J. Pyrhönen

Lappeenranta – Lahti University of Technology LUT · Department of Energy

This paper presents the optimization of semi- magnetic wedges in the open slots of an axially laminated synchronous reluctance machine for a micro gas turbine application. The study analyses a high-speed machine (100 krpm) and considers different permeabilities and geometries of the magnetic wedges. In addition, the effects of protrusion of the mag...

Permanent Magnet Synchronous Machines (PMSMs) are commonly employed in applications demanding a high specific power. To achieve high specific power values, a high pole pair number PMSM with very thin yokes can be built. Such a design leads to a high operating frequency. At high operating frequencies, AC losses can more than double the DC losses if...

In electrical machines, most of the iron loss estimation in finite element modeling is based on Bertotti coefficients obtained from the corresponding data sheet. However, often a more exact estimation of coefficients for the laminated steel material is needed. Especially in the case of high speed machines (where iron loss has the highest contributi...

Practical optimization of the rotor layer thicknesses and arrangement in a 100 krpm axially laminated anisotropic synchronous reluctance machine (ALAsynRM) for a micro-gas turbine generator is presented. The machine utilizes practically available rotor lamination thicknesses that can maintain the rotor's mechanical integrity at this speed. As strai...

The stability of a wind turbine-rotated synchronous generator must be maintained during a sudden change in wind speed or direction. In integral slot winding machines this task is taken care of by rotor damper windings. Tooth-coil permanent magnet generators cannot, however, have a damper winding in the rotor because of the high harmonic content of...

A variable reluctance (VR) resolver with a modular stator design is considered. Its stator consists of four magnetically insulated cores with their own set of windings, which is the minimum number of winding sets required to implement a VR resolver principle. The paper shows the operating principle of the proposed VR resolver, addresses the main de...

This paper proposes a design process for a high-efficiency micro-gas-turbine (MGT)-based range extender(RE). The study includes a conceptual system design and a detailed design of an MGT RE. This design adopts a two-spool intercooled and recuperated high-speed MGT. The study focuses on the design of a low-pressure (LP) rotor system integrated with...

Permanent magnet synchronous machines (PMSM), synchronous reluctance machines (SynRM), and electrically excited synchronous machines (EESM), are used widely in the industry and transportation sectors. Often their rotors are equipped with conducting parts like permanent magnets, thick rotor laminations, real damper windings, a conducting sleeve or e...

High-speed electric machines aim for compact, direct-driven elevated speed applications and highly efficient operation, especially when a gearbox can be avoided. The design of these types of machines is highly iterative, combining multiphysics optimization and leading to custom types of machines that fulfill the application-specific requirements. T...

Active magnetic bearings are commonly applied in high-speed rotors in the medium to high power range to replace rolling-element or oil-film bearings. They require less maintenance and provide a number of unique benefits owing to their contactless suspension and active control. A rotor construction with integrated compressors or turbines results in...

Permanent magnet synchronous machine (PMSM) has been broadly used in a wide range of applications where a high specific power is required. In order to achieve high performance, various geometry modifications can be used. One of the possible geometric modifications is asymmetric stator structure. It is difficult to avoid local saturations at the sta...

Double-fed generator-based wind energy conversion systems (WECS) are becoming popular in recent years because of their high reliability, flexibility, fault-tolerant capability, and cost-effectiveness. One of the main factors forcing stability for WECSs is sudden wind speed or direction changes. In this paper, the stator coil arrangement of a double...

Solid rotors are preferred choice of topology for high-speed applications due to their robustness against high centrifugal forces at high speeds, ease of manufacturability, and higher temperature range. However, for peripheral speeds lower than 200 m/s, laminated rotor structure is preferred because of lower eddy current losses resulting in higher...

The design of high-speed machines requires extensive multidisciplinary approach to achieve a high-performance machine. The design process is highly iterative, and analytical methods can accelerate it with faster design iterations at low computational efficiency to find the optimum parameters at conceptual stage. In this study, an analytical design...

Power-electronic-Inverterconverter-induced motor bearing currents are a widespread problem in the field of electrical drives. Parasitic capacitances between the electrical machines parts provide a path for leakage currents, which finally harm the metallic ball bearings. Remembering that end-windings have a significant contribution in building up st...

An industrial electrical machine prototype is measured with a pulse-width-modulated voltage supply using different switching frequencies; 4, 8, 12 and 16 kHz when the motor is operating at 25 and 40 Hz fundamental frequencies. Typically, the electrical machine losses decrease as a function of the switching frequency and in this case, similar behavi...

