F. Luise

Shipboard Power Generation: Design and Development of a Medium-Voltage dc Generation System

This article reports on the design, development, and validation of advanced prototype 2 MVA generation equipment [i.e., naval package (NP)] for a shipboard medium-voltage dc integrated power system (MVDC IPS). The generation equipment is based on an ultrahigh-speed 22,500-r/min 12-phase alternator, which feeds an ac/dc power electronics converter comprising four diode rectifiers and four insulated-gate bipolar transistor (IGBT) choppers. The prototype realization constitutes a follow-up of a previous NP version employing a wound-field 6,300-r/min alternator feeding noncontrolled ac/dc converters. The major technical challenges faced in the design and development of the advanced NP prototype are outlined in this article, taking the previous lower-speed version as a technology reference. The system performance, as determined by the testing campaign, and lessons learned for future studies are addressed.

Use of Time-Harmonic Finite-Element Analysis to Compute Stator Winding Eddy-Current Losses Due to Rotor Motion in Surface Permanent-Magnet Machines

It is known from the literature that in electric machines with open stator slots, the air-gap flux partly enters the slot openings and induces eddy currents in the conductors placed closest to the air gap, possibly causing local overheating issues. For the study of such phenomenon, time-stepping finite-element analysis (TSFEA) is employed by many authors. This paper presents an alternative approach based on a set of time-harmonic finite-element analysis (THFEA) simulations. The proposed method can be applied to surface permanent-magnet machines and offers the advantage of a shorter computation time with respect to THFEA. It is also more suitable for being integrated into automatic design optimization programs. The accuracy of the approach is assessed by comparing stator eddy-current losses independently computed by THFEA and TSFEA for different machine geometries and operating conditions. Results obtained in the two ways are shown to be in good accordance.

Regenerative Testing of a Concentrated-Winding Permanent-Magnet Synchronous Machine for Offshore Wind Generation—Part I: Test Concept and Analysis

Some high-torque electric machines, such as low-speed wind generators, may be very difficult to test on load because of the large and expensive mechanical equipment required to load them (motors) or to drive them (generators). In this paper, a full-load regenerative testing methodology is described which does not require any rotating equipment to be coupled to the machine where the rated active power flows in a closed loop between the machine and a suitably connected dual-stage converter. The successful application of this methodology to a 780-kW 14-r/min wind generator prototype is addressed as a study case. Relevant experimental results are reported in a companion paper.

Regenerative Testing of a Concentrated-Winding Permanent-Magnet Synchronous Machine for Offshore Wind Generation—Part II: Test Implementation and Results

The on-load factory testing of high-power electric machines may be a challenge due to the large mechanical equipment required to drive or load them. In a companion paper, a regenerative full-load testing strategy has been proposed, where the power flows in a closed loop between the electric machine and a dual-stage converter so that only the power corresponding to system losses needs to be supplied by the test facility and no mechanical equipment is needed. In this paper, the implementation of such testing strategy on a 780-kW 14-r/min permanent-magnet alternator with fractional-slot concentrated stator winding is described. Test results are presented and compared with the predictions made in Part I, showing a satisfactory accordance between theoretical and experimental results.

Extending the speed range of surface permanent-magnet axial-flux motors by flux-weakening characteristic modification

In many electric drive applications where demanding constraints are imposed on motor dimension, the use of axial-flux permanent-magnet synchronous machines is highly advantageous or even mandatory. A major criticality in the design of such machines is the high-speed operation, where a large stator demagnetization current is required for motor flux weakening. This paper describes how the appropriate choice of the flux-wealening characteristic, combined with the use of magnetic wedges, enables to significantly extend the speed range of these machines retaining a conventional motor design technology. And application of the proposed design strategy on a high-performance axial-flux motor is presented along with relevant testing results.

A finite element approach to harmonic core loss prediction in VSI-fed induction motor drives

When an induction motor is supplied by a PWM voltage source inverter (VSI), flux pulsations due to voltage harmonics cause extra power dissipation for hysteresis and eddy-currents in the magnetic core. Based on the expected inverter output voltage spectrum, a finite element analysis method is discussed in this paper to predict supply-related additional core losses. The finite element motor model is tuned based on available ring-test data. Calculation results are compared to the measurements collected during a real motor drive testing.

A high-performance 640-kW 10.000-rpm Halbach-array PM slotless motor with active magnetic bearings. Part I: Preliminary and detailed design

The ongoing gas industry expansion calls for quick and strong advances in turbomachinery-coupled highspeed electric motors. Very high efficiency, dynamic performance and reliability are among the main requirements to be met at competitive costs by electric machine suppliers. This paper reports on an industrial R&D project aimed at finding the best compromise between performance targets and production cost reduction. The development of a 640-kW 10.000-rpm PM motor prototype with slotless stator and Halbach-array magnetically-levitated PM rotor is discussed, including in particular the basic technology selection and design optimization processes. In a companion paper (Part II), prototype manufacturing and testing will be reported to assess the technology and design solutions adopted.

A high-performance 640-kW 10.000-rpm Halbach-array PM slotless motor with active magnetic bearings. Part II: Manufacturing and testing

The ongoing gas industry expansion calls for quick and strong advances in turbomachinery-coupled highspeed electric motors. Very high efficiency, dynamic performance and reliability are among the main requirements to be met at competitive costs by electric machine suppliers. This paper reports on an industrial R&D project aimed at finding the best compromise between performance targets and production cost reduction through the realization of a 640-kW 10.000-rpm PM motor prototype. The preliminary and optimization design of the motor have been covered in a companion paper (Part I). Here the manufacturing and testing of the prototype are covered. The main technology challenges encountered throughout the manufacturing process are addressed. Furthermore, the paper reports on the testing campaign conducted on the motor under converter supply and in different load and speed conditions. The prototype testing was successful and proved the possibility to reach and exceed a 98% motor efficiency target with affordable costs and available technologies.

A new magnetic wedge design for enhancing the performance of open-slot electric machines

In electric permanent-magnet motors for traction applications, an open slot stator design is to be used when the winding is composed of flat-turn coils. The open slot design, combined with rotor permanent magnets, can produce remarkable cogging torque effects. This paper describes a magnetic wedge design which allows for a significant cogging torque reduction and, at the same time, allows for a fine adjustment of stator phase inductance values. The new wedge concept is applied in the paper to a 12-slot surface permanent-magnet motor. Finite-element analysis is used to study the wedge design effects on motor phase inductance and cogging torque amplitude.

Design for improved fault tolerance in large synchronous machines

Fault tolerance is a basic requirement for modern electric motors and generators and can be achieved with a number of integrated approaches, like condition monitoring, post-fault control strategies and suitable system design architectures. In particular, this paper focuses on large synchronous machines (both permanent-magnet and wound-field ones) and discusses the main design provisions that can be adopted to improve their ability to withstand various kinds of fault. The fault-tolerant design solutions recommended for small-power machines are critically reviewed and their scalability to higher machine sizes is discussed also referring to practical industrial realizations. The most promising potential for fault-tolerance design is recognized in large low-speed high-pole-count permanent-magnet synchronous machines (e.g. for ship propulsion and wind power generation) thanks to their suitability for highly-modular multi-unit fractional-slot concentrated-winding architectures.