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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.

Synchronous reluctance (SynRel) motors with rotor flux barriers are gaining increasing attractiveness in automotive applications thanks to their cheap, rugged and magnet-free rotor construction. When equipped with a split-phase stator winding and supplied from multiple inverters, these machines can exhibit further merits as traction motors in regard to enhanced fault tolerance compared to conventional three-phase solutions. Since SynRel motors are usually designed through iterative optimization techniques, it is highly desirable to have accurate and fast methods to predict their performance without the need for time-consuming finite element analysis (FEA) simulations. An analytical procedure is set forth in this paper to analytically model and simulate a SynRel motor with a split-phase stator winding through a magnetic equivalent circuit (MEC) technique. MEC parameters are computed from analytical formulas describing the air-gap magneto-motive force distribution and the magnetic field inside flux barriers. As an output, the air-gap flux density of the SynRel motor can be computed through the presented technique at any operating point. Results are positively assessed by comparison with FEA simulation on a sample SynRel motor including magnetic saturation effects.

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.

Synchronous reluctance motors with rotor flux barriers are a promising type of electric machines thanks to various benefits, among the others, the absence of permanent magnets and rotor excitation. A challenge in the study of these motors is the accurate prediction of their air-gap field analytically taking into proper account the effects of rotor flux barriers. This paper proposes a technique for this purpose based on reluctance network solution and winding functions. The reluctance associated to each flux barrier is computed by means of conformal mapping. Furthermore, the slotting effect is also considered through appropriate permeance function definition. Analytical results are compared to finite element analysis showing a good matching for various machine topologies characterized by a different number of flux barriers.

Induction motors are presently the most widespread kind of electric machinery used in industrial and vehicle applications. In the engineering practice, it frequently happens that designers or final users have to roughly estimate the size, weight and some basic performance data of an induction motor based on few specification requirements such as its rated speed and power. This paper describes a heuristic approach which can help make a first-attempt dimensioning in an approximate but reliable way. The method uses homothety as the theoretical basis and derives practical laws by identifying homothetic law parameters through the statistical analysis of a set of sample built machines. The results obtained are compared to those derived from classical books showing significant discrepancies which fully justify the adoption of more sophisticated heuristic models as those being presented.

Induction motors are presently the most widespread kind of electric machinery used in industrial applications. In the engineering practice, it frequently happens that designers or final users have to roughly estimate the size, weight and some basic performance data of an induction motor based on few specification requirements such as its rated speed and power. This paper describes homothety as an effective answer to this problem. The main principles of homothety as an induction motor sizing approach are discussed and quantitative formulas are derived based on theoretical considerations. The homotetic laws are finally assessed considering a set of sample built four-pole machines (whose data are fully available). The assessment confirms homothety as an actually powerful approach for a first-attempt estimation of many motor data including size, weight, utilization factor, current density, electric loading, etc.

A promising solution to improve tomorrow's all-electric ship onboard power system design and performance relies on moving from 50-Hz or 60-Hz AC distribution to a Medium-Voltage DC (MVDC) grid. This paper provides a review of presently-available and under-development technologies for electric generators to be used in perspective MVDC shipboard systems. The inspiring reason for the survey lies in the fact that an MVDC grid design removes the constraints usually imposed on shipboard generation group design and opens the way for a wide variety of non-conventional machine alternatives. In combination of high-speed gas turbines, that can be employed as prime movers, several electric machine topologies, not yet used for ship applications, can be selected to feed MVDC onboard systems. Along with a review of possible generator types suitable for such use, the paper critically reviews some emerging technologies for their fault-tolerance enhancement through conventional and innovative split-phase architectures.

Various analytical techniques have been proposed in the literature for cogging torque computation in Surface Permanent Magnet (SPM) machines. Among the various available methods, the ones found to be satisfactorily accurate are based on the Maxwell's stress tensor, which involves both normal and tangential air-gap field and lead to quite involved calculation formulas. In this paper, a relatively simple alternative is proposed where permanent magnets are modeled as equivalent field circuits to which a well defined winding function can be associated. The approach leads to a plain cogging torque formulation where only the normal no-load air-gap flux density appears. The accuracy of the method is assessed by Finite Element (FE) analysis on some sample SPM machine geometries. The results are shown to match FE simulations with a satisfactory accuracy compared to Maxwell-stress-tensor-based analytical techniques available from the literature.

