Search

In the design of modern, high-performance switched reluctance machines, the highly restrictive sets of constraints and requirements severely limit the number of feasible solutions. In order to improve the chances of attaining a successful design, this work proposes a novel and fully analytical approach to the preliminary design analysis. Initially, the correct number of independent design variables is identified. Subsequently, constraints and requirements are introduced one by one, in order to progressively discard all of the unfeasible candidates. At the end of this process, the actual design space is attained, whose main characteristic is to be populated only by feasible candidates. A design case study shows how the proposed methodology allows: 1) to verify the design feasibility; 2) to reduce the number of candidates by orders of magnitude; and 3) to gain useful insight into the design problem and thus select the most convenient strategy to finalize it. As a result, a highly effective design process is attained, so that considerable computational resources can be saved.

Permanent Magnet Machines are widespread in the automotive industry, thanks to their high torque density and high efficiency. In automotive applications such as, for example, integrated starter alternators, a very wide Constant Power Speed Range is also required, for electricity generation on-board. To maintain a constant voltage, flux weakening must be employed during generation. With the conventional Electrical Flux Weakening methods, considerable amounts of current would have to be consumed to weaken the strong flux linkage from the magnets, which results on an efficiency decrease. Conversely, mechanical methods adjust the linked flux by manipulating the position of certain machine parts, avoiding the consumption of current. Thus, Mechanical Flux Weakening might be more suitable for the automotive applications, where a very wide Constant Power Speed Range is required, while preserving high levels of motoring torque capabilities. In the present Literature Review, various implementations of Mechanical Flux Weakening, from several authors, are analyzed and compared. The aim is to gain insight on the effectiveness of this method, in comparison with the electrical one, on fulfilling the mentioned automotive requirements.

The use of printed circuit board stators in coreless axial flux permanent magnet machines allows to reduce manufacturing costs and to eliminate the main drawbacks of traditional implementations using Litz wire. This work investigates the design of a coreless axial flux permanent magnet machine having printed circuit board concentrated windings. The field model of the coreless machine is reviewed to obtain closed-form equations for torque, eddy current loss and circulating currents loss are presented. Furthermore, cardinal geometrical parameters of the printed circuit board stator and the latest manufacturing possibilities are investigated, followed by the presentation of important machine design details.

In high power density applications, such as electric or hybrid electric vehicles, heat extraction is a crucial aspect of electrical machine design due to stringent volume specifications. In these cases, it is extremely difficult, if at all possible, to satisfy the maximum temperature requirement when using conventional cooling systems, such as housing fins, shaft-mounted fans or even water jackets. To this end, a novel direct oil cooling system conceived for Torus-type axial-flux permanent-magnet machines is proposed here. In order to demonstrate its effectiveness, lumped thermal equivalent circuit simulations, finite element analyses and experimental tests are presented. The expected performances of the machine using the proposed direct oil cooling are compared to those obtained using state of the art water cooling.

Unmanned aerial vehicles are characterized by a set of requirements, like high efficiency, resiliency, and reliability that conflict with the other main requirement of high power density aimed at minimizing the overall weight and size. This article proposes a novel, modular multiphase drive for a quadrotor drone, realized through the integration of an axial flux permanent magnet machine and a GaN-based power electronic converter. After an overview of the design process, starting from the propeller choice, a brief description of the system components is presented. Focusing specifically on the power electronic converter, the article then presents a full analysis of its electrical and thermal performance. Extensive experimental tests allows to validate the predictions of the design and simulation stages and demonstrated the expected high power density levels.

This work investigates the design of a multiphase coreless axial flux permanent magnet machine with concentrated windings, for the propulsion of an unmanned aerial vehicle. Such a system requires very high power and torque densities, which tend to be in contrast with other important requirements such as high efficiency and resilience. In order to simplify the design of the machine, an original method for the selection of the poles to coils ratio is proposed. The paper then presents a 3D finite element analysis based refinement for the final design; finally, a full scale prototype has been built and a preliminary no load test is reported.

