Arizona State University Armando A. Rodriguez
ASU Professor 




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Design of Fixed- and Multi-Rate Sample-Data Control Systems

The focus of this research is on the modeling and design of practical sample-data (fixed-and multi-rate) digital control systems.

Relevant Application Areas
Relevant application areas include:

  • Aerospace systems
  • Robotic systems
  • Thermal processes
  • Low power DC-DC converters
Relevant Control Challenges
Designing digital controllers with reasonable measurement (sampling) and actuation rates that address each of the following issues:
  • selection of sampling/actuation rates (bandwidth management)
  • time delays and quantization effects associated with A/D converters
  • nonlinear finite precision arithmetic and wordlength/quantization effects associated with embedded processors
  • time delays associated with D/A and zero-order-hold (ZOH)
  • lag associated with anti-aliasing filter (AAF)
  • uncertain nonlinearities (e.g. variable constraints),
  • uncertain high frequency dynamics (i.e. unmodeled differential equations),
  • parametric uncertainty,
  • uncertain actuator and sensor dynamics,
  • centralized versus decentralized control architectures,
  • controller complexity and implementation issues,
  • multiple time-scale dynamics; e.g. multiple measurement/actuation rates,
  • selection of weighting function parameters for dynamical optimization,
  • assessment of fundamental performance limitations and tradeoffs,
  • stabilization,
  • following of varying (typically low frequency) reference commands,
  • attenuation of (stochastic, typically low frequency) disturbances,
  • attenuation of (stochastic, typically high frequency) measurement noise,
  • state estimation,
  • parameter and uncertainty estimation (system identification).
Embedded controller implementation platforms include:
  • PC104s, field programmable gate array (FPGA) technologies.
High-level development tools are exploited to facilitate rapid prototyping for the above embedded system platforms.

Objectives and Goals
The main objective of this research is to develop a systematic design methodology which addresses each of the above sample-data control system design challenges.

Approaches
Synchronous sampled-data systems are periodic systems provided that there is a common sampling/actuation period (frequency); i.e. sampling/actuation periods/rates are integer multiples of a fundamental periods/rate. Given this, modern lifting concepts can be used to exploit the inherent periodicity and permit time invariant representations which can be used for analysis/design purposes. Here, performance-based optimization is the main design approach.

Collaborators and Sponsors
Collaborators include: Professor Petros Voulgaris (University of Illinois, Urbana-Champaign).

This work has been sponsored by the following organizations:
  • National Science Foundation (NSF) and the Consortium for Embedded and Inter-Networking  Technologies (CEINT).

 

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