• Methods of resistance estimation in permanent magnet synchronous motors for real-time thermal management.

      Wilson, Simon Delamere; Stewart, Paul; Taylor, Benjamin P.; University of Sheffield (IEEE, 2010-08-12)
      Real-time thermal management of electrical machines relies on sufficiently accurate indicators of internal temperature. One indicator of temperature in a permanent-magnet synchronous motor (PMSM) is the stator winding resistance. Detection of PMSM winding resistance in the literature has been made on machines with relatively high resistances, where the resistive voltage vector is significant under load. This paper describes two techniques, which can be applied to detect the winding resistance, through “angle” and “magnitude” current injection. Two further methods are described, which discriminate injected current and voltages from motoring currents and voltages: “unipolar” and “bipolar” separation. These enable the resistance to be determined, and hence the winding temperature in permanent-magnet machines. These methods can be applied under load, and in a manner that does not disturb motor torque or speed. The method distinguishes between changes in the electromotive force constant and the resistive voltage. This paper introduces the techniques, while a companion paper covers the application of one of the methods to a PMSM drive system.
    • Robust fault estimation for wind turbine energy via hybrid systems.

      Odofin, Sarah; Bentley, Edward; Aikhuele, Daniel; University of Derby; Nothumbria University; Bells University of Technology (Elsevier, 2017-12-15)
      The rapid development of modern wind turbine technology has led to increasing demand for improving system reliability and practical concern for robust fault monitoring scheme. This paper presents the investigation of a 5 MW Dynamic Wind Turbine Energy System that was designed to sustain condition monitoring and fault diagnosis with the goal of improving the reliability operations of universal practical control systems. A hybrid stochastic technique is proposed based on an augmented observer combined with eigenstructure assignment for the parameterisation and the genetic algorithm (GA) optimisation to address the attenuation of uncertainty mostly generated by disturbances. Scenarios-based are employed to explore sensor and actuator faults that have direct and indirect impacts on modern wind turbine system, based on monitoring components that are prone to malfunction. The analysis is aimed to determine the effect of concerned simulated faults from uncertainty in respect to environmental disturbances mostly challenged in real-world operations. The efficiency of the proposed approach will improve the reliability performance of wind turbine system states and diagnose uncertain faults simultaneously. The simulation outcomes illustrate the robustness of the dynamic turbine systems with a diagnostic performance to advance the practical solutions for improving reliable systems.
    • Internal combustion engine control for series hybrid electric vehicles by parallel and distributed genetic programming/multiobjective genetic algorithms

      Gladwin, Daniel; Stewart, Paul; Stewart, Jill; University of Sheffield; University of Salford (Taylor & Francis, 2010-03-01)
      This article addresses the problem of maintaining a stable rectified DC output from the three-phase AC generator in a series-hybrid vehicle powertrain. The series-hybrid prime power source generally comprises an internal combustion (IC) engine driving a three-phase permanent magnet generator whose output is rectified to DC. A recent development has been to control the engine/generator combination by an electronically actuated throttle. This system can be represented as a nonlinear system with significant time delay. Previously, voltage control of the generator output has been achieved by model predictive methods such as the Smith Predictor. These methods rely on the incorporation of an accurate system model and time delay into the control algorithm, with a consequent increase in computational complexity in the real-time controller, and as a necessity relies to some extent on the accuracy of the models. Two complementary performance objectives exist for the control system. Firstly, to maintain the IC engine at its optimal operating point, and secondly, to supply a stable DC supply to the traction drive inverters. Achievement of these goals minimises the transient energy storage requirements at the DC link, with a consequent reduction in both weight and cost. These objectives imply constant velocity operation of the IC engine under external load disturbances and changes in both operating conditions and vehicle speed set-points. In order to achieve these objectives, and reduce the complexity of implementation, in this article a controller is designed by the use of Genetic Programming methods in the Simulink modelling environment, with the aim of obtaining a relatively simple controller for the time-delay system which does not rely on the implementation of real time system models or time delay approximations in the controller. A methodology is presented to utilise the miriad of existing control blocks in the Simulink libraries to automatically evolve optimal control structures.
    • A novel genetic programming approach to the design of engine control systems for the voltage stabilization of hybrid electric vehicle generator outputs

