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This article investigates the accuracy of the estimation of efficiency maps for permanent magnet (PM) machines using the stator resistance, d - and q -axis flux-linkages versus the corresponding axis current and the iron loss versus the speed characteristic. The ultimate goal is to apply this approach to the experimental measurements, but this article performs initial investigation using only the finite-element (FE) data. Detailed FE data for 50-kW surface PM (SPM) and interior PM (IPM) machines are used to determine the “actual” or exact efficiency map and, hence, the accuracy of using approximations. This article examines the effect on the torque–speed capability curve when ignoring cross-saturation effects. It also examines the modeling of the variation of iron losses as a function of load in the constant torque and power regions. A novel approach based on scaling the no-load (NL) losses as a function of load is proposed and shown to give promising results. FE results from two other machines are also provided, which show good correspondence. Refereed/Peer-reviewed

This paper presents a class of high step-up impedance source inverters. The proposed topologies utilize an optimized coupled transformer with unique structure to reach high voltage boost capability with small turns ratio. In other words, high voltage boost ability is gained by decreasing the turns ratio to 1 which leads to lower cost and volume. The absorbing circuits are exploited to clamp dc-link voltage to reduce the effect of the leakage inductance. So, huge spikes across the inverter bridge are removed effectively. Input inductor and input dc-source are connected in series. It results in continuous input current with low start-up inrush current which is appropriate for renewable energy sources such as fuel cell and photovoltaic (PV). In addition, high output voltage is obtained with small shoot-through (ST) duty ratio and high modulation ratio which causes semiconductor voltage stress reduction and better quality of the output voltage. The simulation results confirm the operation of the introduced inverters. The paper also extracts the mathematical equations of the proposed inverter Refereed/Peer-reviewed

This paper presents the design process, detailed analysis, and a comparative study on the advantages of axial-flux induction machines (AFIM). A radial-flux induction machine (RFIM) is also studied as benchmark motor. Both motors are designed with six poles, 36 stator slots, and 32 rotor bars. Finite-element analysis is used to predict the performance of the two motors under both transient and steady state conditions. A complete comparative study along with the simulation results are reported. It is found that the studied AFIM has higher efficiency and power density. Refereed/Peer-reviewed

This paper presents an improved analytical model for axial-flux induction motors (AFIMs) based on solving the magnetic vector potential equations. The advantage of the proposed approach is its fast simulation time (fractions of a second against minutes/hours in FEA) while maintaining over 95 % accuracy compared to FEA that makes it suitable for an optimization purpose. This method applies a uniform distribution of the current density in the rectangular shaped rotor/stator slots. The equivalent circuit parameters of the studied AFIMs are extracted using the magnetic energy analysis. The proposed model allows the saturation effect in calculation of the motor performance parameters (power factor and efficiency). The accuracy of analytical model is validated using FEA results. A comprehensive design optimization is presented to show its capability for an optimization purpose. The objective functions in this study are maximum efficiency, maximum power factor, maximum efficiency times power factor, minimum mass, minimum price, maximum efficiency over slip, and maximum power factor over slip. The proposed analytical model can be easily used for AFIMs with different number of poles and phases. Refereed/Peer-reviewed

Refereed/Peer-reviewed Subdomain technique is a computationally efficient approach with an acceptable accuracy for performance evaluation of the electric machines. This paper develops the subdomain model of three types of permanent magnet (PM) machines including surface-mounted PM (SPM), Inset PM, and consequent pole PM (CPPM) machines. The performance parameters of the studied machines are extracted via subdomain technique and validated by 2D finite-element analysis (FEA). The airgap flux density is calculated using the vector potentials obtained from the subdomain model. The flux density of the iron parts, that is required to find the core losses, are found using the magnetic vector potentials in the iron parts. The developed model is then employed for optimal design of various wind generators. The optimization is executed through two different scenarios. Firstly, the machines are optimized for maximization of the generator efficiency for a single operating point. In the second scenario, the optimization is done over annual wind regime of an area to maximize the annual energy efficiency. The airgap length, magnet dimensions, stack length, and the rotor and stator diameters are the variables of the optimization problem. The optimal designs are compared to show the advantageous and disadvantageous of the considered machines for the wind generator application.

