Sandira Gayadeen

An internal model control approach to mid-ranging control

Abstract Existing tuning rules for mid-ranging control can be improved. In this paper a novel strategy for mid-ranging control based on Internal Model Control (IMC) principles is presented. The design reformulates mid-ranging control specifications in terms of classical bandwidth and sensitivity requirements. The performance of this design is demonstrated through simulation studies. The overall benefits of the IMC design are that it provides transparent and flexible tuning, and that it offers a natural framework for anti-windup. Both classical IMC and modified IMC structures are considered for anti-windup. Their performance during saturation is demonstrated through simulation studies, where minimal degradation is observed.

Fast orbit beam stabilisation for a synchrotron

Synchrotron light sources can produce very intense beams of X-rays and ultra violet light for a range of applications, including protein crystallography, materials characterization and high resolution imaging. The Diamond Light Source is a 3rd generation synchrotron that has recently been constructed near Oxford, United Kingdom, which produces a 3 GeV electron beam in a ring of circumference of over 560 m. A key requirement of the process is that the vertical and horizontal location of the beam should be controlled to within 10% of the beam size, which corresponds to the RMS variation being less than 12.3 μm in the horizontal direction and 0.6 μm in the vertical direction. The beam location is subjected to disturbances caused by the effects of Insertion Devices and the effect of ground motion, particularly between 16 Hz and 30 Hz, where the ground motion is amplified by the resonances of the girders supporting the ring magnets. To achieve the specification, a fast beam stabilization feedback system is used to regulate the horizontal and vertical position of the beam in the presence of disturbances in the range 1 Hz to 100 Hz, using 170 sensors and actuators in both planes, positioned around the ring at a sampling rate of 10 kHz. This paper describes the design of the controller for this system and the results from the implementation are shown.

Simple robustness measures for control of MISO and SIMO plants

Abstract The robustness properties of multivariable plants with either a single input or single output (but not both) under feedback control can be represented succinctly in the frequency domain. Both the robust stability and robust performance of multi-input single-output plants are considered. These results are illustrated for internal model control design of mid-ranging systems. The robust stability of single-input multi-output plants is also considered.

Discrete-time anti-windup compensation for synchrotron electron beam controllers with rate constrained actuators

By accelerating electrons to relativistic speeds, synchrotrons generate extremely intense and narrow beams of electromagnetic light that are used for academic research and commercial development across a range of scientific disciplines. In order to achieve optimum performance, the stability of the electron beam is a crucial parameter for synchrotrons and is achieved by a beam stabilisation system that is used to control the location of the electron beam and minimise any instability of the electron beam caused by external disturbances. Slew rate limits are common nonlinearities encountered with the actuators in synchrotron feedback systems which can impose significant limitations on the robustness and the performance of the control system. This paper describes an Internal Model Control (IMC) based anti-windup synthesis using an algebraic Riccati equation for a discrete-time control system to compensate against the performance deterioration in the presence of rate constraints. An Integral Quadratic Constraint (IQC) framework is used to analyse the robust stability of the anti-windup augmented closed loop system in the presence of norm-bounded uncertainty. The anti-windup augmented controller is implemented at Diamond Light Source, the UKs national synchrotron facility and improvements in robustness and performance were achieved with respect to the use of no anti-windup compensation.

Uncertainty modeling and robust stability analysis of a synchrotron electron beam stabilisation control system

There are over forty synchrotrons and fourth generation light sources around the world, which generate synchrotron radiation for academic and industry research by bending electrons that are accelerated to relativistic speeds. To preserve the quality of the photon beam used for experiments, a feedback control system is used to reduce variations in the position of the electron beam. This paper describes the design and robust stability analysis of a beam stabilisation controller, which is considered as a cross-directional control system. Fourier series analysis is used to identify the spatially controllable components of the system and develop a realistic uncertainty model that is used in robust stability tests. The robust stability of the controller is determined by considering both the unbounded sector nonlinearity associated with the actuators and the unmodeled spatial plant response within an Integral Quadratic Constraint (IQC) framework, leading to a robust stability condition that is expressed as a linear matrix inequality (LMI). The paper presents results from the implementation of the controller at Diamond Light Source.

Design of multi-array controllers for electron beam stabilisation on synchrotrons

This paper considers the design of electron beam stabilisation control systems for synchrotrons that simultaneously determine the inputs to multiple arrays of actuators for regulating variations in the electron beam position. An approach based on determining the interaction of the controllable subspaces is used. This enables the control problem to be decomposed into a series of single-input, single-output; multiple-input, single output and multiple-input, multiple-output problems. An Internal Model Control structure is used to design the controllers for each case and mid-ranging control is proposed for the case where the control directions align. Results from a simulation study using machine data from the Booster synchrotron of the UKs national synchrotron facility, Diamond Light Source are presented.

Static anti-windup design for discrete-time large-scale cross-directional saturated linear control systems

The paper proposes some design strategies of static anti-windup control schemes for systems describing cross-directional processes. These are processes in which the variations of a variable in a profile orthogonal to the direction of propagation of the variable are controlled. Actually, the anti-windup synthesis approach takes advantages of the particular structure of such systems for which the interaction map between sensors and actuators along the propagation direction is expressed in terms of reduced singular value decompositions. The approach is developed within the framework of a synchrotron machine, in which electrons are accelerated in a closed circular path and bent by strong electromagnetic fields. Different results are proposed with increasing computational complexity to evaluate the potential interest of low dimension problems to solve the anti-windup design problem.