      Gladwin, Daniel; Stewart, Paul; Stewart, Jill; University of Sheffield; University of Lincoln (Institution of Mechanical Engineers, 2011-07-13)
      This paper describes a Genetic Programming based automatic design methodology applied to the maintenance of a stable generated electrical output from a series-hybrid vehicle generator set. The generator set comprises a three-phase AC generator whose output is subsequently rectified to DC. The engine/generator combination receives its control input via an electronically actuated throttle, whose control integration is made more complex due to the significant system time delay. This time delay problem is usually addressed by model predictive design methods, which add computational complexity and rely as a necessity on accurate system and delay models. In order to eliminate this reliance, and achieve stable operation with disturbance rejection, a controller is designed via a Genetic Programming framework implemented directly in Matlab and, particularly, Simulink. The principal objective is to obtain a relatively simple controller for the time-delay system which does not rely on computationally expensive structures, yet retains inherent disturbance rejection properties. A methodology is presented to automatically design control systems directly upon the block libraries available in Simulink to automatically evolve robust control structures.
    • Primary and albedo solar energy sources for high altitude persistent air vehicle operation

      Smith, Tim; Trancossi, Michele; Vucinic, Dean; Bingham, Chris; Stewart, Paul; University of Lincoln; Sheffield Hallam University; Vrije Universiteit Brussel; University of Derby (Multidisciplinary Digital Publishing Institute (MDPI), 2017-04-22)
      A new class of the all electric airship to globally transport both passengers and freight using a ‘feeder‐cruiser’ concept, and powered by renewable electric energy, is considered. Specific focus is given to photo‐electric harvesting as the primary energy source and the associated hydrogen‐based energy storage systems. Furthermore, it is shown that the total PV output may be significantly increased by utilising cloud albedo effects. Appropriate power architectures and energy audits required for life support, and the propulsion and ancillary loads to support the continuous daily operation of the primary airship (cruiser) at stratospheric altitudes (circa 18 km), are also considered. The presented solution is substantially different from those of conventional aircraft due to the airship size and the inherent requirement to harvest and store sufficient energy during “daylight” operation, when subject to varying seasonal conditions and latitudes, to ensure its safe and continued operation during the corresponding varying “dark hours”. This is particularly apparent when the sizing of the proposed electrolyser is considered, as its size and mass increase nonlinearly with decreasing day‐night duty. As such, a Unitized Regenerative Fuel Cell is proposed. For the first time the study also discusses the potential benefits of integrating the photo‐voltaic cells into airship canopy structures utilising TENSAIRITY®‐based elements in order to eliminate the requirements for separate inter‐PV array wiring and the transport of low pressure hydrogen between fuel cells.
    • Assessment of structural integrity of subsea wellhead system: analytical and numerical study

      Maligno, Angelo; Citarella, Roberto; Silberschmidt, Vadim V.; Soutis, Constantinos; University of Derby; University of Salerno; Loughborough University; University of Manchester (Italian Group of Fracture, 2015-01)
      Subsea wellhead systems exposed to severe fatigue loading are becoming increasingly a significant problem in offshore drilling operations due to their applications in wells with higher levels of pressure and temperature, situated at larger depths and in harsher environments. This has led to a substantial increase in the weight and size of offshore equipment, which, in combination with different loading conditions related to the environmental factors acting on the vessel and riser, has greatly increased the loads acting on subsea well systems. In particular, severe fatigue loading acting on the subsea wellhead system was detected. For this reason, a combined analytical and numerical study investigating the critical effect of crack depth on the overall structural integrity of subsea wellhead systems under cyclic loading was carried out. The study is based on a Linear Elastic Fracture Mechanics (LEFM) approach.
    • FEM simulation of a crack propagation in a round bar under combined tension and torsion fatigue loading

