Search

Techniques used for breast cancer detection usually incorporate Infrared Thermography (IRT) to locate abnormal hotspots or asymmetry in a thermal texture map. This can be unreliable due to various individual differences from one person to another. In this paper, a detection method that is independent of the aforementioned limitations is proposed. This technique is a combination of thermal imaging and high-frequency excitation. This technique is based on the fact that the differences in electromagnetic and thermal properties of abnormal (malignant) tissue and the surrounding normal tissue will result in a noticeable difference in temperature increase after exposure to high-frequency excitation. A three-dimensional (3-D) finite-element method (FEM) has been used to simulate the thermal behavior of breast tissue exposed to antenna excitations. Finally, the effectiveness of this technique was tested in a series of experiments using a life-sized breast phantom. [ABSTRACT FROM AUTHOR]

This paper presents a power distribution system that prioritizes the reliability of power to critical loads within a community. The proposed system utilizes reinforcement learning methods (Q-learning) to train multi-port power electronic interface (MPEI) systems within a community of microgrids. The primary contributions of this article are to present a system where Q-learning is successfully integrated with MPEI to reduce the impact of power contingencies on critical loads and to explore the effectiveness of the subsequent system. The feasibility of the proposed method has been proven through simulation and experiments. It has been demonstrated that the proposed method can effectively improve the reliability of the local power system—for a case study where 20% of the total loads are classified as critical loads, the system average interruption duration index (SAIDI) has been improved by 75% compared to traditional microgrids with no load schedule. [ABSTRACT FROM AUTHOR]

This article presents an efficiency optimization of double-sided LCC compensation network for inductive power transfer systems. Compensation factors of the primary and secondary LCC circuit are defined and optimized analytically. The investigation shows that the secondary compensation factor $k_{rx}$ highly influences the copper loss of the wireless coupler, whereas the primary compensation factor $k_{tx}$ should not be large in order to reduce the switching loss and conduction loss of the input inverter. With a proper selection of these compensation factors, it is possible to achieve a high and sustained efficiency over a wide range of load and misalignment. In order to demonstrate the feasibility and validity of the proposed method, a scaled-down prototype has been implemented with the operating frequency of 85 kHz, transfer gap of 170 mm, and misalignment of up to 100 mm. Experimental results show a good agreement with the theoretical analysis. The peak efficiency of the proposed system is 91.6% under the perfect alignment at the coupling coefficient of 0.172. The efficiency still remains at 86.37% even under 100-mm misalignment with the coupling coefficient of 0.123. [ABSTRACT FROM AUTHOR]

Traditional analysis and design of induction machines have been largely based upon lumped-parameter models. An alternative tool used for field-based evaluations of an induction machine is the finite-element method. Although useful, its computational complexity limits its use as a design tool. In this paper, a field reconstruction (FR) method for induction machine simulation is introduced. The FR method utilizes a small number of finite-element evaluations to establish basis functions of normal and tangential flux densities. The basis functions are then used to estimate the magnetic field under arbitrary stator excitation. Using such a tool, evaluation of fields and forces produced by a machine under alternative excitation strategies can be explored efficiently. Moreover, alternative field-based derivation of stator/rotor excitation control can be explored. Index Terms--Field reconstruction (FR), finite element (FE), induction machine, Maxwell stress tensor, torque and radial force.

Traditional analysis of permanent magnet synchronous machines has focused upon establishing a relationship between the quadrature (q) and direct (d) axis stator current (or voltage) and the electromagnetic force created to establish rotation (torque). In this paper, an alternative analysis of electromagnetic force production is considered. Specifically, the influences of q- and d-axis stator current on both the radial and tangential components of the airgap flux densities are first evaluated. Using a Maxwell stress tensor approach, the fields are then used to evaluate both the radial and tangential component of force density created in the airgap of the machine. From this perspective several interesting observations are made. First, it is shown that the d-axis current has zero influence on the average tangential force (torque), as predicted using traditional analysis, but it has a significant influence on the average radial component of force. Second, it is shown that the q-axis current contributes to both the average radial and average tangential components of force. Interestingly, it is also shown that under standard operating conditions, the average radial force far exceeds that of the average tangential component of force. Therefore, one can conclude that the magnetic fields established create a significant component of force in a direction that cannot produce torque. Index Terms--Force density, maxwell stress tensor, permanent magnet synchronous motor (PMSM), torque generation.

