Search

In this article, we present a comprehensive analysis on the thermal response characteristics of the stator winding insulation under static air-gap eccentricity (SAGE) conditions in synchronous generators. Different from previous studies, this article not only takes into account the interactions of both the core-loss-caused heat and the copper-loss-caused heat but also investigates the thermal degrading distribution regularities due to SAGE. The whole work is based on the qualitatively theoretical analysis, the finite-element analysis, and the experimental validation on a nonsalient synchronous generator. The study shows that SAGE will significantly make the temperature rise, resulting in uneven temperature distribution and intensifying the thermal responses, such as the thermal deformations, stresses, and strains, of the insulation. The nose part and the joint between the line winding and the end winding on the smaller air-gap side are the two most dangerous positions. [ABSTRACT FROM AUTHOR]

This article describes a novel analytical methodology for eddy current losses simulation in the windings of permanent magnet synchronous machines. The methodology is based on subdomain modeling technique in conjunction with solving of ordinary differential equations system. The main advantage of the proposed method is high accuracy and significant reduction of simulation time in comparison with finite-element modeling (FEM) technique that is frequently used for eddy current loss modeling. The proposed model allows fast and accurate evaluation of proximity and skin effect in conductors in time domain for an arbitrary current waveform and machine duty cycle. The main difference from previously presented analytical methods is the possibility to evaluate losses for a wider range of conductors geometries, regardless their shape, dimensions, location in the stator slots, and rotor speed. The main contribution and novelty of the proposed analytical approach is simultaneous implementation of subdomain modeling technique and strands segmentation concept followed by the eddy current effect representation through the equivalent circuit. This approach allows reducing the computational time while keeping the accuracy close to the FEM result. The proposed model was compared to FEM, using different types and sizes of conductors and also validated experimentally. [ABSTRACT FROM AUTHOR]

In high performance electric machines, the increase of fundamental frequency leads to additional losses in the winding due to parasitic effects such as the associated skin and proximity effects. In the first part, this paper presents an investigation into accurate modelling of AC losses in the winding using numerical methods and their experimental verification. Then, using experimental motorette setups, this research provides a comparative study between fixed strand positioning and fixed conductor shapes on the AC losses in the winding. It is shown that the exact position of strands in the conductor is not a critical factor; however, it is very important to control the conductor shape inside the slot. In the final section of this paper, an investigation into the relationship between AC losses in the winding and copper filling factor is presented. It is shown experimentally that counter-intuitive design choices such as using a lower copper fill factor and thicker strand diameters may be beneficial in achieving the highest overall efficiency. [ABSTRACT FROM AUTHOR]

This article proposes a modular approachto the power sharing control of permanent magnet synchronous bearingless machine. The selected machine topology features a winding layout with phases distributed into nonoverlapping three phase groups, a solution whose twofold aim is to increase the fault tolerance and to allow for the radial force generation. The three phase subwindings are supplied by standard three-phase inverter, leading to a modular system architecture. A throughout explanation of the methodology used to develop the control algorithm is presented considering the torque and force control in combination with the power sharing management of the machine. Special emphasis is placed on validating the modeling hypotheses based on a finite element characterization of the machine electro-mechanical behavior. The proposed control strategy is also extended to cater the possibility of one or more inverters failure, thus validating the intrinsic advantage of the redundancy obtained by the modularity of the system. An extensive experimental test campaign is finally carried out on a prototyped multi three-phase permanent magnet synchronous drive. The obtained results validate the bearingless power sharing operation in healthy and faulty scenarios, both at steady state and under extreme transient condition. [ABSTRACT FROM AUTHOR]

Sensorless control technologies based on rotor saliency may not operate well due to the effect of magnetic saturation. In this work, a rotor backend (RB) is attached to an existing rotor structure of a permanent magnet synchronous motor (PMSM) to enhance anisotropic features. The geometry of the RB is further optimized to achieve greater current amplitude induced by the RB saliency modulation. The phase sequence direction of the modulation is not electrically synchronized with the rotor reference frame. A fractional slot/pole combination is selected and analyzed to strengthen the saliency modulation signal. Hence, the sensorless techniques will be immune to saturation effect in highly exploited machines. Both low and high-speed performance of the proposed method is verified through the experimental tests. It is demonstrated that the position estimation using saliency modulation of the RB is unaffected by machine saturation due to its electrical asynchronous property. [ABSTRACT FROM AUTHOR]

This article presents a current limitation technique for a multiphase bearingless machine featuring a combined winding system. This winding structure allows the machine to produce both suspension force and motoring torque. The main challenges with the combined winding configuration consist of decoupling the suspension force and torque generation and designing a proper current limitation algorithm. The former topic has been already tackled and presented in previous publications, while the latter will be addressed in this article. In particular, the proposed suspension force control technique will allow to prioritize either suspension force or torque generation. In this article, the priority is given to the rotor levitation, hence the suspension force rather than the torque is essential. Finally, simulation results and experiment validation on a $\text{1.5}\,\text{kW}/3000\,\text{r/min}$ prototype machine are provided. [ABSTRACT FROM AUTHOR]

