Luca Papini

A High-Speed Permanent-Magnet Machine for Fault-Tolerant Drivetrains

This paper details the design considerations of a permanent-magnet three-phase synchronous machine for fault-tolerant operation. A multidisciplinary approach to the optimal design of the machine is adopted, targeted at minimizing the additional losses resulting from faulty operating conditions and accounting for the remedial control strategy implemented. The design of a closed-slot six-slot four-pole machine is presented. The machine is prototyped and tested to validate the analytical-computational performances predicted in the design and analysis stage under healthy and faulty conditions.

Demagnetization Analysis for Halbach Array Configurations in Electrical Machines

This paper proposes and investigates an analytical method for assessing the risk of potential irreversible demagnetization in the permanent magnets (PMs) of electrical machines equipped with n-stages, Halbach arrays. The higher risk of demagnetization, synonymous with Halbach arrays, imposes that the method be both load and temperature dependent. In fact, the proposed method studies the magnetic field distribution in the air gap and PM region, for various operating temperatures and expresses these fields as analytical expressions for the no-load and peak-load conditions. The model can cater for Halbach arrays with up to n stages, thus making it a versatile tool that can be utilized for various Halbach configurations. Finite-element analysis is used to validate the method. The analytical tool is then used for the design and analysis of a high torque density, outer rotor, traction motor. The motor is for an aerospace application and its operating duty cycle imposes very high, short-time, peak-load conditions at elevated temperatures, posing an elevated risk of irreversible PM demagnetization. The model is used to investigate various Halbach configurations for this application, in order to reduce the demagnetization risk and also to improve the general performance of the machine. The analytical method thus provides a computationally efficient tool that can be used to predict and prevent demagnetization in Halbach-equipped electrical machines operating in harsh environments such as the aerospace sector.

High speed solid rotor induction machine: Analysis and performances

The paper presents the design, analysis and testing aspects of high speed induction machines equipped with solid rotor. At first the theoretical background and design aspects of solid rotor for induction machines is presented considering electromagnetic, thermal and mechanical aspects and focusing on the assessment of end-region factor effects. The techniques are benchmarked against a 120 kW solid rotor induction motor designed for power generation application.

Fault Tolerant Design of Fractional Slot Winding Permanent Magnet Aerospace Actuator

This paper introduces a particular permanent magnet motor (PMM) design methodology, considering advanced magnetic material characteristics, for aerospace actuator applications. In this class of problems, increased electromagnetic power density, fault tolerance, and high-temperature withstand properties are of major importance, and favored single-layer (SL) and double-layer (DL) fractional slot concentrated winding (FSCW) optimal topologies with different motor segmentation strategies have been compared. Under such strict nature of specifications, both operational and spatial, the implementation of advanced magnetic materials, particularly Vacoflux50 cobalt iron laminations and NMX-S43SH neodymium PMs, offer great services. The optimization methodology introduced is based on composite cost and penalty functions involving performance, efficiency, reliability, weight, and thermal criteria for multioperational behavior under normal and temporary overload conditions. An appropriate particle swarm optimization algorithm ensures fast convergence of the optimization variables. The resulting optimal SL and DL FSCW PMM configurations present certain complementary advantages, while the former one offering greater efficiency, thermal robustness, and physical segregation of the two motor parts is favored for this class of applications. Finally, the proposed motor configuration has been validated through measurements on a manufactured prototype.

Radial force control of multi-sector permanent magnet machines

The paper presents alternative radial force control technique for a Multi-Sector Permanent Magnet machine (MSPM). Radial force control has been widely investigated for a variety of bearingless machines and can be also applied to conventional PMSM aiming the reduction of the mechanical stress on the bearings as well as reduce the overall vibration. Traditional bearingless motors rely on two independent sets of windings dedicated to torque and suspension respectively. The work presented in this paper takes advantage of the spatial distribution of the winding sets within the stator structure towards achieving a controllable net radial force. In this paper the α-β axis model for the MSPM and the theoretical investigation of the force production principle is presented. A novel force control methodology based on the Single Value Decomposition (SVD) technique is described. The predicted performances of the MSPM have been validated using Finite Element simulations and benchmarked against state of the art control techniques.

