Effects of Degradation in DC-DC Converters on Avionics Systems: A Model Based Approach

TitleEffects of Degradation in DC-DC Converters on Avionics Systems: A Model Based Approach
Publication TypeConference Paper
Year of Publication2010
AuthorsKulkarni, C., G. Biswas, B. Raj, and K. Kyusung
Conference NameMachinery Failure Prevention Technology Conference, MFPT 2010
Date Published04/2010
Conference LocationHuntsville, AL

This paper proposes a model based approach to study the degradation effects of power supply converters on the avionics systems. Avionics systems combine physical processes, computational hardware, and software systems, and present unique challenges to performing root cause analysis when faults occur, and also for establishing the effects of faults on overall system behavior and performance. However, systematic analysis of these conditions are very important for analysis of safety and also to avoid catastrophic failures in navigation systems.

A combined energy-based and physics of failure model approach is adopted for degradation analysis and prognosis of degrading components in DC-DC power converters. We have developed automated methods for generating Simulink models from bond graph representations of physical models. The bond graph models are also used to derive models for diagnostic and prognostic analysis. Further, we have also developed models of the software and hardware components of the GPS and INAV subsystems as Simulink™ modules. The complete system for studying the behaviors of the avionics system (both nominal and faulty) is implemented as a set of integrated Simulink modules.

In avionics systems, degradations and faults in this unit propagates to the GPS and INAV systems. These can cause a variety of faults in these systems, e.g., ripple currents at the power supply output can cause glitches in the GPS position and velocity output, and this, in turn, produces errors in the Inertial Navigation (INAV) system calculations. One of the faults we have been studying in detail is electrolytic capacitor degradation in the power supply, and its effects on the functioning of the GPS unit.

We apply qualitative fault signature methods for detecting and isolating faults in all three components of the avionics system. Fault signature generation is based on establishing causal relations between system parameters and measurements, and estimating the effect of a parameter value change (representing a fault) on the measured values.

In the literature a number of operating conditions that cause capacitor degradation, such as High Voltage conditions, Transients, Reverse Bias, Strong Vibrations and high ripple current have been reported. Some of these conditions are observed by the power supplies embedded in the avionics systems. In this work, we study some of these conditions which lead to capacitor degradation i.e. due to thermal and electrical stresses.

A topological energy based modeling scheme developed on the bond graph (BG) modeling language for building parametric models of multi-domain physical systems has been implemented. A model based approach to studying degradation phenomena enables us to combine the energy based modeling of the DC-DC converter with physics of failures models of capacitor degradation, and to predict using stochastic simulation methods how system performance deteriorates with time. This more systematic analysis may provide a more general and accurate method for computing the remaining useful life (RUL) of the component and the converter system. We adopt a physics of failure model (Arrhenius Law) for equivalent series resistance (ESR) increase in electrolytic capacitors subjected to electrical and thermal stresses. High ripple currents due to degradation lead to frequent resets and even damage in the systems that are downstream from the power supply.

The literature indicates that the fluctuation in power supply voltage and excessive ripple currents could lead to various failures in the GPS receiver module. In this work we have simulated the GPS reset events due to voltage fluctuations. We have also simulated the loss of receiver lock due to excessive ripple current. We have demonstrated using our simulation models the effects of power supply faults on the overall performance of the GPS solution.

Our methodology also provides a framework for developing efficient fault signature methods for fault detection and fault isolation. In future, we will conduct more detailed analysis of degradation effects, and their propagation to the different components of the system. We will also develop methods to quantify the effects of degradation on overall system performance.

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