This paper presents an explicit comparison of the three-phase line-start permanent-magnet synchronous (LSPM) motor with the squirrel-cage induction motor (IM). It investigates the effect of number of rotor bars on the performance of the motors by considering two alternative options including 32 and 45 rotor bars. Finite-element analysis is utilized for design and performance prediction of the studied motors. Both steady-state and dynamic responses of the motors under no-load, constant load, fan load, and step load are investigated. The simulation results confirm that the LSPM motor with 32 rotor bars can remain stable at constant speed when operating in overloaded and variable voltage conditions. The LSPM motor has advantages of high efficiency and high power factor while IM has superior dynamic performance Refereed/Peer-reviewed

Refereed/Peer-reviewed This paper presents the comparative study of two induction machines (IMs). It investigates the conversion of an existing three-phase IM to five-phase IMs and explores the effect of phase number on the performance parameters. The two studied machines in this work have the same number of winding turns per phase and similar rotor but modified stator.2D finite-element analysis and MATLAB are used to extract the performance parameters of the machine. The performance comparison of the machines consists of inductance, resistance, current, torque, power factor, and efficiency. It is found that the five-phase IM is more efficient than three-phase IM considering the same physical characteristics. This study aims to provide useful understanding on the effect of the number of phases on performance of IMs.

Robustness, low cost and high torque density are the main characteristics of switched reluctance machines (SRM) that have made them promising for a variety of applications. In this paper a small diameter, long stack length (small aspect ratio) 6kW SRM is designed. In the first step, the dimensions of the studied SRM are derived based on conventional sizing equations. The significance of the rotor and stator pole arcs and also the effective torque zone as a constraint of the design are discussed. A finite-element study is carried out to validate the analytical model of the proposed SRM. The performance of the machine is comprehensively studied in different operating speeds. Simulation results demonstrate the capability of the machine for operation over a wide speed range.pa Refereed/Peer-reviewed

This paper presents the design and analysis of a novel axial-flux synchronous reluctance motor (AFSynRM). A magnetic equivalent circuit (MEC) model for the proposed axial-flux machine is derived. The feasibility of fabrication is discussed. Finite-element analysis is applied to predict the performance of the proposed motor design. This paper provides a baseline study by comparing the performance of the proposed AFSynRM design with a similar rating radial-flux motor. The motors are designed to have similar volume and both have three rotor barriers. The operating parameters are obtained through static and dynamic FEA. The power, torque, power factor and efficiency of the motors are studied. The saturation and flux distribution in the motor structures are investigated. Refereed/Peer-reviewed

This paper proposes a dual rotor halbach array permanent magnet vernier machine (DRHAVM). Proposed vernier machine demonstrate high power factor with high torque density at low speed which is promising for low speed transportation applications. Proposed permanent magnet vernier machine structure omits necessity of gearbox and directly convert energy to low speed rotation. A comprehensive FEA of proposed DRHAVM including sensitivity analysis, back-EMF, torque density, torque per magnet volume, power factor, core loss, copper loss and efficiency are performed. Additionally, a detailed comparison is conducted between proposed DRHAVM and other types of Vernier machines in the literature. Results display that proposed halbach array vernier machine structure can achieve an appropriate power factor (0.84) and generate higher torque (2850 Nm) at speed rotation of 30 rpm. Refereed/Peer-reviewed

This paper presents a novel dual-stator linear-vernier permanent-magnet (DSLVPM) machine. The proposed machine utilizes consequent-pole permanent magnets (PMs) rather than the adjacent topology of conventional linear-vernier permanent-magnet (LVPM) machines. The proposed structure of DSLPMV is analyzed and compared against the conventional topology of the LVPM machine. 2D finite-element analysis is utilized to evaluate the electromagnetic aspects and performance parameters of the machines at no-load and full-load conditions. To assess the machines with different PM volume usage, indices such as thrust force per magnet volume (FPMV) and back-EMF per magnet volume are introduced. Simulation results display a better performance of the proposed linear vernier machine in comparison with the typical machine due to the optimized usage of magnets in the consequent-pole configuration.

