Recent results in tilt control design and assessment of high-speed railway vehicles

Active tilt control is a well-established technology in modern railway vehicles, for which currently used control approaches have evolved in an intuitive matter. This paper presents work on a set of novel strategies for achieving local tilt control, i.e. applied independently for each vehicle rather than the whole train precedence approach that is commonly used. A linearized dynamic model is developed for a modern tilting railway vehicle with a tilt mechanism (tilting bolster) providing tilt below the secondary suspension. It addresses the fundamental problems associated with straightforward feedback control, and briefly discusses the current industry norm, which employs command-driven with precedence strategy. Two new advanced schemes are proposed, a model-based estimation approach, and an optimal LQG-based approach, and compared to the command-driven with precedence. The performance of the control schemes is assessed through simulation using a new proposed assessment method

Robust control of a high redundancy actuator

The High Redundancy Actuator project deals with the construction of an actuator using many redundant actuation elements. Whilst this promises a high degree of fault tolerance, the high number of components poses a unique challenge from a control perspective. This paper shows how a simple robust controller can be used to control the system both in nominal state and after faults. To simplify the design task, the parameters of the system are tuned so that a number of internal states are decoupled from the input signal. If the decoupling is not exact, there may be small deviation from the nominal transfer function, especially when a fault has occurred. The robustness analysis ensures that the system performs well for all expected behaviour variations

Modelling and control of a high redundancy actuator

The high redundancy actuation concept is a completely new approach to fault tolerance, and it is important to appreciate that it provides a transformation of the characteristics of actuators so that the actuation performance (capability) degrades slowly rather than suddenly failing, even though individual elements themselves fail. This paper aims to demonstrate the viability of the concept by showing that a highly redundant actuator, comprising a relatively large number of actuation elements, can be controlled in such a way that faults in individual elements are inherently accommodated, although some degradation in overall performance will inevitably be found. The paper introduces the notion of fault tolerant systems and the highly redundant actuator concept. Then a model for a two by two configuration with electromechanical actuation elements is derived. Two classical control approaches are then considered based on frequency domain techniques. Finally simulation results under a number of faults show the viability of the approach for fault accommodation without reconfiguration

Requirements analysis for high redundancy actuation

This document introduces the idea of high redundancy actuation. Typical requirements for actuators in different applications are discussed, and a synthesis of the most important parameters is presented. To be successful, a high redundancy actuator needs to satisfy the same kind of requirements. Based on these, tentative parameters for an experimental verification of the high redundancy concept are proposed

Sensor optimisation via H∞ applied to a MAGLEV suspension system

In this paper a systematic method via H∞ control design is proposed to select a sensor set that satisfies a number of input criteria for a MAGLEV suspension system. The proposed method recovers a number of optimised controllers for each possible sensor set that satisfies the performance and constraint criteria using evolutionary algorithms

Sensor optimisation via H∞ applied to a MAGLEV suspension system

In this paper a systematic method via H∞ control design is proposed to select a sensor set that satisfies a number of input criteria for a MAGLEV suspension system. The proposed method recovers a number of optimised controllers for each possible sensor set that satisfies the performance and constraint criteria using evolutionary algorithms

The theory of electromagnetic levitation

Identifies a number of fundamental principles of physics which are involved in applying electromagnetic suspensions to transport. The theory relating to these is developed and typical values are given for important variables and parameters when an overall view of the transport system is taken. A number of simplifications and assumptions are used in order to treat as concisely as possible the important considerations. The control of the electromagnets is considered. Electromagnetic suspension systems are an intriguing area of technology. They combine the properties of magnetic fields with advanced control theory; they incorporate advanced instrumentation and state-of-the-art power semiconductors; they bring together the expertise of electrical electronic, mechanical and civil engineers; and they offer a challenge to the long established technology of wheeled systems

Control systems for magnetic suspensions and other applications

The thesis consists of twelve papers which present work on two distinct but related topics concerning high performance control systems: firstly the design of controllers for electromagnetically suspended vehicles, and secondly methods for efficient design of digital controllers for this and other applications. The first topic is covered by seven papers which range from consideration of the underlying theory through to the specific design of the suspension control system for British Rail's experimental vehicle, also applied to the world's first commercial Maglev system at Birmingham Airport. Not only are the control engineering considerations described, but also the dynamic requirements of providing an adequate ride quality using the electro-magnets alone are addressed in some detail. The remaining five papers consider the problems of translating compensator transfer functions such as phase advances, lagleads, "notch"filters etc. for implementation on microprocessor systems. They introduce a practical method for appraising coefficient sensitivity, which leads on to a novel structure for recursive digital filters using the so-called 0 operator rather than the traditional z operator. Detailed implementation is considered from the point of view of hardware and software, but making use of the new structure which is designed to minimise computation requirements. Specific examples for the digital cont roller methodology are drawn 'from the Maglev control application

Control system studies of an active anti-roll bar tilt system for railway vehicles

This paper describes a theoretical study of an active anti-roll bar tilt control system for a railway vehicle. It presents the rationale behind body tilting, the advantages and disadvantages associated with body tilting and the key tilt control system requirements. The paper also describes the control modelling process and presents some simulation results from control system studies. A number of competing control systems have been designed and analysed, including both classical and optimal control strategies. The performance of the control systems for a variety of curves is considered, as well as their response to track irregularities. The results show that all the strategies provide good tilting performance, the optimal control approach being marginally better

High redundancy in actuation

Actuation, the controlled movement and positioning of objects, is an essential function of many technical systems. It is crucial in many applications from central heating to aircrafts, and without actuation, the function or even the safety of the system would suffers. For example an aircraft is steered using control surfaces, and if the actuation of these surfaces fails, the aircraft may crash. Therefore, actuation is often provided by using several (typically between 2 and 4) redundant actuation elements. If one element fails, another takes over, and harm can be avoided. While this solution works, it involves increased cost, weight and energy use, reducing the efficiency of the system considerable. This project on high redundancy actuation investigates the use of a high number of actuation elements, such as 10 or even 100. This is a bionic (or bio-mimetic) idea: the use of actuation elements is similar to the composition of a muscle from many individual muscle fibres. Just like the muscle is highly resilient to damage in individual fibres (causing sore muscles, but no loss of movement), high redundancy actuation is highly reliable even if several elements have failed. The reliability analysis shows that this approach provides the same level or even superior protection against faults, without the loss of efficiency involved in the traditional solution. The basic advantage is that the law of large numbers applies, which provides a much more accurate prediction of how faults will affect the actuation elements over time. In the aircraft example, this would provide lighter actuators that provide superior reliability, leading to better fuel economy and easier maintenance. The main scientific problem of this project is how to deal with the complexity of using a high number of elements together. The results show that it is possible to determine the reliability of the system, and it is also possible to control the many elements as if they are just one big actuator. The next phase of the project is dealing with the technological challenges of combining many actuation elements. A simple experiment with four elements has been completed, and a demonstrator with 16 elements is being built. These experiments are used to demonstrate the resilience to faults, and understand the practical control issues at hand. A project leading to a more advanced version with up to 100 elements is currently being prepared. While the developed theories can be extended easily to consider such configurations, the practical difficulties of designing and manufacturing such a solution are challenging. The goal is to demonstrate that high redundancy actuation is feasible with the currently available technology, and to get an idea of the manufacturing issues involved