Thermal properties are a key issue in many applications associated with electrical machines. Beca... more Thermal properties are a key issue in many applications associated with electrical machines. Because of its special configuration, an axial-flux electrical machine usually uses self-ventilation. However, this cooling method has a significant impact degrading the machine operating characteristics, and thus, an independent cooling system is desirable. The focus of this paper is on the steady-state thermal modeling and laboratory testing of an axial-flux permanent-magnet (AFPM) electrical machine intended for a traction application. The proposed hybrid cooling arrangement consists of a frame cooling circuit with a water flow inside, a set of copper bars inserted in the teeth, and a segment of potting material around the end windings. Computational fluid dynamics and finite-element analysis are applied for the preliminary design. This paper provides experimental verification of the simulation results on a 100-kW AFPM electrical machine. Index Terms-Electrical machines, hybrid cooling method, liquid jacket, thermal analysis. I. INTRODUCTION A XIAL-FLUX permanent-magnet (AFPM) electrical machines are gaining popularity in electrical vehicles, bicycles, wind power generation systems, and other applications, where high torque density and compact design are required [1]-[6]. An axial-flux machine usually enables inherent selfventilation because of the rotating rotor disks along the whole diameter and an option to arrange multigaps in the rotor body and its support structure to provide higher turbulence, particularly in the two rotors and one stator design [4], [7], which Manuscript
ABSTRACT Permanent magnet (PM) machines with tooth coil windings are designed and analyzed. We st... more ABSTRACT Permanent magnet (PM) machines with tooth coil windings are designed and analyzed. We study how the slot wedge material affects the behavior of PM losses when using tooth coil windings, which generate a significant air gap flux density harmonic content. The losses and cogging torques of a surface permanent magnet rotor and an interior permanent magnet rotor are compared in no-load and load situations. A finite element analysis applying Cedrat’s Flux2D is made. Motors of this size can have high permanent magnet eddy current losses, and therefore, segmented magnets are often preferred even though interior magnets and semi-magnetic wedge material are used. The study shows that tooth coil windings may benefit from using semi magnetic material as a wedge material as it decreases the stator iron losses and, especially, losses in the permanent magnets.
2019 International Aegean Conference on Electrical Machines and Power Electronics (ACEMP) & 2019 International Conference on Optimization of Electrical and Electronic Equipment (OPTIM), 2019
A 5 kW high efficiency induction motor is analyzed using an open-source platform and the results ... more 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 open-source method required less computational time than the commercial software. It is concluded that for 2D applications, open-source software can be used on industrial-scale problems with acceptable results.
2016 XXII International Conference on Electrical Machines (ICEM), 2016
In order to be competitive, companies aim at improving their technologies in terms of production ... more In order to be competitive, companies aim at improving their technologies in terms of production process simplification and reduction in the overall price of products. However, the use of lower-cost materials and a simpler construction can often degrade the machine performance. One of the possible production process simplifications of electrical machines is the use of modular permanent magnet synchronous machines (MPMSM). Some analytical approaches to analyze machines with modular stator can be found in the literature but these fall in the accuracy or do not consider the U-Shape core structure. This paper presents an analytical model to estimate the no-load air-gap flux density distribution of a U-shape MPMSM with tooth-coil winding. The results were verified with 2-D finite element analysis showing good accuracy.
Modern converter-supplied ac motors are exposed to bearing currents. Despite extensive research a... more 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 article focuses on capacitive bearing currents. After a brief explanation of the phenomenon, an unconventional approach for effective mitigation of the capacitive bearing currents is proposed. The approach suggests using grounded electrodes in the slot openings to reduce the stator-windingto-rotor-core capacitance and thereby the bearing currents. Different electrode diameters are considered and evaluated by a finite element method (FEM) analysis. The results are verified by laboratory tests. The bearing voltage ratios of the original and modified induction motor are compared. Index Terms-Ball bearings, electrical discharge machining bearing currents, electrical machines, finite element analysis (FEA), induction machines, variable speed drives.