      Citarella, Roberto; Maligno, Angelo; Shlyannikov, Valery; University of Salerno; University of Derby; Russian Academy of Sciences (Italian Group of Fracture, 2015-01)
      An edge crack propagation in a steel bar of circular cross-section undergoing multiaxial fatigue loads is simulated by Finite Element Method (FEM). The variation of crack growth behaviour is studied under axial and combined in phase axial+torsional fatigue loading. Results show that the cyclic Mode III loading superimposed on the cyclic Mode I leads to a fatigue life reduction. Numerical calculations are performed using the FEM software ZENCRACK to determine the crack path and fatigue life. The FEM numerical predictions have been compared against corresponding experimental and numerical data, available from literature, getting satisfactory consistency
    • Retardation effects due to overloads in aluminium-alloy aeronautical components

      Maligno, Angelo; Citarella, Roberto; Silberschmidt, Vadim V.; University of Derby; University of Salerno; University of Loughborough; Institute for Innovation in Sustainable Engineering; University of Derby; Quaker Way, Derby DE1 3HD UK; Department of Industrial Engineering; University of Salerno; via Giovanni Paolo II, Fisciano SA Italy; Wolfson School of Mechanical and Manufacturing Engineering; Loughborough University; Loughborough UK (Wiley, 2017-02-08)
      Fatigue data are generally derived under constant-amplitude loading conditions, but aircraft components are subjected to variable-amplitude loading. Without interaction effects, caused by overloads and underloads intermingled in a loading sequence, it could be relatively easy to establish a crack growth curve by means of a cycle-by-cycle integration. However, load-spectrum effects largely complicate a crack growth under variable-amplitude cycling. In this paper, fatigue crack growth behaviour of aeronautical aluminium alloy 2024-T3 was studied. Effects of various loading conditions such as stress ratio and amplitude loadings were investigated. In particular, the effect of different overloads on the fatigue crack growth was simulated using Zencrack code. Preliminary analyses on Compact Tension (CT) specimens proved that the numerical results generated were in agreement with the results provided by an afgrow code for the same conditions. A case study was carried out on a helicopter component, undergoing repeated overloads, to compare numerical results obtained implementing yield zone models in Zencrack.
    • An investigation into metal coated additively manufactured polymer lattice structures

      Farhan Khan, Muhammad; Williams, Gavin; Maligno, Angelo; University of Derby (OMICS International, 2016-06-13)
      The performance of polyamide lattices with electro-deposited metal was evaluated. This was achieved by irreversible compaction of the structures involved in the investigation. The versatility of additive manufacturing was utilized in order to fabricate the lattices. It demonstrated that metal coating of polymer lattices could significantly improve their compression properties. This methodology could provide new opportunities in terms of light weight energy absorbing structures in a wide variety of applications.
    • Dynamic model tracking design for low inertia, high speed permanent magnet ac motors

      Stewart, Paul; Kadirkamanathan, Visakan; University of Sheffield (Elsevier, 2007-01-17)
      Permanent magnet ac (PMAC) motors have existed in various configurations for many years. The advent of rare-earth magnets and their associated highly elevated levels of magnetic flux makes the permanent magnet motor attractive for many high performance applications from computer disk drives to all electric racing cars. The use of batteries as a prime storage element carries a cost penalty in terms of the unladen weight of the vehicle. Minimizing this cost function requires the minimum electric motor size and weight to be specified, while still retaining acceptable levels of output torque. This tradeoff can be achieved by applying a technique known as flux weakening which will be investigated in this paper. The technique allows the speed range of a PMAC motor to be greatly increased, giving a constant power range of more than 4:1. A dynamic model reference controller is presented which has advantages in ease of implementation, and is particularly suited to dynamic low inertia applications such as clutchless gear changing in high performance electric vehicles. The benefits of this approach are to maximize the torque speed envelope of the motor, particularly advantageous when considering low inertia operation. The controller is examined experimentally, confirming the predicted performance.
    • Real-time simulation and control systems design by the Response Surface Methodology and designed experiments

