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Contact behavior of electrical vehicle-battery junction box under high shorting and breaking current
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0639
The motor of an electric vehicle and its equipment are connected to the battery via a junction box that contains power relays that ensure current flow when closed but can break the current in abnormal situations. The contacts of such relays have to ensure and maintain a low contact resistance and support a shorting current of a few kA and an acceptable breaking capacity under a normal load of a few hundred amps. We have developed a test involving a shorting current of 4000A passing during 50ms through closed contacts in which we study welding and arcing phenomena. The origin of arcing has been attributed to the shorted contact produced by the electromagnetic repulsion force that is able to counterbalance the contact force and separate the contact. The power arcing burns during the short circuit and a irreversible damage is observed when the accumulated arc energy exceeds a certain critical value. In this paper, the main cause of the repulsion phenomena and minimum arc energy criteria inducing substantial damage and capsule breaking is studied. By varying conditions of current for two relays equipped with different materials, filled with a specific gas and employing a magnetic field we found that shorting damage was not avoided below 2KJ. Fortunately breaking capacity is achieved without damage and relay function is ensured.
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Quantifying the benefits of DG units in distribution network systems
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0738
Today, with the rise in global energy consumption and thus increase its production CO<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub> emission has increased sharply. Research shows that one third of the total CO<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub> emissions are from power plants. Based on the analysis of Energy Technology Perspectives (ETP2008) unless we find an effective way of decreasing CO<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub> level there will be a 130% increase in CO<sub xmlns="http://pub2web.metastore.ingenta.com/ns/">2</sub> emission by 2050. There are many solutions suggested for preventing the excessive production of environmental contaminants such as increasing energy efficiency, utilizing distributed generators and renewable energy sources. The present study in addition to further introducing distributed generation systems as an effective method for energy production, aims to identify useful indexes for the assessment of these systems in the network, in terms of voltage, losses and environmental impacts. Then a model will be introduced for the assessment the impacts these systems have and also evaluation of the resulted financial benefits for consumers, energy companies and the general community. In the end results of the placement of photovoltaic generators as a type of distributed generation will be evaluated. (4 pages)
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High reliability piezoelectric fan cooling for electric machine thermal management
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0154
Electric machine thermal management is critical for the correct operation of high power density aerospace electrical machines. However, with increasing power density, a reliable, fault tolerant cooling mechanism needs to be developed. Piezoelectric fans are presented here as a potential, fault tolerant, forced cooling convective system that may further enhance the overall cooling of electric machines. Particle Image Velocimetry (PIV) techniques were implemented to map and quantify the flow fields generated by one such fan along the fin base and fin side walls of a vertical straight finned motor heat sink. Common fluid flow governing parameters (vibration amplitude, separation distance, and fin length) were investigated; the optimum fin/fan geometry of which resulted in mean flows in excess of 2.48m/s and turbulence values in excess of 2.00m/s. Detailed thermal results indicate that an average convective heat transfer coefficient enhancement of 340% on the fin base and an enhancement of 36% on each of the fin side walls are attainable. This in turn resulted in a 64% reduction in the electric machine heat sink cooling mass relative to natural convection cooling. (6 pages)
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Comparative study of torque-speed characteristics of alternate switched-flux permanent magnet machine topologies
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0257
This paper presents a comparative study of electromagnetic performance in switched flux permanent magnet (SFPM) machines with different topologies, i.e. conventional SFPM machines, multi-tooth, E-core and C-core SFPM machines. With the aid of 2D finite element analysis (FEA), the torque waveform, cogging torque, back-emf and d- and q-axis inductances are investigated and compared with emphasis on the torque-speed characteristics. In conventional SFPM machines, the influence of stator/rotor pole combination on the torque-speed characteristics is also investigated through 12/10, 12/13 and 12/14 SFPM machines. Compared with conventional SFPM machines, which exhibit limited speed range, infinite speed range is observed in multi-tooth, E-core and C-core SFPM machines, among which the highest average torque per ampere is achieved in E-core SFPM machine, albeit with relatively high torque ripples. (6 pages)
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Comparative analysis of unbalanced magnetic force in fractional-slot permanent magnet machines having external rotor topologies
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0272
This paper comparatively investigates the unbalanced magnetic force (UMF) of external rotor machines having pole and slot numbers differed by one but no rotor eccentricity. The 8-pole/9-slot and 10-pole/9-slot machines are firstly optimised for maximum torque density by nonlinear FE analysis. Then, the UMF of both machines are analysed by both analytical model and linear FE model. It shows that the optimised 10-pole/9-slot machine has larger average torque than the 8-pole/9-slot machine for the same copper loss. However, the 10-pole/9-slot external rotor machine has significantly larger UMF than the 8-pole counterpart, which is opposite to the case of internal rotor machines. (6 pages)
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A linear superconducting generator for wave energy converters
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0298
Direct-drive superconducting linear generators can be an alternative for wave energy converter power take-off systems. A novel superconducting generator topology is presented in this paper. The generator has a stationary superconducting field winding fixed to modular magnetic cores. The translator is composed of air-cored copper windings. The generator is suitable for low-speed, high-torque applications. A 640 kW linear generator is designed. The design is validated using FEA tools and the specifications of the generator are presented. (6 pages)
