Overview of Flywheel Systems for Renewable Energy Storage with a Design Study for High-Speed Axial-Flux Permanent-Magnet Machines

Flywheel energy storage is considered in this paper for grid integration of renewable energy sources due to its inherent advantages of fast response, long cycle life and flexibility in providing ancillary services to the grid, such as frequency regulation, voltage support, etc. The fundamentals of the technology and recent developments are reviewed, firstly with an emphasis on the design considerations and performance metrics. Then the progress and development trends in electric motor/generators employed in flywheel energy storage systems (FESS) are summarized, showing the potential of axial-flux permanent-magnet (AFPM) machines in such applications. Design examples of high-speed AFPM machines are provided and evaluated in terms of specific power, efficiency, and open-circuit losses in order to validate their suitability in FESS

Effects of shading and covering material application for delaying harvest on gray mold disease severity

To delay the harvest of Sultani Cekirdeksiz grape variety and to reduce pre and post-harvest botrytis bunch rot severity, shading and covering material application were tested in 2009 to 2010 growing periods. In this study, grape vines were shaded with shading materials which had three different shading densities (35, 55, and 75% shading density) from veraison period to harvest. The grape vines were also covered with four different covering materials (transparent polyethylene, mogul, polypropen cross-stich and lifepack) before rainfall, at the end of August until harvest. The gray mold severity was recorded three times (before shading at unriped grape stage, veraison period, shortly after shading and twice at 20 day interval) during growing period. Based on the results of this study, the highest gray mold (Botrytis cinerea) severity was obtained in the control (uncovered and unshaded) treatment and the lowest disease severity was observed in lifepack treatment with or without shading. Since gray mold disease of grape was the main factor affecting harvest date of the crop lifepack, + 35 or 55% shading could be recommended to delay harvest and reduce the gray mold severity of grape in Manisa province-Turkey.Key words: Sultani seedless, table grape, shading, cover material, delaying harvest disease severity, Botrytis cinerea

Analysis of Torque Production in Axial-flux Vernier PM Machines of the MAGNUS Type

The paper presents a study of the torque production in a novel vernier-type axial-flux permanent magnet (PM) machine topology named MAGNUS. Two computational methods are employed, one based on the 3D FEA Maxwell stress calculations on individual stator and rotor components and one based on the analytical derivation of the air-gap flux density harmonics. Examples are provided for a design with a 40-pole spoke-type PM rotor and two stators, one active including a 3-phase winding with 6 concentrated coils wound around main teeth in a single layer arrangement and a second stator that has neither coils nor main slots and is profiled towards the airgap in the same way as the active stator. It is shown that auxiliary small teeth included in the stator main teeth yield a significant increase in the output torque and that the profiled stator has a lower contribution than the active stator to the total torque. A brief report on the ongoing development of a prototype motor is included

Optimal Study of a High Specific Torque Vernier-Type Axial-Flux PM Machine with Two Different Stators and a Single Winding

This paper presents the optimal study of a verniertype axial-flux permanent-magnet (AFPM) machine, which has a high-polarity spoke-type PM rotor, a wound stator with a low number of coils, and a profiled stator. Both stators have profiled teeth to enhance the magnetic interaction between the rotor PM array and stator windings for torque production. Compared to the topology with two wound stators, the studied one has a smaller total axial length and is expected more suitable for applications where the space is limited in axial direction. Both topologies are optimized through 3-dimensional (3D) finite element analysis (FEA) by the combined design of experiments (DOE) based sensitivity analysis and surrogate-assisted multiobjective differential evolution (DE) algorithm. Key factors affecting the two objectives, i.e., total active material cost and total electromagnetic loss, are identified. The optimization results are presented and compared, providing practical guidelines for the optimal design and operation of such machines. The manufacturing aspects and their impacts on the electromagnetic performance are also discussed

Axial-Field Vernier-Type Flux Modulation Machines for Low-Speed Direct-Drive Applications

This paper proposes different configurations of axial-field machines featuring a very large ratio of the number of rotor poles to stator teeth and coils suitable for low-speed direct-drive traction applications. The machines have a single rotor with spoke-type permanent magnets and the stator teeth include auxiliary slots, the function of which is to enhance the high-polarity component of the stator magnetomotive force interacting with the rotor to produce a net torque. The machines can be constructed with three or two phases, in which case they inherently exhibit high tolerance to faults due to the combined effect of a lack of coupling between phases and a relatively large phase inductance. A preliminary comparative simulation study shows performance improvement over a conventional reference permanent magnet synchronous machine