This article deals with the power-sharing control of bearingless multisector and multithree-phase permanent magnet machines. The proposed control strategy allows to distribute the power flows among the three-phase inverters supplying the machine during bearingless operation of the drive. The control technique is based on the extension of the vector space decomposition modeling approach. The components producing the electromagnetic torque, i.e., the q-axis currents, are controlled independently from the d-axis ones, also with the aim of managing the power flows among the three-phase systems. Conversely, the d-axis currents are exploited for the generation of the radial forces needed to levitate the rotor, while considering the compensation of the forces caused by the q-axis currents in case of unbalanced power sharing strategy. The validity of the proposed method is confirmed by simulations and experimental tests on a prototyped bearingless multisector permanent magnet synchronous machine. The proposed approach is a contribution to the development of advanced control systems employing multiphase drives in the field of bearingless and multiport applications. [ABSTRACT FROM AUTHOR]

A close functional and structural integration of passive elements is required to improve the power density of motor drives. Such power-dense motor drives are prerequisites in aerospace and automotive applications. This article presents a permanent magnet motor with an integrated filter inductor, which not only eliminates inductor losses but also removes its associated weight and volume. The motor with an integrated filter uses motor's inherent magnetics in order to use it as a filter inductance instead of adopting an external inductor option, which is traditionally placed outside the motor. A vector-controlled model, taking modulation and switching effect into account, has been developed by using MATLAB/Simulink tool. To experimentally validate the concept of the motor with an integrated filter inductor, the winding connections of an existing motor are modified. The comparative analysis, between the traditional and integrated motor drive systems, is carried out in terms of the magnitude of switching component, total system losses, weight, and volume. The total losses in the motor with integrated filter are reduced by 34.2% at 2100 r/min and 3-N·m load, when compared to the motor with traditional filter inductor, whereas, its weight and volume in the motor with integrated filter inductor are eliminated completely. [ABSTRACT FROM AUTHOR]

This article presents a comprehensive analysis on the end winding vibration characteristics due to different stator inter-turn short circuit (SISC) positions in synchronous generators. Different from other studies, this article not only pays attention to the effect of SISC on the end winding electromagnetic forces, but also considers the impact of the short circuit position, which is related to the static air-gap eccentricity, on the end winding vibrations at the meantime. The whole work is based on the qualitatively theoretical analysis, the finite element analysis (FEA), and the experimental validation on a 6-pole synchronous generator. The study shows that SISC will considerably enlarge the electromagnetic force and intensify the radial vibration of the end winding, especially at 100 Hz, 200 Hz and 300 Hz. The closer the short circuit position is to the minimum air-gap point, the more severe the end winding vibration will be. [ABSTRACT FROM AUTHOR]

High-speed permanent magnet machine (HSPMM) design is considered with particular attention paid to machine electromagnetic, thermal, and mechanical analyses. In this article, a 140-kW, 15 000 r/min HSPMM is designed with its power losses evaluated at first. Afterward, the machine temperature distribution is obtained based on computational fluid dynamics modeling. HSPMM is prototyped with experimental tests conducted to verify the calculation results. Mechanical strength analysis is performed for the HSPMM rotor structure with pole filler by finite-element method for the rotor at three operational conditions, while the influences from sleeve parameters on rotor strength are comprehensively studied for the HSPMM rotor at the most challenging condition. In this article, stator auxiliary slotting is extensively researched to reduce the rotor eddy current loss with little effects on machine output torque. The air gap flux density for HSPMM with auxiliary slotting is analytically predicted, while the working mechanism is illustrated in-depth. The effects from auxiliary slot dimensions, numbers and positions, on machine performances are further proposed and investigated. The experimental tests also validate the reduction of HSPMM rotor eddy current loss by the application of auxiliary slotting. [ABSTRACT FROM AUTHOR]

This article presents three-phase and single-phase open-circuit fault-tolerant control strategies of radial suspension force and torque generation for bearingless multisector surface mounted permanent magnet synchronous machines. A combined winding topology is installed in the stator so that each phase contributes to both suspension force and motoring torque production. Indeed, a triple sectored three-phase winding is employed. Each three-phase winding is supplied by a power converter to independently control the suspension force vector and torque over each sector. An analytical formulation of the force and torque generation is described considering both three-phase open-circuit and single-phase open-circuit fault conditions. The analytical models of the machine are presented in a generalized matrix form so that they can be applied to any machine with a multisector winding structure. The analytical models are then used to derive the control algorithms that allow us to control the bearingless machine when a whole three-phase winding or one phase of one or two sectors are open circuited. The theoretical analysis is verified with both finite elements analysis and experiment tests. This system shows a good open-circuit fault-tolerant capability. [ABSTRACT FROM AUTHOR]

Nowadays, finite element analysis represents the most accurate tool to analyse electrical machines. However, the time domain resolution of electromagnetic problem, in some cases, requires long simulation time due to the induced nature of the currents. The computational burden increases when the machine features a skewed layout on the stator or rotor structures, since this requires 2D multi-slices approximated analysis or even a full 3D model. In this paper, a general analytical method to model electromagnetic devices is applied to a squirrel cage induction motor featuring a skewed rotor structure. The modelling approach is wisely implemented and adapted to pursue a fair balance between accuracy of the analysis and computational burden, taking advantage of all the symmetries existing in the rotor cage of the machine, aiming to minimize the model complexity. A comparative analysis in term of the inductances between analytical and finite element is proposed. The results provided by the model developed are compared with respect to the corresponding values provided by both finite element and experimental test performed on the reference machine. Such comparisons show that the proposed model is actually able to achieve a pretty good balance between accuracy and computational efficiency. [ABSTRACT FROM AUTHOR]