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Torque-speed performance analysis of fractional slot PM machines having concentrated windings using alternate methods
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0273
Due to high torque density and efficiency, permanent magnet (PM) machines are widely utilized in industrial and commercial applications for all power ranges. When they are operated at high electric loading, the influence of magnetic saturation is usually large. Furthermore, due to the geometric structure of some PM machine topologies, e.g. interior PM machines, such influence can be even more significant. The partial cross-coupling model, which considers that the PM flux is a function of q-axis current and the d- and q-axis inductances are functions of d- and q-axis currents, respectively, is simple but neglects the saturation to some extent. However, as shown by the frozen permeability method in this paper, it can accurately predict the torque-speed characteristics of fractional-slot PM machines having concentrated windings. The analysis is confirmed by experimental results. (6 pages)
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Acoustic noise and vibration of direct-torque-controlled permanent magnet brushless DC drives
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0264
A systematic approach to identify the vibration and acoustic noise sources in a direct-torque-controlled (DTC) PM BLDC drive is presented and compared with that in BLAC DTC drive. Experimental results show that the acoustic noise may be radiated by the radial vibration of the stator and the vibration of connected mechanical parts due to torque pulsation and stator torsional vibration. In the BLDC DTC prototype drive, the interaction between the field harmonics and PWM switching current harmonics appears to be the dominant source of radial vibration and acoustic noise. If the acoustic noise in both BLDC DTC and BLAC DTC is mainly caused by the interactions between the armature reaction field harmonics themselves, and between the armature reaction field harmonics and PM field harmonics, the BLDC DTC drive is expected to produce higher acoustic noise because the phase current and hence the armature reaction field of BLDC DTC drive is rich of non-triplen odd harmonics. However, if the acoustic noise radiated from BLDC DTC and BLAC DTC drives is largely attributed to PWM switching current harmonic induced vibrations, as found in this paper, the sound pressure level in a BLDC DTC drive may be lower than its BLAC counterpart. (6 pages)
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Motion control strategy and operational behaviour of a high speed bearingless disc drive
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0297
In the last decade, bearingless drives have found their way into applications such as pumps for delicate media like blood [1] or sensitive chemicals [9] as well as drives for bioreactors [13] and chemical process chambers [3]. With all these applications running at relatively low speeds below 15.000rpm, the suitability of bearingless drives for high speed operation remained unclear. This paper will give a brief description of a high speed bearingless disc drive, designed to reach speeds beyond 100.000rpm. Aside from special requirements such as rotor material strength and low stator loss characteristics, the control system also faces new tasks arising from the combined motor - bearing unit. Eventually, the operational behaviour of the constructed prototype on the basis of phase current amplitude and resulting rotor orbit is presented. (6 pages)
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Reduction of passive filtering in aerospace starter/generator systems using a multilevel converter with predictive current control
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0250
The application of predictive current control to a multilevel converter is investigated in an aerospace starter-generator system. The use of a multilevel inverter with predictive current control enables the system to reduce the harmonic distortion in the current waveform when compared to a conventional Field Orientated Controller. It is important that the power converter is optimized to control the current harmonics as aerospace starter-generators are typically low inductance machines. Experimental results taken from a prototype inverter show a substantial reduction in THD is achieved using the proposed controller. (5 pages)
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Investigation into the temperature profile of a liquid cooled YASA© AFPM machine
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0281
The developments in Axial Flux Permanent Magnet (AFPM) machines enable higher torque and power densities and higher efficiencies, thus making it a suitable candidate for various applications such as electric road transportation or wind energy generation. Due to the fact that liquids have a higher thermal capacity than air, liquid cooling has been used in high power radial flux electrical machines. This typically involves water being passed through a series of channels in the casing, which will be in thermal contact with the stator. Such a cooling configuration presents a number of thermal resistances between the heat source and the heat sink, limiting the heat transferred and hence the performance of the machine. The knowledge developed for radial flux machines, has been transferred to the design of AFPM machines, with the cooling channels embedded in the stator iron or in the stator plate for single rotor machines. Such liquid cooled machines rely on air-cooling for the copper end windings. The scope of this work is to present a temperature profile for a pole piece for a liquid cooled stator in YASA© electric machine. A high-resolution lumped-capacity thermal model is also presented, and compared to the experiment. The paper shows how a high-resolution model can reveal much more valuable information on the thermal aspects of the stator. (8 pages)
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Field correlation between electromagnetic and high flux stator core tests
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0144
In stator core interlamination insulation fault tests, there is a commonplace expectation that the Quad signal detected by EL CID is correlated to the high flux test, at the rate of 5-10°C/100 mA. Evidence to date has been supportive but inconclusive. A new opportunity has been taken to review 106 reported core fault test results from the field on turbo and hydro-generators, where both tests were conducted on the same fault. A number of normalisation corrections were proposed and applied, which resulted in the population mean trend correlation lying between 8.5-10.7°C/100 mA with a 95% confidence factor. The central quartiles embrace the 6-12°C/100 mA range, close to the expected rate. (6 pages)
