Multiphase permanent-magnet synchronous machines (PMSMs) with fractional-slot concentrated windings (FSCWs) are favored for many uninterruptible applications due to their high fault tolerance and torque density. Two different configurations are often adopted: single layer (SL) and double layer (DL). For SL, each slot is filled with one phase winding, while for DL, two phases can share the same slot. Accordingly, many research papers advise adopting SL in fault-tolerant PMSMs, rather than DL, because SL offers higher physical, thermal, and electromagnetic isolation between phases. However, the lower thermal isolation, as for DL, may enhance the heat transfer. This could be expected to reduce the hot-spot temperature for DL. Thus, the established preference of SL over DL for fault-tolerant PMSMs may be questioned, and further analysis is necessary. This paper compares the temperature distribution of six-phase PMSMs between SL and DL FSCWs under both healthy and faulty conditions, considering open-circuit and short-circuit (interturn) winding faults. For accurate results, finite-element analysis and computational fluid dynamics are employed for the loss calculation and thermal simulation, respectively.

Six-phase permanent-magnet synchronous machines (PMSMs) offer multiple benefits compared with three-phase ones, e.g., increased torque density and reduced phase-current rating. A method has been recently proposed to generate current references ensuring minimum stator copper loss (SCL) per torque for nonsalient PMSM drives with sinusoidal or nonsinusoidal back-electromotive force (back-EMF), while the peak currents were suitably limited (with harmonics) to the maximum instantaneous currents of the inverter even during transient overloads. Furthermore, even greater mean torque could be attained by permitting a certain (limited) torque ripple when needed. However, such technique did not take into account the voltage limits imposed by the dc-link voltage. This paper proposes an alternative method based on look-up tables (LUTs) that provides these functionalities for symmetrical six-phase nonsalient PMSMs, while effectively considering the voltage constraints in the optimization. This makes it possible to minimize the losses and torque ripple per mean torque in not only the entire torque range, but also in the full speed range. To decrease the computational requirements, the offline LUT-generation process is designed so that it identifies the range of operating points where the solution changes, and then the optimization problem is solved only within such range.

Aircraft electrification has received increasing attention due to the significant benefits, such as low carbon emissions, high energy efficiency, low operation cost, and reduced acoustic noise. Limitations on both the low energy density with the present battery technologies and slow battery charging speed highly affect the widespread adoption of electric aircraft, especially for megawatt-scale large aircraft. Thus, this paper presents an isolated integrated on-board battery charger (IOBC) using an existing six-phase surface-mounted permanent magnet (SPM) synchronous propulsion machine for MW-scale electric aircraft. Besides exploiting the existing powertrain apparatuses, i.e., the six-phase motor and inverter, in the propulsion and charging modes of operation, the proposed charger offers galvanic isolation to meet safety standards and code compliance. Moreover, zero average torque production during charging and unity power factor operation at the grid side can be simultaneously achieved. The proposed charger concept entails simple hardware reconfiguration to switch between the propulsion and charging modes of operation. Furthermore, this paper adopts a 36-slot/34-pole fractional slot concentrated winding (FSCW)-based SPM machine, which is designed and optimized based on the magnetic equivalent circuit (MEC) model and the multi-objective genetic algorithm (MOGA) design optimization approach, respectively. Eventually, theoretical findings are verified based on 2D and 3D finite element (FE) simulations.

Considering the rapid urbanization and the road congestion, the development of smart parking solutions becomes more crucial, especially in terms of economic interests. Thanks to IoT-connectivity and the cloud-integrated platforms, drivers can easily find a vacant parking lot with smart parking services. This paper intervenes in the profit of parking management systems. The paper proposes a new technique “paging technique” which increases the utilization factor of parking slots. The proposed method takes advantage of the idle time that exists between two successful parking services in the same slot. Besides, it investigates the possibility of using the idle times from different parking slots to provide a continuous parking time for an additional car. The paging technique is optimally implemented using mixed-integer linear programming that maximizes the utilization factor for the parking slots with minimum car transitions. Moreover, a data model for the parking management system has been constructed while considering the three major customers, namely, regular, prepaid, and walk-in customers. The difference between fixed and dynamic pricing for parking has been investigated. The technique has been validated using GAMS optimization software and hardware using DSP with Coin-or branch and cut solver (CBC) under real-life conditions. The statistical results prove that the revenue for the proposed parking system has increased significantly. Finally, a comparative analysis is performed, benchmarking our proposed method against recent competing algorithms in real world applications to demonstrate its superiority.

The weighting factor (WF) setting is one of the most challenging tasks related to finite control set model predictive control (FCS-MPC) algorithms in different applications. Recently, a new method has been proposed for weighting factor elimination (WFE) in predictive current control (PCC) of asymmetric six-phase induction motor (A6PIM). This method is based on adopting the double dq (2dq) modeling method for prediction and optimization steps. As a result, the proposed cost function consists of four stator current components with the same priority. Thus, equal weighting factors can be assumed. In this paper, the performance of WFE method is assessed experimentally at different operating conditions. Different figures of merit are used to further compare it with the conventional voltage space decomposition (VSD)-based method. The WFE method is found to have reduced average switching frequency and better current quality. By highlighting the potential and limitations of WFE method it can be used properly based on different applications requirements.