While electrical machine designers typically go to great lengths to choose the optimal number of stator slots based on the electromagnetic performance, often the thermal aspects of this selection are overlooked. This article investigates the multi-domain impacts related to the slot number selection, combining both the electromagnetic and thermal aspects. Taking an existing 42-kW 4-pole, 12-slot electrical machine with Halbach-array surface-PM rotor, used within a more-electric marine engine as a case study, performance aspects of the machine with different slot numbers are investigated. The impact of slot number is compared considering the losses, output torque and its quality, as well as the peak temperature. Experimental tests are performed, verifying significant temperature reductions and performance entitlements when the optimal stator slot number from thermal point of view is selected. Finally general guidelines on slot number selection for temperature reduction are provided. [ABSTRACT FROM AUTHOR]

This article proposes an analytical model of modular spoke-type permanent magnet (MSTPM) machines based on air-gap field modulation (AFM) theory. Firstly, a fundamental AFM model of open-circuit MSTPM machines is introduced. The open-circuit air-gap field of MSTPM machines is determined by three fundamental elements including the primitive magnetizing magnetomotive force (MMF) produced by permanent magnet (PM), and two modulators which consist of stator and rotor permeance. The analytical MMF excited by PM (PM-MMF) can be calculated by using magnetic circuit method, while the stator and rotor permeance models are developed based on relative permeance (RP) method. Thereafter, a general model is proposed to calculate the open-circuit back electromotive force (EMF) of MSTPM machines. Further, the winding inductance model is established on the basis of equivalent magnetic circuit method and RP model. Finally, the machine performance is predicted by the analytical model, and verified by both finite element analysis (FEA) and experimental results. [ABSTRACT FROM AUTHOR]

Hairpin windings are gaining increasing popularity in recent years due to their advantages in improving electrical machine performance while reducing manufacturing time and costs. Their geometrical features introduce new challenges and opportunities on thermal management. In particular, spray cooling is increasingly being used, since hairpin windings open up regular and accurately defined gaps in the end-windings compared to the traditional random windings. To date, technical literature on the effectiveness of spray cooling with hairpin windings is lacking, with no practical guidelines available to researchers. In this article, taking an existing hairpin-wound stator, a test rig is developed to investigate the cooling ability of different spray cooling setups on the end-windings. Three types of commercial spray nozzles are chosen to carry out a series of experiments, varying the oil flow rate, pressure, outlet velocity, and number of nozzles. The winding temperature and heat transfer coefficients are presented and discussed. Furthermore, the efficiency of spray cooling is reviewed based on the experimental results. Finally, suggestions on designing similar cooling setups and increasing the cooling efficiency are also provided. [ABSTRACT FROM AUTHOR]

The interest in multiphase machines for high power and reliable drives has been growing, and many control algorithms have been proposed to improve their torque performance. This article presents a new approach to the modeling of a multi three-phase drive, aiming at the minimization of the torque ripple introduced by the pulsewidth modulation (PWM) voltage excitation, by the shift of carrier phase angles among different three-phase inverters. The underlying idea is to use standard three-phase converters feeding the individual segment and to apply a phase shift between the PWM carriers. For the torque ripple analyzed in this article, only the interaction between the armature field, resulting from the PWM voltage excitation, and the fundamental component of the permanent-magnet field is considered. The proposed carrier phase-shift angles are obtained for a case study of a sectored triple three-phase synchronous permanent-magnet machine. Analytical, numerical and finite-element analysis results are presented to explain how the carrier shift angles affect the current and torque ripple. Finally, experimental results are presented to validate the model and the control algorithm. [ABSTRACT FROM AUTHOR]

Electrical machines for transportation applications need to be highly reliable, particularly if they drive safety-critical systems. At the same time, another main requirement is represented by the significant torque density, especially for aerospace, where weight constraints are extremely stringent. For achieving high peak torque, an effective strategy consists in supplying the windings with a current greater than the rated value; thus, thermally overloading the machine for limited time periods. However, if the insulation is overheated, the machine lifetime is shortened and reliability issues can arise. This paper experimentally investigates the influence of short-time thermal overload on the insulation lifetime for low voltage, random wound electrical machines. The analysis is performed on round enameled magnet wire coils, which are aged by accelerated thermal cycles. The obtained results are statistically processed through a two parameter Weibull distribution. According to the findings of the experimental data postprocessing, a lifetime prediction model is built. This model is employed for predicting the lifetime consumption of a motor embedded into an electromechanical actuator for aerospace application. [ABSTRACT FROM AUTHOR]

In this article, a novel post fault control algorithm based on the space vector method is presented and applied to a bearingless multisector permanent magnet synchronous machine with a triple three-phase winding. First, the expressions of the current space vectors, as a function of the electromagnetic suspension force and motoring torque, are introduced. Then, the open-circuit fault is described and a new post-fault algorithm is introduced. The introduced post-fault algorithm, based on the minimization of the stator copper losses, is compared at simulation level with an existing one, where the above-mentioned loss minimization was not considered. The simulation results show a remarkable improvement in the performance when the novel post-fault algorithm is employed. Finally, the developed control algorithm is experimentally validated on a prototype of a bearingless multisector permanent magnet synchronous machine. [ABSTRACT FROM AUTHOR]

This paper presents a validation of the novel motor-shaped rotational inductor. To validate the concept, 12 slots 2 poles rotational inductor is tested at different supply frequencies and rotor speeds. Experimental results have shown that the iron losses reduce as the rotor speed increases to the synchronous speed of the stator supply. The performance of the integrated rotational inductor is also compared with traditional EE core inductor in terms of total losses, synchronous inductance, copper resistance, and total harmonic distortion (THD). The total loss-to inductance ratio of the rotational inductor is reduced by 22.5% when rotor is rotating at 18 kRPM and supply frequency is held at 300 Hz. A significant reduction in copper resistance-to-inductance is also noticed when supply frequency is varied from 0 Hz to 20 kHz. Furthermore, the synchronous inductance and voltage and current's %THD of rotational inductor is found to be superior to EE core inductor. [ABSTRACT FROM AUTHOR]

