Modelling the unbalanced magnetic pull in eccentric-rotor electrical machines with parallel windings

This research work is focused on developing simple parametric models of the unbalanced magnetic pull produced in eccentric-rotor electrical machines. The influence of currents circulating in the parallel paths of the stator winding on the unbalanced magnetic pull is given the main attention. The interaction between these currents and those circulating in the rotor cage/damper winding is also considered. First, a parametric force model for an eccentric-rotor salient-pole synchronous machine is developed. The effects of the parallel stator windings are not considered in this model. Next, a low-order parametric force model is built for electrical machines equipped with parallel stator windings but operating without the rotor cage/damper winding. This force model is applicable to salient-pole synchronous machines as well as to induction motors. And finally, a special force model is developed for electrical machines furnished with parallel paths both in the rotor and stator windings. This model accounts for the equalising currents circulating in the rotor and stator windings and also for the interaction between these currents. This third force model can be applied to a salient-pole synchronous machine and to an induction machine. The parameters of the force models are estimated from the results of numerical simulations applying a soft-computing-based estimation program. All the developed force models with the estimated parameters demonstrate a very good performance in a wide whirling frequency range. The effects of parallel paths in the rotor and stator windings on the unbalanced magnetic pull are investigated numerically. The acquired results reveal that the total unbalanced magnetic pull and its constituents related to the fundamental magnetic field and slotting are strongly affected by the presence of parallel paths in the stator winding. However, unlike the rotor cage, parallel stator windings may instigate anisotropy in the unbalanced magnetic pull. In such cases, the results of the numerical impulse response test may differ significantly from the conventional calculation results. It is also shown that, despite the fact that the number of parallel paths in the stator is often substantially lower than the number of parallel paths in the rotor, parallel stator windings may still provide a more efficient UMP mitigation than the rotor cage/damper winding.reviewe

Mathematical Models for the Design of Electrical Machines

This book is a comprehensive set of articles reflecting the latest advances and developments in mathematical modeling and the design of electrical machines for different applications. The main models discussed are based on the: i) Maxwell–Fourier method (i.e., the formal resolution of Maxwell’s equations by using the separation of variables method and the Fourier’s series in 2-D or 3-D with a quasi-Cartesian or polar coordinate system); ii) electrical, thermal and magnetic equivalent circuit; iii) hybrid model. In these different papers, the numerical method and the experimental tests have been used as comparisons or validations

Electrical Machine Topologies: Hottest Topics in the Electrical Machine Research Community

In this article, the state of the art in electrical machine design is outlined underlining the problems and challenges to be solved by engineers. As highlighted in this article, even if electrical machine design is often considered a mature issue from the technical and technological point of view, every year, new progresses and steps forward are made. New and more sophisticated design tools can be used worldwide, and innovative manufacturing processes, new insulation materials, and higher performance magnetic materials are available on the market. In addition, the evolution of the hardware used in digital control and new powerful power electronic devices represents a constant stimulus to improve the performance of electrical machines and reintroduce electrical machine structures that were not adopted in the past due to technological and technical constraints. As shown in this article, electrical machine design is an evergreen topic, and its importance is rising more each year under the push of more energy-saving requirements and higher-efficiency systems for electromechanical conversion. A green world will not be possible without electrical machines

SRM drives for electric traction

"GAECE" -- PortadaDescripció del recurs: 11 maig 2020GAECE (Grup d’accionaments elèctrics amb commutació electrònica). The group of electronically commutated electrical drives is a research team of Universitat Politècnica de Catalunya (UPC BARCELONATECH), which conducts investigation in four areas: electrical drives, power electronics, mechanics and energy and sustainability. Regarding electrical drives, research focuses on the development of new reluctance, permanent magnet and hybrid electrical drives. The main goal of those electrical drives is the integration of the power converter/controller and the mechanical transmission, being specially intended for the traction of light electric vehicles. That research is carried out by using the analysis of finite elements, taking into account eco-design criteria, considering new materials and new control strategies.First editio

Theoretical and Experimental Investigations of a Permanent Magnet Excited Transverse Flux Machine with a Segmented Stator for In-Wheel Motor Applications

