Field Weakening, Parameters and Operation Range of the Permanent Magnet Traction Motors

The main focus of this thesis is to define the field weakening point of permanent magnet synchronous machine with embedded magnets in traction applications. Along with the thesis a modelling program is made to help the designer to define the field weakening point in practical applications. The thesis utilizes the equations based on the current angle. These equations can be derived from the vector diagram of permanent magnet synchronous machine. The design parameters of the machine are: The maximum rotational speed, saliency ratio, maximum induced voltage and characteristic current. The main result of the thesis is finding out the rated rotational speed, from which the field weakening starts. The action of the machine is estimated at a wide speed range and the changes of machine parameters are examined.

Design Aspects of Megawatt-Range Direct-Driven Permanent MagnetWind Generators

Direct-driven permanent magnet synchronous generator is one of the most promising topologies for megawatt-range wind power applications. The rotational speed of the direct-driven generator is very low compared with the traditional electrical machines. The low rotational speed requires high torque to produce megawatt-range power. The special features of the direct-driven generators caused by the low speed and high torque are discussed in this doctoral thesis. Low speed and high torque set high demands on the torque quality. The cogging torque and the load torque ripple must be as low as possible to prevent mechanical failures. In this doctoral thesis, various methods to improve the torque quality are compared with each other. The rotor surface shaping, magnet skew, magnet shaping, and the asymmetrical placement of magnets and stator slots are studied not only by means of torque quality, but also the effects on the electromagnetic performance and manufacturability of the machine are discussed. The heat transfer of the direct-driven generator must be designed to handle the copper losses of the stator winding carrying high current density and to keep the temperature of the magnets low enough. The cooling system of the direct-driven generator applying the doubly radial air cooling with numerous radial cooling ducts was modeled with a lumped-parameter-based thermal network. The performance of the cooling system was discussed during the steady and transient states. The effect of the number and width of radial cooling ducts was explored. The large number of radial cooling ducts drastically increases the impact of the stack end area effects, because the stator stack consists of numerous substacks. The effects of the radial cooling ducts on the effective axial length of the machine were studied by analyzing the crosssection of the machine in the axial direction. The method to compensate the magnet end area leakage was considered. The effect of the cooling ducts and the stack end area effects on the no-load voltages and inductances of the machine were explored by using numerical analysis tools based on the three-dimensional finite element method. The electrical efficiency of the permanent magnet machine with different control methods was estimated analytically over the whole speed and torque range. The electrical efficiencies achieved with the most common control methods were compared with each other. The stator voltage increase caused by the armature reaction was analyzed. The effect of inductance saturation as a function of load current was implemented to the analytical efficiency calculation.

Saostuman esto prosessiputken pinnalle

Työn tarkoituksena oli tutkia kirjallisuudessa esitettyjen menetelmien soveltuvuutta estää kalsiumkarbonaatin saostuminen PCC – prosessissa paperikonelinjan massansyöttöputkessa. Menetelmien heikkoudet ja toimivuudet arvioitiin lähdetietojen perusteella, joiden perusteella tehtiin johtopäätelmiä niiden toimivuudesta prosessissa ja käytettävyydestä kalsiumkarbonaattisaostuman muodostumiseen. Kirjallisuusselvitys osoittaa, että saostuma voidaan estää kemiallisesti ja sähkökemiallisesti sekä modifioimalla materiaalipintaa. Lisäksi sen muodostuminen voidaan estää ultraääniaaltojen avulla sekä indusoimalla mahdolliseen saostuskohtaan magneetti- tai sähkökenttä. Kokeellisessa osassa keskityttiin kirjallisuuden perusteella tutkimaan kalsiumkarbonaatin saostumista kaupallisilla menetelmillä. Tutkimuksissa käytettiin erilaisia pinnoitemateriaaleja, ultraääniaaltoja sekä magneettikenttää että liuossähkökemiaa. Näiden lisäksi tutkittiin saostumisen kehittymistä putkipinnalle ajan funktiona. Kokeellisten tulosten perusteella kirjallisuudessa esitetyistä menetelmistä ei suoraan mikään sovellu sellaisenaan tutkitussa prosessissa saostuman muodostumisen estoon. Koeparametrien optimointi muuttamalla tunnettuja parametreja prosessitilanteeseen paransi kalsiumkarbonaatin liukoisuutta. Tämän tutkimuksen tuloksena löytyi menetelmäkuvaus, jolla saostumien muodostuminen putkipinnoille voidaan estää.