This paper presents an optimisation study of an 8-pole, 3-phase, 1kW line-start permanent magnet synchronous motor (LSPMSM) designed based on a benchmark induction motor (IM). The initial IM (IM0) is designed using a machine sizing technique and then the initial LSPMSM (L0) is designed based on some modifications in the rotor of the IM0. The finite element method (FEM) is employed to analyze the motor’s performance. The initial LSPMSM (L0) operates with higher efficiency and power factor compared with the IM0. L0 efficiency is categorized in the IE4 efficiency standard class while IM0 efficiency is in the IE3 class. Then, IM0 and L0 are individually optimised based on a FEM optimisation technique using genetic algorithm (GA) to improve their transient and steady-state performance through maximizing the starting torque and the efficiency as two optimisation objectives, respectively. The optimised LSPMSM (L1) has better performance in terms of the starting torque (transient representative) and the efficiency (steady state representative) in comparison to other L0. The results indicate that, it is not necessarily true that a LSPMSM designed based on an optimised IM has better performance than a LSPMSM design based on a non-optimised IM (in this case L0). Refereed/Peer-reviewed

A line-start permanent magnet synchronous motor (LSPMSM) is designed based on modifying the rotor of a 4kW commercial induction motor (IM). The designed LSPMSM provides a higher output power, efficiency and power factor as well as lower maximum operating temperature than the IM. Finite-element electromagnetic and thermal analyses are used to compare thermal behavior of the motors and verify the accuracy of the assumed temperature rise. Refereed/Peer-reviewed

This paper presents an analytical method to design an optimum Line-Start Permanent-Magnet Synchronous Motor (LSPMSM). An initial LSPMSM (L0) is designed by combining an induction motor (IM0) and an interior permanent magnet (IPM0) motor. The IM0 and IPM0 are designed analytically from sizing equations. The optimum LSPMSM is developed from IM cage optimization for starting torque and permanent magnet (PM) optimization of the IPM for efficiency. By combining the rotors of the optimised IM and IPM, an optimum hybrid rotor is obtained for the LSPMSM. The optimized motor has better performance in the transient and steady state compared to L0. The proposed optimisation method based on a mathematical model is implemented using a genetic algorithm (GA). An optimization case study is implemented using both the proposed mathematical method and FEM. The optimization results indicate that the optimum design found using the proposed mathematical method is obtained more rapidly and has comparable performance to that found using FEM optimization.

In this paper, the magnetic vector potential (MVP) equations are solved for a 5.5-kW radial-flux induction machine (RFIM) in five subdomains. The proposed modeling technique considers a uniform distribution of the current density in the rectangular slots of both rotor and stator. The RFIM is represented using a 2D model in the cylindrical coordinate system. The magnetic flux distribution in each region which is used to calculate the core losses and the machine inductances for the steady state analysis of the machine. T-equivalent circuit (T-EC) is considered to study the machine performance parameters. The rotor and stator resistances are calculated based on the geometry of the machine. The results demonstrate the accuracy of the model in prediction of the airgap flux density. The comparison of the machine performance parameters with the 2D FEA results demonstrate the reliability of the analytical model in the prediction of the machine behavior at the rated condition. Refereed/Peer-reviewed

Notice of Violation of IEEE Publication Principles "Performance Improvement of a Line-Start Permanent-Magnet Synchronous Motor" by Solmaz Kahourzade, Amin Mahmoudi and Wooi Ping Hew, in the IEEE Transactions on Industrial Electronics After careful and considered review of the content of this paper by a duly constituted expert committee, this paper has been found to be in violation of IEEE's Publication Principles. This paper was submitted with significant similarity to ideas and applications presented in the thesis listed below. The paper includes a reference to the thesis, but there was no clear delineation between their work and previous work presented in the thesis. Two of the authors, Solmaz Kahourzade and Amin Mahmoudi were found to be responsible for the misconduct. "Line Start Permanent Magnet Motors," by Arash Hassanpour Isfahani, in Ph.D dissertation, Department of Electrical Engineering, Tehran University, Iran, 2011. This paper presents the design and performance analysis of a line-start permanent-magnet synchronous motor to overcome the efficiency and power factor deficiencies of induction motors. Proper start-up and synchronization are considered. An optimization algorithm is applied to improve the rotor bar resistance for the smooth line start of the motor. Dynamic d-q modeling and finite element analysis are performed to predict the transient and steady-state performances of the motor. Based on the presented optimized design, a 3-phase, 4-pole, 2 kW line-start permanent-magnet synchronous motor is fabricated and tested. Simulation and experimental results validate the improved performance of the proposed optimized motor.

