Trade-off analysis and design of a Hydraulic Energy Scavenger

In the last years there has been a growing interest in intelligent, autonomous devices for household applications. In the near future this technology will be part of our society; sensing and actuating will be integrated in the environment of our houses by means of energy scavengers and wireless microsystems. These systems will be capable of monitoring the environment, communicating with people and among each other, actuating and supplying themselves independently. This concept is now possible thanks to the low power consumption of electronic devices and accurate design of energy scavengers to harvest energy from the surrounding environment. In principle, an autonomous device comprises three main subsystems: an energy scavenger, an energy storage unit and an operational stage. The energy scavenger is capable of harvesting very small amounts of energy from the surroundings and converting it into electrical energy. This energy can be stored in a small storage unit like a small battery or capacitor, thus being available as a power supply. The operational stage can perform a variety of tasks depending on the application. Inside its application range, this kind of system presents several advantages with respect to regular devices using external energy supplies. They can be simpler to apply as no external connections are needed; they are environmentally friendly and might be economically advantageous in the long term. Furthermore, their autonomous nature permits the application in locations where the local energy grid is not present and allows them to be ‘hidden' in the environment, being independent from interaction with humans. In the present paper an energy-harvesting system used to supply a hydraulic control valve of a heating system for a typical residential application is studied. The system converts the kinetic energy from the water flow inside the pipes of the heating system to power the energy scavenger. The harvesting unit is composed of a hydraulic turbine that converts the kinetic energy of the water flow into rotational motion to drive a small electric generator. The design phases comprise a trade-off analysis to define the most suitable hydraulic turbine and electric generator for the energy scavenger, and an optimization of the components to satisfy the systems specification

Axial Flux Permanent Magnet Synchronous Generators for Pico Hydropower Application: A Parametrical Study

A pico hydropower plant is an energy harvesting system that allows energy production using the power of the water flowing in small watercourses, and in water distribution network. Axial Flow Flux Permanent Magnet Synchronous Generator (AFPMSG) are particularly suitable for this application, being efficient machines that achieve high power with small dimensions. This paper presents a parametrical study of several configurations and topologies of three-phase and single-phase AFPMSG, for pico hydropower application, to assess the most suitable dimensional characteristics for the most energy production using a safe voltage of 25 V. The AFPMSGs here considered has a simple single stator and rotor configuration, commercial-type permanent magnets, and concentric windings, to facilitate their cost-effective construction and the spread of their use also in developing countries. For each AFPMSG considered, the power output was calculated using 3-D modelling and Finite Element Analysis; besides, the different parameters and features that affect the power output were evaluated at different rotational speeds. The results achieving a power density up to 100 W/cm(3), at 1000 rpm with energy produced to 1.7 kWh/day

Analytical design methodology for wind power permanent magnet synchronous generators

In this paper a novel analytical design methodology for wind power permanent magnet synchronous generators is presented. This kind of electric generator plays a major role in small-scale wind energy conversion systems up to 10 kW. The proposed diameter-cubed sizing equation is based both on the generator requirements, imposed by the application, and the design parameters that rely on the designer criteria. The magnetic field waveforms of both the permanent magnets field and the armature field are considered from the first moment through the winding factors, as well as the slots effects given by the Carter factor. The analytical model of the permanent magnet synchronous generator is validated with the finite element method, showing good agreement, both with no load and under load. As the generator is unsaturated, the main source of divergence between the analytical and the finite element model are the iron losses, due to the nonuniform magnetic field distribution

Design and Application of Electrical Machines

Electrical machines are one of the most important components of the industrial world. They are at the heart of the new industrial revolution, brought forth by the development of electromobility and renewable energy systems. Electric motors must meet the most stringent requirements of reliability, availability, and high efficiency in order, among other things, to match the useful lifetime of power electronics in complex system applications and compete in the market under ever-increasing pressure to deliver the highest performance criteria. Today, thanks to the application of highly efficient numerical algorithms running on high-performance computers, it is possible to design electric machines and very complex drive systems faster and at a lower cost. At the same time, progress in the field of material science and technology enables the development of increasingly complex motor designs and topologies. The purpose of this Special Issue is to contribute to this development of electric machines. The publication of this collection of scientific articles, dedicated to the topic of electric machine design and application, contributes to the dissemination of the above information among professionals dealing with electrical machines

Performance Characteristics Of Non-Arc Double Stator Permanent Magnet Generator

The improvement in the power density in the double stator configurations is feasible with increase in the electrical loading of the electrical machines. This type of newer configuration is finding significant applications in improvising energy generation, more commonly for renewable energy generation. Various double stator configurations with non-arc permanent magnet machines for power density are modelled and analyzed in this paper. Finite Element Method (FEM) is used to simulate for the generation capability including the electromagnetics parameters such as flux linkage and open circuit voltage. A new slotted rotor structure is evolved based on the magnetic flux flow control inside the machine. The proposed structure is then fabricated in the laboratory and tested for operating characteristics with load circuit. The proposed machine produces a maximum power of 600W at speed of 2000 rpm with 75% of maximum efficiency with the micro-hydro generation unit

New synchronous machine rotor design for easy insertion of excitation coils based on surrogate optimisation