Taajuusmuuttajaohjattu kestomagneettitahtikone opetuslaboratoriokäytössä

Kestomagneettien kehittyminen on mahdollistanut sähkökoneen rakentamisen perinteisistä menetelmistä poiketen ja on samalla luonut uudenlaisia ominaisuuksia ja käyttökohteita. Erityisesti kestomagneettitahtikone (PMSM) on kasvattanut suosiota hyvän hyötysuhteen ja luotettavuuden myötä. Työssä esitellään kestomagneettitahtikonetta sen rakenteen ja toimintaperiaatteen avulla. Tarkastellaan kestomagneettien kehitystä ja tulevaisuuden näkymiä. Perehdytään myös taajuusmuuttajaan, mitä käytetään yleensä kestomagneettitahtikoneen ohjaukseen. Lisäksi esitetään taajuusmuuttajan erilaisia säätötapoja. Työn kokeellisessa osuudessa yliopiston opetuslaboratorioon kehitetään koneikko, jonka avulla tutkitaan kestomagneettitahtikoneen toimintaan osana sähkökäyttöä. Työn tavoitteena on selvittää PMSM:n ominaisuuksia sekä suunnitella sähkötekniikan työkurssille soveltuva mittaussarja, mikä johdattaa opiskelijat tässä työssä käsiteltyihin aihealueisiin.

Design and testing of an armature-reaction-compensated permanent magnet synchronous generator for island operation

At present, permanent magnet synchronous generators (PMSGs) are of great interest. Since they do not have electrical excitation losses, the highly efficient, lightweight and compact PMSGs equipped with damper windings work perfectly when connected to a network. However, in island operation, the generator (or parallel generators) alone is responsible for the building up of the network and maintaining its voltage and reactive power level. Thus, in island operation, a PMSG faces very tight constraints, which are difficult to meet, because the flux produced by the permanent magnets (PMs) is constant and the voltage of the generator cannot be controlled. Traditional electrically excited synchronous generators (EESGs) can easily meet these constraints, because the field winding current is controllable. The main drawback of the conventional EESG is the relatively high excitation loss. This doctoral thesis presents a study of an alternative solution termed as a hybrid excitation synchronous generator (HESG). HESGs are a special class of electrical machines, where the total rotor current linkage is produced by the simultaneous action of two different excitation sources: the electrical and permanent magnet (PM) excitation. An overview of the existing HESGs is given. Several HESGs are introduced and compared with the conventional EESG from technical and economic points of view. In the study, the armature-reaction-compensated permanent magnet synchronous generator with alternated current linkages (ARC-PMSG with ACL) showed a better performance than the other options. Therefore, this machine type is studied in more detail. An electromagnetic design and a thermal analysis are presented. To verify the operation principle and the electromagnetic design, a down-sized prototype of 69 kVA apparent power was built. The experimental results are demonstrated and compared with the predicted ones. A prerequisite for an ARC-PMSG with ACL is an even number of pole pairs (p = 2, 4, 6, …) in the machine. Naturally, the HESG technology is not limited to even-pole-pair machines. However, the analysis of machines with p = 3, 5, 7, … becomes more complicated, especially if analytical tools are used, and is outside the scope of this thesis. The contribution of this study is to propose a solution where an ARC-PMSG replaces an EESG in electrical power generation while meeting all the requirements set for generators given for instance by ship classification societies, particularly as regards island operation. The maximum power level when applying the technology studied here is mainly limited by the economy of the machine. The larger the machine is, the smaller is the efficiency benefit. However, it seems that machines up to ten megawatts of power could benefit from the technology. However, in low-power applications, for instance in the 500 kW range, the efficiency increase can be significant.