This paper examines the performance of a three-phase interior permanent-magnet generator used in a portable ac generator when directly driving isolated single-phase (1-ph) ac loads. The performance of the generator was compared under three alternative connections: 1) 1-ph star; 2) 1-ph delta; and 3) a proposed "open delta" connection. The voltage regulation, total harmonic distortion, and efficiency as three main performance criteria of the portable generators were examined using analytical calculation, finite element simulation, and experimental measurements. Refereed/Peer-reviewed

This paper presents the comparative study of two permanent-magnet synchronous machines (PMSMs). It investigates the design of two different motors with different pole numbers and explores the pole effect on the performance of parameters. Considered machines in this study are 4-pole and 40-pole SPMMs with same magnet volume on the rotor. Using sizing equations, physical dimensions of the motor are identified, and performance parameter of the motor are extracted via 2D finite-element-analysis. The performance comparison of the machines includes the flux distribution across the geometry, airgap flux density, flux linkage, cogging torque, torque, and motor losses. This comparative study aims to serve useful understanding on the effect of the number of poles on performance of PMSMs for electrical vehicle applications. Refereed/Peer-reviewed

Step-up DC-DC converters play a determinative role in traction vehicles by providing the required DC- link voltage for traction drives supplied by battery packages or fuel cells. Bi-directional converters are preferred to be used in the construction of battery-based traction drives to charge batteries when drivetrains system work in the generation mode. However, due to the fact that fuel-cells cannot be charged electrically, the bi-directional structure is not required for fuel cell-based traction drives. The proposed step up converter benefits from the resonance between its elements to provide the soft- switching condition for the converter switches. The resonance assists to transmit high power from input and to output while there is no high-frequency transformer or coupled inductor in the converter topology. In brief, the generated resonance not only leads to a high power density converter but also result in a soft-switching which means higher efficiency in comparison to previously introduced high-step up converters working in hard switching condition. So, the proposed high-efficiency high power density high step-up (HHH) converter could be employed as a reliable DC-DC converter for traction vehicles supplied by fuel cells. Refereed/Peer-reviewed

In this paper, two-dimensional (2D) analytical model is proposed for axial-flux induction motor (AFIMs) based on the solution of magnetic vector potential equations, which also considers the saturation's effect on the performance of the machine. The model is developed from the quasi- magneto-static Maxwell's equations, which are analytically solved. It considers a uniform distribution of current density in the rectangular shaped rotor/stator slots. By computing the magnetic energy of the machine, this method obtains the inductances and uses them to assess the design performance parameters. The accuracy of the 2-D analytical solutions is verified against those obtained from the finite element method (FEM). The suggested model is generic and applicable to AFIMs with any number of poles and phases. A case study on optimization axial-flux induction motor is presented to evaluate the performance of the proposed model. The proposed method can replace the FEM in designing and optimization of the AFIMs. Refereed/Peer-reviewed

Amorphous magnetic materials (AMMs) have been used in low-frequency power transformer applications for more than two decades but not commercially utilized in high-frequency rotating electrical machines despite their low iron losses, which is an order of magnitude lower than conventional silicon iron. This was primarily due to the lack of a suitable handling method and an economical cutting technique. This paper reports a novel brushless synchronous permanent magnet rotating electrical machine that combines the benefits of the previous machine topologies while offering higher torque (due to the larger air-gap surface area compared with the flat axial-field machine) and ease of manufacturing from AMM material, which is suitable for a range of high-efficiency, high-power density, and high-speed machine applications. This paper provides the details and the performance characteristics of this novel tapered-field AMM machine as a generator at high speeds using a bonded rotor magnet topology. Refereed/Peer-reviewed

This paper compares the performance of a soft magnetic composite (SMC) surface PM machine with embedded (recessed) stator end-windings with a corresponding conventional laminated stator design with the same overall axial length. Potential advantages include higher power density and stator copper fill factor, and simplified manufacturing, while the disadvantages are associated with the poorer magnetic properties of SMC. The effect of embedding is studied analytically. Then a case study is performed with finite-element analysis comparisons of a prototype SMC design with embedded end-windings against the corresponding laminated design. Refereed/Peer-reviewed

