A magnetic screw is a device that utilizes the magnetic field of permanent magnets to convert between linear and rotational motions while achieving the gearing action simultaneously. This offers conversion between high-speed low-torque rotational motion to low-speed high-force translational motion and vice versa. The most tempting advantage that magnetic screws offer is the contact-free power transfer. This paper discusses the design of the discrete-Halbach magnetic screw since it offers higher thrust force due to its special arrangement of permanent magnets. Analysis for varying the number of segments of discrete-Halbach magnetic screw along with varying both the radial magnetized PM length and PM thickness is conducted using 3-D finite element analysis. Also, fault analysis including eccentricity and demagnetization is conducted.

Unmanned aircraft systems (UAS) have emerged as a useful aid for entertainment, monitoring, and defense activities. A Significant research effort is being invested in UASs to increase the payload capacity and monitoring/processing capabilities. To achieve this, the power density of UAS must be increased. In conventional UAS, for starting the fuel-powered engine, an engine starter is usually used. Once the engine starts, the engine torque is used for driving an alternator, which powers the electrical power system (EPS) of the UAS. This paper presents a novel axial-flux machine-based motor-generator system (MGS), capable to operate as an engine starter thereby eliminating the external starter. The design is targeted to meet the specifications given in the US Army SBIR, to achieve a continuous power density of 3kW/kg for a 7kW power rating. Additionally, the design also meets the dimensional requirements, required to fit with the existing engine. The compact power converter design and control also compliment the motor-generator design. The necessary design steps, and control algorithm to support bidirectional flow are discussed in detail. Finally, detailed simulation results verifying the performance requirement during engine start, generation mode, and emergency mode are also presented.

This paper proposes a method to analyze aging response variance in terms of statistical parameters and geometry specifications of medium voltage power cable. The electric stress distribution in the single-core medium voltage power cable model is logged quantitatively using finite element modeling. The dependable parameters such as electrical conductivity, thermal conductivity, ambient temperature, relative permittivity, defect position and size, act as variables in the model to analyze simulated electric stress in the power cable. The variation in electrical stress distribution under the influence of different factors impact distinctly on cable degradation over time. Moreover, the correlation between these factors is quantified using derived statistical parameters to form a correlation matrix. In this work, both the variation coefficients and mean stress intensity are utilized as response measurement variables. A multivariable linear regression is applied to derive the relationship between the model parameters and the response variables. This study shows that the stress variation is strongly correlated with electrical conductivity and thermal conductivity, while the maximum stress intensity is most impact by defect sizes and position. The implication and consequence of the rest of the model parameters on electric stress distribution are also analyzed and discussed.

In this paper, a novel stator ground fault detection method based on wavelet theory is tested on a lab scale synchronous generator. The lab scale setup is used to mimic the real power generation system and to simulate the fault characteristics particularly at or near the generator neutral of large industrial generators. The experimental results prove the capability of the wavelet algorithm in synchronous generators stator winding ground fault detection.

The current control has an important impact on the performance of three-phase voltage source converters. A common approach is to adopt a two-degree-of-freedom scheme by which the reference-tracking and disturbance-rejection response are independently adjusted. On the one hand, a conventional current controller, such as a proportional-integral or resonant controller, is tuned to optimize the reference-tracking dynamics. On the other hand, an active resistance is selected to improve the disturbance rejection without altering the reference tracking. There are methods to further enhance the disturbance rejection by, e.g., adding extra selective controllers, but this increases complexity and requires the knowledge of the frequencies to be compensated. Therefore, it is still desirable to ameliorate the disturbance rejection to a greater extent, in a simple manner and without a priori information about the disturbance frequencies. This paper proposes to improve the disturbance rejection by means of an active inductance, without affecting the optimum reference tracking. Concerning the transient response, the overshoot (and hence, the integrated error) is significantly reduced. Furthermore, the steady-state attenuation of harmonics becomes larger in the lower part of the spectrum, where the harmonic disturbances usually arise. Simulation results supporting the functionality of the proposal are provided.

Multiphase machines are attracting significant attention due to their advantages over three-phase ones. When using pulsewidth modulation (PWM), a zero-sequence signal can be injected so that the dc-link utilization is improved. For instance, in five-phase machines, for a certain dc-link voltage the fundamental component is increased in this way in 5.1 %. Instead of PWM, it is possible to apply a square voltage waveform, which permits even better dc-link exploitation (27.3% with respect to conventional without zero sequence). Given the substantial voltage distortion, filters with large impedance at the low-impedance no-torque subspaces were devised. In any case, some of the square-waveform harmonics are mapped into the torque-producing plane without being attenuated by the filters, thus generating torque ripple. This paper proposes a carrier-based PWM method for five-phase drives that include a filter for circulating currents. This PWM technique takes advantage of the no-torque-producing components, which see a high filter impedance, to exploit the dc link to a degree similar to square voltage waveforms (23.1 % versus 27.3%), but without the extra torque ripple. Simulation results are provided.