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The impact of variable and fixed DC supplies on the design of EV traction drives
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0194
Electric vehicles (EV's) are a gradually growing field for electric traction machines due to energy and environmental related constraints [1, 2]. The traction system of an EV consists of an electric traction machine (TM), power conversion electronics and energy source(s). The energy source(s) provide a DC link supply for the traction system. The impact on the electric traction machine design from the DC link variation is investigated in this paper. (2 pages)
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Rotor losses in laminated magnets and an anisotropic carbon fiber sleeve
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0282
High speed fault tolerant permanent magnet machines have strong asynchronous airgap harmonics, making them susceptible to rotor eddy-current losses. These losses can be reduced by using novel high resistivity materials like plastic bonded magnets and carbon fiber reinforced retaining sleeves. This paper examines by numerical studies the consequences for the losses of using these materials. The effect of laminating the magnets and the losses in the anisotropic sleeve are analysed with 3D simulations, using simplifications determined with 2D simulations. The anisotropic resistivity of the sleeve roughly doubles the losses compared to an isotropic sleeve, while laminating the magnets in n slices reduces the losses by 1/n<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">1.8</sup>. (6 pages)
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The comparison and analysis for loss of excitation protection schemes in generator protection
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0071
Loss-Of-Excitation (LOE) condition of a generator may cause severe damages on both generator and the interconnected systems. This paper analyses the behaviours of different LOE protection schemes, such as R-X, G-B, P-Q and U-I schemes, for a hydro generator, which is connected to an infinite bus. Based on the simulation results, the reliability and stability of existing LOE protection schemes are compared and a preferred scheme is selected. An improvement to the scheme is also proposed to prevent the LOE relay incorrect operation during external faults, such as short-circuit faults on busbar or transmission lines. (6 pages)
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Analytical determination of the orthotropic material behavior of stator bars in the range of the end windings
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0283
The end windings of generators are excited to vibrations due to electromagnetic forces which can cause severe damage (especially in case of resonance) and noise. To avoid this, it is important to predict the natural frequencies and modes of the end windings with finite elements during the design process. Hence, a material model of the complete stator bar is necessary. This paper shows the development of such a material model. The composite structure of a stator bar is quite complex and makes it impossible to provide a quick calculation of the eigenvalues. That's the reason for using a suitable, homogeneously, geometry based solid model. (8 pages)
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A extended-range hybrid powered scooter
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0355
As the electric scooter market grows, one of the major problems facing designers of pure EVs is getting sufficient range from batteries that can't cope with long journeys. The alternative is to have a range extender of hybrid powered scooter in which a small size of fuel cell stack combines with a battery powered electric motor. However, in such models, electric-only range is restricted to just a few miles. However, adding a small range-extender fuel cell to drive a hybrid power output or charging the battery when idle or low power periods allows range to be increased to an increase of miles. The problem with this solution, though, is cost. This paper shows both the modelling and simulation of a hybrid powered scooter and the experimental results. There is other, more detailed feasibility on fuel cell range-extender for a hybrid powered electric scooter. In experimental data, the result of electric scooter can unceasingly run by increasing the range from 100 kilometres to 126 kilometres at a fixed speed of 45 km per hour with a PEMFC of range extender by using 134 litres of hydrogen fuel. The experimental data are also compared with the pure battery powered scooter. Not only can the range of adding a small size of fuel cell be increased further, but also the test performance can be more brilliant than that of a pure battery powered scooter. (7 pages)
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A comparison of cage and nested-loop BDFM rotors
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0294
The Brushless Double-Fed Machine (BDFM) is a type of variable speed generator or drive. Using theoretical analysis of simple BDFM rotors this paper establishes trends in how rotor structures determine the rotor's equivalent circuit resistance, leakage inductance and turns ratio. The variation in measured parameters of five prototype rotors is then analysed in light of the trends found. Both the theory and experimental results suggest a significant performance advantage in using cage+loops type rotors as opposed to the simple nested loop type more usually employed. (6 pages)
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1MW multi-stage air-cored permanent magnet generator for wind turbines
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0319
The development of a 1MW PM generator topology for the offshore wind applications is outlined. The concept has been proven at lab scale, and now it is being scaled up to the MW level, where the technology has greatest potential. Detailed electromagnetic, structural and thermo-fluid modelling is described along with experimental investigation on full scale modules. The experimental work provides confidence in the design and modelling work completed allowing the design to be finalised. (6 pages)
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Extending the life of a generator through power management
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0190
This work will outline the endeavours taken in the attempt of modelling the behaviour of a generator in an OWC with the aim of obtaining in-service load profile. Temperature and voltage stress-levels are calculated using mathematical models. These models, in conjunction with a chosen deterioration model of the electrical insulation systems, are used to predict the life of the generator. The paper then proposes power management strategies to extend the working life of the machine in case no maintenance is possible. (6 pages)