      Stewart, Paul; Fleming, Peter J.; MacKenzie, Sheena A.; University of Sheffield (Taylor and Francis, 2010-06-03)
      This paper examines two cases where the fitting of a model to experimental data makes possible the solution of extremely difficult design and simulation problems. In the first (aerospace) case, designed experiments were conducted on a permanent magnet AC motor which provided the motive power for a flight surface actuator in a more electric aircraft application. The Response Surface Methodology is applied to the measured data to achieve inclusion of the component in a real-time distributed aircraft simulation. In the second (automotive) case, oscillatory acceleration responses are controlled via an electronically actuated (drive by wire) throttle. Designed experiments were conducted on the test vehicle to achieve a systematic excitation of the vehicle driveline. An approximation to the measured data is achieved by the Response Surface Methodology allowing a controller to be designed extremely rapidly.
    • Commutation of permanent-magnet synchronous AC motors for military and traction applications

      Stewart, Paul; Kadirkamanathan, Visakan; University of Sheffield (Institute of Electrical and Electronic Engineers, 2003-06-05)
      The permanent-magnet ac (PMAC) motor requires accurate position information to be supplied to the controller so that the applied currents can be modulated in synchronism with the rotor. In the flux-weakening region of operation, accurate rotor position information is critical to control the relative phase of the applied stator voltages. The design of controllers, which can operate without direct position feedback, have been the subject of intense development. The most commonly cited justifications for the elimination of the absolute position encoder are those of cost, and the reduction of the overall dimensions of the motor. However, certain military specifications apply stringent constraints to the use of both sensors and estimation techniques. Absolute encoders are frequently prohibited for applications such as tank turret drives due to their relatively fragile nature. Fully sensorless operation has been the focus of development for all classes of electric motors, but again is precluded not only in certain military applications, but also in traction applications for a number of manufacturers.
    • Torque maximisation of the Pmac motor for high performance, low inertia operation

      Stewart, Paul; University of Sheffield (Wiley, 2008-10-22)
      This paper describes the techniques applied to maximise the torque envelope of the permanent magnet AC (PMAC) motor operating under current and voltage constraints. Standard steady-state descriptions of the system are often suitable for control purposes when the rotor velocity is varying relatively slowly. In low inertia applications such as clutchless gearchange operations, where in the pursuit of driveability, the motor is required to accelerate and decelerate its own rotor inertia as quickly as possible. In this case, the voltage drop due to the current dynamics start to become significant. This paper presents a method to reserve voltage headroom dynamically in the field-weakening region in order to maximise the torque envelope when the effective inertia is low. Experimental results show the effectiveness of this approach.
    • Tailoring force-displacement characteristics in medium-stroke linear variable reluctance actuators

      Clark, Richard E.; Jewell, Geraint; Stewart, Paul; Howe, Dave; University of Sheffield (Institute of Electrical and Electronic Engineers, 2002-12-10)
      The paper is concerned with the design of medium-stroke variable reluctance actuators that exploit the tangential component of force. A method of compensating for the roll-off in force as the stator and armature come into full alignment is presented, and the scope which this offers to tailor the force-displacement characteristic to meet the demands of a particular application is illustrated by means of a case study. The case study includes finite element analysis and experimental measurements on an actuator having a stroke of 8 mm and a rated force capability of 60 N.
    • Dynamic model reference PI control of permanent magnet AC motor drives