This paper presents a closed-loop flux-weakening controller for hybrid-excitation synchronous machine drives based on separate regulation of amplitude and phase angle of the armature voltage. Operating point analysis is carried out to investigate the dynamic properties of the drive and to give guidelines in the tuning of the controller. Finally, experimental tests validating the theoretical derivations are performed on a prototype hybrid-excitation drive.

For high power density applications, such as electric or hybrid electric vehicles, heat extraction is a crucial aspect in electrical machine design due to stringent machine volume specifications. In these cases, it is extremely difficult if at all possible, to satisfy the maximum temperature requirement when using conventional cooling systems such as housing fins, shaft-mounted fans or even water jackets, due to insufficiently low thermal resistances. To this end, a novel direct oil cooling system conceived for Torus-type axial-flux permanent-magnet machines, is proposed here. In order to demonstrate its effectiveness, lumped thermal equivalent circuit simulations, finite element analyses and experimental tests are presented. Furthermore, the expected performances of the machine using the proposed direct oil cooling are compared to those obtained using state-of-the-art water cooling.

Extended Electro Motive Force Observers in the estimated synchronous reference frame allow to estimate rotor position at medium and high speeds for Interior Permanent Magnet Synchronous Machines. This paper focuses on the analysis of the dynamic performances of these observers. Use of complex vector modeling allows to demonstrate that these performances are speed dependent. In order to overcome this problem, a Complex Vector Observer is proposed. It is proven that this structure achieves good robustness against load torque and speed variations over different operating conditions. An improved phase detector is also presented, to solve the common speed reversal problems of the back-EMF based methods.

This paper investigates an original solution that can be used in the design of axial-flux permanent-magnet (AFPM) machines whenever a constrained shaft height requirement penalizes a standard design. A machine is tailored for electrical traction, but the ideas that are set forth are valid for any application with a constrained shaft height. Two design solutions that comply with a constrained shaft height are investigated, i.e., a standard Torus AFPM machine and an asymmetrically wound Torus machine, which is named “Ω AFPM” due to the shape of the stator winding. It is shown that the Ω AFPM machine has lower losses and higher efficiency. Finite-element simulations and experimental tests on a full-scale prototype confirm the validity of the proposed solution.

This paper presents the design, the finite element analysis validation of a double-stator single-rotor fractional-slot concentrated-winding axial-flux permanent magnet machine with tooth-wound coils. In this particular topology, the flux travels axially through the permanent magnets, from one stator to the opposite, so that there is no need for any rotor back-iron. In order to guarantee sufficient mechanical stiffness of the rotor, the support of the permanent magnets is made of stainless steel. Three different variants of this support are proposed, with the aim of minimizing the induced losses therein. Machine performances both at no load and at rated load are analyzed by using time-stepped 2D FEA and losses in the rotor are compared for the different support variants. A full scale prototype has been built and preliminary experimental results are given.

Axial flux permanent magnet (AFPM) machines are being increasingly used in a variety of industrial direct drive applications which benefit from their extreme axial compactness. In particular, slotted AFPM machines are of great interest since they allow to achieve high torque densities together with an acceptable constant power speed range. This paper analyzes a particular aspect related to the design of such machines, i.e., the use of soft-magnetic-composite wedges to close stator slots. This paper is the continuation of a previous investigation dedicated to the analysis of the no-load performance variation introduced by the magnetic wedges. Here, the attention is focused on the load performance by studying the effect of the wedges on d-q-axis stator flux linkages, torque production, and losses. The 2-D and 3-D finite element analyses are performed on a 10-kW AFPM machine, various magnetic wedge configurations are studied, and the load performance is compared with that of the same machine using nonmagnetic wedges, in terms of stator flux linkage, average and ripple torque, and magnetic losses. Finally, experimental tests and results on a full scale prototype machine mounting magnetic wedges are reported.

Hybrid excitation synchronous machines are a class of machines that allow to reduce PM costs while keeping high torque density and that guarantee very high constant power speed range. They come in a wide variety of topologies and not all possible solutions have been explored yet. Aim of this paper is to provide a systematic analysis of all the possible configurations that can be obtained by changing the axis along which the hybrid excitation is placed. Both single-axis and bi-axial excitations are considered. A comparative analysis is carried out with respect to performance indices like torque capability, constant power speed range, power factor and losses.