The effects of manufacturing stresses on the overall magnetic properties of electrical steel core applied in the stator and transversally-laminated rotor of Synchronous Reluctance motors are studied. In addition, it is investigated how the -manufacturing-degraded electrical steel core affects the electromagnetic performance of two different Synchro...

High-speed machines are used in a growing range of applications, including in compressors and turbines. We spoke to Professor Lassi Aarniovuori, Professor Juha Pyrhönen and M.Sc. Juuso Narsakka about the work of the MUSK 2 project in developing a megawatt class universal high-speed machine, which they ultimately aim to bring to the commercial marke...

The energy efficiency of non-road mobile machinery can be improved by using e.g., an electric drive system as a servo controller of a hydraulic machine to get an efficient electro-hydraulic (EH) converter. However, the cooling of EH devices require more understanding and new innovations. This work presents a design of a 7-kW integrated EH machine a...

Direct-on-line (DOL) permanent-magnet generators (PMSGs) can be applied in small-scale hydropower plants (< 10 MW). The Commission Regulation (EU) 2016/631 defines the boundary conditions to operate these generators in parallel with the grid. According to the regulation, fault-ride-through (FRT) capability is required in some cases. We study the FR...

Design optimization of a permanent magnet eddy current brake (PM-ECB) is performed by applying multiobjective particle swarm optimization (MO-PSO) for cost minimization. A previously designed and patented PM-ECB is used as a reference model in the study. A quasi-3-dimensional (3D) analytical modeling approach based on a reluctance network consideri...

This paper presents a comparison of optimized tooth-coil-winding modular permanent-magnet synchronous machines (TCW-MPMSMs) with H-shape and U-shape stator segments for fault-tolerance applications. Four optimization objectives are studied by means of a Particle-Swarm-Optimization (PSO) based routine: maximum rated torque, minimum torque ripple, ma...

A direct-on-line synchronous reluctance motor (DOLSynRM) with a rotor topology defined by the natural flux line curve approach is studied as an alternative to an induction motor using a 1.5 kW, 50 Hz synchronous reluctance motor as an example. If an induction motor stator is used, a direct squirrel-cage rotor replacement by a synchronous reluctance...

High-speed solid-rotor induction machines (HSIMs) are popular within high-speed applications because of their high rotor structural integrity and their fairly well-established manufacturing process guaranteeing high quality series products. Designing a new high-speed electric machine requires a multidisciplinary team to accomplish the machine perfo...

The paper considers an idea of a novel modular approach to a resolver design. The rotor of the resolver represents a simple piece of laminated steel with variable reluctance as in commercial resolvers. The stator part, however, is different. Each stator tooth is replaced with an H-core segment, which contains two windings: excitation and sensing. T...

This study provides an insight in the analytical estimation of the electric field along the surface of a stress grading system (SGS) in the end-winding region of an electrical machine. An analytical approach is derived for the field grading materials (FGMs) having power-law electric-field-dependent conductivity. Despite some limitations, the introd...

A fully submersible permanent magnet synchronous machine (PMSM) is introduced in this paper. Underwater operation requires that the machine parts have to be resistant to corrosion, and the electrically conducting parts need to be properly insulated from water. The machine under study consists of a rotor-surface permanent magnet rotor, protected by...

Most permanent-magnet (PM) loss studies consider only eddy current loss and neglect hysteresis. In this paper, the hysteresis behavior of two NdFeB PM grades with different magnetic properties is assessed when applied in a PMSM. Data from vibrating sample magnetometer measurements and hysteresis modelling are used as a base. In addition to the main...

The applicability of heat generation data obtained after cylindrical Li-ion cells discharging with a constant current was analyzed thoroughly to determine cell degradation mechanisms. Different commercial and noncommercial cylindrical Li-ion cells, wherein graphite was used for negative electrode creation, were considered in this study and the degr...

The impact of the current vector angle on the performance of a synchronous reluctance motor (SynRM) with an axially laminated anisotropic (ALA) rotor intended for high-speed applications is studied. The paper shows that the current vector angle not only impacts on the stator winding Joule losses and iron losses, but also strongly influences eddy cu...

Modern converter-supplied AC motors are exposed to bearing currents. Despite extensive research and development, the industry still does not have a final solution with acceptable cost and high efficiency. This paper focuses on capacitive bearing currents. After a brief explanation of the phenomenon, an unconventional approach for effective mitigati...