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An innovative oil immersed power stack for wind power conversion using series connected GCTS
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0242
A novel 450 kW DC wind power generator has been built using Active Stator technology, with an integrated oil immersed power electronic converter. The converter utilises unpackaged series connected Reverse Blocking Gate Commutated Thyristors (RB-GCT), operating at unity gain, to achieve high power density within a sealed `i-CAN' stack enclosure. The stack is cooled with synthetic ester oil which is also utilised as a liquid dielectric to provide 3 kV isolation in a small converter footprint.. The Active Stator machine is capable of operating in four quadrants for either motoring or generating. (5 pages)
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Control of an AC brushless permanent-magnet machine using long supply cables
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0265
The use of a long cable between an inverter and motor is recognised as problematic and a cause of insulation failure in motors. The cable also introduces a voltage drop and phase shift in the fundamental voltage at the motor terminals, reducing the available motor torque in open-loop control, and affecting the stability of a closed-loop controller. This paper investigates the performance of a brushless, permanent magnet motor in order to determine the maximum operating distance between the motor and its inverter. The study develops simulation models of the motor in open and closed-loop modes, with and without the inclusion of a line filter. The ability to track changes in reference speed and reject torque disturbances is shown to depend on the resistance of the damper circuits in open-loop control, but is not an issue in closed-loop control. The maximum operating distance depends on cable resistance, and a practical operating limit of 2km is given for the motor-cable combination studied. (6 pages)
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Online optimized stator flux reference approximation for maximum torque per ampere operation of interior permanent magnet machine drive under direct torque control
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0266
This paper presents an online optimized stator flux reference approximation scheme for application of direct torque control (DTC) technique to interior permanent magnet (IPM) brushless AC (BLAC) drives with maximum torque per ampere (MTPA) operation. It is found that by considering dq-axis stator flux components instead of stator flux magnitude, straightforward mathematical functions for computing stator flux reference from the relevant torque reference to achieve MTPA operation can be derived. It is also demonstrated that by properly selecting initial value for approximating the proposed stator flux equation utilizing the Newton-Raphson method, a high degree of accuracy can be obtained utilizing only one computing step. It is shown that MTPA operation can be achieved for a DTC-based IPM BLAC drive using the proposed stator flux reference approximation scheme. Simulation results confirm validity of the proposed method. (6 pages)
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Directional reactive power undervoltage protection - a protection concept for connecting decentralized renewable energy sources
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0001
With their increasing number, it is getting important that decentralized and renewable energy sources are supporting the stabilization of the system voltage after short voltage dropouts. Often, in the past, these generators were disconnected during network faults. This is not adequate anymore, as it would lead to a loss of a considerable amount of feed-in power. However, if the generators stay connected, it must be ensured that they are not receiving reactive power, as this would lead to a collapse of the grid. In Germany, a number of legal requirements and grid codes are regulating the connection of such generators. These documents also stipulate the use of Directional Reactive Power Undervoltage Protection (Q→& U< protection) that would disconnect such energy sources if they received reactive power during faults on the network. This paper gives an overview about the legal documents and an introduction to the protection function mentioned above. The basic principle of the Q→& U< protection is explained by means of its requirement specifications. Furthermore, the paper will show up standardized test methods evaluating the Q→& U< protection. It will describe how to test the releasing functions, the reactive power direction determination and also all binary inputs and outputs that are necessary for the protection function. (5 pages)
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Innovative injection-based 100% stator earth-fault protection
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0112
Injection-based 100% stator earth-fault protection has been used for many years. However traditionally signals with frequency between 10Hz and 25Hz have been injected into the stator winding. To inject such a signal, either a dedicated grounding transformer with secondary grounding resistor or injection on primary side of the grounding circuit, is normally used. This paper will present a novel approach to such protection. Injection signal with frequency slightly higher than the power system rated frequency is used (e.g. 87Hz signal in a 50Hz power system). Such signal frequency enables the following advantages for new injection-based protection: 1. Injection is always performed on secondary side of a transformer. This transformer can be either a grounding transformer or a voltage transformer. Thus no change to the primary grounding circuit of the machine (e.g. splitting of the primary resistor in the star point) is required. 2. Injection via neutral point VT or even via open delta VT located at the generator terminals is possible. This ensures readily available injection point for almost any unit-connected generator. 3. Injection via a VT enables this protection to be applied to ungrounded or inductance/resonance grounded stator windings. 4. Because of the higher injection frequency the injection unit and the injection transformer are relatively small. (6 pages)
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Modelling and analysis of electromagnetic torque in direct drive PM machines with rotor eccentricity
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0278