Hybrid Excitation Synchronous Machines allow broad flux regulation, and therefore a very wide Constant Power Speed Range. Literature shows that it is possible to build them both with a Single-Axis and with a Bi-Axial excitation. This paper presents a unified approach for the analysis, comparison and performance prediction of the two structures. Finite element simulation and experimental tests are carried out on a Torus-type Axial-Flux prototype, which — having two rotors, one equipped with PM and one with WE — allows for an easy structure reconfiguration on the same machine.

This paper reviews the progress that has been made in the analysis and design of axial-flux permanent-magnet machines over the past decade, with particular attention to aspects such as electromagnetic and thermal modeling, materials, manufacturing, pulsating torque, and extended speed range. Comparisons with other machine types and applications are also reviewed.

This paper presents a single-phase slotless axial-flux permanent-magnet synchronous machine for induction heating gensets. A full-scale prototype of the machine (110 kVA, 400 Hz, 690 A) has been designed and subsequently analyzed through finite element analysis (FEA). Induced current distributions in the permanent magnets and in the rotors have also been calculated through FEA, showing that the resulting losses are kept at bay due to the low armature reaction. An effective way of achieving regulation of the power transferred to the load has been analytically derived. The prototype has also been built, and experimental tests confirm the aforesaid analyses.

The paper presents a closed loop flux weakening controller for Hybrid Excitation Synchronous Machines. The control is achieved though regulation of the voltage amplitude and of the phase angle between voltage and current. An operating point analysis is carried out, in order to determine the dynamic behavior of the drive. Finally, experimental tests are conducted on a prototype of axial flux hybrid excitation machine.

In this paper, two methods for flux linkage regulation in a starter/alternator with an axial-flux permanent magnet (AFPM) machine are proposed and compared. Desired regulation is achieved by two different mechanical solutions, each of them capable of modifying the amount of flux linkage through displacement of the two rotors in the AFPM machine. Constant power generation is thus achieved with very inexpensive devices that do not require external energy sources since energy in the airgap doesn't change. The main difference between the two proposed solutions is that the speed dependant device is ideally a constant voltage source while the torque-dependant device behaves as a constant current source. Even if some improvements are still needed, both devices introduce the totally innovative concept of mechanical flux weakening for AFPM power regulation in a wide speed range. Finally, the paper demonstrates that the introduction of these devices doesn't modify machine behavior in starting mode, so that the particular features of AFPM machines in terms of high torque density and overload capability remain unaffected

This paper investigates methods to achieve a wide constant power speed range (CPSR) in electric drives using hybrid excitation synchronous machines; five strategies are presented and compared. These range from state-of-the-art flux weakening based on demagnetizing armature current injection, to algorithms based on wound excitation (WE) current regulation, all the way to techniques involving both armature and WE current regulation. It is shown that one of these latter strategies allows a theoretically infinite CPSR and unity power factor operation throughout. This result is also verified experimentally, and a 10:1 range is demonstrated. Finally, a discussion is presented on practical limiting issues such as harmonic flux linkage components, inductance variations, and high-speed iron losses.

This paper presents an axial-flux machine with hybrid excitation (HE), in which the flux linkage can be regulated in an extremely wide range by using a rotating excitation winding. This machine shows a theoretically infinite constant power speed range and also exhibits a high degree of fault tolerance against uncontrolled generator operation. The machine has a single-stator double-rotor topology, with one rotor mounting permanent magnets and the other supporting the excitation winding. After a review of the state of the art of HE machines, this paper examines the principle of operation of this machine. Subsequently, a prototype is designed, analyzed with finite-element analysis, and built. Finally, experimental results are reported to confirm the theoretical predictions and the benefits and drawbacks of this novel topology.