Development of a precise dynamic model is a critical step in design and analysis of optimal control strategies for switched-reluctance machines (SRM). This paper is focused on important issues concerning the development of such models and their subsequent use in designing control strategies for SRM drives. The main goal in modeling is to provide a good accuracy over the entire speed and torque range. To achieve this objective, the following requirements need to be met: 1) a good accuracy in matching the inductance of each stator phase; 2) inclusion of mutual effects when significant overlap among phases exists; 3) inclusion of short flux-path operation in each electrical cycle when significant overlap among adjacent phases exists; and 4) capability for autocalibration to cope with parameter variations incurred by manufacturing imperfections and operational conditions. In this paper, in addition to an in-depth discussion of the above factors, a practical modeling approach along with an autocalibration strategy is presented. A simple test collects the necessary data in developing the proposed model. Inherent separation among mechanical, electrical, and control time constants has been used to develop the autocalibration process. Experimental results are presented to validate the proposed method. Index Terms--Long flux path, mutual inductance, self-inductance, short flux path, switched reluctance machines (SRMs).

Vibration caused by torque ripple and radial force harmonics is a concern in many applications of permanent magnet synchronous machines (PMSMs). Alternative methods of machine design and/or stator excitation to minimize torque ripple have received considerable attention in recent years. Comparatively, methods to minimize radial force harmonics have received less attention. In this paper, a field reconstruction (FR) method is derived that provides a designer with the capability to rapidly determine the radial and tangential components of force under arbitrary stator excitation. Using the field reconstruction method, stator current waveforms that minimize the ripple of both torque and radial force are derived subject to the constraint of maintaining a satisfactory level of torque density. Index Terms--Finite element analysis (FEA), force density, permanent magnet machine, torque ripple.

Fault tolerance is a critical attribute in automotive electrical and propulsion systems. In this paper, a control scheme is presented that allows an induction motor drive system to operate in the event of multiple sensor failures. Automatic diagnosis of sensor fault and recovery is performed and used to reconfigure the drive system controls to achieve the best performance in lieu of component degradation. This approach couples a new digital delta-hysteresis regulation scheme with a model reference adaptive system scheme in order to provide fault tolerance for both phase-current and rotor position (speed) sensors. Simulation and experimental results are provided to show the effectiveness of the proposed scheme. Index Terms--Current regulation, induction drives, model reference adaptive system (MRAS) speed identification, sensor fault diagnosis, sensor fault tolerance.

Switched reluctance machines (SRM) offer attractive attributes for automotive applications. These include robustness to harsh operational conditions, rugged structure, fault resilient performance, and a wide range of speed. The main debate over the adequacy of switched reluctance drives in automotive applications has often focused on efficiency and position sensorless control over the entire speed range, adaptation of control algorithms in the presence of parameter variations, and high levels of acoustic noise and vibration. The present paper demonstrates three key technologies developed over the past few years that have resulted in tangible improvements in the performance of SRM/generators (SRM/G) as related to the above areas of interest. This paper intends to illustrate the new possibilities and remaining challenges in applications of SRM in automotive industry. The proposed technologies have been validated by simulation and experimental results. Index Terms--Acoustic noice, switched reluctance machines (SRM), vibration.