Mitigating noncirculating bearing currents by a correct stator magnetic circuit and winding desig... more Mitigating noncirculating bearing currents by a correct stator magnetic circuit and winding design," in IEEE Transactions on Industrial Electronics.
Direct liquid cooling (DLC) of electrical machine windings is a clearly effectual cooling method ... more Direct liquid cooling (DLC) of electrical machine windings is a clearly effectual cooling method for high-torque and high-power-density applications needed, especially, in heavy vehicles. Usually, in electric vehicles, the stator copper winding losses are the most dominating losses during the accelerating or decelerating (recuperation) modes, and therefore, traditional windings may heat up significantly during high-torque periods. Removing the heat directly from the winding in which most of the heat is generated, allows the most straightforward and effective way of cooling. This paper investigates the feasibility of the direct liquid cooling in a radial-flux permanent-magnet traction motor. This case provides experimental information of the behavior of the direct liquid cooling of the windings. The prototype motor equipped with directly liquid-cooled windings is installed in an electric bus so that typical bus load cycles can be tested.
In this paper, a direct liquid cooling method is proposed for a radial-flux permanent-magnet moto... more 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 heavy-duty chassis dynamometer capable of simulating the inertia, weight, and road loads that the buses are subjected to in the normal on-road operation. The electricity consumption on the real bus route of Espoo line 11 in Finland was 0.61 kWh/km. Test results of the cooling solution show that the motor is capable of meeting the most challenging requirements of the load cycle even with a full payload. The highest winding temperature rise in the test driving cycles was only 26 C, which proves the effectiveness of direct-liquid-cooled coils in a vehicle motor. INDEX TERMS Electric machines, permanent magnet motors, rotating machines, traction motors, direct liquid cooling.
2012 XXth International Conference on Electrical Machines, 2012
ABSTRACT External rotor machine design analytical algorithm is presented in this paper to calcula... more ABSTRACT External rotor machine design analytical algorithm is presented in this paper to calculate the main dimensions of the stator and rotor lamination. This procedure is based on the well known Lagrange multiplier method, where the airgap apparent power is maximized under tangential stress constraint Results of this procedure are used to generate an improved torque estimation algorithm based on the non-ideal structure of the machine. Finite element analysis is used to compare these results, establishing a good agreement with the analytical approach.
2014 International Conference on Electrical Machines (ICEM), 2014
New combination of an electrical machine and a two-step planetary gear for high torque traction a... more New combination of an electrical machine and a two-step planetary gear for high torque traction applications is introduced. This kind of a machine can act as a propulsion motor for working machines such as e. q. agricultural tractor that needs to generate very high traction forces and also higher travelling speeds. The technology also suits in some road vehicle use e.g. for buses or trucks. Detailed information about the electrical machine design is provided. The machine has tooth-coils in the stator, embedded permanent magnets in the rotor and its cooling is arranged via the gear lubrication as the chamber is semi-filled with oil.
2012 XXth International Conference on Electrical Machines, 2012
ABSTRACT A traction motor design process is described. Not only the application but also the cont... more ABSTRACT A traction motor design process is described. Not only the application but also the control and the converter hardware set their own boundaries for the machine design. In traction applications the driving speed often varies from low speeds up to deep field weakening at high speed. As electrical drives are utilized in hybrid or full electric working machines or vehicles to improve their energy efficiency the electric drive efficiency should be high over the machine's whole operating speed range. To achieve high enough acceleration the low speed torque demand is usually set high which can be challenging from the electric machine design point of view. In the low speed area a high torque is needed and all the current reserves of the converter hardware are often used to achieve the highest possible torque. At high speeds the iron losses rise proportionally to the square of the speed. Losses in the permanent magnets depend both on the armature current and frequency. As an example different traction motor versions with the rated power of 110 kW, 2.5 p.u. starting torque and maximum 2.5 p.u. speed will be studied in the paper.
