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The paper is aimed at an analytical prediction of the air gap flux density distribution of a spoke type interior permanent magnet machine, based on its magnetic equivalent circuit (MEC) incorporating the rotor position. The study is initiated by an elaboration of the machine MEC in two particular rotor positions corresponding to the maximum and null magnetic coupling between the stator and rotor which enable the prediction of the direct and quadrature components of the air gap flux density, respectively. The decomposition of the armature magnetic reaction into direct and quadrature components enables the generalization of the prediction of the air gap flux density waveform for any rotor position. The accuracy of the proposed approach is improved taking into account the stator and rotor slotting effects that are analytically incorporated considering complex permeance functions.

In the literature, the effect of the mismatch due to manufacturing tolerances on PV plant productivity has been investigated under the hypothesis of plant operation in Standard Test Conditions (STC). In this paper, mismatch impacts are evaluated in more realistic terms taking into account various possible operating conditions. Results are illustrated through the study case of a 1 MWp solar park for which module datasheets as well as flash test data are available. The plant production is evaluated assuming operating conditions that comply with the European efficiency standards. It is shown how the effect of a given mismatch on the annual productivity estimation can significantly change depending on the operating conditions.

Direct-drive generators to be used in off-shore wind farms are very large low-speed electric machines which pose remarkable design and manufacturing challenges. Demand forecasts for this kind of machines are urging manufacturers to work out design and technological solutions capable of facilitating series production at competitive costs. This paper presents the development of an interior-permanent magnet generator design and technology aimed at reducing series manufacturing costs while preserving good performance levels. The focus is placed on two of the most critical issues in the machine design and analysis, namely the prediction and reduction of eddy-current losses in stator conductors and in permanent magnets. The proposed design solutions are validated through the construction and testing of a 780 kVA generator prototype conceived for easy scalability to higher power ratings (up to around 2.5 MVA) by core length increase.

In permanent-magnet motors used for vehicle traction application a well-known problem is the need to weaken the flux at high speeds. This is generally done by injecting a suitable demagnetizing current along the d axis. An alternative method has been recently proposed by the authors based on an Interior-Permanent-Magnet (IPM) synchronous motor equipped with a mechanical device which activates at high speeds by centrifugal force causing a significant reduction in the permanent magnet flux with no need for injecting d-axis stator currents. The performance of a road vehicle traction drive employing this machine under a maximum-torque-per-ampere control is investigated in this paper assuming a typical driving cycle. It is shown that remarkable benefits can be achieved in terms of energy saving, overload capability enhancement and speed range extension potential.

This paper investigates the hydraulic system drive used onboard ships to actuate stabilizing fins. The hydraulic drives are often characterized by low efficiencies, heavy maintenance, frequent oil leaks and large weight and size. To overcome these draw-backs, in this paper a concept design of a full-scale permanent magnet linear synchronous motor directly coupled to the shipboard fin stabilizer, is presented, used as a servo-motor. The innovative electric drive is based on prototype of high thrust linear motor built in a previous research. A complete Simulink model, where electric, mechanical and hydraulic domains can be connected, has been realized. Simulations has been performed to evaluate the hydraulic drive efficiency and in order to assess the servo-assistance capabilities. The results show the feasibility of the proposed solution for a future practical application. This research has been carried out in the framework of the Italian Defence Research National Program for the development of ‘dual use’ technologies.

The complex relative permeance function is a useful mathematical tool to study the magnetic field of electric machines with slotted air gap. In the literature, the complex permeance function is usually identified by means of numerical techniques based on conformal mapping. In this paper an alternative analytical approach is proposed. The method is based on solving the magnetostatic differential field equation over a portion of the slotted air gap by imposing suitable boundary conditions in the slot opening region. Such boundary conditions exploit the mathematical law which governs the divergence of the magnetic field in the neighborhood of corner-shaped ferromagnetic regions. Furthermore, the results of Carter theory on slot fringing effects on the air gap field are used. A simple easy-to-compute formula is obtained for the complex permeance function. Its accuracy is assessed by comparison with Finite Element Analysis (FEA).

Alternatives to hydraulic drives used on board ship are under study for the Italian Navy in order to reduce the use of the oil which cause environmental problems and high cost. The hydraulic system drive used onboard ship are affected by low efficiencies and generally require intensive maintenance, very high encumbrance. So that the Italian Navy has commissioned a research project for the construction and installation of an innovative oil-free electric drive based on a permanent magnet linear actuator. The new electric motor is more efficient, fault-tolerant, reduces the encumbrance and ensures a greater control.

Hydraulic drives used on board ship to empower rudders, stabilizing fins, anchor winches, etc., are often characterized by low efficiencies, heavy maintenance, frequent oil leaks and large weight and size. To overcome these drawbacks, oil-free inverter-fed alternative drives can be conceived. In this paper a concept design of a full-scale permanent magnet linear synchronous motor directly coupled to a twin rudder on board ship is presented, used as a servo-motor. The servo-assistance capabilities are simulated and evaluated by using a complete model of the electro-mechanic-hydraulic system in Simulink environment. The results show the effectiveness of the electromagnetic drive servo-assistance. This research has been carried out in the framework of the Italian Defence Research National Program for the development of `dual use' technologies.