Design of a 1 kW 150 rpm permanent-magnet synchronous generator for stand-alone wind-power applications

A program for calculating low-speed low-power synchronous machine is presented. A permanent-magnet synchronous generator for 1 kW 150 rpm is designed. Optimization of magnet’s and coil’s dimensions was made.

Wind Turbine Direct-Drive Permanent-Magnet Generator with Direct Liquid Cooling for Mass Reduction

Today’s electrical machine technology allows increasing the wind turbine output power by an order of magnitude from the technology that existed only ten years ago. However, it is sometimes argued that high-power direct-drive wind turbine generators will prove to be of limited practical importance because of their relatively large size and weight. The limited space for the generator in a wind turbine application together with the growing use of wind energy pose a challenge for the design engineers who are trying to increase torque without making the generator larger. When it comes to high torque density, the limiting factor in every electrical machine is heat, and if the electrical machine parts exceed their maximum allowable continuous operating temperature, even for a short time, they can suffer permanent damage. Therefore, highly efficient thermal design or cooling methods is needed. One of the promising solutions to enhance heat transfer performances of high-power, low-speed electrical machines is the direct cooling of the windings. This doctoral dissertation proposes a rotor-surface-magnet synchronous generator with a fractional slot nonoverlapping stator winding made of hollow conductors, through which liquid coolant can be passed directly during the application of current in order to increase the convective heat transfer capabilities and reduce the generator mass. This doctoral dissertation focuses on the electromagnetic design of a liquid-cooled direct-drive permanent-magnet synchronous generator (LC DD-PMSG) for a directdrive wind turbine application. The analytical calculation of the magnetic field distribution is carried out with the ambition of fast and accurate predicting of the main dimensions of the machine and especially the thickness of the permanent magnets; the generator electromagnetic parameters as well as the design optimization. The focus is on the generator design with a fractional slot non-overlapping winding placed into open stator slots. This is an a priori selection to guarantee easy manufacturing of the LC winding. A thermal analysis of the LC DD-PMSG based on a lumped parameter thermal model takes place with the ambition of evaluating the generator thermal performance. The thermal model was adapted to take into account the uneven copper loss distribution resulting from the skin effect as well as the effect of temperature on the copper winding resistance and the thermophysical properties of the coolant. The developed lumpedparameter thermal model and the analytical calculation of the magnetic field distribution can both be integrated with the presented algorithm to optimize an LC DD-PMSG design. Based on an instrumented small prototype with liquid-cooled tooth-coils, the following targets have been achieved: experimental determination of the performance of the direct liquid cooling of the stator winding and validating the temperatures predicted by an analytical thermal model; proving the feasibility of manufacturing the liquid-cooled tooth-coil winding; moreover, demonstration of the objectives of the project to potential customers.

Project Resource Management in R&D Public Sector Organization

In R&D organizations multiple projects are executed concurrently. Problems arises in managing shared resources since they are needed by multiple projects simultaneously. The objective of this thesis was to study how the project and resource management could be developed in a public sector R&D organization. The qualitative research was carried out in the Magnetic Measurements section at CERN where the section measures magnets for particle accelerators and builds state of the art measurement devices for various needs. Hence, the R&D and measurement projects are very time consuming and very complex. Based on the previous research and the requirements from the organization the best alter- native for resource management was to build a project management information system. A centralized database was constructed and on top of it was built an application for interacting and visualizing the project data. The application allows handling project data, which works as a basis for resource planning before and during the projects are executed. It is one way to standardize the work-flow of projects, which strengthens the project process. Additionally, it was noted that the inner customer’s database, the measurement system and the new application needed to be integrated. Further integration ensures that the project data is received efficiently from customers and available not only within the application but also during the concrete work. The research results introduced a new integrated application, which centralizes the project information flow with better visibility.