Despite the high popularity of lithium-ion batteries there is still a lack of simple and easily applicable methods for determining the Li-ion cell thermal parameters. Information about the specific heat capacity and thermal conductivity of Li-ion cells is required to ensure appropriate operation of the thermal control system of the Li-ion battery,...

This paper investigates the losses of a 5-kW converter-fed induction motor. The loss evaluation sensitivity in Finite Element Analysis using different calculation time steps is studied. The motor losses are studied experimentally using a sinusoidal or PWM voltage supply at different operation points. In the experiments, the recorded voltage samplin...

Electrification of transportation is one of the most effective means to reduce emissions. However, widespread adoption of electric vehicles faces challenges because of the limited availability of raw materials of batteries. Because of these concerns, hybrid electric technology is seen as an alternative. This paper presents the mechanical design for...

The impact of the air-gap length and usage of semi-magnetic wedges on the performance of a synchronous reluctance motor (SynRM) with an axially laminated anisotropic (ALA) rotor aimed at high-speed applications was studied. The studied ALA rotor is intended to be manufactured by heat treatment of a stack of special magnetic and nonmagnetic material...

Many waste heat recovery and biomass applications offer opportunities for small-scale steam turbines to produce electricity and to improve systems' energy efficiency. However, the currently used axial turbine-based technology is generally characterized by a relatively large physical size and poor design and off-design performances. To overcome thes...

More and more commonly, the rotating field machine drives are equipped with a frequency converter. The frequency converters enable the control of the magnetization state, torque and speed of the machine according to the needs of applications and, in principle, save energy. In turn, the pulse-width-modulation (PWM) creates additional harmonic losses...

The problem of bearing currents as a parasitic phenomenon in electrical machines is a problematic issue in the modern industry. Although the origins and generation mechanisms of the phenomenon have been actively studied a general solution has not been given. The study presented here offers one countermeasure proposal. Not only the lamination stack...

The phenomenon of third-order harmonics in synchronous reluctance motors (SynRMs) with an axially laminated anisotropic (ALA) rotor is studied. The paper shows that a specific rotor geometry can distort the air-gap flux density and induce third-order currents in the stator winding if it is delta connected. The third-order currents in different phas...

5 kW high-efficiency induction motor is analyzed using 2D open-source platform and the results are compared with commercial software and measurements. The importance of equivalent circuit parameters in 2D analyses is highlighted. The non-commercial and commercial software give similar results. The motor is further analysed in the 2.5D domain and th...

A self-holding three-position electric tubular actuator (SHTPETA) is described in the paper. The proposed linear actuator can be applied in a clutch system, where it is necessary to change certain mover positions over time. Other potential applications of such actuators can be shift of gears, coupling (decoupling) of various moving (rotating) mecha...

The impact of the thickness of the magnetic and nonmagnetic layers in an axially laminated anisotropic (ALA) rotor in a synchronous reluctance motor (SynRM) aimed at high-speed applications was studied. Considering possible manufacturing issues, the layers are desired to be thick rather than thin. At the same time, the layer thickness is related to...

This paper proposes an analytic coupled magneto-thermal analysis of an axial-flux (AF) permanent-magnet-assisted (PMA) eddy-current brake (ECB) at high-temperature working conditions. In the topology investigated, permanent magnets (PMs) are placed into stator slot openings to increase the braking torque production capability. This modification ena...

This paper presents an analysis of a permanent magnet synchronous machine (PMSM) with an unequal teeth width. The use of the concentrated nonoverlapping winding, also known as tooth-coil winding, has certain advantages. In addition, asymmetric features can be exploited by adopting this winding configuration to improve the machine performance. The p...

Different mechanisms by which bearing currents flow inside the electrical machine are well studied. In contrast, investigation and development of different techniques to mitigate these currents remain a field for improvement, and the final common solution to the problem has not been provided yet. In pursuit of addressing the problem, this paper dea...

A new method for computing convection heat transfer coefficients in axial flux permanent magnet synchronous machines (AF‐PMSMs) is introduced. The method is based on a two‐step finite element analysis (FEA). In the first step, a simple 2D model is introduced and fluid flow and temperature fields are studied using computational fluid dynamic (CFD) t...

The performance capabilities of an axially laminated anisotropic rotor (ALA) in a high-speed synchronous reluctance motor (SynRM) were studied. A 12 kW ALASynRM was designed as an alternative to a high-speed induction motor (IM) with a solid rotor. The electromagnetic design was implemented taking into account possible issues related to the new man...