This paper presents research work on a 12-slot ten-pole tapered axial-flux permanent-magnet machine utilizing amorphous magnetic material in the stator core. Novel loss separation techniques are described, including mechanical loss and locked-rotor tests. Mechanical loss estimation is based on a combination of experimental tests and 3-D finite-element model analysis using an uncut stator. The locked-rotor test is introduced to separate the stator and rotor losses by eliminating the uncertainty associated with mechanical loss. High rotor yoke losses were identified in the baseline design. The rotor design was modified and a significant improvement in efficiency was demonstrated. Refereed/Peer-reviewed

This paper investigates the performance of three magnetic materials: silicon iron, soft magnetic composite and amorphous magnetic material, as the stator of an axial-flux permanent-magnet machine. Three stators, one of each material, are built and tested with the same rotor. The losses of each of the machines are separated using a combination of 3D finite-element analysis and experimental testing under open-circuit and loaded conditions. Refereed/Peer-reviewed

This paper presents two design-and-analysis cases of a line-start axial-flux permanent-magnet motor: with solid rotor and with composite rotor. For a novel structure of the motor, two concentric unilevel spaced raised rings are added to the inner and outer radii of its rotors to enable auto-start capability. The composite rotor was coated by a thin (0.05 mm) layer of copper. The basic equations for the solid rotor ring were extracted. The motor's lack of symmetry necessitated 3D time-stepping finite element analysis, conducted via Vector Field Opera 14.0, which evaluated the design parameters and predicted the motor's transient performance. Results of the FEA show the composite rotor significantly improving both starting torque and synchronization capability over solid rotor. Refereed/Peer-reviewed

This paper presents the design process, detailed analysis, and prototyping of a novel-structured line-start solid-rotor-based axial-flux permanent-magnet (AFPM) motor capable of autostarting with solid-rotor rings. The preliminary design is a slotless double-sided AFPM motor with four poles for high torque density and stable operation. Two concentric unilevel-spaced raised rings are added to the inner and outer radii of the rotor discs for smooth line-start of the motor. The design allows the motor to operate at both starting and synchronous speeds. The basic equations for the solid rings of the rotor of the proposed AFPM motor are discussed. Nonsymmetry of the designed motor led to its 3-D time-stepping finite-element analysis (FEA) via Vector Field Opera 14.0, which evaluates the design parameters and predicts the transient performance. To verify the design, a prototype 1-hp four-pole three-phase line-start AFPM synchronous motor is built and is used to test the performance in real time. There is a good agreement between experimental and FEA-based computed results. It is found that the prototype motor maintains high starting torque and good synchronization. Refereed/Peer-reviewed

This paper presents the design and performance analysis of a line-start permanent-magnet synchronous-motor (LSPMSM) to overcome the efficiency and power factor deficiencies of induction motors. Proper start-up and synchronization are obtained through the design. An optimization algorithm is applied to improve the rotor bar resistance for the smooth line start of the motor. Dynamic d-q modeling and finite element analysis (FEA) are performed to predict the transient and steady state performance of the motor. Refereed/Peer-reviewed

This paper presents the design process of a novel axial-flux permanent-magnet (AFPM) motor capable of auto-starting. The preliminary design is a slot-less double-sided solid-rotor line-start AFPM motor with 4 poles for high torque density and stable rotation. One spaced raised ring was added to the inner radii of the rotor disc for smooth line-start motor. The design allows the motor to operate at both starting and synchronous speeds. The basic equations for the solid ring of the rotor for the proposed axial-flux permanent-magnet motor are presented. Non-symmetry of the designed motor led to its 3D time-stepping finite element analysis (FEA), which is used to evaluate the design parameters and predict the transient performance. The designed motor was fabricated and tested; sample experimental result showed good agreement with those of FEA based simulated results. The prototype motor showed excellent characteristics (high starting torque, good synchronization), and excellent steady-state performance. Refereed/Peer-reviewed