Development of a reliable, smooth, and precise position sensorless startup routine is an integral part of the switched reluctance machine (SRM) control. The proposed sensorless startup method presented in this paper presents high grade performance and does not require additional hardware or memory. Further, the proposed sensorless technique is extended to rotating shaft conditions. These capabilities are highly demanded by automotive applications such as starter/alternator and electric power steering systems. An assessment of the impact of motor parameters and diagnostic signal measurement on the quality of the sensorless startup method is also included. This will help practicing engineers to make judicious selections for implementation of the proposed technique. Experimental and theoretical results are included to validate our claims. Index Terms--Diagnostic signal measurement, switched reluctance machine (SRM).

This paper presents the results of an investigation of components of the electromagnetic force in the air gap of an 8/6 switched reluctance machine (SRM). Using a Maxwell stress method, variations of radial and tangential force components due to saliency of the machine and saturation have been studied. Access to distribution of the force components acting on the rotor and stator enables us to provide a more accurate picture of the torque generation and vibration in this family of electric machines. Furthermore, distribution of magnetic forces under multiphase excitation has been studied in detail. Our findings show that bipolar excitation of SRM phases, resulting in a short flux path magnetic circuit, favors its efficiency and power quality while generating higher torque with less pulsation. This is a significant improvement, particularly for automotive applications where the difference in the required number of power electronics components can be justified. An experimental 2-kW 42-V 8/6 SRM drive which has been designed and manufactured in our energy system laboratory was targeted for this study. In addition to our extensive finite-element analysis, experimental results have been provided to prove theoretical claims. Index Terms--Bipolar, normal force, switched reluctance machine (SRM), tangential force.

Current vehicle architectures utilize belt driven components such as the coolant pump, air-conditioner, power steering pump, etc. However, the trend toward more electric vehicles requires electromechanical energy conversion devices to replace these inefficient mechanical components. It is essential that electrical machines used in automotive applications to be compatible with the corresponding mechanical and electrical terminals. Furthermore, replacement of belt driven components with electrical drives should be performed as efficient and cost effective as possible. Bipolar switched reluctance machines (SRM) are both cost effective and very robust to the effects of temperature variation. They also offer a very wide speed range and an excellent mechanical integrity, which optimally suits a range of automotive applications including electric propulsion. This paper presents a detailed investigation of the performance indices for bipolar SRM drives. Using a Maxwell stress method, variations of radial and tangential force components due to saliency of the machine and saturation have been studied. Access to distribution of the force components acting on the rotor and stator enables us to provide a more accurate picture of the torque generation and vibration in this family of electric machines. Furthermore, distribution of magnetic forces under multiphase excitation has been studied in detail. Our findings show that bipolar excitation of SRM phases, resulting in a short flux path magnetic circuit, favors its efficiency and power quality while generating higher torque with less pulsation. This is a significant improvement, particularly for automotive applications where the difference in the required number of power electronics components can be justified. An experimental, 2-kW, 42-V, 8/6 SRM drive which has been designed and manufactured in our energy system laboratory was targeted for this study. In addition to our extensive finite-element (FE) analysis, experimental results have been provided to prove theoretical claims. Index Terms--Bipolar, normal force, switched reluctance machines (SRM), tangential force.

Proper synchronization of the excitation with respect to the rotor position is essential in optimal control of switched reluctance motor (SRM) drives. To avoid additional cost, size, and unreliability caused by the external position sensors, magnetic status of the SRM can be directly monitored to detect commutation instants. A one-to-one correspondence between magnetic status of the SRM and rotor position removes the need for an explicit access to the rotor position. In order to obtain a good precision over the entire speed range, educated modifications on the structure of the sensorless strategy is necessary. This is due to the impact of the operational regions on dynamic behavior of the SRM. In addition, introduction of SRM technology to industrial and domestic applications has raised the need for four-quadrant operation of the SRM drives. The present paper introduces a range of strategies that are necessary to accommodate this requirement in a sensorless format. Our experimental findings indicate that high-grade sensorless operation in a four-quadrant SRM drive is possible and can be integrated in a variety of applications. Index Terms--Rotor position, switched reluctance motor (SRM) drives.

