A Contract-Based Methodology for Aircraft Electric Power System Design

Abstract

In an aircraft electric power system (EPS), a supervisory control unit must actuate a set of switches to distribute power from generators to loads, while satisfying safety, reliability and real-time performance requirements. To reduce expensive re-design steps in current design methodologies, such a control problem is generally addressed based on minor incremental changes on top of consolidated solutions, since it is difficult to estimate the impact of earlier design decisions on the final implementation. In this paper, we introduce a methodology for the design space exploration and virtual prototyping of EPS supervisory control protocols, following the platform-based design (PBD) paradigm. Moreover, we describe the modeling infrastructure that supports the methodology. In PBD, design space exploration is carried out as a sequence of refinement steps from the initial specification towards a final implementation, by mapping higher-level behavioral models into a set of library components at a lower level of abstraction. In our flow, the system specification is captured using SysML requirement and structure diagrams. State-machine diagrams enable verification of the control protocol at a high level of abstraction, while lowerlevel hybrid models, implemented in Simulink, are used to verify properties related to physical quantities, such as time, voltage and current values. The effectiveness of our approach is illustrated on a prototype EPS control protocol design.

Optimized Selection of Reliable and Cost-Effective Cyber-Physical System Architectures

“…Based on this intuition, we develop strategies that increase the reliability of the solution, albeit at a higher cost, by enforcing a larger number of redundant components and interconnections. We have recently reported an iterative approach similar to ILP-MR, based on a set of ad hoc strategies, customized for the specific problem at hand [4], [7]. In Algorithm 2, we introduce instead a generic template that can directly apply to the general problem formulation in Section II, hence to a broader set of applications.…”

“…Fig. 1c illustrates a sample architecture in the form of a single-line diagram, a simplified notation for three-phase power systems [4]. Typically, aircraft Electric Power System (EPS) components include power sources, such as the left and right generators (L/R-GEN) and the auxiliary power units (APU) in Fig.…”

“…For instance, we can prescribe that any rectifier must be directly connected to only one AC bus, and that all DC buses that are connected to a load or another DC bus must be connected to at least one rectifier to receive power from an AC bus. Power-flow constraints are used to enforce that the total power provided by the generators in each operating condition is greater than or equal to the total power required by the connected loads, by using expressions as in (4). Finally, a reliability constraint prescribes that the probability that a load gets unpowered because of failures should be less than a desired threshold.…”

“…This compositional approach allows us to formulate two algorithms to concurrently optimize for reliability and cost. Instead of formulating a single, "flat" optimization problem, the ILP-MR algorithm avoids the expensive generation of symbolic reliability constraints via an iterative approach inspired by the ILP Modulo Theory paradigm [3], [4]. On the other hand, the ILP-AR algorithm aims to efficiently solve a single optimization problem, albeit of a larger size, without repetitive calls to the exact reliability analysis function, which may also be expensive.…”

Variable elimination for scalable receding horizon temporal logic planning

“…To apply these specifications to continuous domains, the system and its operating environment are usually represented by a discrete abstraction over which the problem can be specified. It is desirable to be able to automatically create provably correct reactive controllers from these specifications, and several methods for doing so have been presented, such as those in [5], [7], [12], [9]. In particular, efficient methods have been developed for the Generalized Reactivity (GR(1)) fragment of LTL.…”