This paper proposes a novel, low-cost, effective way to improve the thermal performance of electrical machines by extending a part of the back-iron into the slot. This modification helps in reducing the thermal resistance path from the center of the slot to the coolant; however, its thermal benefits must be clearly evaluated in conjunction with the electromagnetic aspects, due to the higher iron losses and flux leakage, and furthermore such an extension occupies space, which would otherwise be allocated to the copper itself. Taking a case study involving an existing 75-kW electric vehicle traction motor, the tradeoffs involving the losses, flux leakage, output torque, torque quality, and the peak winding temperature with and without back-iron extension are compared. Finally, experimental segments of the aforesaid motor are tested, verifying a significant 26.7% peak winding temperature reduction for the same output power with the proposed modification. [ABSTRACT FROM AUTHOR]

In the design of electrical machines, the increase in power density has become one of the main research themes. With most of the power loss in high power density electrical machines often being generated in the stator winding assembly, it is necessary to reduce these losses. The effects of strands and bundle positions in the slot on the ac losses in the winding are often overlooked. Taking as a case-study an existing high-frequency machine, this article analyzes and provides an in-depth insight into such effects. Exploiting the rapid advancements in precision three-dimensional printing, it is found and experimentally verified that by controlling the position of the conductors within the top of the slot the ac losses can be markedly reduced. [ABSTRACT FROM AUTHOR]

Brushless doubly fed generator (BDFG), a class of adjustable-speed machine with a special structure, shows great prospect in wind power generation. Since different rotor structures lead to great differences in the BDFG performance, the research of BDFG rotor structure has been a hotspot. However, only a few of the research studies have paid attention to the rotor and stator slot combination of the BDFG, especially for the BDFG with a novel hybrid rotor. Improper slot combination will lead to efficiency decrease, additional loss increase, and undesirable torque in an electrical machine. In order to study the principle of slot combination of the BDFG with the hybrid rotor, the combination approach of theoretical analysis and experiments is presented in this paper. Furthermore, a coupling factor which reflects the coupling ability of the BDFG with different slot combinations is proposed. Moreover, the best slot combination of the proposed BDFG is determined, and several parameters such as useful harmonic contents, total harmonic voltage distortion (THDu), core loss, and copper loss are considered as major criteria for judgment. [ABSTRACT FROM AUTHOR]

The long and enduring history of utilization of the wound-field synchronous generator in a large number of applications makes it one of the most known and consolidated electrical machine technologies. Thus, its design, modeling, and analysis processes have been widely exploited and implemented through various and different methods, including the equivalent circuit approach. When a damper cage is embedded within the rotor of the synchronous generator, its theoretical analysis becomes quite complicated. Thus, today numerical tools are being used. In this paper, an alternative way of modeling symmetric damper cages of salient-pole synchronous generators is presented. The proposed approach is embedded in the circuital model of the generator. A hybrid analytical–numerical model is implemented, permitting to accurately predict the voltage waveforms of the generator with excellent accuracy, however, at a lower cost of computational resources than the pure numerical method. A case study of an off-the-shelf 400 kVA machine is considered to develop and validate the proposed technique. The results are compared with the corresponding finite-element and experimental evaluations for validation purposes. [ABSTRACT FROM AUTHOR]

Phase-shift or pole-shift method can reduce the detent force of the double-sided permanent magnet linear synchronous motor (DS-PMLSM) dramatically. However, this method causes a decrease in thrust and an increase in normal force simultaneously. To overcome this drawback, a novel slot-shift structure whose slots on the two sides of the primary component are staggered by an optimal distance is proposed in this paper. The models of the detent force including the end force and cogging force is established theoretically, and then verified by finite element analysis. The windings in the upper primary and the lower primary are arranged differently to improve the average thrust. The thrust characteristics of the DS-PMLSM under different shifted distances are analyzed and compared in detail. Furthermore, the primary component employing two kinds of core laminations is proposed to reduce both the dc component and ripple of the normal force. Finally, a DS-PMLSM prototype is tested, and the experimental results are compared with the analytical results to verify the effectiveness of the theoretical and simulation research. [ABSTRACT FROM AUTHOR]

The main purpose of this paper is to investigate the influence of winding location on back electromotive force (EMF) and armature inductance in flux-switching permanent-magnet (FSPM) machines. To obtain an analytical solution, a double-stator-pitch model is built based on the equivalent magnetic circuit method. Then, the open-circuit characteristics in FSPM machines with different winding layouts are analyzed by both the analytical model and finite-element-analysis method. The analysis reveals that winding inductance is easier influenced by the winding location than the permanent-magnet flux linkage and corresponding back EMF. Finally, the analytical and finite-element predictions are verified by experimental results. [ABSTRACT FROM AUTHOR]

