Robustness Modelling of Complex Systems - Application to the Initialisation of a Hybrid Electric Vehicle Propulsion System

Robustness is particularly important in complex systems of systems due to emergent behaviour. This paper presents two novel, techniques developed as part of a framework for design for robustness of complex automotive electronic systems, but in principle could be applied to a broad range of distributed electronic systems. The overall framework is described to give the context of use for the techniques. The first technique is a “robustness case” which is a structured argument for the robustness of a system analogous to a safety case. The second is a model based approach to early robustness verification of complex systems.

The approaches are demonstrated by their application to the system initialisation of the propulsion control system of a hybrid electric vehicle. The hybrid system initialisation process is discussed in terms of the key objectives and the technical implementation, illustrating the level of complexity underlying a simple high level requirement. The hybrid system initialisation model structure is presented in the form of a set of interlinked state-charts representing the five electronic control units and two control network systems which are the key system elements. An approach to model based robustness verification is described, covering a method of defining test objectives based on a structured robustness argument. The key steps in the testing of the model based on; coverage, parameter variation and fault insertion are described and illustrated with results. Finally, conclusions on the usefulness and limitations of the approach are given, with recommendations for further work.