Direct-drive generators to be used in off-shore wind farms are very large low-speed electric machines which pose remarkable design and manufacturing challenges. Demand forecasts for this kind of machines are urging manufacturers to work out design and technological solutions that can facilitate series production at competitive costs. This paper presents the development of an interior-permanent magnet generator design and technology aimed at reducing series manufacturing costs while preserving high performance levels. The proposed solutions are validated through the construction and testing of a 780 kVA generator prototype conceived for easy scalability to higher power ratings (up to around 2.5 MVA) by core length increase.

Transport industry is facing a paradigm shift towards the most promising and sustainable solution represented by the transportation electrification. This concept has not only been adopted for the propulsion powertrains, but also for the auxiliary systems. Indeed, in the last few decades electrification has come to smart actuators to improve both safety and comfort of the passengers. In this contest, multiphase electrical machines and drives represent a promising solution to satisfy the challenging requirements imposed by the applications, such as reduced weight and volume, high efficiency, low vibrations and noise, robustness and fault tolerance. With reference to the technical literature and applications, this paper presents an overview of the multiphase technology for the transportation electrification in road vehicle, rail vehicles, air transports and shipboard applications.

The use of linear machines (LMs) is increasing in research and industry fields. All kinds of LMs are studied: synchronous, induction, flux switching. Research is leading to overcome the known drawbacks of all these machines. Anyway the use of innovative direct-drive solutions are under study to obtain more efficient energy conversion, such as for marine field. As alternative to classical systems, linear force can be used to obtain a more efficient plant. Hydraulic drives used on board ship to empower rudders, stabilizing fins, anchor winches, etc., are often characterized by low efficiencies, heavy maintenance, frequent oil leaks and large weight and size. To overcome these drawbacks, an oil-free inverter-fed alternative drives can be conceived. In this paper a concept design of full-scale permanent magnet linear synchronous motor directly coupled to a twin rudder on board ship is presented, used as a servo-motor. A complete model of the electro-mechanic-hydraulic system in Simulink environment was built. Several simulations are performed to evaluate the servo-assistance capabilities. The results show the effectiveness of the electromagnetic drive servo-assistance and an increased overall efficiency of the steering gear. This research has been carried out in the framework of the Italian Defence Research National Program for the development of `dual use' technologies.

Hydrostatic drives used on board ships are often characterized by low efficiencies, heavy maintenance, frequent oil leaks and large weight and size. To overcome these drawbacks, oil-free inverter-fed alternative drives can be proposed. This paper analyzes the ship rudder hydraulic drive performances, and a proposal for improvements is shown. A full-scale permanent magnet linear synchronous motor directly coupled to a twin rudder is presented, used as a servo-motor. Both servo-assistance features and performance and efficiency improvements are evaluated by using a complete physical model in Simulink environment.

Electric drives with a three-phase structure are commonly utilized in road vehicles for propulsion and in aeronautics as control-surface actuators. In recent times, some concerns have emerged on the use of three-phase drives in such applications in regard to power capability, efficiency and fault-tolerance. A way to effectively cope with these concerns is the adoption of multiphase drives. In this sense, a five-phase drive is a promising solution as it does not imply an excessively complicated structure. In this paper a five-phase PM BLDC drive is considered and its torque capabilities are investigated for square-wave current supply. Specifically, the torque developed by a five-phase drive is first compared to the three-phase counterpart; torque comparison is carried out by keeping motor size and loading unchanged and by considering two hypotheses: equal phase back-emf and equal phase rms current. Then the torque available from a five-phase drive is determined under various supply modes, characterized by the simultaneous conduction of a reduced number of phases; the torque available is determined by imposing an equal rms phase current in the supply modes.

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.

Load-Commutated Inverters (LCIs) are today one of the main converter topologies used for very-high-power drive applications, although new topologies, based on PWM technology and employing IGBT or IGCT as power switches instead of SCR's, have been recently gaining attractiveness also for increasing power ratings. The paper presents an overview of today's LCI technology and its applications, highlighting its strengths and weaknesses. Furthermore, the most promising lines of development are drawn along which LCI drive technology is being improved to overcome its major drawbacks and maintain competitiveness with Voltage-Source-Inverter (VSI) based counterparts.

The ships have long been an easy play-ground for hydraulic technologies. When high torques and low speeds are demanded on board ship, both technical and traditional reasons usually lead to hydraulic solutions. In fact, the conventional electrical machines are better suited for low-torque, high-speed applications, and coupling gears must be used to reduce the speed. However, oil-free direct-drive alternatives can be conceived, by new concepts of low-speed permanent-magnet actuators fed by low-frequency inverters. This paper shows the experimental results obtained with a linear permanent-magnet motor designed for direct coupling to rudder stocks or stabilizing fins. The prototype weights 700kg and features a thrust-to-weight ratio of 5. Even better results can be obtained by using composite materials for the machine frame. The machine features a full structural redundancy and inherent fault tolerance, thanks to the modular construction. The present research has been carried out in the framework of the Italian Defence's Research National Program.