This paper presents the concept of a novel hybrid-excitation machine. This machine is of the parallel excitation type and has rotor poles in which both PMs and wound-excitation co-exist to produce the total no load magnetomotive force; for this reason it is named mixed-pole hybrid-excitation machine. Due to its parallel excitation nature, the machine has excellent flux linkage regulation properties and its use is therefore envisaged for applications that require wide constant power speed ranges. A very useful property that stems from this particular topology is that the designer is able to select the relative contributions of PM and wound-excitation flux by simply designing the relative portions of the PM part and wound-excitation part of the rotor poles. Although both radial flux and axial flux versions can be designed, this paper concentrates on the latter type. A proof-of-concept prototype is designed for a 600–6000 rpm constant power speed range and the machine's performances are analysed with finite element simulations.

The variable-speed driven pump can result in significant energy conservation where reduced flow rates are required for long periods of time. In regard to adjustable-speed pump drives, one major contribution of this paper is the demonstration that a permanent magnet (PM) motor based on the slotless axial-flux permanent magnet machine (AFPM) topology can be a suitable candidate to advantageously compete with the induction motor for such a low-cost drive application. For the purpose of a cost comparison, the paper discusses design and construction of a prototype machine which has been conceived to replace a 1.2 HP induction motor being used in a standard adjustable-speed pump drive. Results taken from laboratory tests of the prototype machine are reported, together with an assessment of the machine manufacturing cost.

This contribution investigates an original solution that can be used in the design of AFPM machines, whenever a constrained shaft height requirement penalizes a standard design. The machine is tailored for electrical traction, but the ideas that are set forth are valid for any application with constrained shaft height. Two design solutions are investigated that comply with the constrained shaft height: a standard Torus AFPM machine and an asymmetrically wound Torus machine, named “Ω AFPM” due to the shape of the stator. It is shown that the Ω AFPM machine has lower losses and a higher efficiency. FE simulations and experimental tests on a full-scale prototype confirm the validity of the proposed solution.

The aim of the paper is to present the thermal modeling of a Kaman type Axial-Flux Permanent-Magnet machine with fractional-slot concentrated-winding. This machine is air-cooled and equipped with specific arrangements to enhance heat dissipation. Thermal paths inside the machine are quite complex and require three-dimensional modelling. This is achieved through a lumped parameter network and subdivision of machine into cuboidal elements. The paper describes how thermal modeling is achieved and compares simulations with experimental results taken from a full scale prototype equipped with a number of thermocouples.

In slotted axial-flux permanent-magnet (PM) (AFPM) machines, two possible concentrated-winding arrangements can be used: integral slot and fractional slot. Integral-slot concentrated windings (ISCWs) have a number of slots/pole/phase equal to one and have long been a preferred choice with machine designers due to their simple layout. On the other hand, fractional-slot concentrated windings (FSCWs) have a number of slots/pole/phase less than one and have been the focus of a significant amount of international research in the past decade. This paper presents an original comparison between two 10-kW AFPM machine prototypes with concentrated windings: a 20-pole 60-slot ISCW machine and a 20-pole 24-slot FSCW machine. The design of both machines is described, highlighting the constraints that have been set to allow a fair comparison between them. Static and time-stepped finite-element-analysis results are presented. Comparative no-load and load experimental tests are performed on full-scale prototypes, and the results are reported: Important tradeoffs in key aspects such as peak cogging torque, constant power speed range, and additional losses are demonstrated. Finally, conclusions are made regarding the performances and required tradeoffs for both machines.

This paper presents an axial-flux machine with hybrid excitation, in which the flux linkage can be regulated in an extremely wide range through an excitation winding. Therefore, this machine shows a theoretically infinite constant power speed range and exhibits also an high degree of fault tolerance against uncontrolled generator operation. The machine has a single-stator double-rotor topology, one rotor mounting permanent magnets and the other supporting an excitation winding. After a review of the state of the art, the paper examines the principle of operation of this machine. Subsequently, a prototype is designed, studied through FEA, and constructed, in order to verify the benefits of the proposed solution.