Thermal properties are a key issue in many applications associated with electrical machines. Beca... more Thermal properties are a key issue in many applications associated with electrical machines. Because of its special configuration, an axial-flux electrical machine usually uses self-ventilation. However, this cooling method has a significant impact degrading the machine operating characteristics, and thus, an independent cooling system is desirable. The focus of this paper is on the steady-state thermal modeling and laboratory testing of an axial-flux permanent-magnet (AFPM) electrical machine intended for a traction application. The proposed hybrid cooling arrangement consists of a frame cooling circuit with a water flow inside, a set of copper bars inserted in the teeth, and a segment of potting material around the end windings. Computational fluid dynamics and finite-element analysis are applied for the preliminary design. This paper provides experimental verification of the simulation results on a 100-kW AFPM electrical machine. Index Terms-Electrical machines, hybrid cooling method, liquid jacket, thermal analysis. I. INTRODUCTION A XIAL-FLUX permanent-magnet (AFPM) electrical machines are gaining popularity in electrical vehicles, bicycles, wind power generation systems, and other applications, where high torque density and compact design are required [1]-[6]. An axial-flux machine usually enables inherent selfventilation because of the rotating rotor disks along the whole diameter and an option to arrange multigaps in the rotor body and its support structure to provide higher turbulence, particularly in the two rotors and one stator design [4], [7], which Manuscript
ABSTRACT Permanent magnet (PM) machines with tooth coil windings are designed and analyzed. We st... more ABSTRACT Permanent magnet (PM) machines with tooth coil windings are designed and analyzed. We study how the slot wedge material affects the behavior of PM losses when using tooth coil windings, which generate a significant air gap flux density harmonic content. The losses and cogging torques of a surface permanent magnet rotor and an interior permanent magnet rotor are compared in no-load and load situations. A finite element analysis applying Cedrat’s Flux2D is made. Motors of this size can have high permanent magnet eddy current losses, and therefore, segmented magnets are often preferred even though interior magnets and semi-magnetic wedge material are used. The study shows that tooth coil windings may benefit from using semi magnetic material as a wedge material as it decreases the stator iron losses and, especially, losses in the permanent magnets.
2019 International Aegean Conference on Electrical Machines and Power Electronics (ACEMP) & 2019 International Conference on Optimization of Electrical and Electronic Equipment (OPTIM), 2019
A 5 kW high efficiency induction motor is analyzed using an open-source platform and the results ... more 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 open-source method required less computational time than the commercial software. It is concluded that for 2D applications, open-source software can be used on industrial-scale problems with acceptable results.
2016 XXII International Conference on Electrical Machines (ICEM), 2016
In order to be competitive, companies aim at improving their technologies in terms of production ... more In order to be competitive, companies aim at improving their technologies in terms of production process simplification and reduction in the overall price of products. However, the use of lower-cost materials and a simpler construction can often degrade the machine performance. One of the possible production process simplifications of electrical machines is the use of modular permanent magnet synchronous machines (MPMSM). Some analytical approaches to analyze machines with modular stator can be found in the literature but these fall in the accuracy or do not consider the U-Shape core structure. This paper presents an analytical model to estimate the no-load air-gap flux density distribution of a U-shape MPMSM with tooth-coil winding. The results were verified with 2-D finite element analysis showing good accuracy.
Modern converter-supplied ac motors are exposed to bearing currents. Despite extensive research a... more 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 article focuses on capacitive bearing currents. After a brief explanation of the phenomenon, an unconventional approach for effective mitigation of the capacitive bearing currents is proposed. The approach suggests using grounded electrodes in the slot openings to reduce the stator-windingto-rotor-core capacitance and thereby the bearing currents. Different electrode diameters are considered and evaluated by a finite element method (FEM) analysis. The results are verified by laboratory tests. The bearing voltage ratios of the original and modified induction motor are compared. Index Terms-Ball bearings, electrical discharge machining bearing currents, electrical machines, finite element analysis (FEA), induction machines, variable speed drives.