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.

The increasing complexity of electric grids including renewable sources causes significant impacts in terms of power quality. This implies that new generators are to be designed so that they can withstand larger and larger disturbances in the amplitude and frequency of the grid to which they are connected. This purpose can be attained by appropriate provisions in the generator electromagnetic design. In this paper, some case studies will be presented comparing the transient stability performance of possible alternative electromagnetic designs of a 4.7-MVA 6-kV for power station based on an Organic Rankine Cycle. The fault-tolerance capabilities of the alternative design solutions are assessed through lumped-parameter simulations in the Matlab-Simulink environment used to predict machine compliance with typical transient functional requirements.

Vehicular traction motors are usually designed to operate over a wide speed range and require important flux weakening capabilities at high speeds. This paper presents and innovative design intended to endow an interior permanent magnet (IPM) motor with an intrinsic capability of reducing its own rotor flux at high speeds. The design does not involve any additional current source nor control systems for rotor flux regulation. It relies on a purely mechanical device that establishes a partial magnetic short circuit between rotor permanent magnets. The device is able to self-activate due to centrifugal force when the speed exceeds a given threshold that can be fixed by the designer. The design features of the proposed IPM motor are illustrated in the paper and its static and dynamic performance prediction through finite element analysis (FEA) methods is presented. A prototype construction is presently in progress to experimentally validate the solution.

Permanent-magnet synchronous motors are widely used in vehicular traction applications due to their high efficiency and torque density. A critical point of their operation is the flux weakening needed at high speed, which usually implies injecting a d-axis demagnetizing current by the inverter. This paper presents a critical survey of the alternative approaches found in the literature and patent databases to enhance flux-weakening performance by acting on motor mechanical and electromagnetic design.

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.

In modern ships of large size, the main propulsion system, consisting of either an internal-combustion engine or an electric drive, is assisted by auxiliary propulsion equipment composed of thruster propellers, used for low-speed, transversal, docking and station-keeping maneuvers. Thruster motors are typically induction machines, connected to the on-board grid either directly or through autotransformer or variable-frequency converters. This paper describes the main issues connected with the choice and design of thruster motors. In particular, the problems of integrating thruster motors into the on-board electric system are addressed. Moreover, the typical requirements and constraints imposed on thruster motor performance are highlighted along with the strategies adopted to fulfill them in the design and development stage.

Over the last few decades, the production of liquefied natural gas (LNG) has been pushing the development of electric drives with increasingly high power ratings, up to several tens of megawatts. A consolidated technology in this field entails dual-star two-pole synchronous motors fed by load-commutated inverters with supply frequencies between 50 and 80 Hz. This paper presents a novel drive concept for very high-power and high-performance LNG applications based on a 45-MW four-pole 100-Hz quadruple-star synchronous motor supplied by four pulsewidth modulation multilevel voltage source inverters. The genesis, development, and industrial implementation of this new design concept are outlined. Full-load drive system testing and commissioning results are presented which successfully validate the proposed solution.

The adoption of multi-phase stator topologies in electrical machine design brings well-known advantages in terms of power segmentation, reliability and performance. In addition to these functional benefits, which are independent of machine size, this paper highlights how the use of more than three phases can lead to construction advantages when applied to electric machines of large size. The advantages relate to the winding manufacturing technology, which can be retained similar to that of small machines in presence of a multi-phase solution, while a traditional three-phase one would imply a more costly Roebel bar construction. The point is justified in terms of machine sizing equations and is assessed referring to some built high-power multi-phase machines for industrial and ship propulsion use.

The paper presents a small-signal stability analysis of voltage control systems employed onboard all-electric cruise liners. To realize the stability analysis, a model of shipboard power station voltage control system has been determined, moving from dynamic models of alternators, voltage regulators and loads. Reduced order models of alternators have been utilized, to simplify at best the analysis. Analysis results have been validated through numerical simulations, using a simulator of power station electromechanic quantities developed at the University of Trieste. Such simulator includes alternators, voltage and frequency regulators, breakers, protections and R-L loads. Numerical results obtained from simulations of both complete and reduced order models fully validate the analytical findings, while computation times are in the order of real-time simulations.

A simple fault-tolerant induction motor drive with v/f speed control included in the electrical auxiliary equipment of railway locomotives is presented in the paper. The employment of fault tolerant on-board electrical auxiliary equipment increases the dependability and then the quality of the railway service. The fault tolerance technique consists of some emergency countermeasures applied in case of fault. It includes a fault diagnosis procedure based on the analysis of the current vector, the connection of the stator winding neutral point to the dc-link middle point and the variation of the v/f law, taking into account the contribution of the zero-sequence impedance and the need for a flux weakening in order to avoid saturation. Some experimental results are reported showing the improved performance of the motor drive under fault conditions by means of the proposed remedial strategy.