The influence of rotor eccentricity on torque oscillations as well as average output torque of permanent magnet (PM) machines with integral number of slots per pole per phase has been studied using 1-dimensional (1D) analytical modelling and 2-dimensional (2D) finite element (FE) method. It is shown that cogging and ripple torque are amplified by rotor eccentricity due to the contribution of new flux density components created by eccentricity, while this amplification follows a quadrature function against the eccentricity degree. Furthermore, it is shown that the average electromagnetic torque can be increased by rotor eccentricity provided that magnetic saturation is negligible. The analytical predictions have been validated by FE analysis of a direct drive PM machine. (5 pages)
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Comparison of 3- and 9-phase brushless PM drive systems for aerospace actuation
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0249
Nearly all electric vehicles (EVs), hybrid electric vehicles (HEVs), more electric aircraft, electric ship propulsion and others power conversion industrial applications uses power electronic inverters to convert AC to DC or vis versa, as in the starter/generator machine system and generation/regeneration process of the traction motor. Also, it has become possible to integrate HEVs power electronics component in one package with one set of liquid cooling. Recently, compactness and reliability of the power conversion and generation system design in automotive, in particular, and in aerospace industries are growing with global necessity of shifting from conventional airborne emission vehicles and aircrafts to the green all electric ones. Therefore, an advanced technology in the area of energy storage, conversion and dc-link capacitors, which account for a major fraction of the volume, weight and also cost of the inverter, is demanded by the developer of HEVs and other industrial areas. In three-phase system a dc-link voltage source inverters (VSI) are fed via controlled or uncontrolled rectifier bridges from a main source. Here, a dc-link capacitor is usually used to maintain a stiff dc-link voltage across the VSI, and to perform other tasks, as in [1]. Such that, in this application, the dc-link capacitor deals with the main voltage fluctuation and provides a dc-link current ripple to suppress the generated electromagnetic interface (EMI) caused by pulsating current (ripple current) associated with the inverter switching. It is recognized in the literature [1-7] that for voltage stiff inverter the dc-link capacitor adequate selection, sizing and minimizing presents a major issue for improving electrical system compactness and utilization. Lai et al discusses the use of low-inductance high current film capacitor in a high-power dc-bus inverter for battery-powered traction motor drives [2]. Another discussion that shows merits of an advanced film capacitor technology over conventional electrolytic capacitor for dc-link applications was presented by Grinberg et al [3]. A dc-link capacitor minimization method via direct capacitor current control has been described by Gu and Nam [4]. Such that, the dc-link capacitor can be minimized by making the converter side dc-link current similar to the inverter side dc-link current waveform in a pulse width modulation (PWM) converter-inverter system. However, the dc-link capacitor reduction technique of Gu et al is not for stiff voltage-source inverter. A simple analytical expression for current stress on the dc-link capacitor caused by the load-side inverter of the voltage dc-link converter system is derived by Kolar and Round [1]. Conclusions have been obtained by some of the previous papers, which declare that the dc-link capacitor of practical systems usually determined by the effective capacitor current stress and not, for example, by a given maximum admissible value of the amplitude of the dc-link voltage ripple [1]. In Dahono paper [5], analysis and minimization of output current ripple of multiphase PWM inverters was presented. The minimization of this current ripple is achieved for three-phase PWM inverter by injecting a twenty-five percent third harmonic in the reference sinusoidal signal. Whilst, minimization of the output current ripple of a multiphase PWM inverters can not be attained and it will become unsymmetrical if harmonics are injected into the sinusoidal reference signal [5]. Also the paper discussed by Dahono mentioned that multiphase PWM inverters with number of phases equal to multiple of three will give better results than the one that is not a multiple of three, for example, if the number of phases is a multiple of three, the multiphase PWM inverter can be operated as several three-phase PWM inverters. As for the authors knowledge, no verification nor investigation of this claim have been found in depth in the literature. In the paper, 3-phase and 9-phase PWM inverter modules with different threeand nine-phase brushless permanent magnet (BLPM) machine configurations will be analysed in detail to show the adequate use of this configuration to either eliminate the need or significantly reduce the size of the dc-link capacitor that suppress the generated EMI caused by pulsating current associated with the inverter switching for stiff voltage-source inverter. In addition, different operating points on the general torque speed curve for different BLPM machine drive configurations will be investigated to give decision of the adequate and best machine drive configuration, in terms of improving power and torque capabilities with the minimization of output torque ripple, which can be practically implemented and used in many promising industrial areas. (2 pages)
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Equivalent capacity of the lower voltage ride through for wind farm from overcurrent protection in power collection lines
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0075
Magnitude and duration of voltage sags are the most important two factors to the Lower Voltage Ride Through (LVRT) capacity of the wind generator. Since most voltage sags are caused by the system faults, and sag durations are controlled by the tripping time of overcurrent relay in power collection lines based on the sags' magnitude. The specification of the LVRT capacity of wind generator is introduced into the operation characteristics of the relay in power collection lines. The evaluation model of equivalent LVRT capacity to overcurrent protection is proposed in paper, and the equivalent LVRT capacities from zone I and zone II relay are quantified. Improvement measures are also proposed. (5 pages)
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Thermal modelling of a low speed air-cooled axial flux permanent magnet generator
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0271
This paper presents the assessment of air flow in a multi-stage Axial Flux Permanent Magnet (AFPM) prototype which is set to operate at 100rpm. The CFD models are validated using experimental results to give a greater understanding of the air flow developed in the generator. The proposed ventilation design reduces the pressure loss at the entry resulting in a 10% reduction in maximum stator coil temperature in the CFD modelling. (7 pages)