In slotted axial-flux permanent magnet machines two possible concentrated-winding arrangements can be used: integer-slot and fractional-slot. The former type, i.e. windings with a number of slots/pole/phase equal to one, has long been a preferred choice with machine designers due to its simple layout. On the other hand, fractional-slot concentrated-winding machines have been the focus of a significant amount of international research in the past decade. This paper presents an original comparison between two 10 kW axial-flux permanent magnet machine prototypes with concentrated-windings: a 20 pole, 60 slot integer-slot concentrated-winding machine and a 20 pole, 24 slot fractional-slot concentrated-winding machine. The design of both machines is described, highlighting the constraints that have been set to allow a fair comparison between them. Static and time-stepped finite element analysis results are presented. Comparative no-load and load tests are performed on full scale prototypes and the results are reported. Finally, conclusions are made regarding the performances and required trade-offs for both machines.

Aim of the paper is to evaluate a particular aspect of the design of axial flux permanent magnet (AFPM) machines, i.e. the use of SMC wedges to close stator slots. This contribution is the continuation of a previous investigation dedicated to the analysis of the no-load performance variation introduced by the magnetic wedges. Here, attention is focused on the load performance, by studying the effect of the wedges on d-q axis stator flux linkages, torque production and losses. 2D finite element analyses (FEA) are performed on a 10 kW AFPM machine adopting various magnetic wedge configurations; the load performance is compared with that of the same machine using non-magnetic wedges in terms of stator flux linkage, average and ripple torque and rated load losses.

This paper presents the design, finite-element analysis (FEA), and experimental verification of a single-stator double-rotor fractional-slot concentrated-winding axial-flux permanent-magnet machine with core-wound coils. The advantages that are obtained by adopting such coil construction in terms of shorter end-winding connections higher fill factor, and mechanical robustness of the magnetic structure are highlighted. Machine performances both at no load and at rated load are analyzed through static FEA, and a simple index is introduced to compare induced losses in the permanent magnets for various machine configurations. Time-stepped transient FEA is used to validate the index. The construction and experimental testing of a full-scale prototype is described to confirm the expected performances and to characterize the prototype in terms of losses (both at no-load and in loaded conditions), cogging torque, and main machine parameters.

Axial flux permanent magnet (AFPM) machines are being increasingly used in a variety of industrial, direct drive applications which benefit from their extreme axial compactness. In particular, slotted type AFPM machines are of great interest, since they allow to achieve high torque densities together with an adequate constant power speed range. This paper analyzes a particular aspect related to the design of such machines, i.e. the use of soft magnetic composite (SMC) wedges to close stator slots. 2D and 3D finite element analyses (FEA) are performed on a 10 kW AFPM machine adopting various magnetic wedge configurations; the no-load performance is compared with that of the same machine using non-magnetic wedges in terms of flux linkage, cogging torque and no-load losses.

The paper presents a single phase, slotless axial flux permanent magnet synchronous machine for induction heating gen sets. A full scale prototype of the machine (110 kVA, 400 Hz, 690 A) has been designed and subsequently analyzed through FEM analysis (FEA). Induced current distributions in the permanent magnets (PMs) and in the rotors are also calculated through FEA and it is seen that the resulting losses are kept at bay due to the large air gap. This key feature allows the machine to achieve a high rated efficiency (94%). The prototype has also been built and experimental tests confirm the results obtained by FEA.

The new high speed railway lines, under construction in Italy, are electrified in 2times25 kHz - 50 Hz and, in order to avoid interference problems between traction and signaling current, make use of a signaling system based on audio frequency track circuits (AF-TC), ranging from 2.1 kHz to 16.5 kHz. Problems could arise from the fact that traction currents required by high-speed locomotives, equipped with electronic static converters, show a harmonic spectrum which includes audio frequencies. Since the tracks are means of propagation of both traction and signaling currents, interference problems in the standard operation can occur with possible impact on transportation regularity. Thus, preliminary studies of the compatibility between traction and signaling system (where the traction load is a disturbance source and the signaling circuit is a disturbance victim), under standard and failure conditions, are required. In this context, a measurement campaign on the AF-TC of the new high speed railway system Rome-Naples has been made and some results are reported in this paper

Because of their high compactness and lightness, together with high efficiency, Axial-Flux PM (AFPM) machines are among the most suitable candidates for several automotive applications. As a drawback, they are limited in speed range because voltage rises linearly with speed. For this reason, they are generally considered not well-suited for applications such as starter/alternators. As a solution, in this paper an AFPM ironless machine prototype with extended flux weakening capabilities is proposed. Flux weakening, and therefore output voltage regulation, is achieved mechanically through a small-sized actuator that displaces each other the two adjacent windings that compose the stator.

