Computer-aided design for robust control using the QFT method

This report outlines the full work on the final year project. The project’s title is ‘CAD for robust control using the QFT design method ’. The aim of the project is to develop software tools, suitable for the robust control design of highly uncertain SISO systems. The design of these systems is based on I Horowitz’ s QFT method. This is a frequency domain loop-shaping design technique, which is fully described in Chapter 2. The report is a step-by-step guide to the design. It includes an introduction to control and robust systems, an explanation of the QFT method, and the problem definition of the design using an illustrative example. It continues with designs of phase lead and lag compensators via graphical techniques. Next the application of optimisation methods for the design of optimal PD and PID controllers is discussed. Designing an appropriate pre-filter completes the design procedure. Finally, a number of simulations show that the design technique was successful and meets the given specifications. The report concludes with a summary of the project work and its results and suggests future directions, which can be followed in order to improve certain aspects of the design. The Appendix summarises aspects of the theories used for the purposes of the project and a list of Matlab files created and used

Combining active structural damping and active suspension control in flexible bodied railway vehicles

There is a desire to design lightweight railway vehicle bodies for future high speed trains. Previously, suppression of structural vibration of the flexible lightweight vehicle body was attempted via use of active suspensions (conventional actuators) or by structural damping via piezoelectric actuators, with the aim being to improve the ride quality. In a railway vehicle the typical active suspension setup comprises front and rear suspension conventional actuators, while adding more macro-actuator elements to minimise structural vibrations can substantially impact vehicle weight and location considerations. In this paper, we show that piezoelectric actuator control can provide complementary action to active suspensions. Decentralized control is adopted for combined active structural damping and active suspension design via Linear Quadratic Gaussian (LQG) method and modal control with skyhook damping respectively. The side-view model of a flexible-bodied railway vehicle integrated with piezoelectric actuators and appropriate sensor outputs is derived and the placement of the piezoelectric actuators and sensors is addressed via structural norms. It is shown that vibrations of both the flexible modes and rigid modes are suppressed effectively. This suggests that with the combined approach, control by both piezoelectric actuators and suspension actuators could be used in a more efficient way to address vibrations in light railway vehicle bodies

New insights from fractional order skyhook damping control for railway vehicles

Active suspensions for railway vehicles have been a topic of research for a number of decades and while their applications in service operation are limited it seems clear that they will in due course see widespread adoption. Railway suspension design is a problem of compromise on the non-trivial trade-off of ride quality vs track following (guidance), and the skyhook damping control approach has been paramount in illustrating the potential benefits. Since skyhook damping control, various advanced control studies appeared contributing to redefine the boundaries of the aforementioned trade-off. Yet there is no study on the impact of fractional order methods in the context of skyhook railway active suspensions, and in particular related to skyhook damping control. This is the area to which this paper strongly contributes. We present findings from a current project on fractional order controllers for railway vehicles active suspensions, in particular work on the effect of fractional order methods in basic skyhook damping control schemes, i.e. pure and intuitively-based skyhook. Firstly we present a brief review of conventional skyhook damping control and then proceed to a rigorous investigation of the impact of fractional order on the ride quality / track following trade-off. The relevant benefits from fractional order methods are appraised and new insights highlighted

Optimized sensor configurations for a Maglev suspension system

This paper discusses a systematic approach for selecting the minimum number of sensors for an Electromagnetic suspension system that satisfies both optimised deterministic and stochastic performance objectives. The performance is optimised by tuning the controller using evolutionary algorithms. Two controller strategies are discussed, an inner loop classical solution for illustrating the efficacy of the evolutionary algorithm and a Linear Quadratic Gaussian (LQG) structure particularly on sensor optimisation

PLC-BASED DISCRETE FRACTIONAL-ORDER CONTROL DESIGN FOR AN INDUSTRIAL-ORIENTED WATER TANK VOLUME SYSTEM WITH INPUT DELAY

We present PLC-based fractional-order controller design for an industrial -oriented water tank volume control application. The system comprises input delay which is a typified characteristic in such industrial process control applications. The particular contribution of this work is on discrete fractional-order PID implementation via PLC and its application to the aforementioned realistic water tank test bed. Stability and robustness properties of fractional-order discrete PID feedback-loops for different approximation methods and orders are also shown. Fractional-order controllers are obtained for a variety of stability margin choices, and benefits of the non-integer-order controllers compared to the integer-order PID control are illustrated via simulation and experimental runs on a realistic test-bed

Modelling and control of railway vehicle suspensions

This chapter uses a railway vehicle as an example of a mechanical dynamic system to which control can be applied in a manner that yields significant benefits from an engineering and operational viewpoint. The first part describes the fundamentals of railway vehicles and their dynamics: the normal configuration, the suspension requirements, how they are modelled and an overview of the types of control concept that are currently applied or under consideration. The second part provides a case study of controller design issues

Optimized Ziegler-Nichols based PID control design for tilt suspensions

PID control design using optimized modified Ziegler-Nichols tuning is for active suspensions of tilting nature is presented. The study of this refers to non-precedent tilt active suspensions for railway vehicles which comprises a cumbersome design trade-off. No study exists on detailed Ziegler-Nichols PID tuning for Single-Input-Single-Output type non-precedent tilt control. We therefore investigate such an approach, referred to here as simple3 tilt, emphasizing control performance that can be achieved in such type of tilting suspension problem. The aim is to provide a baseline design tool for control practicioners, in active suspensions of that nature, who may be more familiar with traditional PID tuning rules. Without loss of generality the suggestions in this paper can be considered in other applications of tilting suspension nature

Optimized active disturbance rejection control for DC-DC buck converters with uncertainties using a reduced-order GPI observer

The output voltage regulation problem of a PWM- based DC-DC buck converter under various sources of uncertainties and disturbances is investigated in this paper via an optimized active disturbance rejection control (ADRC) approach. Aiming to practical implementation, a new reduced-order generalized proportional integral (GPI) observer is first designed to estimate the lumped (possibly time-varying) disturbances within the DC- DC circuit. By integrating the disturbance estimation information raised by the reduced-order GPI observer (GPIO) into the output prediction, an optimized ADRC method is developed to achieve optimized tracking performance even in the presence of distur- bances and uncertainties. It is shown that the proposed controller will guarantee the rigorous stability of closed-loop system, for any bounded uncertainties of the circuit, by appropriately choosing the observer gains and the bandwidthfactor. Experimental results illustrate that the proposed control solution is characterised by improved robustness performance against various disturbances and uncertainties compared to traditional ADRC and integral MPC approaches

Construction of control Lyapunov function with region of attraction using union theorem in sum-of-squares optimization

Control Lyapunov function (CLF) paves the way for designing a certified controller with a known stable region, which is the out-most importance in control systems. Sum-of-Squares (SOS) optimization is one method to construct the CLF with this stable region known as a region of attraction (ROA). However, existing methods yield quite conservative results. A new approach for constructing CLF overcoming existing limitations is proposed in this paper. The proposed method is based on the Union Theorem in sum-of-squares optimization, which enables the application of more than one variable size region generated by positive functions known as the Shape Function. Numerical simulations demonstrate the effectiveness of the proposed method, which outperforms the existing methods and provides a significantly enhanced ROA