Many shipboard loads requiring high torques at very low speeds, like capstans, bow thrusters, rudders, stabilizing fins, etc., are presently driven by hydrostatic actuators. This paper presents an innovative inverter-fed electric linear motor prototype conceived to replace hydrostatic drives with large expected benefits in compactness, maintenance, efficiency and reliability. The linear motor prototype has been designed through special optimization algorithms based on finite element analysis to maximize the force density. The electromagnetic and mechanical structure has been also selected to achieve superior reliability by means of structural simplicity, robustness and redundancy. Along with design criteria, the paper outlines the prototype technology and the construction issues and provides some testing results collected during the experimental performance assessment.

Permanent magnet synchronous machines, especially if designed with open stator slots, may suffer from important cogging torque issues. A special magnetic wedge design has been presented in a companion paper to cope with this problem. The design of such wedge is herein processed through a genetic algorithm in order to find the optimal configuration, which leads to cogging torque minimization. An optimal design configuration is found and compared to non-optimal ones to quantify the benefits that can be achieved by genetic optimization.

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.

Inverter-fed Induction motor performance is known to be noticeably affected by the supply voltage waveform. Nevertheless, the prediction of how supply voltage harmonics impact on motor operation in terms of losses, noise and thermal behavior is still a problem that can be hardly approached through simulations and analysis, therefore experimental data constitute an important source for information. In this paper the test results of two high-power induction-motor drives are presented showing their performance under different voltage waveforms. Among the other things, it is shown how low-frequency distortions in the supply voltage may have considerably stronger impacts on motor behavior than PWM harmonics, although the overall THD under PWM supply is higher.

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.

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.

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.

DC distribution is an attractive solution for onboard integrated power systems of new-generation all-electric ships, especially thanks to the benefits it offers in terms of reducing generation system size, weight and power consumption. Technologies have already been implemented in full-scale prototypes based on synchronous generators feeding the DC grid through rectifiers. In these proven solutions, the voltage control is allocated either to the generator excitation system or to the rectifier control. This paper investigates a design variant where both voltage control loops exist and act simultaneously. The basic design of the system is presented along with its modeling in the Matlab/Simulink environment. Simulation results obtained from the Simulink models are finally reported illustrating the system behavior during various electrical and electromechanical transients. (6 pages)

The problem of accurately computing rotor eddy-current losses in synchronous machines subject to non-sinusoidal phase currents is usually approached with Time-Stepping Finite-Element Analysis (TSFEA), where rotor motion and armature current distortion effects are naturally included. The drawbacks of TSFEA are the long computation times and the need to wait for steady-state conditions to extract results. Such features make TSFEA unsuitable for integration into automatic design optimization programs. This paper illustrates how the problem can be alternatively solved by Time-Harmonic Finite-Element Analysis (THFEA) on a set of modified machine models conceived so that rotor motion and current distortion effects can be accounted for. As an illustrative example, the proposed method is applied to a Surface Permanent-Magnet (SPM) generator whose electromagnetic design is being processed through genetic optimization algorithms. Eddy-current losses are independently computed by both TSFEA and TFFEA in different generator operating conditions and design configurations showing that results are in good accordance. Furthermore, the proposed approach takes much smaller simulation times and can be easily incorporated into the overall optimization process.

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.

Over the last few decades an increasing sensitivity has been spreading towards energy saving technologies. In particular, as far as electric drives are concerned, a strong demand for high efficiency motors has been raising in many industry sectors. This paper describes the development of an innovative high-efficiency solution for highspeed motors targeted for industrial turbomachinery applications in the 500–1000 kW power range at 10000–15000 rpm The technology presented features a slotless stator and a magnetically-levitated Halbach permanent-magnet rotor. A full-scale motor prototype is being manufactured for the assessment of the proposed technology. Design optimization techniques, based on genetic algorithms and multi-disciplinary analysis tools, have been employed in the prototype design stage to maximize motor efficiency and performance figures. A multilevel cascaded-cell converter with optimized voltage output is under parallel development for motor supply. Prototype full-power and full-speed qualification tests are planned to take place within the current year to demonstrate the effectiveness of the design and technology presented in this paper.

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.

