G. De Donato

Recent Advances in Axial-Flux Permanent-Magnet Machine Technology

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.

AC brushless drive with low-resolution Hall-effect sensors for surface-mounted PM Machines

An ac brushless drive in which Hall-effect sensors are used as rotor position sensors is presented in this paper. Three different methods to obtain a high-resolution position estimation from the low-resolution sensors are described and compared through simulation and experimental testing. The proposed control algorithms most innovative feature is its adaptability to the entire speed range, including startup, when using any of the three estimation algorithms. The control algorithm has been implemented and tested in order to drive a slotless axial-flux permanent-magnet (PM) machine for domestic appliance applications.

Erratum to "Implementation Issues and Performance Evaluation of Sinusoidal, Surface-Mounted PM Machine Drives With Hall-Effect Position Sensors and a Vector-Tracking Observer"

This paper presents the implementation and evaluation of a high-resolution position estimation system for sinusoidal, surface phase modulation machines based on Hall-effect sensors and a vector-tracking observer. First, the tuning of the observer is presented and a speed-dependent gain scheduling strategy is proposed. Then various harmonic decoupling strategies are investigated to improve the performance of the observer, particularly at low speeds. Stability analysis is performed leading to the definition of local stability limits, within which the actual position is tracked with bounded estimation error. Both simulation and experimental testing illustrate the performance and limitations of the proposed observer topology and of the drive when this observer is used for state feedback.

Axial-Flux Permanent-Magnet Generator for Induction Heating Gensets

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.

Integral-Slot Versus Fractional-Slot Concentrated-Winding Axial-Flux Permanent-Magnet Machines: Comparative Design, FEA, and Experimental Tests

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.

Fractional-Slot Concentrated-Winding Axial-Flux Permanent-Magnet Machine With Core-Wound Coils

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 PM starter/alternator machine with a novel mechanical device for extended flux weakening capabilities

In modern vehicles, the demand for on-board electric energy generation is rapidly growing in order to satisfy new requirements for passengers comfort and safety. This growth, which is predicted to reach 6 kW in the very next years, is forcing manufacturers to explore new solutions concerning the whole electrical system inside the vehicle. In particular, novel topologies of alternators are under research since the currently used Lundell type (claw-pole) alternator is reaching its power limits. In this paper an original torque dependant mechanical device is proposed in order to extend the speed range of an axial flux PM machine. This device displaces the rotors realizing a mechanical flux weakening with constant output power in generation. Simulations and experimental tests on a prototype realized in the lab are fully discussed.

Influence of magnetic wedges on the no-load performance of axial flux permanent magnet machines

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.

Fault-Decoupled Instantaneous Frequency and Phase Angle Estimation for Three-Phase Grid-Connected Inverters

Frequency and phase angle estimation is a key aspect for grid-connected inverters that are required to guarantee low-voltage fault-ride-through capability. Over the past two decades, a number of estimation algorithms have been proposed, mostly based on the well-known phase-locked loop (PLL). It has been demonstrated that standard PLLs do not perform correctly in abnormal grid conditions, due to the oscillations produced in the frequency and phase angle estimates by the voltage harmonics. This paper introduces a new, general approach to harmonic decoupling and presents a highly intuitive and simple scheme, applying it to an αβ-PLL; compensation of any desired number of harmonic components is possible. Two implementations of this decoupling scheme are presented. It is shown that the performances of the resulting fault-decoupled PLLs are comparable with those of other advanced frequency and phase angle estimation structures.

Sinusoidal surface-mounted pm machine drive using a minimal resolution position encoder

This paper presents a high resolution position estimation system for sinusoidal surface PM machines based on a vector-tracking observer and a 90deg resolution encoder. It is shown here that this is the minimum amount of resolution needed for sinusoidal PM drives. The key implementation issues of this system are presented, and stability analysis is performed, leading to the definition of local stability limits, within which the actual position is tracked with bounded estimation error. The effect that non-uniform sector widths have on position estimation is also explored and a straightforward compensation method is proposed. Both simulation and experimental testing illustrate the performance and limitations of the proposed observer topology and of the drive when this observer is used for state feedback.