This paper presents a novel analytical model for a switched-reluctance machine (SRM) based on decomposition of its inherent double joint magnetic saliencies due to rotor and stator salient poles and saturation of magnetic field at high stator currents. With this method, the magnetic characteristics of the motor, such as flux linkage and incremental inductance, are decomposed to vector functions of rotor position and phase current. Dynamic state and torque equations for the SRM are derived on the basis of this representation. The proposed model is appropriate for online identification and for sensorless position control algorithms. It is easy to implement and computationally efficient. Comparison of the predicted motor magnetic characteristics to machine data from finite-element analysis verifies the accuracy of the model. Index Terms--Flux linkage, incremental inductance, magnetic saliency, model identification.

This paper covers the range of topics related to sensorless control of switched reluctance motor (SRM) drives from their fundamentals to their limitations and state of the art and future trends. This should help the reader to develop a systematic understanding of the sensorless techniques that have been developed over the past two decades. The inherent vulnerability to mechanical failures, extra cost, and size associated with external position sensors such as optical encoders, resolvers, and custom-designed Hall-effect sensors has motivated many researchers to develop sensorless control techniques for SRM drives. Ideally, it is desirable to have a sensorless scheme, which uses only terminal measurements and does not require additional hardware or memory while maintaining a reliable operation over the entire speed and torque range with high resolution and accuracy. Recent advances in the development of low-cost digital-signal-processor-based microcontrollers have paved the way for the fulfillment of this objective. It is, furthermore, our view that the existing trends in the development of more powerful processors will ultimately replace the concept of sensorless controls with the concept of eliminating the need for position sensing, a concept that will further revolutionize the motor drive technology. Index Terms--Adjustable-speed motor drives, motor controls, motor drives, reluctance motors, sensorless controls, switched reluctance motors, variable reluctance motors.

A bidirectional hybrid switched inductor converter (BHSI) is proposed in this paper. The converter uses an inductor switching cell in order to achieve a wide voltage conversion range, smaller passive components, and lower stress on the active devices. Apart from these advantages, the introduction of the additional inductor in the switching cell does not increase the complexity of the control structure, as is usually the case with other topologies with multiple components. The BHSI is compared, in terms of inductor/capacitor energies and total device stress, to other state‐of‐the‐art topologies and its advantages are highlighted. Two 3 kW prototypes were built, using Si‐MOSFETs and GaN‐FETs, in order to analyse their performances from the efficiency point of view, and to validate the theoretical findings. The stability analysis of the converter is performed and tested in a supercapacitor storage application, resulting in a good operation in both charge and discharge modes. [ABSTRACT FROM AUTHOR]

In this article, a simplified 3D magneto-thermal model to study the temperature distribution over the housing of a Switched Reluctance Machine (SRM) is proposed. The main objective of such model is to study the temperature distribution profile on the body of the machine under various working conditions in order to introduce a temperature based signature to develop condition monitoring procedures. The analysis of fluid flow and heat transfer inside the SRM supports the hypothesis that the effect of turbulent flow of the fluid and the complex heat transfer phenomenon of the rotating parts can be simplified to a heat flux boundary condition representation of the heat loss. The accuracy of the model is validated through simulation and experimental results on a prototype SRM. The developed simplified model can be used as for prediction of temperature profile on SRM surface, well suited for fault diagnosis in SRM. The proposed methodology can be modified applied in developing a thermal model for other types of electric machines. [ABSTRACT FROM AUTHOR]