This paper proposes an integrated method of three-phase ac excitation and high-frequency voltage signal injection (HFVSI) for sensorless controlled starting of brushless synchronous machines (BSM) used as starter/generator in variable frequency ac power systems of civil aircraft. Fixed 400 Hz of the three-phase ac power is adopted both for the ac excitation and HFVSI in the initial starting process to eliminate the bulky rotor position sensor for BSM. The resulting 6th sequence harmonic voltage determined by the rotating rectifier is utilized as the HFVSI into the field-winding of main generator without any extra high-frequency signal injection. The rotor position is estimated by the high-frequency response signals extracted from the armature windings of main generator. Due to the nonlinear rotating rectifier linked in the HFSI chain, a novel frequency-insensitive asynchronous demodulation strategy is proposed in this paper for rotor position estimation. Furthermore, the initial rotor position detection is calibrated by polarity decision of the induced currents of the armature windings within the establishment procedure of field current of the main generator at standstill. The effectiveness of the ac excitation and feasibility of rotor position estimation for sensorless starting control of BSM are validated by the simulation and experimental results. [ABSTRACT FROM AUTHOR]

In an electrical machine design, thermal management plays a key role in improving the performance and reducing size. End-windings are commonly identified as the machine hot-spot. Hence, lowering and predicting end-windings temperature are crucial tasks in thermal management of electrical machines. This paper proposes and investigates a noninvasive but effective cooling method that aims for a uniform cooling of a machine's winding by implementing direct cooling on its end-windings. Modeling and experimental results show that a 25% hot-spot temperature reduction on a particular application can be achieved. To analyze the proposed technique in detail, an accurate but computationally economic lumped parameter thermal network is developed. Comparison between a “standard” thermal network and its simplified equivalent (with less nodes) is presented where the models are developed and fine-tuned based on experimental data. All the above is used to investigate the potential of the proposed end-winding cooling method with different configurations of the methodology. [ABSTRACT FROM AUTHOR]

This paper presents a droop-based distributed control strategy for multithree-phase machines that provides augmented controllability during power sharing transients. The proposed strategy is able to mitigate the mutual interactions among different sets of windings without controlling any subspace variable, also offering a modular and redundant design. On the contrary, in a centralized configuration, subspaces would be controlled using the vector space decomposition, but fault tolerance and reliability levels required by the stricter regulations and policies expected in future transportation systems would not be satisfied. The proposed method is analytically compared against the state-of-the-art power sharing technique and equivalent models and control design procedures have been derived and considered in the comparison. Uncontrolled power sharing transients and their effects on mutual couplings among isolated sets of windings have been compared against the proposed regulated ones. Experimental results on a 22-kW nine-phase multithree-phase synchronous machine rig validate the design procedures showing good agreement with the expected performances. [ABSTRACT FROM AUTHOR]

In this paper, two novel double-sided hybrid-excitation flux-reversal linear motors (DSHEFRLM) with the surface (S-) and interior (I-) permanent-magnet(PM) arrangements are proposed and comparatively investigated. The proposed motors feature an asymmetrical double-sided primary configuration which enables the armature and field excitations to be placed separately. Through 2-D finite-element method (FEM), two motor structures with different slot/pole combinations are optimized, and then, the magnetic fields and electromagnetic performances are calculated, including inductances, no-load flux linkage, thrust characteristics, and PM demagnetization capability. By comparison, it is found that S-DSHEFRLMs show larger thrust density while I-DSHEFRLMs exhibit superior flux-adjusting capability. Finally, these predicted results are validated by 3-D FEM. [ABSTRACT FROM AUTHOR]

The use of solid materials in tubular, linear machines has significant manufacturing benefits, as this removes the need for an axially laminated stator. However, this comes at the cost of extra eddy current losses. In this paper, a detailed analysis of the behavior of eddy currents in a tubular permanent magnet machine that comprises unconventional magnetic circuit is given, highlighting the importance of the field distribution and current directions, when compared with conventional magnetic circuits. This analysis is then used to identify and investigate the appropriate eddy current reduction methods for tubular machines, when a solid material stator is being used. Accurate three-dimensional models have been built and then validated on previously built testing setups. Different winding configurations have been accounted. Finally, considerations of these techniques are given when being implemented into an actual, tubular machine design, highlighting the improved performance and losses. [ABSTRACT FROM AUTHOR]

This paper proposes and investigates an innovative methodology that can have a significant impact on the market potential of wound field, small–medium size synchronous generators (SGs). The technique proposed here is aimed at removing the need for the traditional stator skewing that is so commonly used in SGs to achieve acceptable values of voltage total harmonic distortion. To do this, a nonstandard damper cage configuration is proposed that comprises modulation of the damper bars’ positioning. An off-the-shelf, 400-kVA generator is used as a benchmark machine. Its rotor is optimized and modified according to the proposed technique. The results of the final machine are then compared to the benchmark machine highlighting the excellent advantages that can be achieved through this technique. A full-scale prototype of the modified generator is then built to experimentally validate the concept. Finally, a detailed analysis on all the performance aspects of the prototype is carried out, to guarantee that the proposed technique has no negative impact whatsoever on the generator's performance. [ABSTRACT FROM AUTHOR]

Compulsators are popular choices for high-end railgun power supplies. In order to increase the power density, air-core compulsators are proposed by using composite materials instead of ferromagnetic materials. Compared with the conventional iron-core machines, armature conductors of the air-core machines are not surrounded by the ferromagnetic teeth, resulting in the conductors been exposed to highly dense revolving magnetic field, which causes eddy current losses in the conductor strands. On the other hand, high-frequency currents flow through the armature winding during the self-excitation and discharge process, which also causes skin effect and proximity effect losses. Therefore, an effective winding design is essential to ensure proper current density distribution and eddy current losses of armature conductors to avoid local overheating. This paper deduced the calculation model of eddy current losses of a single conductor under alternating magnetic fields and then established the eddy losses calculation model of the air-core compulsator’s armature winding. The expression indicates that the eddy current losses of a conductor are determined by both the radial and tangential components of the flux density, which can be obtained by finite-element analysis. Based on the calculation model, the performance of two particular armature designs (a solid conductor and a compacted type-8 litz wire with the same area) are analyzed and discussed. The conductor eddy current losses are estimated and compared for both designs. Finally, an optimization study is carried out to find the best choice of strand diameter to minimize the total losses. [ABSTRACT FROM AUTHOR]

