Petar Iordanov

State-space μ-analysis for an experimental drive-by-wire vehicle

This paper considers the application of the skewed structured singular value to the robust stability of systems subject to strictly real parametric uncertainty. Three state-space formulations that counteract the discontinuous nature of this problem are detailed. It is shown that the calculation of the supremum of the structured singular value over a frequency range using these formulations transforms into a single skewed structured singular value calculation. Like the structured singular value, the calculation of the exact value of the skewed structured singular value is a NP-hard problem, therefore alternative, less computationally demanding algorithms to determine upper and lower bounds are necessary. Two algorithms that determine upper and lower bounds on the skewed structured single value are presented. These algorithms are critically assessed by performing a robust stability analysis on a safety-critical experimental drive-by-wire vehicle.

Dithered multi-bit sigma-delta modulator based DPWM for DC-DC converters

Multi-bit sigma-delta based digital pulse width modulators (DPWM) are used in the control of DC-DC converters in order to achieve high resolution and therefore high output voltage accuracy at switching frequencies up to multiple MHz. The standard sigma-delta modulators which have mainly been used in these DPWMs to date generate idle tones in the applied duty cycle which result in large oscillations in the output voltage. A dithered sigma-delta modulator is instead implemented here which eliminates these oscillations in the output voltage by adding a random signal before the quantizer in the sigma-delta modulator. The power spectral density of the duty cycle produced by the dithered sigma-delta modulator based DPWM shows a reduction in the undesirable idle tones and this is also verified experimentally using a buck converter prototype.

CONTROL PROBLEM CLASSIFICATION FOR A PLASMA PROCESS

Abstract The use of first-principles based models of plasma processes is discussed in this paper. Such processes are essentially highly nonlinear, feature complex interactions and are difficult to analyse. As an illustration of the nature of first-principle based models, a characterisation of a simple plasma process is presented in this work. Quantification of the nonlinearity in terms of steady-state and dynamics behavior, is carried out for the studied process. The use of Hammerstein model and its applicability to the plasma process is also investigated. A basic stabilising controller for the simple plasma process is designed and its performance is analysed.

Discrete-time Modelling and Robust Analysis of a Buck Converter

Abstract A discrete-time state-space representation of a Buck converter is presented. This analytical state-space model provides explicit insight on how circuit parameters influence the stability and transient performance for this converter type. Variations in the power rail components and parasitic resistances are accommodated, which are typically neglected in compensator synthesis for switched mode power supplies. With this representation, robust stability and feedback performance can be readily assessed. Moreover, the model can be employed directly for the design of digital robust compensators, and it provides a basis for the development of compensators in analytical form rather than the use of numerical discretisation techniques.

Robust analysis and synthesis design tools for digitally controlled power converters

A new suite of Matlab-compatible robust analysis and synthesis design tools for digitally-controlled switched-mode power supplies has been developed. The objective of developing this tool suite is to assist control engineers to design and/or assess digital compensators that are robustly stable. The tool suite comprises of nonlinear, linearized and discrete-time continuous conduction mode and discontinuous conduction mode models, robust analysis algorithms and robust synthesis algorithms. To promote ease of use and adoption, a front-end graphical user interface has also been developed.

Control-oriented modelling of an experimental Ar-O 2 plasma process

Development of a control-oriented model of an experimental plasma reactor is presented in this paper. The model structure is suitably partitioned in order to facilitate any subsequent control design. In the model, the linear dynamical part is conveniently separated from a static nonlinearity, which in turn allows identification to be performed for both parts independently. Validation results indicate that the model gives a reasonable representation of the studied plasma process.

WORST CASE ANALYSIS OF A SIMPLE MIMO MASS-SPRING-DAMPER SYSTEM

Abstract This paper considers the application of the structured singular value, μ, and the skewed structured singular value, abbreviated “skew μ”, to the analysis of a (deceptively) simple MIMO mass-spring-damper system. This example highlights some pertinent outstanding μ analysis questions, namely the effect of strictly real, possibly repeated parameters and the limitation of classical grid-based methods. It is shown that by transforming the original μ problem and using skew μ to calculate the worst case that more reliable and certifiably safe answers to the analysis question are determined. A comparison with more conventional μ analysis methods is presented.