This paper reports on the design, development and validation of an advanced prototype 2MVA generation equipment (Naval Package) for a shipboard Medium-Voltage DC integrated power system. The generation equipment is based on a ultra-high-speed 22500-rpm 12-phase alternator which feeds an AC/DC power electronics converter composed of four diode rectifiers and four IGBT choppers. The prototype realization constitutes a follow-up of a previous Naval Package version employing a wound-field 6300-rpm alternator feeding non-controlled AC/DC converters. The major technical challenges faced in the design and development of the advanced Naval Package prototype are outlined in this paper taking the previous lower-speed version as a technology reference. The system performance highlighted by the testing campaign are finally addressed along with the lesson learnt to be capitalized for future developments.

Multiphase machines are AC machines characterized by a stator winding composed of a generic number n of phases. In today’s electric drive and power generation technology, multiphase machines play an important role for the benefits they bring compared to traditional three-phase ones (Levi, 2008; Levi et al., 2007). Such benefits have been widely highlighted by existing literature (Levi et al., 2007) and are mainly related to: an increased fault tolerance; higher power ratings achieved through power segmentation; enhanced performance in terms of efficiency and torque ripple. The use of multiphase machines is spreading both in small-power safety-critical applications as well as in very high-power industrial drives (Tessarolo et al., 2010), in electric-propulsion drives (Castellan et al., 2007) and power generation systems (Sulligoi et al., 2010). Regardless of whether they are used as motors or generators, multiphase electrical machines are almost always connected to power electronics systems (inverters for motors, rectifiers for generators), which interface them to the electric grid (Sulligoi et al., 2010; Castellan et al. 2008). Therefore, if the dynamic behaviour of a multiphase machine is to be predicted through simulations in the design and development stage, it is essential to do this by means of system-level simulations, where not only the electric machine is included, but also the power electronics and control systems that interact with it. Such a system-level simulation approach makes it difficult to use Finite-Element (FE) methods due to the complexity of the domain to be modelled and to the well-known computational heaviness of time-stepping FE simulations. Conversely, lumped-parameter models, to be implemented in the Matlab/Simulink environment, may provide designers with a powerful mean of analysis and investigation, provided that all the system components to be studied are modelled with an adequate level of accuracy and completeness. As concerns power electronics systems usually interfaced to multiphase machines, whether operating as motors or generators, the Matlab/Simulink environment offers wide and complete libraries where the designer can find reliable pre-defined blocks (for electronic switches, snubbers, diodes, etc.) to be used in building the application-related apparatus models. The same pertains to control and regulation blocks, which can be built up directly based on their transfer functions and logics. A possible criticality can be encountered when it comes to build the multiphase machine model. In fact, no predefined blocks are presently available in the Matlab/Simulink environment for this purpose. On the other side, building a dedicated user-defined machine

For several reasons, relating to reliability, power segmentation and performance enhancement, it may be convenient for an induction motor to be supplied by two (if not more) three-phase inverters. The most common design solution for this purpose is the split-phase one, where the stator wining is split into two three-phase sections displaced by 30 electrical degrees apart, each fed by an inverter. An alternative possibility is explored in this paper where the two motor windings are not displaced and they are suitable for being fed by in-phase supply voltage systems. The solution has been implemented in a 13 MW induction motor drive. Its performance is reported in this paper based on measurements taken during system testing.

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.

Split-phase machines are multi-phase machines whose stator phases are split into two or more three-phase windings. When all windings are equally loaded, the split-phase topology produces a better air-gap field than the usual three-phase one, with beneficial effects on rotor additional losses and torque quality. This does not occur when the windings are differently loaded, as typically occurs is split-phase motors with one or more out-of-service supplying inverters. This paper presents an analytical approach to accurately predict the air-gap field distortion in split-phase mechines with unequally-loaded windings and in presence of possible phase current distortion. Results obtained with the proposed method are assessed by comparison with FE simulations.

In the design of electric machinery concentric coil windings are often used where each end-turn consists of straight conductors connected by circular arcs. This paper proposes an analytical approach to the evaluation of end-turn leakage inductance for this winding geometry. The technique employs an asymptotical series expansion of Neumann integrals and, unlike existing methods, does not require to approximate the end-turn shape by a succession of elementary straight filaments. The computation formulas obtained have the advantage of a fast convergence speed and are easy to implement for practical use. Their correctness is assessed against direct numerical integration results.

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.