      Stewart, Paul; Kadirkamanathan, Visakan; University of Sheffield (Elsevier, 2001-11)
      The permanent magnet AC motor drive (PMAC) is a multivariable, non-linear, closely coupled system subject to saturation due to finite DC supply voltage and hard current limits for protection of the drive hardware. Model following controls can be applied to this class of motor with PI current controllers enabling tracking of quadrature current command values. The presence of a finite supply voltage constraint results in reduced system performance when the current regulators saturate. A dynamic model reference controller is presented which includes the currents and voltage limits, constraining the magnitude of the command signals, operating the system to just within the bound of saturation, allowing the PI controllers to accurately track the commanded values and retain control of the current vectors. This regime ensures maximum possible dynamic performance of the system. The system and controller is simulated and experimentally verified, controller gain being found by Monte Carlo simulation.
    • Toward a more realistic, cost-effective, and greener ground movement through active routing: A multiobjective shortest path approach

      Chen, Jun; Atkin, Jason A. D.; Locatelli, Giorgio; Weiszer, Michal; Ravizza, Stefan; Stewart, Paul; Burke, Edmund K.; University of Derby (IEEE, 2016-10-31)
      This paper draws upon earlier work, which devel- oped a multiobjective speed profile generation framework for unimpeded taxiing aircraft. Here, we deal with how to seamlessly integrate such efficient speed profiles into a holistic decision- making framework. The availability of a set of nondominated unimpeded speed profiles for each taxiway segment, with respect to conflicting objectives, has the potential to significantly impact upon airport ground movement research. More specifically, the routing and scheduling function that was previously based on distance, emphasizing time efficiency, could now be based on richer information embedded within speed profiles, such as the taxiing times along segments, the corresponding fuel consumption, and the associated economic implications. The economic implica- tions are exploited over a day of operation, to take into account cost differences between busier and quieter times of the airport. Therefore, a more cost-effective and tailored decision can be made, respecting the environmental impact. Preliminary results based on the proposed approach show a 9%–50% reduction in time and fuel respectively for two international airports: Zurich and Manchester. The study also suggests that, if the average power setting during the acceleration phase could be lifted from the level suggested by the International Civil Aviation Organization, ground operations may simultaneously improve both time and fuel efficiency. The work described in this paper aims to open up the possibility to move away from the conventional distance-based routing and scheduling to a more comprehensive framework, capturing the multifaceted needs of all stakeholders involved in airport ground operations.
    • Condition parameter estimation for photovoltaic buck converters based on adaptive model observers

      Cen, Zhaohui; Stewart, Paul; Derby University (IEEE, 2016-10-31)
      DC-DC power converters such as buck converters are susceptible to degradation and failure due to operating under conditions of electrical stress and variable power sources in power conversion applications, such as electric vehicles and renewable energy. Some key components such as electrolytic capacitors degrade over time due to evaporation of the electrolyte. In this paper, a model-observer based scheme is proposed to monitor the states of Buck converters and to estimate their component parameters, such as capacitance and inductance. First, a diagnosis observer is proposed, and the generated residual vectors are applied for fault detection and isolation. Second, component condition parameters, such as capacitance and inductance are reconstructed using another novel observer with adaptive feedback law. Additionally, the observer structures and their theoretical performance are analyzed and proven. In contrast to existing reliability approaches applied in buck converters, the proposed scheme performs online-estimation for key parameters. Finally, buck converters in conventional dc–dc step-down and photovoltaic applications are investigated to test and validate the effectiveness of the proposed scheme in both simulation and laboratory experiments. Results demonstrate the feasibility, performance, and superiority of the proposed component parameter estimation scheme.
    • Multifunctional unmanned reconnaissance aircraft for low-speed and STOL operations

