1,716 research outputs found
Modeling and analysis of special electrical machines for distributed generation
No full textNowadays, the pollution caused by the massive use of fossil fuel is a well-known critical issue makes the design of the electrical machines a crucial task because the vast majority of the industrial or household applications are integrated with this kind of technology; hence improving the efficiency of electric motors is expected to result in an extraordinary benefit in terms of energy saving. On the other side, the increasing use of renewable energies (like wind energy, hydropower, tidal energy), combined with the distributed generation concept, call for new electric machine technology and for modern design approaches.
This doctoral thesis has been mainly focused on finding analytical procedures to model and analyze some types of electrical machines which are of interest for renewable and distributed generation. The use of analytical approaches is, in some cases, fundamental because numerical methods, mostly based on Finite Element Analysis (FEA), are very inefficient in terms of required time and computation resources.
The types of electrical machines considered in this work are various. The attention is first placed on the slotless surface permanent magnet (SPM) topology (with different types of rotor magnetization). Wound-field synchronous generators with both three phase or multiphase stator are then considered. For the various kinds of the machines taken into account, some modeling, design and analysis studies have been conducted in the attempt to fill some gaps in the existing technical literature.
In the first part of the thesis the purely analytical modeling of slotless SPM machines is addressed. In the work, it has been considered how the stator slotless design can be combined with different surface permanent magnet rotor topologies. The main efforts of the study have been addressed to the purpose of finding an explicit analytical expression to compute slotless machine torque and no-load back-EMF, covering all the SPM rotor topologies of interest.
The subsequent part of the thesis, is about the analytical computation of end-coil leakage inductance in concentric windings. For a good dynamic modeling of machines equipping this kind of winding, it is useful that their mathematical model is implemented and that model parameters are identified with good accuracy. The proposed technique shows a very good accordance compared with a 3D FEA simulation and is also validated though tests conducted on a dedicated experimental set-up.
Multiphase machines are attractive for many energy-saving fault-tolerant applications thanks to their higher efficiency and intrinsic resilience to faults. A challenging task in the modeling of multiphase machines for design and simulation is identifying the self and mutual inductances due to leakage fluxes. In this thesis is also presented a novel approach for the leakage inductance determination in multiphase machines based on routine tests combined with very simple 2D magnetostatic FEA simulations.
The subsequent part of the thesis is about the design of wound-field synchronous generators specifically required to operate in a distributed generation system where significant fluctuations are known to frequently occur in both voltage and frequency. Design provisions are investigated to improve the generator resilience to these grid disturbances.
In the last part of this thesis the attention is focused on multiphase alternators interfaced to DC distribution systems through multiple rectifiers. As a new finding presented as a part of this investigation, it is shown that a short circuit fault occurring on AC/DC rectifier terminals generates a strongly oscillatory behavior with much larger current peaks than could be predicted with conventional models regarding short circuit transients in DC networks
A sizing equation for slotless surface-mounted radially-magnetized permanent-magnet machines
No full textSlotless surface permanent-magnet (SPM) machines are attractive for many applications where it is important to minimize the cogging torque and or the eddy-current losses due to slotting effects. The design of these machines is often approached through Finite Element Analysis (FEA) simulations interfaced to design optimization programs, leading to a significant computational burden. In this paper, a compact but accurate sizing equation is established linking machine maximum torque to the main design data. The sizing equation can be used for a fast first-attempt sizing of the machine with no need for FEA simulations and no need for complicated magnetic field solutions. The proposed sizing approach is based on an explicit fully-analytical expression of machine torque, which is validated by FEA simulations
Stator inductance matrix diagonalization algorithms for different multi-phase winding schemes of round-rotor electric machines. Part I, Theory
No full textThe stator winding of multi-phase machines can be designed according to different schemes, which differ by either the number or the spatial arrangement of phases. For control and analysis purposes, it is often useful that the stator inductance matrix is reduced to a diagonal form. This allows for the multiphase machine to be split into independently-controllable systems and directly leads to stator harmonic impedance determination. Simple and compact diagonalization algorithms are established in this paper covering all possible multi-phase schemes of practical importance with a unified approach, under the hypothesis of uniform air-gap and negligible magnetic saturation. In a companion paper, All the proposed equations are experimentally assessed though dedicated tests on several multiphase winding schemes
Cogging torque fast computation method for surface permanent magnet machines based on winding function theory
