Flight control

This thesis considers the design of ultrareliable multicomputers for control applications. The fault tolerance problem is divided into three subproblems: software, processing node, and communication fault tolerance. Design is performed using layers of abstraction, with fault tolerance implemented by dedicated layers. For software fault tolerance, new constructs for concurrent n-version programming are introduced. For processing node fault tolerance, the distributed fault tolerance (DFT) concept of Chen and Chen is extended to allow for arbitrary failures. Communication fault tolerance is achieved with multicasting on a fault-tolerant graph (FG) network. Reliability models are developed for each of the layers, and a performance model is developed for the communication layer. An example flight control system is compared to currently existing architectures.

Until recently, control design techniques for multivariable
systems, such as pole placement or optimal control design,
have been either too complex to be usable, or yielded
designs which were liable to instability if the parameters
of the plant varied from those used in the design. A
technique which uses the singular values of the system
transfer function matrix is now available. This technique
yields control designs which are guaranteed to be robust
with respect to plant parameter variations. This technique,
combined with a novel technique for shaping the frequency
responses of the singular values is used to design a control
system for a gas turbine jet engine. It is shown that
adjusting the crossover frequency of the open loop singular
values affects the closed loop time and frequency response
in the same manner that adjusting the open loop gain affects
the response of a single-input/single-output control system.