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Optimal split ratio and torque comparison of surface-mounted permanent magnet machines having inner or outer rotor
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0159
Permanent magnet (PM) machines are widely used in many applications. They can have inner (IR) or outer rotor (OR). These two configurations are optimized individually and compared in this paper based on surface-mounted PM (SPM) machines. The optimal split ratio and flux density ratio are derived analytically for both topologies. The analytical models are verified by finite element (FE) analyses. Their optimal designs are compared when they have the same overall size and copper loss. It shows that the OR designs have significantly higher split ratio while the IR designs require much higher flux density ratio for the maximum torque. For SPM applications, the OR designs exhibit higher torque than IR designs. (6 pages)
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Torque distribution strategy for a front and rear wheel driven electric vehicle
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0316
Electric vehicles (EVs) with a distributed drive train configuration offer great potential and flexibility for improving the system efficiency, performance, reliability as well as safety. This paper investigates a torque distribution scheme for a front and rear wheel driven EV in order to improve the drive train efficiency over a wide torque and speed range as a part of the EU funded P-MOB project. It has been shown the maximum efficiency is achieved if the total torque required by the vehicle is shared equally between the two identical motors. In addition, the distribution of the energy consumption over a New European Driving Cycle (NEDC) is analyzed and the regions of high speed, low torque are identified to have a high level of energy consumption, where the motor efficiency improvement in these regions is the most important. Therefore, this paper further proposes to operate just one motor to provide the total required torque in the low torque region. A clutch may be employed between one motor and gearbox (differential), thus “switching off” its idle loss (no-load loss, flux-weakening loss), and improving the drive train efficiency. An online optimized torque distribution algorithm has been devised based on the motor efficiency map to determine whether the second motor should be disengaged by the clutch in the low torque region. With the proposed optimization scheme, the drive train efficiency can be improved by 4% over the NEDC cycle. Experimental test results validate the proposed torque distribution strategy. (6 pages)
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Optimum look-up table for reduction of current harmonics in direct torque controlled dual three-phase permanent magnet brushless ac machine drives
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0183
This paper presents an investigation into application of direct torque control (DTC) methodology to a dual three-phase (DTP) permanent magnet (PM) brushless AC (BLAC) machine drive. Fundamentally, DTP topology including two sets of three-phase windings shifted by 30 electrical degrees in space together with two isolated neutrals enables cancellation of the 6th harmonic torque component and therefore results in enhancement of torque production. However, since the stator phase current harmonic components which do not participate in electromagnetic torque production are let freely circulate inside the machine and only limited by values of the stator phase resistance and leakage inductance, the stator phase current waveforms under the DTP topology are seriously non-sinusoidal. Therefore, a voltage vector selection scheme together with an optimum look-up table (LUT) for DTC technique is proposed to minimize these useless current harmonic components. Simulation results confirm validity of the proposed method. (6 pages)
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A novel electromagnetic core structure for axial radial flux permanent magnet electric motor
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0163
Most of the automobile companies are in to the research and development of electric and hybrid vehicles to promote fuel efficient and environment friendly vehicles. Being one of the major energy consuming part in hybrid and electric vehicles, an electric motor should have high efficiency, high torque density in all the drive cycles and must be compact in design. This paper presents a structure for the permanent magnet electric motor which has both axial and radial magnets and a common electromagnetic core for both. This common core provides path for both axial and radial flux. This structure enhances the magnetic loading and hence developed torque and facilitates more air flow inside the motor. A comparison study on air gap flux and developed torque between motors having conventional core structure and proposed core are presented and these are validates with Finite Element analysis. (6 pages)
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Analytical modelling of parasitic force in permanent magnet machines accounting for slotting effect
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0276
Based on the subdomain field model accounting for tooth-tips, the force distribution and unbalanced magnetic force of surface-mounted PM machines are analytically calculated respectively for open-circuit only, armature reaction only and on-load. The finite element results confirm that the developed model has excellent accuracy, while the complex permeance model shows a large error in the predicted unbalanced magnetic force and lowest spatial order harmonic of the force distribution, especially on light load. (6 pages)
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Optimal magnet shaping with third order harmonic for maximum torque in brushless AC machines
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0275
This paper describes the optimal magnet shaping techniques to increase the torque capability in brushless AC machines by utilising the 3<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">rd</sup> order harmonic in inverse cosine shape airgap and sinusoidal shape magnet. It is analytically found that for different types of magnet shaping methods, the optimal magnitude of the 3<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">rd</sup> order harmonic is always 1/6 of that of the fundamental, which is validated by the finite element analysis. By utilising the optimal 3<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">rd</sup> order harmonic, the average torque of two 10-pole/12-slot machine can be increased by ~11%, while their torque ripple is only slightly increased by less than 1.5%, compared to machines employing magnet shaping techniques without the 3<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">rd</sup> order harmonic. (6 pages)