Analytical Thermal Model for Fast Stator Winding Temperature Prediction

This paper introduces an innovative thermal modeling technique which accurately predicts the winding temperature of electrical machines, both at transient and steady state conditions, for applications where the stator Joule losses are the dominant heat source. The model is an advanced variation of the classical lumped-parameter thermal network approach, with the expected degree of accuracy but at a much lower computational cost. A seven-node thermal network is first implemented and an empirical procedure to fine-tuning the critical parameters is proposed. The derivation of the low computational cost model from the thermal network is thoroughly explained. A simplification of the seven-node thermal network with an equivalent three-node thermal network is then implemented, and the same procedure is applied to the new network for deriving an even faster low computational cost model. The proposed model is then validated against experimental results carried on a permanent magnet synchronous machine which is part of an electro-mechanical actuator designed for an aerospace application. A comparison between the performance of the classical lumped-parameter thermal network and the proposed model is carried out, both in terms of accuracy of the stator temperature prediction and of the computational time required.

Design aspects of a high torque density machine for an aerospace traction application

In this paper, design aspects for the development of high torque density machines are addressed. The main aim of this paper is to describe the electro-magnetic design and optimisation procedures developed in order to achieve an optimal design. The procedures are investigated by considering a high performance, aerospace, electrical machine used for aircraft traction. The selection of the optimal machine technology and topology is introduced. An analytical method for the selection of the optimal machine topology is proposed and validated by finite element results. The same tool is also applied to obtain a reliable demagnetisation prediction tool. Experimental results, measured from a built prototype are used to validate the design and modelling techniques described.

Direct Driven Hydraulics: What can possibly go wrong? -A thermal analysis

This paper focuses on a thermal analysis of Direct Driven Hydraulics (DDH). DDH combines the benefits of electric and hydraulic technologies in a compact package with high power density, superior performance and increased controllability. It enables a reduction of hydraulic losses therefore achieves better fuel efficiency. The main advantages of the presented architecture compared to a conventional valve-controlled system are the reduced hydraulic tubing and the amount of potential leakage points. DDH however represents a challenge for the prediction of the thermal behavior and its management as the temperature is a determining parameter of performance, lifespan, and safety of the system. Therefore, the electro-hydraulic model of a DDH involving a variable motor speed, two fixed-displacement internal gear pump/motors was developed at a system level for thermal analysis. In addition, losses dependent on temperature were validated by measurements under various operating conditions set by a cold chamber to 20, 10, and -5 °C. A model investigation predict heat dissipation from the electrical machine to the rest of the system. The electric machine heat dissipation plays an important role in the system temperature balance while the DDH is operated in extreme continuous operating condition. Furthermore, expected challenges for the future development of DDH concept are discussed.

High speed drives review: Machines, converters and applications

The development of new power electronic device and high performance magnetic materials are the main technological factors that have led both industries and research community to focus their attention on high speed electrical drives. Several papers have already outlined the electrical machine and/or converter topology choice for certain high speed application. This choice obviously depends on the applications under study. This paper aims to identify the most important high speed applications. For each of them, the main design challenges are highlighted and an overview of the already available product on the market is presented.

Active Magnetic Bearing system design featuring a predictive current control

Active Magnetic Bearing (AMB) technology is becoming attractive for several reasons such as high speed operations, high reliability and vibrations exemption. Moreover, AMB can behave as active vibration dampers and provide a real-time control of the shaft. For all these advantages, AMBs are particularly attractive for high power - high speed applications. These desirable features come at the cost of an increased complexity of the system, which now includes a power electronic converter and a control system dedicated to the AMBs. This paper focus on the overall system design, from the AMB design, to the power electronic converter design and control, for an AMB featuring Wheatstone bridge winding configuration. The magnetic design has been developed analytically and validated by means of Finite Elements simulation, to generate up to 2kN of axial forces. The power conversion system is based on three full bridges, one to magnetize the bearing and two to control the axial forces independently on the x and y axes. In order to achieve high bandwidth current control able to generate the desired orthogonal forces, a predictive control strategy has been proposed, for the several advantages it can provides such as fast dynamic response, no need of modulation, easy inclusion of nonlinearities and constraints of the system, possibility of incorporating nested control loops in only one loop and the flexibility to include other system requirements in the controller. The control system has been validated in Matlab/PLECS simulation, including the effect of parameters mismatches in the coils.