      Trancossi, Michele; Bingham, Chris; Capuani, Alfredo; Das, Shyam; Dumas, Antonio; Grimaccia, Francesco; Madonia, Mauro; Pascoa, Jose; Smith, Tim; Stewart, Paul; et al. (SAE International, 2015-09-15)
      This paper presents a novel UAS (Unmanned Aerial System) designed for excellent low speed operations and VTOL performance. This aerial vehicle concept has been designed for maximizing the advantages by of the ACHEON (Aerial Coanda High Efficiency Orienting-jet Nozzle) propulsion system, which has been studied in a European commission under 7th framework programme.This UAS concept has been named MURALS (acronym of Multifunctional Unmanned Reconnaissance Aircraft for Low-speed and STOL operation). It has been studied as a joint activity of the members of the project as an evolution of a former concept, which has been developed during 80s and 90s by Aeritalia and Capuani. It has been adapted to host an ACHEON based propulsion system. In a first embodiment, the aircraft according to the invention has a not conventional shape with a single fuselage and its primary objective is to minimize the variation of the pitching moment allowing low speed operations. The shape with convex wings has been specifically defined to allow a future possibility of enabling stealth operations.Main objective of the design activity has been focused on low speed flight, very short take off and landing, and a control possibility by mean of two mobile surfaces in the front canard, which allow changing the pitch angle, and allows an almost complete plane control in combination with an ACHEON variable angle of thrust propulsion system. The design considers has been specifically to allow flying at a speed which is lower than 12 m/s with an high angle of attach (over 7°), without losses in terms of manoeuvrability and agility. These features allow innovative uses such as road monitoring, and police support and are characterized by a breakthrough performance level.A complete optimal sizing of the aircraft has been performed, together with an effective performance analysis, which allows identifying the strong points and the potential problems of the project. An effective energy analysis has been performed also. An effective prototyping is expected in about one year.
    • Optimal speed profile generation for airport ground movement with consideration of emissions

      Chen, Jun; Weiszer, Michal; Stewart, Paul; University of Derby (IEEE, 2015-09)
      Emissions during the ground movement are mostly calculated based on International Civil Aviation Organisation (ICAO) emission databank. The fuel flow rate is normally assumed as a constant, hence the emission index. Therefore, no detailed discrimination of power settings during ground movement is considered to account for different emissions at different power settings. This may lead to a suboptimal and often unrealistic taxi planning. At the heart of the recently proposed Active Routing (AR) framework for airport ground movement is the unimpeded optimal speed profile generation, taking into account both time and fuel efficiency. However, emissions have not been included in the process of generating optimal speed profiles. Taking into account emissions in ground operations is not a trial task as not all emissions can be reduced on the same path of reducing time and fuel burn. In light of this, in this paper, a detailed analysis of three main emissions at the airports, viz. CO, Total Hydrocarbon (HC), and NOx, are carried out in order to obtain a minimum number of conflicting objectives for generating optimal speed profiles. The results show that NOx has a strong linear correlation with fuel burn across all aircraft categories. For the heavy aircraft, HC and CO should be treated individually apart from the time and fuel burn objectives. For medium and light aircraft, a strong correlation between HC, CO and time has been observed, indicating a reduced number of objectives will be sufficient to account for taxi time, fuel burn and emissions. The generated optimal speed profiles with consideration of different emissions will have impact on the resulted taxiing planning using the AR and also affect decisions regarding airport regulations.
    • Preference-based evolutionary algorithm for airport runway scheduling and ground movement optimisation

      Weiszer, Michal; Chen, Jun; Stewart, Paul; University of Derby (IEEE, 2015-09-15)
      As airports all over the world are becoming more congested together with stricter environmental regulations put in place, research on optimisation of airport surface operations started to consider both time and fuel related objectives. However, as both time and fuel can have a monetary cost associated with them, this information can be utilised as preference during the optimisation to guide the search process to a region with the most cost efficient solutions. In this paper, we solve the integrated optimisation problem combining runway scheduling and ground movement problem by using a multi-objective evolutionary framework. The proposed evolutionary algorithm is based on modified crowding distance and outranking relation which considers cost of delay and price of fuel. Moreover, the preferences are expressed in a such way, that they define a certain range in prices reflecting uncertainty. The preliminary results of computational experiments with data from a major airport show the efficiency of the proposed approach.