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Design of high torque traction motors for automotive applications using modulated pole SMC machines
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0311
This paper gives details of an ongoing collaborative project in the area of automotive traction drive machine design. The relationship between electrical frequency, torque, pole number and iron loss in modulated pole machines is investigated with respect to fulfilling an industrially relevant specification. A number of alternative topology configurations are simulated, presented and discussed. (6 pages)
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Performance of axial flux permanent magnet generator for human power application
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0306
This paper presents the design and performance of a prototype axial flux permanent magnet generator for human power application. An improved model is developed to achieve better match between measured and predicted performance. Results show that there is good agreement between measured and predicted EMF voltage. However, significant differences still exist between measured and predicted losses especially at low rotational speeds. (5 pages)
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An improved torque density Modulated Pole Machine for low speed high torque applications
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0262
This paper presents a new topology for three-phase Modulated Pole Machines. This new topology the “Combined Phase Modulated Pole Machine” is analysed and compared to the more traditional technology of three separate single phase units stacked axially with a separation between phases. Three- dimensional Finite Element calculations are used to compare performance of the machines under the same conditions, it is shown that the new Combined Phase topology produces a greater torque whilst reducing the number of components required to assemble the machine and increasing its mechanical integrity. (6 pages)
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Fidelity requirements in brushless permanent magnet motor modelling
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0277
The paper discusses the development and validation of motor simulation models to aid in the design of actuators for use with automotive variable geometry turbochargers. The specific focus is on the benefit of increasing the fidelity of the motor model, against the tradeoff of increased complexity. Several separate models of the same brushless permanent magnet motor are developed and validated against measurements made from a sample motor. These results, along with the simulation time required for different types of model, are presented and used to draw conclusions on the appropriate fidelity of model for different types of analysis. (6 pages)
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A novel permanent magnet motor with large axial channels for downhole applications with high-torque requirements
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0279
The innovative electric motor concept is presented. The main feature of the novel concept is accommodation of relatively large axial channels in a slim electric motor without sacrificing its torque density and radial dimensions. The motor is analyzed and the analysis is then validated by the experiments. The resulting motor performances are given and applications for the motor proposed. (6 pages)
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The design of AC permanent magnet motors for electric vehicles: a computationally efficient model of the operational envelope
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0251
Salient brushless AC (BLAC) permanent magnet (PM) motors are a preferred topology in the rapidly growing area of electric vehicle traction due to their inherent high efficiencies and excellent power densities. In the design of these systems it is important to appraise the motor performance across the entire torque-speed envelope. This paper presents computationally efficient techniques that allow rapid and accurate modelling of the entire operational envelope of any BLAC PM motor, enabling the generation of torque/speed characteristics and loss maps that can be used in an iterative design process. The proposed techniques are validated against test data from an in-house 35kW interior PM motor design and a comparison between a measured and computed efficiency map for the 2004 Toyota Prius motor is undertaken. (6 pages)
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Zero-speed sensorless drive capability of fractional-slot inset PM machine
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0269
This paper investigates the capability of an inset PM motor with concentrated coils fractional-slot winding to be controlled by means of sensorless techniques using high frequency signal injection. The inset PM motor considered is a 12-slot 10-pole motor, whose performance has been obtained by means of both finite elements simulations and experimental measurements. It will be shown that the motor presents good performance to be controlled by sensorless techniques, and the expected performance agree with the experimental results. (6 pages)
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Modelling and analysis of airgap flux density in direct drive PM machines with rotor eccentricity
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0184
The influence of rotor eccentricity on airgap flux density components in direct-drive permanent magnet (PM) machines has been studied using 1-dimensional (1D) analytical model and 2-dimensional (2D) finite element (FE) method. The flux density components have been classified with respect to their MMF and permeance origins, while the rotor eccentricity impact has been decomposed into time and space domains using 2D FFT. Based on the study it is shown that the influence of rotor eccentricity on slotting permeance components is much more significant than that on the PM MMF components, which explain the underestimated increase of the cogging and ripple torque based on 1D analytical model. Furthermore, it is shown that larger rotor eccentricities give rise to more airgap flux density side bands which are expected to contribute to the cogging and ripple torque. (5 pages)
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Impact of synthetic inertia from wind power on the protection/control schemes of future power systems: simulation study
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0030
