Gabriele Borocci

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.

Control strategy for Bidirectional HBCS Converter for supercapacitor applications

This paper proposes the basic average model and the design of the control system for the Half Bridge Current Source (HBCS) Bidirectional DC to DC Converter. This converter is intended to interface a High Voltage DC link and a Low Voltage DC Storage Device in transportation applications. Firstly, the basics of the converter operation, high-level control and the simplified modeling are presented. Then, a cascaded control approach for the whole system is discussed and validated through simulations.

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.

Flux regulation strategies for hybrid excitation synchronous machines

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.

Ω Shaped axial-flux permanent-magnet machine for direct-drive applications with constrained shaft height

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.

A comparison of hybrid excitation solutions for single-axis and bi-axial synchronous machines

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.

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.