This paper presents a gearless wheel motor drive system specifically designed for fuel cell electric and hybrid electric vehicle propulsion application. The system includes a liquid-cooled axial flux permanent-magnet machine designed to meet the direct-drive requirements. The machine design implements techniques to increase the machine inductance in order to improve machine constant power range and high-speed efficiency. The implemented technique reduces machine spin loss to further improve efficiency. The machine design also optimizes the placement of magnets in the rotor to reduce cogging and ripple torque. An original cooling system arrangement based on the use of high thermal conductivity epoxy joining machine stator and liquid-cooled aluminum casing allows the very effective removal of machine power loss. Design details and experimental results are presented

In hybrid electric vehicle (HEV) drive-trains an electrical generator is coupled onto the shaft of an internal-combustion engine (ICE) in order to process either the entire or a given fraction of the traction power required by the vehicle wheels. As such an ICE-driven generator is being confined within the vehicle hood and is exposed to heating resulting from ICE operation, high compactness, totally-enclosed construction and suitable machine cooling arrangement become challenging targets the generator design must, deal with. Due to unique characteristics such as higher torque per volume and higher efficiency compared to other machine topologies, the axial-field permanent magnet machine (AFPM) topology was selected for the development of a 15 kW @ 4500 rev/min rated generator prototype that would be utilized in a demonstrator of HEV drive train. This paper describes the original solutions adopted for the design of such a HEV generator and reports experimental results taken from the prototype machine.

Among innovative conversion systems for alternative energy, fuel cells (FCs) are ideal in applications as distributed power generation or automotive. The connection of FCs to domestic or industrial loads requires a DC/AC converter also acting as an energy buffer to match the different dynamics of FCs and loads. In the last years, a new type of electrolytic capacitors called super-capacitors (SCs), has been designed using double layers technology. Such components are able to store more energy than electrolytic capacitors maintaining the capability to swap it at high power levels. Firstly, different solution used to connect SCs to a FC based conversion system are considered. Then, a comparison of bi-directional DC/DC converters designed to manage SCs energy is performed. Finally, the converter design and a laboratory prototype of the adopted solution are reported.

In the last years a growing number of four-stroke vehicles, called maxi-scooters, came into European market as a solution to solve mobility problems in large urban areas. On the other hand, in the field of purely electric vehicles, only low-performance electric scooter solutions have been presented in the past. Aim of this paper is to present a new, high performance, prototype of a three-wheeled electric scooter with extended driving range. This prototype is propelled by two AFPM wheel-motors placed on the rear wheels and includes integrated linear Hall effect position sensors. This solution provides a low cost alternative to traditional encoders and resolvers, which are not viable in traction applications.

A system, the mercury-gap ring collector (MGRC) for supplying current to the rotating armature of the double armature generator (DAG) is discussed. The MGRC can be considered as a valid alternative to conventional collector rings with solid brushes. It offers several advantages over sliding contacts with carbon brushes, especially when the machine has high rating currents and high rotating speed. The design of a prototype is presented. Tests are reported and a comparison between the MGRC and a conventional carbon brush collector is discussed. >

In brushless DC motor drives devoted to electric vehicles (EVs) a bi-directional DC-DC power converter can be used to control suitably both motoring and regenerative braking operations in order to improve the motor drive performance. In consideration of such an application, this paper deals with the experimental study of a buck-boost bi-directional DC-DC power converter topology which has been conceived for the use in EVs propelled by means of wheel-direct-coupling axial-flux PM motor drives. The paper discusses the power converter modes of operation and reports experimental results taken from a 20 kW water-cooled prototype of the proposed power converter topology. >