A 5 kW high efficiency induction motor is analyzed using an open-source platform and the results are compared with measured data and commercial software. Comparison of the results shows that the open-source platform gives good results that are close to measured and commercial software computed values – especially for torque, current and losses. The...

This paper studies a modular permanent magnet synchronous machine (MPMSM) converted from a traditional single-core 24-slot 20-pole tooth-coil winding permanent magnet synchronous machine (TCW PMSM). The performance of the TCW PMSM is compared with the performance of the MPMSM (rearranged from this TCW PMSM) by the finite element method (FEM). It is...

A high demand for electrification of the transport sector has resulted in a need to provide compact and reliable electric power trains where the electric machine is a key element. The cooling system has a strong impact on the specific torque and power capability of the machine. The selection of the cooling solution should not be based on the steady...

New global energy efficiency classification standard IEC 61800-9-2 for frequency converters and motor systems has been recently launched. It classifies the energy efficiency of the converters and motor-drive systems and introduces three different methods to determine a voltage source converter (VSC) losses for the classification. In here, experimen...

The frequency converter driven IM can be used as a reference for the efficiency level of a drive system. In here, the losses and efficiency of a 75 kW IE3 -rated modern squirrel-cage induction motor are investigated experimentally. First, the result of IEC loss segregation with sinusoidal supply is used to create a reference point. Secondly, five d...

Rare-earth-permanent-magnet excitation can provide considerable improvement in the energy efficiency of electrical machines. Tolerating motor terminal short circuit and avoiding magnet irreversible demagnetization must be studied during the design and prototyping stage of a permanent-magnet motor. Electrical machinery design increasingly relies on...

A novel stainless core and submersible permanent magnet synchronous generator (PMSG) for tidal energy is investigated in this paper. The materials to be used must be resistant to marine environments. Therefore, there are two alternatives: using stainless magnetic materials and non-corrosion resistant materials can be used by protecting them by coat...

Finite-element analysis (FEA) is one of the most significant tools in the designing and analyzing of electrical machines, which mainly includes the transient-magnetic (TM), magnet-static (MS) and time-harmonic (TH) solutions. The transient-magnetic (TM) solution in FEA is capable of considering both the harmonic effects and eddy-current effects acc...

A novel method for the state of health (SoH) estimation and determination of the degradation mechanisms of cylindrical Li-ion cells after long storage time is presented. The proposed method is based on differential curves obtained with the help of temperature and heat flux measurements on the surface of a cylindrical lithium iron phosphate (LFP) ce...

Off-road traction applications require extremely high torque, especially, at low speeds. Such a high torque can be reached by gearing up the torque of an electrical machine. A tooth-coil permanent magnet synchronous machine with an integrated planetary gear is proposed as a solution for heavy off-and on-road traction applications. The key benefits...

The applicability of the presented modified calorimetric method is analyzed. The uncertainty of the method and its comparison with the potentiometric method are presented for different test scenarios. The recommendations for the test scenario selection of the proposed method are done. This research was enabled by the financial support of Academy of...

The entropy change (Δ S ) of a Li-ion battery during its charging and discharging is one of the important parameters, which has a strong effect on the heat generation in a Li-ion battery during its operation. Moreover, the behavior of the entropy change during an aging of the Li-ion battery may be used for the analysis of the battery degradation, t...

In this paper, a direct liquid cooling method is proposed for a radial-flux permanent-magnet motor. To demonstrate the feasibility of the cooling method, a test motor with a rated output of 205 kW was designed, constructed, and tested in an actual vehicle application, an electric city bus. The energy consumption tests were conducted by applying a h...

High-speed solid-rotor induction machines (IMs) suffer from higher rotor eddy-current losses ( as a result of the air-gap flux density harmonics) more than any other type of high-speed machines, because of the solid-rotor steel. A double-layer short-pitch asymmetric winding arrangement with prefabricated coils is proposed in this paper to mitigate...

This paper introduces a new nonlinear multidisciplinary design approach (NMDA) for axial-flux (AF) eddy current brakes (ECBs). The proposed NMDA is developed by nonlinear magnetic-thermal-structural coupled modelling. The nonlinear behaviors of the AF-ECB covering the BH curve, resistivity, heat capacity, thermal conductivity and the temperature ar...

A permanent magnet traction motor integrated with a planetary gearbox is studied. A machine of this kind can be employed as a propulsion motor in off-road machines like agricultural tractors that have to produce either very high traction forces at low speeds or reach higher traveling speeds at lower torques. In principle, a constant power curve as...