Performance comparison of conventional synchronous reluctance machines and PM-assisted types with combined star-delta winding

This paper compares four prototype Synchronous Reluctance Motors (SynRMs) having an identical geometry of iron lamination stacks in the stator and rotor. Two different stator winding layouts are employed: a conventional three-phase star connection and a combined star-delta winding. In addition, two rotors are considered: a conventional rotor without magnets and a rotor with ferrite magnets. The performance of the four SynRMs is evaluated using a two-dimensional (2D) Finite Element Model (FEM). For the same copper volume and current, the combined star-delta-connected stator with Permanent Magnets (PMs) in the rotor corresponds to an approximately 22% increase in the output torque at rated current and speed compared to the conventional machine. This improvement is mainly thanks to adding ferrite PMs in the rotor as well as to the improved winding factor of the combined star-delta winding. The torque gain increases up to 150% for low current. Moreover, the rated efficiency is 93.60% compared to 92.10% for the conventional machine. On the other hand, the impact on the power factor and losses of SynRM when using the star-delta windings instead of the star windings is merely negligible. The theoretical results are experimentally validated using four identical prototype machines with identical lamination stacks but different rotors and winding layouts

The analysis and design of some windings for linear induction machines

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On the Modeling, Analysis and Development of PMSM: For Traction and Charging Application

Permanent magnet synchronous machines (PMSMs) are widely implemented commercially available traction motors owing to their high torque production capability and wide operating speed range. However, to achieve significant electric vehicle (EV) global market infiltration in the coming years, the technological gaps in the technical targets of the traction motor must be addressed towards further improvement of driving range per charge of the vehicle and reduced motor weight and cost. Thus, this thesis focuses on the design and development of a novel high speed traction PMSM with improved torque density, maximized efficiency, reduced torque ripple and increased driving range suitable for both traction and integrated charging applications. First, the required performance targets are determined using a drive cycle based vehicle dynamic model, existing literature and roadmaps for future EVs. An unconventional fractional–slot distributed winding configuration with a coil pitch of 2 is selected for analysis due to their short end–winding length, reduced winding losses and improved torque density. For the chosen baseline topology, a non–dominated sorting genetic algorithm based selection of optimal odd slot numbers is performed for higher torque production and reduced torque ripple. Further, for the selected odd slot–pole combination, a novel star–delta winding configuration is modeled and analyzed using winding function theory for higher torque density, reduced spatial harmonics, reduced torque ripple and machine losses. Thereafter, to analyze the motor performance with control and making critical decisions on inter–dependent design parameter variations for machine optimization, a parametric design approach using a novel coupled magnetic equivalent circuit model and thermal model incorporating current harmonics for fractional–slot wound PMSMs was developed and verified. The developed magnetic circuit model incorporates all machine non–linearities including effects of temperature and induced inverter harmonics as well as the space harmonics in the winding inductances of a fractional–slot winding configuration. Using the proposed model with a pareto ant colony optimization algorithm, an optimal rotor design is obtained to reduce the magnet utilization and obtain maximized torque density and extended operating range. Further, the developed machine structure is also analyzed and verified for integrated charging operation where the machine’s winding inductances are used as line inductors for charging the battery thereby eliminating the requirement of an on–board charger in the powertrain and hence resulting in reduced weight, cost and extended driving range. Finally, a scaled–down prototype of the proposed PMSM is developed and validated with experimental results in terms of machine inductances, torque ripple, torque–power–speed curves and efficiency maps over the operating speed range. Subsequently, understanding the capabilities and challenges of the developed scaled–down prototype, a full–scale design with commercial traction level ratings, will be developed and analyzed using finite element analysis. Further recommendations for design improvement, future work and analysis will also be summarized towards the end of the dissertation

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

Design aspects of high performance synchronous reluctance machines with and without permanent magnets