Adjustable speed motor drives are among the most representative types of non-linear systems which can exhibit rich varieties of complex dynamic behaviours. This study presents the investigation of chaotic phenomena in the switched reluctance (SR) motor drive employing digital speed regulator and hysteresis current controller. For conducting stability analysis, a small signal discrete-time model of the SR drive has been derived and analysed for a range of control parameters. The simulation results of time-domain and frequency-domain analysis and phase portraits of the SR drive system are also demonstrated and discussed. Two influencing factors for chaotic behaviour in the SR drive system are identified and examined in detail: the feedback delay of the speed regulator and measurement imperfection from a rotary incremental encoder. For verification, an 8/6 pole 2.3 kW SR drive is employed in experimental tests. The bifurcation diagrams of the reference signal, waveforms of phase current, and the corresponding frequency spectra are recorded and illustrated for both normal and chaotic operations, which reveal the pattern of chaos exhibited from this type of electric drive system. [ABSTRACT FROM AUTHOR]

Recently, LLC resonant converters have attracted significant research from industry and academia for AC-DC and DC-DC power conversion with high efficiency and remarkable power density. They are appealing candidates for numerous vehicular and renewable energy applications including battery chargers for electric vehicles and drivers of LED lights. This study introduces a mathematical model of LLC resonant half-bridge DC-DC converter, which captures its steady-state behaviours for both continuous conduction mode and discontinuous conduction mode operations. One major advantage of the proposed model lies in accurate estimation of the switching frequency of power switches under a wide range of parametric variations. This benefit is, however, not offered by the prevailing method based on the first harmonic approximation (FHA). The analytical derivations of the system's state-space model, as well as equations for calculating the switching frequency by FHA, are discussed in details. For illustration, a 340 W digitally controlled LLC resonant converter is targeted in this study. The simulation analyses of current and voltage waveforms for light and heavy load conditions are presented. Moreover, the experimental results, along with the comparison of switching frequency estimation for both methods, are demonstrated and discussed, which confirms the validity and effectiveness of the proposed model. [ABSTRACT FROM AUTHOR]

With the development of high-temperature wide bandgap power semiconductors, such as SiC MOSFET and GaN HEMT, it becomes possible to integrate the power converter directly into motors. However, the leakage magnetic flux in the motor may cause interference with the operation of the electronic circuit. In this article, the electromagnetic compatibility of the power converter integrated in an induction motor is investigated. The simulation shows that the leakage magnetic flux of the end-winding will penetrate into the nearby area, and it will cause interference with the Hall-effect current sensors if the power converter is mounted in the space between the motor end cap and the end-winding. A prototype of the GaN-HEMT-based power converter is built and integrated into a 3-hp induction motor. The leakage magnetic flux is scanned by the linear Hall-effect sensors and the measured result is aligned with the finite-element simulation. [ABSTRACT FROM AUTHOR]

Vibration and acoustic noise are considered as major factors preventing the widespread use of switched reluctance motor (SRM) drives in industrial and commercial applications. In this paper, a new active vibration cancellation strategy for radial vibration is proposed based on the optimal current switching instants. The mechanical impulse response method has been used to estimate the radial vibration of the stator and an optimization routine was developed to define the optimal instants for phase current switching in such a way that the resulting vibration would cancel the vibration caused by prior switching. Experimental verification was conducted on an 8/6 SRM and the results show significant reduction in the stator radial vibration which in turn contributes to reduction of acoustic noise. [ABSTRACT FROM AUTHOR]

Vibration and acoustic noise in switched reluctance motor (SRM) drives have been investigated and addressed frequently. However, the focus of most the paper is on vibration of the stator frame due to radial electromagnetic forces acting on the stator teeth. In this paper, a comprehensive vibration analysis for a SRM assembly using finite element (FE) method is conducted, which considers the stator and rotor vibrations due to radial electromagnetic force as well as the effect of mechanical coupling on the vibration between the stator and rotor. First, an experimental modal test was performed to extract modal parameters and to observe the coupling effect. The parameters were then used to adjust and validate the FE model that was used to obtain transfer functions for vibration characterization. Using the frequency domain representation of the radial magnetic force vector and the calculated transfer functions, radial and tangential vibration components have been predicted. [ABSTRACT FROM AUTHOR]