Liquid cooling solutions for rotating permanent magnet synchronous machines

In the design of electrical machines, efficiency improvements have become very important. However, there are at least two significant cases in which the compactness of electrical machines is critical and the tolerance of extremely high losses is valued: vehicle traction, where very high torque density is desired at least temporarily; and direct-drive wind turbine generators, whose mass should be acceptably low. As ever higher torque density and ever more compact electrical machines are developed for these purposes, thermal issues, i.e. avoidance of over-temperatures and damage in conditions of high heat losses, are becoming of utmost importance. The excessive temperatures of critical machine components, such as insulation and permanent magnets, easily cause failures of the whole electrical equipment. In electrical machines with excitation systems based on permanent magnets, special attention must be paid to the rotor temperature because of the temperature-sensitive properties of permanent magnets. The allowable temperature of NdFeB magnets is usually significantly less than 150 ˚C. The practical problem is that the part of the machine where the permanent magnets are located should stay cooler than the copper windings, which can easily tolerate temperatures of 155 ˚C or 180 ˚C. Therefore, new cooling solutions should be developed in order to cool permanent magnet electrical machines with high torque density and because of it with high concentrated losses in stators. In this doctoral dissertation, direct and indirect liquid cooling techniques for permanent magnet synchronous electrical machines (PMSM) with high torque density are presented and discussed. The aim of this research is to analyse thermal behaviours of the machines using the most applicable and accurate thermal analysis methods and to propose new, practical machine designs based on these analyses. The Computational Fluid Dynamics (CFD) thermal simulations of the heat transfer inside the machines and lumped parameter thermal network (LPTN) simulations both presented herein are used for the analyses. Detailed descriptions of the simulated thermal models are also presented. Most of the theoretical considerations and simulations have been verified via experimental measurements on a copper tooth-coil (motorette) and on various prototypes of electrical machines. The indirect liquid cooling systems of a 100 kW axial flux (AF) PMSM and a 110 kW radial flux (RF) PMSM are analysed here by means of simplified 3D CFD conjugate thermal models of the parts of both machines. In terms of results, a significant temperature drop of 40 ̊C in the stator winding and 28 ̊C in the rotor of the AF PMSM was achieved with the addition of highly thermally conductive materials into the machine: copper bars inserted in the teeth, and potting material around the end windings. In the RF PMSM, the potting material resulted in a temperature decrease of 6 ̊C in the stator winding, and in a decrease of 10 ̊C in the rotor embedded-permanentmagnets. Two types of unique direct liquid cooling systems for low power machines are analysed herein to demonstrate the effectiveness of the cooling systems in conditions of highly concentrated heat losses. LPTN analysis and CFD thermal analysis (the latter being particularly useful for unique design) were applied to simulate the temperature distribution within the machine models. Oil-immersion cooling provided good cooling capability for a 26.6 kW PMSM of a hybrid vehicle. A direct liquid cooling system for the copper winding with inner stainless steel tubes was designed for an 8 MW directdrive PM synchronous generator. The design principles of this cooling solution are described in detail in this thesis. The thermal analyses demonstrate that the stator winding and the rotor magnet temperatures are kept significantly below their critical temperatures with demineralized water flow. A comparison study of the coolant agents indicates that propylene glycol is more effective than ethylene glycol in arctic conditions.