Compulsators are popular choices for various high-power electromagnetic launch applications, especially for the electromagnetic railgun. A two-axis-compensated compulsator with lower internal impedance and higher power density was proposed in the authors’ previous paper. The field windings and compensating windings are allocated electrical orthogonally, providing the opportunity to design the direct-axis and quadrature-axis compensations independently. Due to the excitation function of the field windings, as well as field windings and compensating windings at the same rotor periphery, the ratio between $d$ -axis and $q$ -axis compensation is determined not only by the waveform of the air-gap flux density but also by the occupied space of windings, electromagnetic force during discharge and temperature rise and cooling condition. All these aspects mentioned above were analyzed in this paper. Furthermore, the output performance for single pulse discharge of a 2-m railgun with 100-g armature and multiple pulses discharge of a 5-m railgun with 300-g armature was simulated and compared. The results indicated that the two-axis compensation could obtain benefits by introducing more sinusoidal discharge currents for single pulse mission comparing to traditional compensation structure, whereas no obvious advantages for a flat-topped current waveform for multiple pulses mission. [ABSTRACT FROM AUTHOR]

This paper investigates high-speed surface PM machine design for portable turbo-generator applications. The rotor radius is fixed to achieve certain optimal characteristics of the magnet retention mechanism. The objective of this paper is to design and select the stator. The stator designs are populated by different slot/pole combinations, winding arrangements, and over a range of possible stack lengths. However, the design is constrained by physical diameter, stack length, and electrical volt–ampere constraints. A large number of preliminary machine designs do not satisfy the specified turbo-generator torque/speed requirements under the given volt–ampere constraints and therefore it is ineffective to perform finite element analysis on all preliminary design variations. In order to establish the feasibility of a machine design to fulfill the specified turbo-generator torque/speed requirements, the concept of inductance-limits is presented and then linked with stator design parameters. By application of this analysis strategy, a confined optimal set of stator designs are obtained and are subjected to detailed finite element simulations. A final machine design is selected and fabricated. Experimental results are presented for the validation of the final machine design. [ABSTRACT FROM AUTHOR]

The traditional generating set is usually comprised of a classical, wound-field, salient-pole, or cylindrical rotor synchronous generator, excited by a separate smaller machine, via a rotating, uncontrolled diode rectifier. The effects of the commutation processes of the diode bridge are often overlooked and neglected. However, due to the uncontrolled nature of this process, the rectified voltage available at the main generator's rotor terminals can be significantly lower than the expected value. This is especially true for low-to-medium power rated systems. In this paper, a detailed investigation of these aspects is done and an accurate voltage drop prediction model is then proposed. The model is validated with finite-element analysis and with experimental results for a particular low–medium rated generating system in the 400 kVA power range. The validated tool is then integrated into an innovative design tool, which first performs an analytical presizing procedure and then utilizes a genetic algorithm approach to identify an optimal excitation system design, aimed at minimizing the voltage drop ensuing from the diode commutations, with minimum impact on the overall efficiency. [ABSTRACT FROM AUTHOR]

This paper presents design optimization of a short-term duty electrical machine for extreme environments of high temperature and high altitudes. For such extreme environmental conditions of above 80 °C and altitudes of 30 km, thermal loading limits are a critical consideration in machines, especially if high power density and high efficiency are to be achieved. The influence of different material on the performance of such machines is investigated. Also, the effect of different slot and pole combinations are studied for machines used for such extreme operating conditions but with short duty. In the research, a nondominated sorting genetic algorithm (NSGAII) considering an analytical electromagnetic model, structural and thermal model together with finite element methods are used to optimize the design of the machine for such environments achieving high efficiencies and high power density with relatively minimal computational time. The adopted thermal model is then validated through experiments and then implemented within the genetic algorithm. It is shown that, generally, the designs are thermally limited where the pole numbers are limited by volt-amps drawn from the converter. The design consisting of a high slot number allows for improving the current loading and thus, significant weight reduction can be achieved. [ABSTRACT FROM AUTHOR]

Compulsator is a specially designed generator capable of delivering high current pulses to a low-impedance load, such as the electromagnetic railgun. In order to increase the tip speed of the rotor, advanced composite materials have been used in the recent compulsator prototype, which is mentioned as air core instead of the traditional iron core. For typical air-core compulsators, there are no slots and steel teeth to place the armature windings due to the nonmachinability of composite materials. Therefore, concentric windings in racetrack style are often adopted instead of traditional lap winding in most cases, since it is more convenient to be fixed by composite materials. However, overlap occurs at the end winding part for multiphase compulsators, which are not easy to be formed during the manufacture process. In this paper, a fractional slot multiphase air-core compulsator with concentrated windings is proposed and analyzed. The main advantage of fractional slot configuration is that it can offer a concentrated winding structure under certain conditions, which means each coil only spans one “tooth,” and will not cause any intersection between each phase at the end winding. Two referenced fractional slot air-core compulsators with two phases, six poles, and four “slots” or eight “slots” (q = 1/3 and q = 2/3, q is the “slot” per pole per phase) are analyzed and compared with the performance of a traditional integral slot machine. The results indicated that the output voltage and self-excitation performance of a fractional slot compulsator can reach the same level with an integral slot one, and the discharging performance can reach an acceptable level. Thus, the fractional slot multiphase concept can be further used to improve the manufacture process of the winding in the future. [ABSTRACT FROM PUBLISHER]