With ever-increasing concerns on clean environment and global warming, there is special interest in electric vehicles (EVs) to be used instead of conventional vehicles with internal combustion engines (ICEs). Among competing machine types, permanent magnet (PM) brushless motor is the most commonly employed motor type for this technology due to their important advantages of high power density, high efficiency. Furthermore, higher fault tolerant capability at low speed which can be achieved by combining a coaxial magnetic gear (MG) with an outer rotor PM brushless machine resulting in a Permanent magnet vernier (PMV) machine. The performance of a fault-tolerant PMV machine depends on the proper selection of slots/poles combination which offers low speed/high torque operation and eliminates the effect of low order harmonics in the stator magneto motive force and hence reduces the vibration and stray loss. In this paper, three outer rotor five-phase PMV machines with the same dimensions and different slots/poles combinations are designed. The number of flux modulating poles (FMPs) is optimized to obtain better torque curves and efficiency. A simulation study is carried out using 2D-Finite element method (2D-FEM) to compare the performance of the three machines at rated condition.

Machines with modular structure significantly simplify the manufacturing process, particularly the stator winding, and highly increase the slot fill factor. The non-overlapping concentrated winding, or single tooth winding, is the most compatible winding layout with segmented structure. This technology is well-established for permanent magnet family machines. However, their incompetence to produce a sinusoidal MMF distribution provides a key challenge to apply single tooth winding to induction machines. This paper introduces a new single tooth winding layout for a single-phase induction motor with segmented stator. The proposed winding layout is based on dual two-phase windings shifted in space by 450 electrical degrees to completely cancel out both the third and fifth order harmonics. The proposed winding entails 8 slots per pole pair. Although the number of active conductors in the proposed winding is higher than a conventional distributed winding layout to produce the same MMF magnitude, the significant reduction in the end turn copper and the increase in the slot fill factor compensate this copper volume increase while maintain approximately the same machine volume, which introduces it as a promising candidate in high frequency motor applications. A prototype machine is used for experimental verification.

The interest in multiphase drives has been steadily growing during the last decade due to the promising potentials offered by multiphase machines over conventional three-phase counterpart. In this context, six-phase induction machines are preferably used in many diversified high-power applications. Generally, thanks to its improved flux distribution, the asymmetrical six-phase winding topology fed from two three-phase voltage source inverters (VSIs) is commonly employed with isolated neutral points to prevent the flow of zero sequence currents and to limit the number of current controllers to four instead of five when neutral points are connected. In this paper, an innovative design of a six-phase dc-ac inverter is proposed for such type of six-phase ac machines based on the single-ended primary-inductance converter (SEPIC) topology. The proposed topology employs only four active-legs with eight switches with the same output voltage magnitudes as in conventional VSIs and without the mandatory dead-time between switches in the same-leg. Also, it naturally delivers a pure sinusoidal waveform at the output stage. The principle of operation of the proposed inverter topology is investigated in details and assessed through a detailed simulation study of an open-loop control system.

In this paper, a grid-connected version of the switched PV array will be presented. The PV array consists of n parallel-connected strings and m series-connected modules per string, i.e. an array with a dimension of (m × n). Using the proposed switched PV approach, each string can be reconfigured to form two parallel strings of m/2 modules per string resulting in a new array with a dimension of (m/2 × 2n). The new array may yield a higher extracted power compared to the original configuration during partial shading, as a parallel connection of modules is invulnerable to partial shading conditions. Although the proposed system provides a lower power enhancement compared to the distributed MPPT converters and differential power processing approach, it is more simple and cost effective. The simulation results show a possibility of enhancing the PV array extracted output power during partial shading with the proposed system.

Dual three-phase (asymmetrical six-phase) induction motors have received significant attention in high power medium voltage drive applications. Typically, two three-phase voltage source converters are needed to feed such a drive system. In medium voltage applications, multilevel inverters are preferred as they provide a stepped output voltage waveform that reduces dv/dt stresses and provides a better output current waveform, which reflects positively on the machine developed torque and overall drive performance. Among different multilevel inverters, the Modular Multilevel Converter (MMC) has recently shown promise in medium and high voltage applications. For a dual three-phase machine, two MMCs with 6 arms each, are needed. This paper proposes a nine-arm MMC (9A-MMC) to drive such a motor. The proposed approach reduces the number of involved arms by 25%, i.e. reduces the number of required dc capacitors, semiconductor devices and their gate drive circuits, which reduces system complexity and cost. A complete analysis of the proposed system is presented and a simulation model is used to verify the proposed concept.