Recently, a growing interest in the efficiency and the cost of electrical machines has been observed. The efficiency of electric motors is important because electric motors consume about 40%-45% of the produced electricity worldwide and about 70% of the industrial electricity1. Therefore, some types of electric motors have been classified in proposed standard classes1 based on their efficiency. By consequence, efficient and low cost electric motors are necessary on the market. Several types of electric motors are used in industrial applications such as permanent magnet synchronous motors (PMSMs), induction motors (IMs) and reluctance motors (RMs). Due to the high cost of PMSMs and due to the rotor losses of the IMs, the RMs can be considered as promising and attractive candidates. Moreover, they have a robust and simple structure, and a low cost as there are no cage, windings and magnets in the rotor. There are two main types of RMs: switched reluctance motors (SRMs) and synchronous reluctance motors (SynRMs). However, there are some disadvantages of these types of machines. On the one hand, the SRMs have problems of torque ripple, vibrations and noise. In addition, their control is more complicated than that of three-phase conventional motor drives, a.o. because of the high non-linearity of the inductance. On the other hand, the SynRMs have a low power factor, so that an inverter with a high Volt-Ampère rating is required to produce a given motor output power. Therefore, adding a proper amount of low cost permanent magnet (PM) material - such as ferrite - may be a good option to boost the power factor. The PMs also increase the efficiency and torque density. These types of motors are ---------------------------------------------------------------------------------------------------------------------- 1Waide, P. and C. Brunner (2011),”Energy-Efficiency Policy Opportunities for Electric Motor Driven Systems”, IEA Energy Papers, No. 2011/07, OECD Publishing, Paris.xiv Summary called permanent magnet-assisted synchronous reluctance motors (PMaSynRMs). In this thesis, both SynRMs and PMaSynRMs are investigated. The main focus is given to the rotor design, magnetic material grade and winding configuration. In addition, the modelling and control of SynRMs and PMaSynRMs is also investigated. First, parametrized models are made of the machines. The finite element method (FEM) is used to obtain the dq-axis flux-linkages λd(id, iq, θr) and λq(id, iq, θr) of the SynRM in static 2D simulations, as a function of d-axis current id, and q-axis current iq and rotor position θr. As known, the performance (output torque, power factor and efficiency) of SynRMs depends mainly on the ratio between the direct (d) and quadrature (q) axis inductances (Ld/Lq). This ratio is well-known as the saliency ratio of the SynRM. As magnetic saturation causes significant changes in the inductances and by consequence in the saliency ratio during operation, a SynRM model based on constant inductances (Ld and Lq) is not good enough. It can lead to large deviations in the prediction of the torque capability compared with the real motor. How large these deviations are, is clarified in this thesis by comparing several models that do or do not take into account saturation, cross-saturation and rotor position effects. It is found that saturation and cross saturation must be included in the model for an accurate representation of the SynRM performance and control. This means the flux linkages should be function of id and iq. The rotor position needn’t be included. Apart from the currents, the FEM contains many parameters for the flux barrier geometry, which have a strong influence on the torque and torque ripple of the machine. Next to static simulations, also dynamic simulations are done. In these simulations, the flux-linkages are stored in lookup tables, created a priori by FEM, to speed up the simulations. Based on the SynRM FEM model, the design of the SynRM rotor is investigated. Choosing the flux-barrier geometry parameters is very complex because there are many parameters that play a role. Therefore, an optimization technique is always necessary to select the flux-barrier parameters that optimize the SynRM performance indicators (maximize the saliency ratio and output torque and minimize the torque ripple). To gain insight in the relevant parameters, first a sensitivity analysis is done: the influence of the flux-barrier parameters is studied on the SynRM performance indicators. These indicators are again saliency ratio, output torque and torque ripple. In addition, easy-to-usexv parametrized equations are proposed to select the value of the two most crucial parameters of the rotor i.e. the flux-barrier angle and width. The proposed equations are compared with three existing literature equations. At the end, an optimal rotor design is obtained based on an optimized technique coupled with FEM. The optimal rotor is checked mechanically for the robustness against mechanical stresses and deformations. Apart from the geometry, the electric steel grade plays a major role in the losses and efficiency of an electric machine. Therefore, several steel grades are compared with respect to the SynRM performance i.e. output torque, power factor, torque ripple, iron losses and efficiency. Four different steel grades NO20, M330P-50A, M400-50A and M600-100A are considered. The steel grades differ in thickness and in the losses they produce. It was found that the “best” grade NO20 had in the rated operating point of the considered SynRM 9.0% point more efficiency than the “worst” grade M600-100A. Next to energy-efficiency, a large interest in recent research is dedicated to obtain a high torque density. One of the main techniques to improve the machine torque density is to increase the fundamental winding factor through an innovative winding layout. Among several configurations, the so-called combined star-delta winding layout was proposed in literature several years ago. In the PhD, the combined stardelta winding is compared with the conventional star winding in terms of output torque, torque ripple and efficiency. A simple method to calculate the equivalent winding factor of the different winding connections is proposed. In addition, the modelling of a SynRM with combined star-delta winding is given. Furthermore, the effect of different winding layouts on the performance of the SynRM is presented. To compare both windings experimentally, two stators are made, one with combined star-delta windings and one with conventional star windings, having the same copper volume. Measurements revealed a 5.2% higher output torque of the first machine at rated current and speed. In order to even further improve the power factor and the output torque of the SynRM, ferrite PMs are inserted in the center of the rotor flux-barriers. The rotor geometry of the resulting PMaSynRM is the same as the conventional SynRM. Hence, two rotors with identical iron lamination stack were built: one with PMs and a second one without magnets. Having the two stators and two rotors, a comparison of fourxvi Summary prototype SynRMs is done in the PhD, each of 5.5 kW. Several validation measurements have been obtained. The combined-star delta SynRM with PMs in the rotor had up to 1.5 % point more efficiency than the SynRM with star winding and rotor without magnets at the rated current and speed. As an application of SynRM, an efficient and low cost photovoltaic (PV) pumping system employing a SynRM is studied. The proposed system does not have a DC-DC converter that is often used to maximize the PV output power, nor has it storage (battery). Instead, the system is controlled in such a way that both the PV output power is maximized and the SynRM works at the maximum torque per Ampère, using a conventional three phase pulse width modulated inverter. The design and the modelling of all the system components are given. The performance of the proposed PV pumping system is presented, showing the effectiveness of the system