The thesis reviews the development of traditional synchronous machine design and point out one problem with the manufacture of wound rotor synchronous machines. Install and repair process of the rotor windings can be considered labor-costly and time-consuming in synchronous machine design. The conclusion indicates a new winding method would be helpful for not only the new machines but also for rewound machines. A new rotor design for the easy insertion and repair of the rotor windings is then introduced. This new asymmetrical rotor shows good potentials for reducing the maintenance and repair costs of synchronous machines, making it suitable for manufacturers within the mass production markets such as gen-sets, steam turbines, wind power generators. Simulation results from 2-D finite element analysis and experimental results from testing a 27.5 kVA prototype machine have verified the performance of the new rotor. The results show that the asymmetrical machine’s electromagnetic performance is worse than traditional design and need to be optimised. The shape of the rotor is then optimised based on novel surrogate method in order to achieve the lowest power loss under the maximum power output. This method combines surrogate optimistaion with finite element method. It significantly reduces the time cost of the optimization process and can be applied with very complicated geometry design of the rotor. The performance of the new rotor is examined in 2-D finite element software and validated by experiments. After optimisation, the efficiency of the new rotor can reach the same level of the traditional rotor in electromagnetic performance in addition to its easy insertion and repair feature

Maximum power point tracking control of hydrokinetic turbine and low-speed high-thrust permanent magnet generator design

River-based hydrokinetic turbine power generation systems have been studied to introduce an effective energy flow control method. Hydrokinetic turbine systems share a lot of similarities with wind turbine systems in terms of physical principles of operation, electrical hardware, and variable speed capability for optimal energy extraction. A multipole permanent magnet synchronous generator is used to generate electric power because of its ability to reach high power density and high thrust at low speed. A 3-phase diode rectifier is used to convert AC power from the generator into DC power and a boost converter is used to implement energy flow control. On the load side, an electronic voltage load is used for test purposes to simulate a constant DC bus voltage load, such as a battery. A dynamic model of the entire system is developed and used to analyze the interaction between the mechanical structure of water turbine and electrical load of the system, based on which a maximum power point tracking control algorithm is developed and implemented in the boost converter. Simulation and experimental results are presented to validate the proposed MPPT control strategy for hydrokinetic turbine system. Similar to the wind turbine system, hydrokinetic turbine system usually requires a gear box to couple the turbine and the generator because the operating speed range for the hydrokinetic turbine is much lower than the operating speed range for most PMSGs. However, the gear box coupling adds additional transmission power losses. Therefore a high-thrust low-speed permanent magnet synchronous generator is designed to couple with the water turbine without a gear box --Abstract, page iii

Generator design for, and modelling of, small-scale wind turbines

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Hydrodynamics and drive-train dynamics of a direct-drive floating wind turbine

Floating wind turbines (FWTs) are considered a new lease of opportunity for sustaining growth from offshore wind energy. In recent years, several new concepts have emerged, with only a few making it to demonstration or pre-commercialisation stages. Amongst these, the spar-buoy based FWT has been extensively researched concept with efforts to optimise the dynamic response and reduce the costs at acceptable levels of performance. Yet, there exist notable lapses in understanding of these systems due to lack of established design standards, operational experience, inaccurate modelling and inconsistent reporting that hamper the design process. Previous studies on spar-buoy FWTs have shown inconsistencies in reporting hydrodynamic response and adopted simplified mooring line models that have failed to capture the coupled hydrodynamic behaviour accurately. At the same time, published information on drive-trains for FWTs is scarce and limited to geared systems that suffer from reliability issues. This research was aimed at filling the knowledge gaps with regard to hydrodynamic modelling and drive-train research for the spar-buoy FWT. The research proceeds in three parts, beginning with numerical modelling and experimental testing of a stepped spar-buoy FWT. A 1:100 scale model was constructed and tested in the University of Edinburgh’s curved wave tank for various regular and irregular sea states. The motion responses were recorded at its centre of mass and nacelle locations. The same motions were also simulated numerically using finite element method based software, OrcaFlex for identical wave conditions. The hydrodynamic responses were evaluated as Response Amplitude Operator (RAO) and compared with numerical simulations. The results showed very good agreement and the numerical model was found to better capture the non-linearities from mooring lines. A new design parameter, Nacelle Magnification Factor, was introduced to quantify coupled behaviour of the system. This could potentially encourage a new design approach to optimising floating wind turbine systems for a given hub height. The second part of the research was initiated by identification of special design considerations for drive-trains to be successfully integrated into FWTs. A comparative assessment of current state of the art showed good potential for directdrive permanent magnet synchronous generators (PMSG). A radial flux topology of the direct-drive PMSG was further examined to verify its suitability to FWT. The generator design was qualified based on its structural integrity and ability to ensure minimal overall impact. The results showed that limiting the generator weight without compromising air-gap tolerances or tower-foundation upgrades was the biggest challenge. Further research was required to verify the dynamic response and component loading to be at an acceptable level. The concluding part of research investigated the dynamic behaviour of the directdrive generator and the various processes that controlled its performance in a FWT. For this purpose, a fully coupled aero-hydro-servo-elastic model of direct-drive FWT was developed. This exercise yet again highlighted the weight challenge imposed by the direct-drive system entailing extra investment on structure. The drive-train dynamics were analysed using a linear combination of multi-body simulation tools namely HAWC2 and SIMPACK. Shaft misalignment, its effect on unbalanced magnetic pull and the main bearing loads were examined. The responses were found to be within acceptable limits and the FWT system does not appreciably alter the dynamics of a direct-drive generator. Any extra investment on the structure is expected to be outweighed by the superior performance and reliability with the direct-drive generator. In summary, this research proposes new solutions to increase the general understanding of hydrodynamics of FWTs and encourages the implementation of direct-drive generators for FWTs. It is believed that the solutions proposed through this research can potentially help address the design challenges of FWTs