As power supplies, compulsators are popular choices for high-end railgun power supplies. In order to increase power and energy density, air-core compulsators are proposed by using composite materials instead of traditional iron-core compulsators. Due to the absence of ferromagnetic material, the flux density in the air-core compulsator can reach to 4–6 T instantaneously, which is much higher than the saturation field strength in traditional iron-core machines. Therefore, self-excitation topology is essential for the air-core compulsator to obtain up to 100-kA field current. This paper carried out research on the key parameters of self-excitation efficiency first, and then focus on the large magnetic energy remained in the inductive field winding after one shot, an implementation scheme and control strategy of energy recovery of air-core compulsator was proposed and analyzed. By controlling the field rectifier working at active inverter state after one discharge process, the magnetic energy stored in the field winding can be converted to rotor kinetic energy again. The simulation results indicate that the energy recovery efficiency can reach to 70% for a reference air-core compulsator. The continuous discharge number of times increased from 3 to 4 during one kinetic energy charging, which means that the delivered energy density increases 33.3%. [ABSTRACT FROM PUBLISHER]

Early detection of incipient faults in ac drives is one of the most difficult challenges for condition monitoring, especially for faults related to insulation degradation of the windings. In low power motors, the insulation degradation is principally due to the steep voltage variations caused by the voltage source converters that drive the machines. In the last years, with the coming to market of new no-Si based power devices, which achieve great values of dv/dt, fast tracking of electrical fault has became a topic of primary importance. In this paper, a new method to detect the presence of incipient faults in ultrareliable electric machines is presented and compared with a previous solution. The different methods were extensively evaluated by means of experimental results. It is shown that potential winding faults can be detected at an early stage of fault inception and thus measures can be taken to limit propagation. [ABSTRACT FROM PUBLISHER]

The benefits of implementing a damper winding in salient-pole synchronous generators are widely known and well consolidated. It is also well known that such a winding incurs extra losses in the machine due to a number of reasons. In order to improve the overall efficiency and performance of classical salient-pole, wound field synchronous generators that employ the traditional damper cage, an improved amortisseur winding topology that reduces the inherent loss is proposed and investigated in this paper. This is essential in order to meet modern power quality requirements and to improve the overall performance of such “classical” machines. The new topology addresses the requirements for lower loss components without compromising the acceptable values of the output voltage total harmonic distortion and achieves this by having a modulated damper bar pitch. As vessel for studying the proposed concept, a 4-MVA salient-pole synchronous generator is considered. A finite element model of this machine is first built and then validated against experimental results. The validated model is then used to investigate the proposed concept with an optimal solution being achieved via the implementation of a genetic algorithm optimization tool. Finally, the performance of the optimized machine is compared to the original design both at a steady state and transient operating conditions. [ABSTRACT FROM PUBLISHER]

This paper presents a three-phase open-end winding induction motor drive. The drive consists of a three-phase induction machine with open stator phase windings and dual-bridge inverter supplied from a single dc voltage source. To achieve multilevel output voltage waveforms, a floating capacitor bank is used for the second of the dual bridges. The capacitor voltage is regulated using redundant switching states at half of the main dc-link voltage. This particular voltage ratio (2:1) is used to create a multilevel output voltage waveform with three levels. A modified modulation scheme is used to improve the waveform quality of this dual inverter. This paper also compares the losses in the dual-inverter system in contrast with a single-sided three-level neutral point clamped converter. Finally, detailed simulation and experimental results are presented for the motor drive operating as an open-loop v /f controlled motor drive and as a closed-loop field-oriented motor controller. [ABSTRACT FROM PUBLISHER]

Future transportation challenges include a considerable reduction in pollutant emissions at a time when significant increase in demand is predicted. One of the enabling solutions is the electrification of transport systems as this should lead to improved operability, fuel savings, emission reduction, and maintenance. While state-of-the-art technology has demonstrable benefits there needs to be considerable advancement to meet future transportation affordability and emission targets. Primarily, electrical drives need an improved power density, an increased reliability, and a reduced specific cost. For this reason, integrated modular motor drives (IMMDs) present an attractive solution. Modularity leads to redundancy and easier integration. This paper presents a novel speed-drooped control system applied to motors fed by modular paralleled converters. This control technique allows precise speed regulation and power sharing among different segments showing improved fault tolerance and reliability. The design procedure and the power sharing dynamic have been presented and analyzed by means of MATLAB/Simulink and validated in a 3-kW experimental rig, showing good agreement with the expected performances. [ABSTRACT FROM PUBLISHER]

In this paper, a novel magnetically levitated coreless planar motor with three-layer orthogonal overlapping windings is shown to have higher power density and higher space utilization compared with other coreless planar motors. In order to achieve maximum forces with minimum cost and minimum space, a multiobjective optimization of the novel planar motor is carried out. In order to reduce the computational resources required for finite-element (FE) analyses, a fast but accurate analytical tool is developed, based on expressions of the flux density of the permanent-magnet array, which are derived from the scalar magnetic potential method. The validity and accuracy is verified by 3-D FE results. Based on the force formulas and the multiobjective function derived from the analytical models, a particle swarm optimization (PSO) algorithm is applied to optimize the dimensions of the planar motor. The design and optimization of the planar motor is validated with experimental results, measured on a built prototype, thus proving the validity of the analytical tools. [ABSTRACT FROM PUBLISHER]