Spin Polarization and Normal Reflection at Nanoscale Point Contacts

This thesis presents point-contact measurements between superconductors (Nb, Ta, Sn,Al, Zn) and ferromagnets (Co, Fe, Ni) as well as non-magnetic metals (Ag, Au, Cu, Pt).The point contacts were fabricated using the shear method. The differential resistanceof the contacts was measured either in liquid He at 4.2 K or in vacuum in a dilutionrefrigerator at varying temperature down to 0.1 K. The contact properties were investigatedas function of size and temperature. The measured Andreev-reflection spectrawere analysed in the framework of the BTK model – a three parameter model that describescurrent transport across a superconductor - normal conductor interface. Theoriginal BTK model was modified to include the effects of spin polarization or finitelifetime of the Cooper pairs. Our polarization values for the ferromagnets at 4.2 K agree with the literature data, but the analysis was ambiguous because the experimental spectra both with ferromagnets and non-magnets could be described equally well either with spin polarization or finite lifetime effects in the BTK model. With the polarization model the Z parametervaries from almost 0 to 0.8 while the lifetime model produces Z values close to 0.5. Measurements at lower temperatures partly lift this ambiguity because the magnitude of thermal broadening is small enough to separate lifetime broadening from the polarization. The reduced magnitude of the superconducting anomalies for Zn-Fe contacts required an additional modification of the BTK model which was implemented as a scaling factor. Adding this parameter led to reduced polarization values. However, reliable data is difficult to obtain because different parameter sets produce almost identical spectra.

Unequal Teeth Widths for Torque Ripple Reduction in Permanent Magnet Synchronous Machines With Fractional-Slot Non-Overlapping Windings

Permanent magnet synchronous machines with fractional-slot non-overlapping windings (FSPMSM), also known as tooth-coil winding permanent magnet synchronous machines (TCW PMSM), have been under intensive research during the latest decade. There are many optimization routines explained and implemented in the literature in order to improve the characteristics of this machine type. This paper introduces a new technique for torque ripple minimization in TCW PMSM. The source of torque harmonics is also described. The low order torque harmonics can be harmful for a variety of applications, such as direct drive wind generators, direct drive light vehicle electrical motors, and for some high precision servo applications. The reduction of the torque ripple harmonics with the lowest orders (6th and 12th) is realized by machine geometry optimization technique using finite element analysis (FEA). The presented optimization technique includes the stator geometry adjustment in TCW PMSMs with rotor surface permanent magnets and with rotor embedded permanent magnets. Influence of the permanent magnet skewing on the torque ripple reduction and cogging torque elimination was also investigated. It was implemented separately and together with the stator optimization technique. As a result, the reduction of some torque ripple harmonics was attained.

Analytic evaluation of three-phase short circuit demagnetization and hysteresis loss risk in rotor-surface-magnet Permanent-Magnet Synchronous Machines

Permanent magnet synchronous machines (PMSM) have become widely used in applications because of high efficiency compared to synchronous machines with exciting winding or to induction motors. This feature of PMSM is achieved through the using the permanent magnets (PM) as the main excitation source. The magnetic properties of the PM have significant influence on all the PMSM characteristics. Recent observations of the PM material properties when used in rotating machines revealed that in all PMSMs the magnets do not necessarily operate in the second quadrant of the demagnetization curve which makes the magnets prone to hysteresis losses. Moreover, still no good analytical approach has not been derived for the magnetic flux density distribution along the PM during the different short circuits faults. The main task of this thesis is to derive simple analytical tool which can predict magnetic flux density distribution along the rotor-surface mounted PM in two cases: during normal operating mode and in the worst moment of time from the PM’s point of view of the three phase symmetrical short circuit. The surface mounted PMSMs were selected because of their prevalence and relatively simple construction. The proposed model is based on the combination of two theories: the theory of the magnetic circuit and space vector theory. The comparison of the results in case of the normal operating mode obtained from finite element software with the results calculated with the proposed model shows good accuracy of model in the parts of the PM which are most of all prone to hysteresis losses. The comparison of the results for three phase symmetrical short circuit revealed significant inaccuracy of the proposed model compared with results from finite element software. The analysis of the inaccuracy reasons was provided. The impact on the model of the Carter factor theory and assumption that air have permeability of the PM were analyzed. The propositions for the further model development are presented.