Future power systems face several challenges; one of them is the use of high power converters that decouple new energy sources from the AC power grid. This decreases the total system inertia affecting its ability to overcome system frequency's disturbances. The wind power industry has created a controller to enable inertial response on wind turbines generators: Artificial, Emulated, Simulated, or Synthetic Inertial. This paper deals with issues related to the synthetic inertia of wind turbines based on full-converters and their effect on the frequency protection/control schemes during the recovery period after system frequency disturbances happen. The main contribution of this paper is to demonstrate (based on simulations) the recovery period of under-frequency transients on future power systems which integrate wind turbines with synthetic inertia capability not completely avoid worse scenarios in terms of under-frequency load shedding. The extra power delivered from a wind turbine during frequency disturbances can substantially reduce the rate of change of frequency providing time for the active governors to respond. However, synthetic inertia might not completely avoid under-frequency load shedding. (6 pages)
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Measurement of heat generation rate in the permanent magnets of rotating electrical machines
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0287
This paper presents an experimental method for measuring heat generation rate in the permanent magnets of rotating electrical machines. The results obtained from the experimental work are used to derive an empirical correlation which is subsequently used to predict the total thermal energy stored in a magnet after a speed varying torque load. The results of an uncertainty analysis are offered in order to show the usefulness of the technique. An axial flux permanent magnet machine has been used as a case study in this work, though the methodology could certainly be applied to other topologies. (6 pages)
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Observer based state feedback controller design for pseudo direct drive<sup xmlns="http://pub2web.metastore.ingenta.com/ns/">®</sup> using genetic algorithm
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0263
The paper describes a technique, based on a genetic algorithm GA, for the design and tuning of a state feedback controller with a reduced order observer, for a Pseudo Direct Drive Permanent Magnet Machine PDD. The controller was designed to eliminate torsional oscillations caused by the low stiffness of the magnetic gear, and provide smooth transient and good speed tracking based on ITAE performance index. (6 pages)
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Examination of new current control methods for modern PMW controlled AC electric locomotives
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0314
A railway electrification system supplies electrical energy to railway locomotives and multiple units. There are several different electrification systems in use throughout the world. The single-phase AC network systems are widespread (25 kV 50 Hz or 15 kV 16 2/3 Hz). The Hungarian system is 25 kV 50 Hz AC. This article is just dealing with the AC network supplied locomotives. Nowadays in our country the series wound DC traction motor driven locomotives are still widely used. These vehicles are equipped with diode or thyristor rectifier circuits that inject harmonics into the AC line and distort the line voltage. In our work we examined and compared current control methods that can be achieved by "network-friendly" locomotives connected to distorted line. We worked out a new current control strategy that possesses several advantages. The modern locomotives endeavour to consume sinusoidal current from the AC network, in phase with the network voltage fundamental. In generator mode these endeavour to supply back to the grid sinusoidal current in antiphase to the voltage fundamental. We compared current control methods with this "common" strategy. One of them can reduce the consumed root mean square (RMS) or fundamental current of a distorted line connected modern locomotive in motor mode. Other one can increase the generated RMS and fundamental current in generator mode. With these strategies the harmonic currents can be used for active power. Moreover it turned out that the harmonic content of the network can be reduced by the "new" strategies. For the study, we built a test system. We can model the line side converter of a modern locomotive DC-link frequency converter with the system. A common solution in locomotives is when several line-side converters feed two DC-links. In the test system we modelled these with one converter, while the motor-side voltage source inverters and the electric traction motors were taken into account as a controllable current source DC-link. (5 pages)
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High torque density permanent magnet machine for automotive applications
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0186
This paper presents work done on the analysis of a new permanent magnet machine topology using finite element in order to achieve high torque density specifically for an automotive application. Also different types of electric motors that are suitable for automotive applications are shown. A comparison between these different machines is given by highlighting some of their advantages and disadvantages. (6 pages)
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Comparison of electromagnetic performance of 2- and 3-phase PM brushless AC machines for low speed applications
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0280
This paper compares the electromagnetic performance, such as average torque, torque ripple, iron loss, and magnet losses, of 2- and 3-phase permanent magnet brushless AC machines for low speed applications, with consideration of different slot/pole number combinations. Each machine is optimized to achieve the maximum torque under the same operation speed and thermal constraints by finite element method. The comparison shows that 2- and 3-phase PM machines have similar torque density and efficiency, although 2-phase machines have significantly larger magnet losses, and higher torque ripple than 3-phase machines for the same pole/slot number combination. (6 pages)
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An efficient dynamic control of modern renewable distributed generators for intentional islanding operation
http://dl-live.theiet.org/content/conferences/10.1049/cp.2012.0008
This paper presents a new power controller for inverter-based renewable power generators, which is based on direct power control of active and reactive power. The controller included fast PLL and ROCOF units in order to function in both grid-connection and islanding operations. The controller's performance was tested by detailed computer simulation of a 2MVA renewable power generator with a DC-link energy storage bank. Application tests were carried out within a 20kV primary feeder in parallel with a 0.91MVA diesel generator for different control-modes, in both grid-connection and intentional islanding operations. Transient performance tests, when transferring from grid-connection to islanding and back to grid-connection, demonstrated a seamless effect of control-mode transfer on the distribution network. (6 pages)