Giulio De Donato

No-Load Performance of Axial Flux Permanent Magnet Machines Mounting Magnetic Wedges

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 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. Magnetic circuit-based analyses and 2-D and 3-D finite-element analyses are performed on a 10 kW AFPM machine; various magnetic wedge configurations are adopted; the no-load performance is compared with that of the same machine using nonmagnetic wedges in terms of flux linkage, cogging torque, and no-load losses. Finally, experimental tests and results on a full-scale prototype machine mounting magnetic wedges are reported.

On the Use of Magnetic Wedges in 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 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.

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. Here, single and multiple Hall-effect sensor faults are analyzed, and a method to detect, identify, and mitigate such faults is investigated. The method is general, and 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.

Analysis, modeling and control of half-bridge current-source converter for supercapacitor applications

The objective of this paper is to investigate the properties of the Half Bride Current Source bidirectional DC to DC converter used to interface supercapacitors with batteries in a hybrid storage system. This work focuses on the benefits of applying synchronous rectification to the switches of the primary and the secondary side, both in terms of efficiency and control simplicity. In fact, by using this modulation scheme, it can be demonstrated that a single parameter (the duty ratio, D, of the dc link side top switch) can be used to control the converter under every operating condition. Furthermore, an average model of the converter valid in every operating condition is derived and utilized as a tool for the design of the control system. This model includes the effects of parasitic elements (mainly the leakage inductance of the transformer) and snubbers. Both the synchronous rectification switching scheme and the average model, have been experimentally validated with a 3 kW converter prototype. Also, the performance of a control strategy designed with such model are shown experimentally.

Closed-Loop Flux-Weakening Control of Hybrid-Excitation Synchronous Machine Drives

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.

Ω-Shaped Axial-Flux Permanent-Magnet Machine for Direct-Drive Applications With Constrained Shaft Height

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.

A general approach for the analysis and comparison of hybrid synchronous machines with single-axis or Bi-Axial excitation

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.

Closed-loop, flux weakening control for hybrid excitation synchronous machines

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.