This paper proposes a novel single layer winding layout for a permanent magnet machine with improved torque density for electric vehicle applications. In this paper, two permanent-magnet (PM) machines with outer rotors and single layer fractional slot concentrated windings are compared based on two different slot/pole combinations, namely 20 slots/18 poles and 20 slots/22 poles. The two machines are inherently five-phase machines; however, a winding layout is employed to create three-phase stator terminals. Hence, the proposed machines exploit the advantages of multiphase machines while providing three phase terminals allowing for standard three-phase converters. Two machines are designed with same rotor and stator dimensions and same stator winding layout but with different number of rotor poles. The comparison is carried out using finite element analysis.

One of the main issues accompanied with the high penetration of PV distributed generation (DG) systems in low voltage (LV) networks is the overvoltage challenge. The amount of injected power to the grid is directly related to the voltage at the point of common coupling (PCC), which necessitates limiting the amount of injected power to the grid to conservative values compared to the available capacity from the PV panels particularly at light loading. In order to mitigate the tradeoff between injecting the maximum amount of electrical power and voltage rise phenomena, many control schemes were suggested in order to optimize the operation of PV DG energy sources as well as maintaining safe voltage levels. Unlike these conventional methods, this paper proposes a combined PV inverter-based distributed generation and flywheel energy storage system to ensure improved voltage regulation as well as making use of the maximum available power from the PV source at any instant, decoupling its relation with the terminal voltage. The concluded assumptions were simulated through Matlab/Simulink and verified experimentally.

Modular Multilevel converters (MMC) have become one of the most promising topologies for DC-AC conversion in recent years. Capacitor voltage balancing is a vital issue for proper operation of the MMC. Generally, conventional sensor-based balancing techniques require a significant amount of measurements, 2m(N-1) voltage sensors and 2m current sensors are required for a N-level m-phase converter. In this paper, a sensorless voltage balancing technique (self-balancing) is proposed for the MMC. The proposed technique eliminates all measurement boards used for monitoring capacitor voltages and arm currents, which in turn reduces system complexity and cost. Simulation and experimental results support and validate the proposed concept.

Multiphase machines have become serious contenders for safety-critical applications that require wide fault tolerant capabilities and higher system reliability. However, this adds more complexity to the adopted power converters. Alternatively, passive transformation is a viable solution to obtain an n-phase supply from the three-phase grid. This paper investigates the existing connections of passive transformation and proposes a transformation, based on the well-known Scott connection, to convert the three-phase grid voltages to an n-phase supply. In comparison with other connections in the literature, the proposed connection uses only two magnetic cores with less number of total coils, hence less total transformer volume. The paper also introduces the general per-phase equivalent circuit for three-phase to n-phase transformer, and the required modifications to conventional open-loop and short-circuit tests to estimate the transformer parameters. A prototype transformer is designed and built to investigate the proposed connection.

The evolution of public transportation exhibits high potential nowadays due to the consistent demand of clean transportation with low pollution rates. Therefore electrified railway systems become viable with their environmentally friendly properties. This study aims to improve the efficiency of DC power supplied railways via employing energy storage technology to maximize the overall energy efficiency. A flywheel energy storage system has been applied to store the regenerated energy during braking instead of dissipating it in the form of heat; then this stored energy can be used to compensate system disturbances and imbalance periods. A 75 kW/90 kJ squirrel cage induction machine based flywheel energy storage system is dedicated with a 600 VDC electric railway system to control the energy between the traction motor and the DC bus. The proposed control strategy is simulated using MATLAB/Simulink and simulation results have been shown. An experimentally FESS is built to support the study by experimental results.

Transformer-less photovoltaic (PV) inverters are the major functional units of modern grid-connected PV energy production systems. In general, two power conversion stages are required when low-voltage unregulated photovoltaic (PV) output is conditioned to generate AC power. In this paper, the boost inverter topology that achieves both boosting and inversion functions in a single stage is used as a building block to develop a three phase grid connected PV system which offers high conversion efficiency, low-cost and compactness. The proposed system employs a modified modulation scheme for the three phase boost inverter to control both active and reactive power injected to the grid. This modified modulation scheme enhances the boosting capability of the boost inverter and improves the THD of the grid injected current. Moreover, it reduces the voltage stress on the capacitors and switching devices. Analysis and simulation results are presented to confirm the advantages and efficiency of the proposed modulation technique.

In renewable energy-fed grid-connected applications, voltage source converters (VSC) offer high flexibility and system controllability features. In addition to the stepped down nature of its output voltage, the VSC is inherently defenseless against faults. On the other hand, boost Inverters provides voltage boosting characteristic and complete blocking capability between the AC grid and the DC side fault which protects the semiconductor devices during DC faults. A simulation study to compare the performance of VSC and boost inverters during DC side faults is conducted in this paper. The simulation results elucidate a significant decrease in the DC fault current in case of boost inverter due to its blocking capability.