DC distribution networks are often employed in isolated power systems like in marine and aeronautical applications. An interesting alternative to DC machines for the supply of DC grids is constituted by a three-phase alternator feeding an AC/DC rectifier. In this paper, alternative solutions are investigated where the AC alternator is equipped with more (N) three-phase windings and feeds the DC load through more (N) cascade-connected rectifiers. The advantages of this solution with respect to the conventional three-phase topology are highlighted along with their dependence on the number (N) of the alternator windings. For this purpose, test results are reported and discussed on a prototype generator whose stator coils can be differently connected to obtained one, two, three or four windings. The major benefits (in terms of DC output current quality and field current ripple) are found when passing from the three-phase solution to the dual winding topology; conversely, relatively little advantage is gained by increasing the number of stator windings above two.

In high-power electric drives the use of multiple three-phase stator windings, supplied by voltage-source PWM inverters, is a design strategy for power rating, performance and reliability enhancement. Possible drawbacks, highlighted in the literature, come from the high-frequency circulation currents that originate in motor phases due to PWM switching. When a synchronous machine is used as the motor, low-frequency current harmonics can arise too, as a consequence of the non-uniform air-gap permeance. This paper discusses the point focusing on a PWM-fed 22-MW salient-pole synchronous motor with dual three-phase stator arrangement conceived for electric ship propulsion. The machine behavior under voltage-source supply is studied through time-stepping Finite-Element Analysis and predicts high internally-generated circulating currents, with a dominant 5th harmonic component. Before its application to the 22-MW motor study, the time-stepping FE methodology for current harmonic prediction is assessed against measurements on a real synchronous machine and on a laboratory prototype.

Salient-pole synchronous generators are conventional electric machines which have been widely studied over decades. Nevertheless, some aspects still constitute a challenge for designers and need to be approached with state-of-the-art modeling and computation techniques. An example is illustrated in this paper dealing with a 14 MVA synchronous generator. Different design solutions for its damper cage are studied and implemented on full-scale machine prototypes. Transient finite-element analyses are used to predict the influence of damper design on machine sub-transient reactances. Comparisons are presented between experimental results and finite element simulations and a physical interpretation is provided of the relationship found between damper structure and machine sub-transient reactances.

Electric motors equipped with multiple three-phase windings are often used for the advantages they offer in terms of reliability, performance, and inverter power segmentation. When the windings are fed by independent voltage-source inverters (VSIs), circulation harmonic currents can occur in stator phases. If the motor is an induction machine, circulation currents are known to originate form transient imbalances in the applied voltages due to inverter switching. This paper investigates the problem when a synchronous machine is used and shows how additional (and possibly major) sources for circulation currents can arise in this case (even with a round-rotor design) due to the nonsinusoidal air-gap flux distribution. The phenomenon is illustrated for a 45-MW quadruple three-phase synchronous motor supplied by four medium-voltage (MV) multilevel VSIs. Its circulation currents are predicted with two alternative methods, i.e., analytically and from time-stepping finite-element simulation. The results obtained in both ways are shown to well match measurement results collected on the actual motor during full-load system testing.

In this paper, a demonstrative technological implementation of a shipboard 2.15 MVA generation system is described along with its modeling, numeric simulation and some factory tests. The system, named Naval Package (NP), is part of a demonstrative programme commissioned by Italian Navy for preliminary evaluations of Medium-Voltage DC (MVDC) supply technologies aimed at equipping her future vessels. The NP is made by a dual-star alternator, whose two stator three-phase windings respectively feed two diode-rectifier full-bridges. The alternator (rated speed 6300 rpm) is designed to be moved by a 22000 rpm gas turbine through a gearbox. This paper will present NP innovative issues, with reference to design solutions, operative requirements, dynamic modeling under normal and faulty conditions and some factory tests.

Multi-phase machines are of increasing importance in today’s electric drives and generation systems. While in three-phase machines stator leakage flux phenomena are usually described with a single parameter, a higher number of independent leakage inductances is required as the number of phases increases. The impact of leakage inductances on multi-phase machine performance, especially in PWM inverter-supplied motors, is proved by many studies. Hence the need originates for the electromagnetic designer to have easy-to-use but sufficiently accurate calculation formulas giving the complete set of mutual inductance in a multi-phase machine. This paper aims at providing such formulas making abstraction of the particular phase arrangement in the stator winding and under the hypothesis of equal phase belts. The computation algorithms provided are assessed against measurements on actual machines wherever possible; otherwise accurate Finite Element (FE) analyses are used for validation.

