F. Giulii Capponi

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.

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.

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.

Three-wheeled electric maxi-scooter for improved driving performances in large urban areas

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.

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.

Mixed-pole hybrid-excitation machine

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 machines performances are analysed with finite element simulations.

Influence of magnetic wedges on the load performance of axial flux permanent magnet 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.

Thermal modelling of a fractional-slot concentrated-winding Kaman type Axial-Flux Permanent-Magnet machine

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.

Fault tolerant rotor position and velocity estimation using binary Hall-effect sensors for low cost vector control drives

High-resolution position and velocity estimation algorithms based on binary Hall-effect sensors for low-cost vector control drives have been the subject of significant research in recent years. While different estimation algorithms have been proposed and analyzed, no contribution so far has dealt with Hall-effect sensor faults and their repercussion on the drive. This paper intends to fill this gap by analyzing single and multiple Hall-effect sensor faults and by proposing a method to detect, identify and mitigate such faults. The method is general, it ensures proper operation of the drive and is not dependent on the particular estimation algorithm that is used; by way of example, here it will be applied to a vector-tracking observer. Limitations on the performances of the faulty system are discussed and experimental results are reported to confirm the theoretical analysis.

Integer-slot vs fractional-slot concentrated-winding axial-flux permanent magnet machines: Comparative design, FEA and experimental tests

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.