No full textVarious analytical techniques have been proposed in the literature for cogging torque computation in Surface Permanent Magnet (SPM) machines. Among the various available methods, the ones found to be satisfactorily accurate are based on the Maxwell's stress tensor, which involves both normal and tangential air-gap field and lead to quite involved calculation formulas. In this paper, a relatively simple alternative is proposed where permanent magnets are modeled as equivalent field circuits to which a well defined winding function can be associated. The approach leads to a plain cogging torque formulation where only the normal no-load air-gap flux density appears. The accuracy of the method is assessed by Finite Element (FE) analysis on some sample SPM machine geometries. The results are shown to match FE simulations with a satisfactory accuracy compared to Maxwell-stress-tensor-based analytical techniques available from the literature
Stator inductance matrix diagonalization algorithms for different multi-phase winding schemes of round-rotor electric machines. Part II, Examples and validations
No full textThe stator winding of multi-phase machines can be designed according to different schemes, which differ by either the number or the spatial arrangement of phases. For control and analysis purposes, it is often useful that the stator inductance matrix is reduced to a diagonal form. This allows for the multiphase machine to be split into independently-controllable systems and directly leads to stator harmonic impedance determination. Simple and compact diagonalization algorithms have been established in a companion paper covering all possible multiphase schemes of practical importance with a unified approach, under the hypothesis of uniform air-gap and negligible magnetic saturation. In this paper, the theory and algorithms proposed for inductance matrix diagonalizations are illustrated and validated by applying them on a on several multi-phase winding schemes implemented in a prototype machine with a reconfigurable stator winding
A motor design with self-adjusting flux capability for wide-speed-range auto motive applications
No full textOne of the most common issues in permanent magnet motors for automotive applications is to improve their capability of operating over very wide speed ranges. For this purposes, various motor design techniques have been proposed in the literature. After a brief review of these techniques, the paper presents an idea for improving the flux weakening capability of permanent-magnet reluctance-assisted motors. The idea is based on using an auxiliary field circuit embedded in flux barriers and used to partly demagnetize the motor above the base speed. The field circuit is fed by a brushless permanent-magnet exciter and a diode rectifier. While at low speed the field is not energized, it automatically activates above the base speed by means of a centrifugal switch. As discussed in the paper, the auxiliary field current increases linearly with the speed so as to progressively reduce motor flux with a consequent beneficial reduction in the current to be fed by the inverter for flux regulation
On the validity of the harmonic superposition principle for computing rotor eddy current losses in permanent magnet machines
No full textModeling of Split-Phase Machines in Park’s Coordinates. Part I: Theoretical Foundations
No full textA split-phase machine is a special electric machine whose stator winding is split into multiple (N) three-phase sets. The possibility to supply it through N independent inverters makes it attractive especially when high power and reliability are required. So far, the dq0 refeence frame representation, originally introduced for three-phase machines, has been applied in detail to split-phase configurations in the N=2 case only. In this paper, the extension to an arbitrary number of stator sets is investigated from an analytical viewpoint. In particular, the paper shows that when N exceeds two, the d-axis and q-axis stator voltage equations are no more decoupled, in general, as it happens for N=1 and N=2. Such d-q cross-coupling is explained in terms of mutual leakage inductances, regardless of possible rotor saliencies and magnetic saturation. The implications of these results in terms of equivalent circuit representation will be presented in a companion paper (Part II)
On the use of conformal mapping in the analysis of electric machines
No full textConformai mapping is a widespread mathematical technique to approach the electromagnetic study of electric machines. In its practical application, however, it is relatively easy to incur in errors which make results unreliable. In this paper, some fundamental but possibly deceitful facts in conformal mapping application are described, focusing in particular on: energy conservation in magnetostatic and time-harmonic problems; current source assignment in the transformed domain; transformation of the flux density components through conformal mapping. The addressed topics are first investigated from a theoretical point of view; then some application examples, based on Finite Element Analysis are provided for illustration and validation purposes
Explicit Torque and Back EMF Expressions for Slotless Surface Permanent Magnet Machines with Different Magnetization Patterns
No full textSlotless permanent magnet machines are attractive in some modern drive and power generation fields, where the cogging torque and additional losses need to be minimized or removed. The stator slotless design can be combined with different surface permanent magnet (SPM) rotor topologies. In this paper, explicit analytical expressions are derived to analytically compute the slotless machine torque and no-load back Electro-Motive Force in the case of segmented SPM rotor with parallel, radial, or Halbach-array magnetization patterns. The expressions are found by solving the magnetic field due to the slotless stator winding and to the permanent magnet blocks; the latter modeled through equivalent surface current densities. The accuracy of the method is successfully assessed by comparison with the finite-element analys is (FEA). The proposed formulas are an effective alternative to
the FEA to quickly compare different design solutions as well as to optimize them. Application examples are provided in which the presented method is adopted to define the machine cross section that maximizes the torque density
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