In this paper two possible design alternatives are investigated for a high-power synchronous motor propulsion drive employing two voltage-source inverters for motor supply. The two arrangements are compared based on their steady-state behavior in both normal and faulty conditions (i.e. with one out-of-service inverter), predicted by time-stepping finite-element simulations. Simulation results found consistent with the results expected theoretically and based on previous studies. Pros and contras of the two design alternatives are highlighted together with the possible design strategies that could help mitigate their drawbacks.

In the field of poly-phase electric machines, a variety of stator winding alternatives is possible in terms of phase physical arrangements. The specific winding scheme, in addition to the number of phases, needs to be taken into account as far as the machine dynamic modeling is concerned. In particular, the Vector-Space Decomposition (VSD) method, which is widely used for n-phase machine analysis, requires different transformation matrices to be used depending on the displacement angle between successive phases, as discussed in a companion work. The explicit forms of such matrices are illustrated in this paper, taking the VSD of a five-phase motor, for different possible phase arrangements, as a numeric case study and validation example.

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.

The possibility of equipping the stator winding of an electric machine with more than three phases is an increasingly important strategy in today's drive design for its beneficial implications in terms of power rating, reliability enhancement and design degrees-of-freedom. Vector-Space Decomposition (VSD) is an important technique recently introduced for poly-phase machine modeling and analysis. A consolidated VSD technique exists covering symmetrical poly-phase machines, where the n stator phases are displaced by 360/n electrical degrees apart; conversely, other poly-phase configurations cannot be reduced to such a scheme and require some more dedicated treatment. Particularly, this paper shows how the VSD method can be effectively extended to poly-phase windings where a half phase progression (equal to 180/n electrical degrees) is used, as typically occurs in split-phase machines.

In this paper an analytical-numeric method for stator end-coil leakage inductance computation is presented based on the solution of Neumann integrals. The method extends an approach already introduced for three-phase machines to the case of an arbitrary phase number and arrangement. Moreover, some original contributions are proposed to enhance the calculation of end-coil self inductances, for which Neumann integrals cannot be directly used. Measurements on three machines with different numbers of poles and phases are presented to assess the accuracy of the method.

In conventional three-phase electric machines, coil pitch ratio is usually selected around 5/6 so as to minimize the 5 th and 7 th flux linkage harmonics. In the electromagnetic deign of inverter-fed multi-phase motors different criteria should be adopted, depending on motor and inverter typology and possibly on the number of phases too. In this paper the main design issues involved in this choice are discussed showing that the final decision has to be the best compromise among various design needs and objectives.

In this paper a high-power electric drive based on a quadruple-three-phase synchronous motor and four load commutated inverters (LCI) is investigated to evaluate its feasibility and performance. Based on accurate simulation analyses, the advantages of the proposed solution compared to the technologically-proven dual three-phase scheme are highlighted in terms of torque quality and motor efficiency improvement.

Phase-split synchronous motors supplied by multiple three-phase Load Commutated Inverters are of importance in high power applications. A criticality of such systems is the possibility that commutations within different stator windings may overlap. The analysis of the resulting transients is complicated by the magnetic interference of motor phases among them and with rotor circuits. In this paper the complete dynamic model of phase-split synchronous machines is manipulated to derive a simple analytical and circuital description of commutation transients, including the case of multiple simultaneous commutation events. Numeric simulation results are presented to cross-check the proposed model.

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.

Electric propulsion for cruise liners has now become a standard owing to its several advantages. However propulsion drives have a large impact on the ship power system. This gives rise to the requirement for designers to understand in depth the effects of propulsion drives on the ship network in different operating conditions. For this purpose computer simulations have proved to be a very useful tool. In the paper a typical propulsion drive for an all-electric cruise liner is described and simulation results are shown. Owing to the model complexity, simulations turn out to be computationally quite heavy. For this reason a simplified model has been developed. Simulation results, from the ship network viewpoint, proved to be close to the detailed model ones.

In this paper a DC power plant for base transceiver station power supply is investigated. The supply system employs clean alternative energy sources, namely photovoltaic (PV) modules, wind turbines, a fuel cell as backup generator and a storage battery bank. A detailed description is made and experimental data are shown of a prototype system where the PV modules are directly connected to the DC bus and an on/off strategy is used to control the power flow to the battery bank and to the load. The system is modeled and the model is validated comparing simulation results with experimental data. It is then investigated the possibility to add a DC-DC converter for optimized control of the energy generated by the PV strings. Simulation results show that the addition of a DC-DC converter between the PV modules and the DC bus brings a remarkable increase in the produced energy.