Here we present a comprehensive analysis of structural performance of Induction Machine (IM) and Switched Reluctance Machine (SRM) rotors under different operational conditions. Electric machines are susceptible to forces of diverse origins. In addition to traditionally considered magnetic and centrifugal forces, this article discusses independent and inclusive effects of thermal expansion and shaft attachment techniques on structural integrity of the machines. A comparative analysis of structural performance of IMs and SRMs has also been performed, under a range of scenarios, to facilitate application-specific machine selection from a structural perspective. [ABSTRACT FROM AUTHOR]

The performance of lithium-ion batteries is contingent on the operational temperature and applied current rate. Especially in electric vehicle application, repeated heavy-duty drive cycles impose intense thermal stress on batteries, resulting in safety concerns. This paper explains the electrochemistry within the battery and analyzes the dependence of battery internal parameters on temperature and current rate based on their electrochemical nature. In addition, this interdependence is used in the equivalent circuit model to predict the battery behavior under different drive cycles. Finally, the behavior under different drive cycles is analyzed to improve the battery performance in electric vehicles. [ABSTRACT FROM AUTHOR]

In this study, a combined ON/OFF and conformal mapping method is applied to the permanent magnet shape optimisation of the surface-mounted permanent magnet synchronous motor (SPMSM). The magnet shape has a profound impact on the cogging torque and torque profile of the SPMSM. The proposed method is based on the combination of the conformal mapping and ON/OFF methods, which can reduce computation time significantly as compared with methods that are based on the finite-element method (FEM). For the optimisation process, genetic algorithms are used and applied to three cases. Finally, the FEM is used to verify the magnetic model and characteristics of the optimised machine. [ABSTRACT FROM AUTHOR]

Switched reluctance motor (SRM) optimal control parameters, which maximize torque per ampere, are calculated using a dynamic SRM model. In order to include the effect of the magnetic nonlinearity, static torque and flux-linkage data are used in the dynamic model. The static data are generated experimentally. To recreate these control parameters, online, artificial neural networks are used. Two separate networks are trained. One is trained with the low-speed control parameters for torque control at low speed, while the other is trained with the high-speed control parameters for torque control at high speed. The speed at which the SRM makes a transition from chopping control to single-pulse operation (i.e., low-speed to high-speed operation), commonly referred to as base speed, is torque (current) dependent. A small table is maintained in the controller to identify the base speed for different torque demands. When the motor exceeds the base speed for a certain torque demand, the controller switches from the low-speed neural network to the high-speed neural network and vice versa. It is also shown that the SRM is capable of producing an extended constant-horsepower operation with this optimal control. The power factor (the energy ratio) is shown to improve in this extended speed constant-horsepower range. Simulation and experimental results are presented to demonstrate the effectiveness of the proposed control scheme. Index Terms--Electrical drives, neural network control, switched reluctance machine.

Land vehicles need their drivetrain to operate entirely in constant power in order to meet their operational constraints, such as initial acceleration and gradability, with minimum power rating. The internal combustion engine (ICE) is inappropriate for producing this torque--speed profile. Therefore, multiple gear transmission is necessary with the ICE in a vehicle. Some electric machines, if designed and controlled appropriately, are capable of producing an extended constant power range. The purpose of this paper is to investigate the capabilities of the switched reluctance motor (SRM) for electric vehicle and hybrid electric vehicle applications. This investigation will be carried out in two steps. The first step involves the machine design and the finite-element analysis to obtain the static characteristic of the motor. In the second step, the finite-element field solutions are used in the development of a nonlinear model to investigate the dynamic performance of the designed motor. Several 8-6 and 6-4 SRM geometries will be investigated. Effects of different stator and rotor pole widths and pole heights on the steady state as well as on the dynamic performance of the motor will be studied. The air gap for each motor will be made as small as manufacturally possible. The aspects of performance to be compared for each design motor are: 1) the range of the constant power operation; 2) drive efficiency in this extended constant power range; 3) the power factor in this operational range; and 4) the short time overload capability. The first performance index defines the rated power of the motor. The longer the constant power range, the lower is the power rating for the same vehicle performance. Hence, special emphasis will be given to this. In the high-speed operation of the SRM, there will be considerable phase overlapping. Hence, thicker back iron than usual might be needed to prevent the back iron from saturating. However, since flux peaking of each phase occurs at different rotor positions, the phase overlapping might not necessitate special designing of the back iron. However, the possibility of the back iron being saturated will not be neglected and will be investigated. The optimal control parameters of the SRM, which maximize the constant power range with maximum torque per ampere, will be calculated. A performance comparison will be made for this optimal operation. Simulation results of the designed SRM will be presented for vehicle acceleration. To demonstrate the capability of the SRM in producing an extended constant power range, experimental results will be presented, however, for a reduced size motor available commercially. Index Terms--Constant power range, electric vehicle, hybrid electric vehicle, switched reluctance motor drive.