Analytical prediction of the electromagnetic torques in single-phase and two-phase AC motors

The single-phase and two-phase versions of AC motors can be modelled by means of the two-axis (d-q) theory with sufficient accuracy when the equivalent circuit parameters are correctly estimated. This work attempts to present a unified approach to the analytical prediction of the electromagnetic torque of these machines. Classical d-q axes formulation requires that the reference frame should be fixed on the frame where the asymmetries arise, i.e. the stator and rotor. The asynchronous torques that characterize the induction motors are modelled in a stationary reference frame, where the d-q axes coincide with the physical magnetic axes of the stator windings. For the permanent magnet motors, that may exhibit asymmetries on both stator and rotor, the proposed solution includes: a series of frame transformations, followed by symmetrical components decomposition. As in single-phase and two-phase systems the homopolar component is zero; each symmetrical component – negative and positive – is further analysed using d-q axes theory. The superposition principle is employed to consider the magnets and rotor cage effects. The developed models account for the most important asymmetries of the motor configuration. These are, from the stator point of view, different distribution, conductors' dimensions and number of effective turns, non-orthogonal magnetic axes windings and from the rotor point of view, asymmetrical rotor cage, variable reluctance, and permanent magnets effect. The time and space harmonics effect is ignored. Test data are compared with the computed data in order to observe how the simplifying assumptions affect the level of accuracy. The analytical prediction methods make possible torque computation according to the nature of the torque being computed, namely, induction, reluctance and excitation (permanent magnet). The results are available for quasi steady-state, steady-state (rated or synchronous speed) and dynamic analyses. All the developed mathematical models can be used in preliminary design for further optimisation and accurate estimation in complex numerical models. Another important feature of the analytical models for single-phase and two-phase AC motors, is that they can be directly implemented in any suitable electrical drives control strategy.reviewe

High-speed induction motor with an integrated gearbox for propulsion

Induction motors with a planetary gear are a viable option for the transportation industry as they are a relatively inexpensive electric drive solution. Designing a prototype of a high-speed induction motor with a planetary gear is the focus of this project. This will be the proof of concept, to demonstrate a compact and cost-efficient electric drive solution, when compared to electric drives with lower speeds and no gearbox. Using a high-speed electric motor and gearing it down will provide a high torque density and power. A prototype with a high power density and efficiency will provide a competitive alternative to other electric drive solutions. The design choices of the prototype are covered. 3D modeling software is used for the mechanical design that integrates the planetary gear and the induction motor. Finite Element Method (FEM) simulations are completed to determine the final design. The geometry and properties of the induction motor are optimized using FEM. Electromagnetics, torque, and the losses of the induction motor are analyzed. The prototype design presented in this thesis is analyzed to determine the overall efficiency, cost, and feasibility for the transportation industry. The design allows for future development by ensuring easy changes and additions that can be made to the prototype. The development of the high-speed motor should continue with the use of models and design presented in this thesis. The design presented in this thesis is another step towards the final prototype production. The possibilities for future thesis topics and improvements will be discussed at the end of this thesis. One possibility for future development is the use of additive manufacturing to build the induction motor

Design and Control of Electrical Motor Drives

Dear Colleagues, I am very happy to have this Special Issue of the journal Energies on the topic of Design and Control of Electrical Motor Drives published. Electrical motor drives are widely used in the industry, automation, transportation, and home appliances. Indeed, rolling mills, machine tools, high-speed trains, subway systems, elevators, electric vehicles, air conditioners, all depend on electrical motor drives.However, the production of effective and practical motors and drives requires flexibility in the regulation of current, torque, flux, acceleration, position, and speed. Without proper modeling, drive, and control, these motor drive systems cannot function effectively.To address these issues, we need to focus on the design, modeling, drive, and control of different types of motors, such as induction motors, permanent magnet synchronous motors, brushless DC motors, DC motors, synchronous reluctance motors, switched reluctance motors, flux-switching motors, linear motors, and step motors.Therefore, relevant research topics in this field of study include modeling electrical motor drives, both in transient and in steady-state, and designing control methods based on novel control strategies (e.g., PI controllers, fuzzy logic controllers, neural network controllers, predictive controllers, adaptive controllers, nonlinear controllers, etc.), with particular attention to transient responses, load disturbances, fault tolerance, and multi-motor drive techniques. This Special Issue include original contributions regarding recent developments and ideas in motor design, motor drive, and motor control. The topics include motor design, field-oriented control, torque control, reliability improvement, advanced controllers for motor drive systems, DSP-based sensorless motor drive systems, high-performance motor drive systems, high-efficiency motor drive systems, and practical applications of motor drive systems. I want to sincerely thank authors, reviewers, and staff members for their time and efforts. Prof. Dr. Tian-Hua Liu Guest Edito