particular, in Guidance, Navigation & Control (GNC) systems of satellites, spacecraft, and aircraft vehicles.
A number of potential domains of applications has been identified in this document, including:
Wind energy conversion systems
Solar power plants
Smart grids
Other types of distributed systems, including large industrial facilities
In our view, therefore, the energy market is one of the main sectors that may benefit from this offer.