Multiphase drives are particularly attractive for safety-critical applications, due to their enhanced fault tolerance. Most of the faults in electric drives occur in the power electronics. Switch faults can be divided into open- and short-circuit ones. The conventional techniques to handle switch faults in two-level converters mainly consist in either keeping the corresponding phases open or connecting the stator terminal to the de-link midpoint through a triode for ac (TRIAC). However, the former results in lower maximum torque and larger stator copper loss (SCL), whereas the latter leads to a reduction in the maximum speed and has not been considered in the context of two-level multiphase drives. This paper proposes to adequately combine these approaches in two-level multiphase drives, depending on the speed, the faulted switches and the neutral configuration, so that the total operating region of the drive is extended and the SCL is decreased, when compared to the conventional strategies. It is also shown and exploited that, for multi phase drives based on multiple three-phase winding sets, turning on or off a TRIAC placed between their neutrals as a function of the speed allows further improvement of the postfault performance. Simulation results are provided to confirm the theory.

This paper presents a rotor core design parameter study of double layer rotor type interior permanent magnet synchronous motor (TPMSM) for numerous objective functions. A specific study approach is proposed, and 16 distinct cases are evaluated using finite element analysis (FEA) and a two-level fractional factorial design introduced in the paper. FEA yields more accurate results for the objective functions than the magnetic equivalent circuit method because the rotor structure has a complicated arrangement of permanent magnets, barriers, bridges, and lips. A prototype was manufactured based on the multi-objective optimal design developed using the proposed study method. The simulation results are experimentally verified using the prototype.

In this paper a soft switched ac link ac-ac converter is employed as a variable frequency drive (VFD). The proposed configuration is a reliable, efficient, and compact converter with unity power factor at the input side. It is, in fact, a partial resonant converter i.e. only a small time interval is allocated to resonance in each cycle. Hence, while the resonance facilitates zero voltage turn on of the switches and soft turn-off, the LC link has low reactive ratings and low power dissipation. Due to the soft switching of the switches, the switching frequency can be increased and the high frequency of the link minimizes the size of the passive components. Both buck and boost operations in forward and reverse directions are feasible through this converter. Moreover, this converter is capable of increasing and decreasing the frequency over a wide range. Other than regulating the output current pulses to control the speed of motor the control algorithm also controls the input power factor and therefore no external power factor correction circuitry is required. In this paper field-oriented control scheme is applied to the proposed VFD for controlling the speed of the motor. Both simulation and experimental results are included in this paper to verify the performance of the proposed VFD.

A calibration method is presented to overcome phase unbalance and eccentricity effects in zero speed position estimation of surface-mount permanent magnet synchronous motors (SPMSM). Mechanical tolerances and random nature of winding cause sample to sample variation in phase inductances and saturation saliencies. Finite element simulations were performed to investigate the effects of eccentricity and winding unbalances on phase inductances. To confirm this behavior, experiments were performed on a set of SPMSMs manufactured in the same batch to measure actual sample to sample variation of saliency ratios and offsets. The simulation and experimental results indicate a significant variation in the average value of the phase inductances from sample to sample, which evince the need for separate calibration of each motor unit for accurate initial position estimation. The paper proposes six calibration parameters to model the inherent unbalances, which can be used to estimate the standstill position of SPSM.

A new resonant three-phase ac-ac converter with a high-frequency ac link, soft switching characteristic, unity input power factor, galvanic isolation, and bidirectional power flow is introduced in this paper. The galvanic isolation is realized with only one single-phase high-frequency transformer, which is substantially small. The converter's ac link is formed by the magnetizing inductance of the high-frequency transformer and two considerably small ac capacitors; no bulky short-life electrolytic capacitor is used. Moreover, the converter's switches are turned on at zero voltage and are turned off with low loss; therefore, the converter's switching losses are significantly low, which subsequently permits the switching frequency to be high. The operation of the topology comprises 16 distinct modes and is described in detail. The analysis of the proposed topology is carried out to reveal the converter's behavior in different operating conditions. Simulation results are also given to demonstrate the effectiveness of the power converter.

Several design aspects of a recently introduced magnetic device are studied in this paper. The device, named Trans-Rotary Magnetic Gear (TROMAG), resembles a mechanical lead-screw. It can convert linear motion to rotation, and vice-versa, through magnetic fields, while offering a gearing action. For instance, high force, low speed translation can be converted to high speed, low torque rotation. Once integrated with a conventional winding, the resultant system may be used as a compact machine for high force linear motion applications. The paper investigates the design of the TROMAG by means of two-dimensional (2D) and three-dimensional (3D) Finite Element Analysis (FEA). Piece-wise helix effects, 2D approximation, demagnetization possibility, magnet dimensions impact, scaling, and flux density distribution are studied.

Effective sensorless speed estimation is desirable for both online condition monitoring of induction motor and sensorless adjustable speed AC drive applications. In this paper we present a neural network-based sensorless adaptive speed filter for induction motors. Only nameplate information and the actual motor currents and voltages are required for the initial setup of the proposed neural network-based speed filter. The speed filter gives acceptable steady state and transient speed response. The paper demonstrates the feasibility of adaptive speed filtering for induction motor which could be used for both diagnosis and control purposes.