Transcranial magnetic stimulation (TMS) is a non-invasive neuro-stimulation based on the principle of electromagnetic induction that uses brief, strong magnetic pulses of electric current delivered to a coil placed on the subject’s head to induce an electric field in the brain. This electric field could stimulate and modulate neural activity. Induced E-field inside brain generated by repetitive TMS (rTMS) can produce changes in neural activity that extends beyond the period of stimulation. Therefore, rTMS can be used as a probe for exploring higher brain functions and as potential treatment technique for psychiatric and neurological disorders. However, based on the chosen shape of the excitation coil, there exists a tradeoff between the excitation focality in the brain and the depth to which the field penetrates. In this paper, a new design of TMS coil is proposed to enhance the performance of the traditional figure-of-eight (FOE) coil. 3-D finite-element method has been used to simulate and compare the electric field induced inside the model of a human brain under the influence of both coil designs. An experimental verification was then followed to validate the advantages of the proposed coil design over the classic FOE coil. [ABSTRACT FROM AUTHOR]

This paper proposes a control method to balance capacitor voltages in a four-switch single-stage two-phase-switched-reluctance motor drive with integrated power factor correction during startup and at low speeds. Initial alignment process is incorporated for switched-reluctance machine before startup. However, the phase currents are unbalanced during that time. This will cause overvoltage on dc capacitors in split-ac configuration leadings to their failure. This problem also exists when the motor speed is very low, as observed in the startup process of compressors. Based on a unified model, an effective control method is proposed to eliminate the voltage difference between the capacitors. This method does not require any additional circuits or components. It also does not affect the performance during normal mode of operation. Experiments are performed to verify the feasibility of the control method. [ABSTRACT FROM PUBLISHER]

The double-stator configuration of the switched reluctance machine (SRM) aims to maximise the energy conversion efficiency by optimising the ratio of motional force to the total magnetic force. Maintaining the attractive features of SRM, the double-stator switched reluctance machine (DSSRM) proves to have higher torque/power density than the conventional SRM, which is a crucial feature for traction applications. The original winding configuration used in DSSRM is the full-pitch winding, which yields high-power density but causes significant heat within the machine's end windings. As end windings do not take part in torque generation, concentrated windings were proposed to reduce the heat as well as to reduce the size, cost, and weight of the machine. This study provides a detailed comparative analysis of the effects that the winding configuration has on the performance of a 100 kW DSSRM, with emphasis on flux density distribution, efficiency, and heat generation. It is concluded that the concentrated windings are a better alternative to the full-pitch windings in DSSRM. [ABSTRACT FROM AUTHOR]