A three-phase transverse flux permanent magnet (PM) motor with flux concentrating (FC-) topology that has a segmented stator is studied in this dissertation. The phases of the stator have been placed around the rotational axis of the machine instead of placing them in a classical way over each other along the axial direction. Through this phase arrangement, the electrical and mechanical shifts between the phases are considered to ensure proper operation of the transverse flux machine (TFM) without the need of extra components such as a start-up capacitor or a special designed power supply. The segmented stator construction has required that the conventional ring coils to be replaced by a type of concentric winding that take a saddle shape enabling parallel magnetic circuits to take place. This has initiated studying the effect of the distances located between the phases on all over the performances of the machine. In order to select an initial construction for the stator, a preliminary assessment study of some conventional PM-TFMs having ring coils are carried out, through which they are re-designed as outer rotor motors and compared based on the level of electromagnetic torque and the inductance profile. As the main application of the design is to achieve a compact construction for an outer rotor, low noise and speed too for possible future in-wheel applications, the most interesting issue in this study is how to bring all the phases of the machine around the shaft in one layer without losing the torque productivity as when the phases are placed under each other in the conventional way. Therefore, the designed machine is set in further theoretical evaluation studies via finite element method (FEM) with the conventional layered TFM, and it shows that the TFM with segmented windings has a better torque density as its correspondence in the conventional layered structure. This result is in favor to the segmented structure, in particular, about 31% of the PMs number in the segmented structure (i.e., total number of PMs located between the phases) will not have an active role in the torque production. A detailed mathematical theory has been analytically developed and investigated to show the validity and limitation of the design. The study has incorporated how the segmentation of each phase and placement of the two parts opposite to each other can improve the mechanical balance of the TFM and hence quite rotation. The approach has been shown for two- and three-phase PM-TFMs. Moreover, illustration for applying the same principle of segmented stator to surface PM topology of TFMs is analytical verified and shown via FEM. Possible constructions with segmented stators are developed in a periodical table format to give the machine designer a shortcut for a possible construction with the selected number of magnets, number of segments per phase and the desired space between the phases. Since the noise is a well-known problem of TFMs, due to the ripple in the electromagnetic torque waveform and the natural magnetic normal forces, the normal and axial forces in PM-TFM with segmented stator have been investigated too, where introducing more segments per phase will reduce their effects. In order to validate the theoretical investigation, a low-scaled test machine is designed, constructed and a complete test bench has been built to experimentally test the machine. The experimental investigations have included generator and motor operation modes as well as measuring the ratings, performances of the machine and the starting methods. The test machine has reached via the conducted tests an average torque of about 2.1 Nm with an efficiency of 53% and it has a great development potential to be improved via shaping of stator poles, the room available for the windings, fill factor and more optimization possibilities. Based on the theoretical and experimental investigations, the operation of the segmented winding design of PM-TFM proves itself to work and to have a future for compact motors in industrial operation, or as in-wheel outer rotor motor for mobile platforms. For higher power applications, a machine with such type of stator should be designed with big diameters that will allow the utility of more PMs as well as more segments per phase, where both are involved in the torque production, i.e., more torque density for the segmented TFM

Design of a high speed high power switched reluctance motor

PhD ThesisAn increase in the price of rare earth materials in 2009 prompted research into alternative motor technologies without permanent magnets. The SRMs have become more of an attractive solution as they are relatively simpler to construct than other machines technologies hence cost effective. Furthermore, the rugged structure of the rotor makes it suitable for high speed operation, if appropriately designed. This thesis investigates the design, analysis and prototype manufacture of an SRM, that from electromagnetic point of view, meets the power output of the PM machine used in the Toyota Prius, although operating at a higher speed of 50,000 rpm. As a result, the required torque is considerably less than an equivalent motor with the same output power running at lower speed, hence this approach allows for much smaller frame sizes. To achieve the required torque, careful choice of stator/rotor tooth combination, coil number of turns and number of phases is needed. Running at high speed, increases the AC copper loss (consisting of skin effect and proximity effects) and iron loss. These shortcomings are extensively discussed and investigated. The mechanical design of this motor requires careful consideration in order to minimise the high mechanical stresses acting upon the rotor, which are due to the high radial forces caused by the centripetal force at high speed. In order to address the mechanical constraints caused by the hoop stress, a structure common to flywheels is applied to the rotor. In this approach, the shaft bore is removed and the laminations are sandwiched together using cheek plates, which are secured using tie rods. The cheek plates have their extending shafts, which consequently will transfer the torque to the rest of the system. The proposed model is analysed for both the electromagnetic and mechanical aspects, successfully demonstrating a promising rotor topology for the design speed. A high speed motor design needs to take into account shaft design, rotor design and bearing design. The high speed operation of the salient rotor gives dramatic rise to the windage loss. These factors are carefully considered in this work and the results are presented

A study of fault and generating operation of the switched reluctance machine

No abstract available