Mitigating noncirculating bearing currents by a correct stator magnetic circuit and winding desig... more Mitigating noncirculating bearing currents by a correct stator magnetic circuit and winding design," in IEEE Transactions on Industrial Electronics.
Direct liquid cooling (DLC) of electrical machine windings is a clearly effectual cooling method ... more Direct liquid cooling (DLC) of electrical machine windings is a clearly effectual cooling method for high-torque and high-power-density applications needed, especially, in heavy vehicles. Usually, in electric vehicles, the stator copper winding losses are the most dominating losses during the accelerating or decelerating (recuperation) modes, and therefore, traditional windings may heat up significantly during high-torque periods. Removing the heat directly from the winding in which most of the heat is generated, allows the most straightforward and effective way of cooling. This paper investigates the feasibility of the direct liquid cooling in a radial-flux permanent-magnet traction motor. This case provides experimental information of the behavior of the direct liquid cooling of the windings. The prototype motor equipped with directly liquid-cooled windings is installed in an electric bus so that typical bus load cycles can be tested.
In this paper, a direct liquid cooling method is proposed for a radial-flux permanent-magnet moto... more 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 heavy-duty chassis dynamometer capable of simulating the inertia, weight, and road loads that the buses are subjected to in the normal on-road operation. The electricity consumption on the real bus route of Espoo line 11 in Finland was 0.61 kWh/km. Test results of the cooling solution show that the motor is capable of meeting the most challenging requirements of the load cycle even with a full payload. The highest winding temperature rise in the test driving cycles was only 26 C, which proves the effectiveness of direct-liquid-cooled coils in a vehicle motor. INDEX TERMS Electric machines, permanent magnet motors, rotating machines, traction motors, direct liquid cooling.
2012 XXth International Conference on Electrical Machines, 2012
ABSTRACT External rotor machine design analytical algorithm is presented in this paper to calcula... more ABSTRACT External rotor machine design analytical algorithm is presented in this paper to calculate the main dimensions of the stator and rotor lamination. This procedure is based on the well known Lagrange multiplier method, where the airgap apparent power is maximized under tangential stress constraint Results of this procedure are used to generate an improved torque estimation algorithm based on the non-ideal structure of the machine. Finite element analysis is used to compare these results, establishing a good agreement with the analytical approach.
2014 International Conference on Electrical Machines (ICEM), 2014
New combination of an electrical machine and a two-step planetary gear for high torque traction a... more New combination of an electrical machine and a two-step planetary gear for high torque traction applications is introduced. This kind of a machine can act as a propulsion motor for working machines such as e. q. agricultural tractor that needs to generate very high traction forces and also higher travelling speeds. The technology also suits in some road vehicle use e.g. for buses or trucks. Detailed information about the electrical machine design is provided. The machine has tooth-coils in the stator, embedded permanent magnets in the rotor and its cooling is arranged via the gear lubrication as the chamber is semi-filled with oil.
2012 XXth International Conference on Electrical Machines, 2012
ABSTRACT A traction motor design process is described. Not only the application but also the cont... more ABSTRACT A traction motor design process is described. Not only the application but also the control and the converter hardware set their own boundaries for the machine design. In traction applications the driving speed often varies from low speeds up to deep field weakening at high speed. As electrical drives are utilized in hybrid or full electric working machines or vehicles to improve their energy efficiency the electric drive efficiency should be high over the machine's whole operating speed range. To achieve high enough acceleration the low speed torque demand is usually set high which can be challenging from the electric machine design point of view. In the low speed area a high torque is needed and all the current reserves of the converter hardware are often used to achieve the highest possible torque. At high speeds the iron losses rise proportionally to the square of the speed. Losses in the permanent magnets depend both on the armature current and frequency. As an example different traction motor versions with the rated power of 110 kW, 2.5 p.u. starting torque and maximum 2.5 p.u. speed will be studied in the paper.
Uploads
Papers by P. Lindh