Visitors’ perceived trust in sincere, authentic, and memorable heritage experiences

The success of cultural destinations often centres on whether consumers trust the provenance and integrity of the heritage assets, activities, and services therein. However, few studies examine whether this ‘perceived trust’ influences the authenticity, sincerity, and memorability of cultural heritage consumption. To investigate the relationships between these constructs, we surveyed 320 visitors to Iranian cultural heritage sites. The findings suggest that perceived trust positively influences visitors’ perceptions of sincerity, existential authenticity, and object-based authenticity, stimulating memorable experiences in the process. This, in turn, emphasises the antecedent importance of perceived trust in shaping consumption. In the face of increasing commercialization within the cultural heritage sector more generally, we therefore encourage practitioners to prioritise safeguarding the integrity of their offerings, promoting heritage assets in a manner that stimulates perceived trust

Visitors’ perceived trust in sincere, authentic, and memorable heritage experiences

The success of cultural destinations often centres on whether consumers trust the provenance and integrity of the heritage assets, activities, and services therein. However, few studies examine whether this ‘perceived trust’ influences the authenticity, sincerity, and memorability of cultural heritage consumption. To investigate the relationships between these constructs, we surveyed 320 visitors to Iranian cultural heritage sites. The findings suggest that perceived trust positively influences visitors’ perceptions of sincerity, existential authenticity, and object-based authenticity, stimulating memorable experiences in the process. This, in turn, emphasises the antecedent importance of perceived trust in shaping consumption. In the face of increasing commercialization within the cultural heritage sector more generally, we therefore encourage practitioners to prioritise safeguarding the integrity of their offerings, promoting heritage assets in a manner that stimulates perceived trust

Design Optimization of Coreless Axial-Flux PM Machines with Litz Wire and PCB Stator Windings

Coreless axial-flux permanent-magnet (AFPM) machines may be attractive options for high-speed and high-power-density applications due to the elimination of core losses. In order to make full use of the advantages offered by these machines and avoid excessive eddy current losses in windings, advanced technologies for winding conductors need to be employed to suppress the eddy effect, such as the Litz wire and printed circuit board (PCB). In this paper, the best practices for designing Litz wire/PCB windings are discussed and a brief survey of state of the art PCB winding technology is provided. Three coreless AFPM machines are mainly considered. A design optimization procedure based on the multi-objective differential evolution algorithm and 3-dimensional (3D) finite element analysis (FEA) is proposed to take into account the ac winding losses of Litz wires and PCB traces in the machine design stage. Selected designs are being prototyped and will be tested with a customized test fixture

On the Modeling of Bearing Voltage and Current in PWM Converter-Fed Electric Machines Using Electromagnetic Finite Element Analysis

Bearing voltages and resulting currents in electric machines driven by PWM converters with fast switching and high dv/dt can cause premature bearing failures. With the transition from conventional Si devices to wide bandgap (WBG) devices and increase in switching frequency, bearing voltages and currents become more significant and need to be addressed from the early design stage. This paper proposes to use coupled field-circuit electromagnetic finite element analysis (FEA) to model bearing voltage and current in electric machines, which takes into account the influence of distributed winding conductors and frequency-dependent winding RL parameters. The three known bearing current types are explained and modeled in a unified way by using the proposed approach with simple calculation examples. Potential bearing current issues in axial-flux machines, and possibilities of computation time reduction, are also discussed

Design Optimization of a Very High Power Density Motor with a Reluctance Rotor and a Modular Stator Having PMs and Toroidal Windings

This paper proposes a new high power density permanent magnet (PM) motor design for traction applications to achieve the 50kW/L target set by the US Department of Energy by increasing the torque capability and operating speed compared to conventional PM machine topologies. A large-scale multi-objective design optimization based on 2D finite element analysis (FEA) and differential evolution algorithm was conducted to achieve the best trade-off among high efficiency, high power density and high power factor. The torque-speed envelopes are also checked for the Pareto front designs to make sure they have a constant power speed ratio of at least 3:1. An open frame lab prototype (OFLP) motor has been fabricated and tested to validate the principle of operation and design optimization approach, and to identify the potential challenges in manufacturing and testing. Ongoing work on further pushing the electromagnetic performance to the limit and improving the manufacturing and cooling techniques are also discussed