In this paper, a new breast cancer detection method is presented that combines thermography and high-frequency excitation techniques. The proposed method uses distribution and variation of the temperature on the breast surface to estimate the location and size of a malignant tissue (a cancerous tumor). The idea of this paper stems from the analysis of the radio frequency (RF) radiation effects on the human body. In this paper, a description of RF effects on the human body and simulation results are provided. To validate the proposed method, a multilayer 3-D breast model is simulated. First, breast tissue is excited with different types of RF antennas, which is followed with an electromagnetic analysis. Next, the heat transfer equation is applied for thermal analysis to estimate the distribution of surface temperature. Simulation results show that both the temperature and the specific absorption rate increase as the tumor becomes bigger or closer to the surface. Finally, thermal responses of multiple tumors are employed to estimate breast cancer existence. [ABSTRACT FROM AUTHOR]

This paper introduces an analytical approach to investigate the stator vibration in permanent magnet synchronous motor due to variable-speed drives. The origin of vibration is studied first. Using an electromechanical impulse response, a direct link between the electrical input to the stator windings and acceleration of the stator is established. This model allows for efficient and accurate computation of the stator vibration in permanent magnet synchronous machines. Simulations and experiments are conducted to validate the claims. [ABSTRACT FROM PUBLISHER]

In this paper, a novel technique for improving the torque characteristics of the Interior Permanent Magnet Synchronous Motor is proposed using rotor shape optimization. The main objective is to decrease the torque ripple while increasing average torque. The improvement process is performed for the maximum torque-angle operating point, and then studies are carried for other currents and angles. Defining a multi-element grid on rotor surface regions in which each element could be either iron or air, the best practical rotor surface topology could be obtained to improve the overall torque characteristics of IPMSM. The best motor performance is achieved using practical rotor shapes obtained from a cluster of points in average torque versus torque ripple plane. Finally, for torque ripple cancellation, two or three alternate rotor configurations with optimized average torque and out of phase torque pulsation have been selected. This selection will guarantee improved average torque while mitigating torque pulsation by a significant margin. Using this method, a rotor topology obtained in which torque ripple is reduced by 80% with slightly improved average torque. [ABSTRACT FROM AUTHOR]

The symmetric structure conventionally used in two-phase switched reluctance machines (SRMs) leads to dead torque zone and issues with startup. When a phase is at the fully aligned position with respect to the rotor, the complimentary phase is completely unaligned. Within this region, excitation of either phase fails to generate sufficient startup torque. Significant research has been focused on the design of machines with large, unidirectional startup torque specific to the direction of rotation required by the given application. In this work, a conventional two-phase SRM is analyzed to reveal the underlying geometric constraints leading to startup difficulties. To overcome this, a phase shift design strategy is proposed to ensure both large starting torque and bidirectional startup capability. The design is investigated and validated through both simulation and experiments, and the results show the validity of this new configuration. [ABSTRACT FROM PUBLISHER]

This paper proposes a stability optimization method based on virtual resistor and nonunity voltage feedback loop for cascaded dc–dc converters. Oscillating phenomenon or instability would occur occasionally with two or more closed-loop dc–dc converters in series. The virtual resistor and nonunity voltage feedback are used to modify the feedback loop instead of only a direct voltage feedback to improve stability and get rid of oscillating behavior. Based on the stability analysis of dc–dc converters with distributed parameters, several cases have been derived. After that, relative to different cases, two modified methods based on virtual resistor and nonunity voltage feedback loop are proposed to stabilize the overall system. With these methods, no extra power loss would be generated, and it is easy to embed them into any conventional control system. Experimental results verified the theoretical analysis and feasibility of the proposed control methods. [ABSTRACT FROM PUBLISHER]

This paper introduces a distributed economic dispatch strategy for microgrids with multiple energy storage systems. This strategy overcomes the challenges of dynamic couplings among all decision variables and stochastic variables in a centralized dispatching formulation. The proposed strategy can be implemented in the microgrid central controller as multiple problems with simplified and decomposed formulations. It can also be implemented in the local controllers and managed by the central controller. Numerical studies and experimental results illustrate the effectiveness of the proposed dispatching systems. [ABSTRACT FROM PUBLISHER]