This study presents the design, analysis and prototyping of a low-cost monopole machine capable of battery charging. The designed monopole machine encompasses a rotor disc including eight permanent magnets with the same magnetising direction and a stator consists of a magnetic core and three windings: power coil winding, trigger coil winding and recovery coil winding. This machine includes an electronic circuit as a trigger and a magnetic circuit that converts electrical energy to mechanical energy and vice versa. The machine captures energy in the form of back-electromagnetic force generated by a collapsing field in the stator and rotor to avoid wasting energy and stores it in a battery. To simulate the machine, electromagnetic and electrical analyses were conducted simultaneously to predict the design parameters and machine performance: three-dimensional finite element analysis via Vector Field Opera, and MATLAB/Simulink. To validate the simulation results accuracy, the machine was fabricated and tested. Experimental data were compared with simulation results, and showed good agreement with that of simulation. Refereed/Peer-reviewed

In high-voltage capacitor bushings, there is maximum field intensity at the edge of the aluminum foil and where foils overlap. Any technique decreasing much field intensity in those regions will significantly optimize the bushings’ electrostatic characteristics. This paper presents the study of the effect of edge diversion in the overlapped region of an aluminum foil and of the shape of aluminum foil edge in improving the maximum field intensity of the overlapped region. Electrostatic analysis was used to minimize the field intensity. 2D and 3D simulations and analyses were run, respectively via finite element method magnetic (FEMM) and Vector Field Opera. Techniques improving field intensity distribution of capacitor bushing are presented. Results show that foils that are not folded and have the inner edge placed lower than the outer edge better distribute the field around the edges. Key words: Capacitor bushing, cavities, electric field, electrostatic simulation, finite element analysis.

This paper presents the design, analysis, and prototyping of a novel axial-flux permanent-magnet (AFPM) motor capable of auto-starting. The preliminary design is a slot-less double-sided solid-rotor line-start AFPM motor with 4 poles for high torque density and stable rotation. One spaced raised ring was added to the inner radii of the rotor disc for smooth line-start motor. The design allows the motor to operate at both starting and synchronous speeds. The basic equations for the solid ring of the rotor of the proposed axial-flux permanent-magnet motor are presented. Non-symmetry of the designed motor led to its 3D time-stepping finite element analysis (FEA) via ANSYS 13.0, which evaluated the design parameters and predicted the transient performance. The designed motor was fabricated and tested, the experimental results showing good agreement with FEA simulation results. The prototype motor showed high starting torque and good synchronization. Refereed/Peer-reviewed

This paper presents an online trained fuzzy logic and adaptive wavelet based high precision fault detection of broken rotor bars for squirrel cage induction motor (IM). Motor faults which consist of broken rotor bars, bearing decay, eccentricity, etc. appears as different frequencies in the stator current signals. The winding function is used to obtain stator current and speed signals at different fault and load conditions. These signals are analysed through the adaptive continuous wavelet transform (CWT) to detect the amplitudes and frequency components corresponding to different fault and load conditions. The coefficients of CWT are adapted online based on the harmonics amplitude, which are the output of CWT. These amplitudes and frequencies are applied to train a fuzzy logic controller (FLC) in simulation. Then the adaptive CWT and trained FLC are applied to detect the fault condition of a large size motor in both simulation and realtime. The experimental results found that the proposed adaptive CWT and FLC based fault detection method can detect the motor fault conditions accurately. Thus, the proposed method could be a potential candidate to detect the motor fault, especially for large size industrial motors Refereed/Peer-reviewed

Low impedance restricted earth fault protection is one of the protection functions to protect the transformer winding with earthed star point. This paper presents a critical comparison of restricted earth fault between General Electric algorithm and Siemens Algorithm. Advantages and disadvantages of selected algorithms are investigated based on speed, sensitivity and security. The relay operation characteristic curves and restraint currents for each of algorithms are simulated by MATLAB SIMULINK. Refereed/Peer-reviewed

For portable ac electric generator sets, it is desired to maintain a constant output voltage under load. With wound-field synchronous generators, this is done using field current (excitation) control. This type of control is not possible with permanent magnet (PM) machines; however, theoretical analysis is used to show that acceptable output voltage regulation can be obtained by two alternative design approaches for interior PM machines. The design of an example 4-pole 16-kW machine is described, and experimental results are provided, demonstrating its sinusoidal output waveform, high voltage regulation, and high efficiency. Refereed/Peer-reviewed