This paper investigates the influence of the slot/pole (S/P) combination on inter-turn short-circuit (SC) current in fault-tolerant permanent magnet (FT-PM) machines. A 2-D sub-domain field computational model with multi-objective genetic algorithm is used for the design and performance prediction of the considered FT-PM machines. The electromagnetic losses of machines, including iron, magnet, and winding losses are systematically computed using analytical tools. During the postprocessing stage, a 1-D analysis is employed for turn–turn fault analysis. The method calculates self- and mutual inductances of both the faulty and healthy turns under an SC fault condition with respect to the fault locations, and thus SC fault current, considering its location. Eight FT-PM machines with different S/P combinations are analyzed. Both the performance of the machine during normal operation and induced currents during a turn–turn SC fault are investigated. To evaluate the thermal impact of each S/P combination under an inter-turn fault condition, a thermal analysis is performed using finite element computation. It is shown that low-rotor-pole-number machines have a better fault tolerance capability, while high-rotor-pole-number machines are lighter and provide higher efficiency. Results show that the influence of the S/P selection on inter-turn fault SC current needs to be considered during the design process to balance the efficiency and power density against fault-tolerant criteria of the application at hand. [ABSTRACT FROM AUTHOR]

In this paper, the design and development of a double-sided air-cored tubular generator (DSTG) is presented. The characteristics of air-cored slot-less structures are investigated in terms of power density and efficiency. This is highly desirable for small- and medium-sized renewable energy conversion systems. In this paper, an analytical tool based on the magnetic vector potential method is built in order to achieve a fast but accurate method by which the machine is analyzed. The analytical model is validated by finite-element (FE) analysis. Further design improvements based on the analytical and FE models are then suggested in order to enhance the performance of the DSTG. The final design of the DSTG is validated by the test results from a developed prototype of the DSTG. [ABSTRACT FROM AUTHOR]

This paper proposes a novel permanent magnet planar motor with moving multilayer orthogonal overlapping windings. This novel motor topology can achieve a five-degrees-of-freedom drive using two sets of $x$ -direction windings and two sets of $y$ -direction windings in a coreless configuration. The orthogonal multilayer construction guarantees a high utilization of the magnetic field and realizes decoupling between the $x$ -direction thrust and the $y$ -direction thrust. The topology and operating principle of the planar motor are introduced in this paper. The analytical modeling of the motor is established based on the equivalent current method, and the expressions of forces are derived. The force characteristics of the two-layer and three-layer winding topologies are compared, and the design guidelines of a planar motor are proposed. The analytical and 3-D finite-element model results are validated with the experimental results of a tested prototype. [ABSTRACT FROM AUTHOR]

This paper introduces a comparative study on the design of aerospace actuators concerning induction motor and permanent-magnet motor technologies. In the analysis undertaken, the two candidate configurations are evaluated in terms of both their electromagnetic and thermal behaviors in a combined manner. On a first step, the basic dimensioning of the actuators and their fundamental operational characteristics are determined via a time-stepping finite-element analysis. The consideration of the thermal robustness of the proposed motor configurations is integrated in the design procedure through the appropriate handling of their respective constraints. As a result, all comparisons are carried out on a common thermal evacuation basis. On a second step, a single objective optimization procedure is employed, considering several performance and efficiency indexes using appropriate weights. Manufacturing and construction-related costs for both investigated topologies are considered by employing specific penalty functions. The impact of the utilized materials is also examined. The resultant motor designs have been validated through manufactured prototypes, illustrating their suitability for aerospace actuation. [ABSTRACT FROM PUBLISHER]

This paper details the design considerations of a permanent-magnet three-phase synchronous machine for fault-tolerant operation. A multidisciplinary approach to the optimal design of the machine is adopted, targeted at minimizing the additional losses resulting from faulty operating conditions and accounting for the remedial control strategy implemented. The design of a closed-slot six-slot four-pole machine is presented. The machine is prototyped and tested to validate the analytical–computational performances predicted in the design and analysis stage under healthy and faulty conditions. [ABSTRACT FROM AUTHOR]

A novel fault-tolerant flux-switching permanent-magnet synchronous machine drive topology is presented, which is able to operate during open- and short-circuit winding and converter faults. The scheme is based on a dual winding motor supplied from two separate vector-controlled voltage-sourced inverter drives. The windings are arranged in a way so as to form two independent and isolated sets. Simulation and experimental work will detail the drive's performance during both healthy and faulty scenarios including short-circuit faults and will show the drive robustness to operate in these conditions. [ABSTRACT FROM PUBLISHER]

This paper describes an analytical model to evaluate the short-circuit (SC) current resulting from an interturn fault by computing the self and mutual inductances under SC fault condition. Two different concentrated winding configurations, i.e., horizontally and vertically placed conductors in the slot of a fault-tolerant permanent magnet synchronous machine are considered. By computing the associated slot-leakage and air-gap fluxes, the self inductance of both healthy and faulty windings as well as the mutual inductance between them, the SC current can be determined for any position and number of shorted turns. The proposed model is verified with finite-element analysis and validated experimentally. It will be shown that the magnitude of an interturn SC current depends on both the number of shorted turns and their position in the slot. The measured SC inductance shows that a new proposed concentrated vertical winding configuration can inherently limit the SC current and reduce its dependence on the position within the slot. [ABSTRACT FROM PUBLISHER]