Cost Reduction of Permanent Magnet Synchronous Machines

Electrical machine drives are the most electrical energy-consuming systems worldwide. The largest proportion of drives is found in industrial applications. There are, however many other applications that are also based on the use of electrical machines, because they have a relatively high efficiency, a low noise level, and do not produce local pollution. Electrical machines can be classified into several categories. One of the most commonly used electrical machine types (especially in the industry) is induction motors, also known as asynchronous machines. They have a mature production process and a robust rotor construction. However, in the world pursuing higher energy efficiency with reasonable investments not every application receives the advantage of using this type of motor drives. The main drawback of induction motors is the fact that they need slipcaused and thus loss-generating current in the rotor, and additional stator current for magnetic field production along with the torque-producing current. This can reduce the electric motor drive efficiency, especially in low-speed, low-power applications. Often, when high torque density is required together with low losses, it is desirable to apply permanent magnet technology, because in this case there is no need to use current to produce the basic excitation of the machine. This promotes the effectiveness of copper use in the stator, and further, there is no rotor current in these machines. Again, if permanent magnets with a high remanent flux density are used, the air gap flux density can be higher than in conventional induction motors. These advantages have raised the popularity of PMSMs in some challenging applications, such as hybrid electric vehicles (HEV), wind turbines, and home appliances. Usually, a correctly designed PMSM has a higher efficiency and consequently lower losses than its induction machine counterparts. Therefore, the use of these electrical machines reduces the energy consumption of the whole system to some extent, which can provide good motivation to apply permanent magnet technology to electrical machines. However, the cost of high performance rare earth permanent magnets in these machines may not be affordable in many industrial applications, because the tight competition between the manufacturers dictates the rules of low-cost and highly robust solutions, where asynchronous machines seem to be more feasible at the moment. Two main electromagnetic components of an electrical machine are the stator and the rotor. In the case of a conventional radial flux PMSM, the stator contains magnetic circuit lamination and stator winding, and the rotor consists of rotor steel (laminated or solid) and permanent magnets. The lamination itself does not significantly influence the total cost of the machine, even though it can considerably increase the construction complexity, as it requires a special assembly arrangement. However, thin metal sheet processing methods are very effective and economically feasible. Therefore, the cost of the machine is mainly affected by the stator winding and the permanent magnets. The work proposed in this doctoral dissertation comprises a description and analysis of two approaches of PMSM cost reduction: one on the rotor side and the other on the stator side. The first approach on the rotor side includes the use of low-cost and abundant ferrite magnets together with a tooth-coil winding topology and an outer rotor construction. The second approach on the stator side exploits the use of a modular stator structure instead of a monolithic one. PMSMs with the proposed structures were thoroughly analysed by finite element method based tools (FEM). It was found out that by implementing the described principles, some favourable characteristics of the machine (mainly concerning the machine size) will inevitable be compromised. However, the main target of the proposed approaches is not to compete with conventional rare earth PMSMs, but to reduce the price at which they can be implemented in industrial applications, keeping their dimensions at the same level or lower than those of a typical electrical machine used in the industry at the moment. The measurement results of the prototypes show that the main performance characteristics of these machines are at an acceptable level. It is shown that with certain specific actions it is possible to achieve a desirable efficiency level of the machine with the proposed cost reduction methods.

Evaluation of the Efficiency of Line-Start Permanent-Magnet Machines as a Function of the Operating Temperature

The standard squirrel-cage induction machine has nearly reached its maximum efficiency. In order to further increase the energy efficiency of electrical machines, the use of permanent magnets in combination with the robust design and the line start capability of the induction machine is extensively investigated. Many experimental designs have been suggested in literature, but recently, these line-start permanent-magnet machines (LSPMMs) have become off-the-shelf products available in a power range up to 7.5 kW. The permanent magnet flux density is a function of the operating temperature. Consequently, the temperature will affect almost every electrical quantity of the machine, including current, torque, and efficiency. In this paper, the efficiency of an off-the-shelf 4-kW three-phase LSPMM is evaluated as a function of the temperature by both finite-element modeling and by practical measurements. In order to obtain stator, rotor, and permanent magnet temperatures, lumped thermal modeling is used.