Stator Stack Research Articles

Modelled optimisation approaches for laser cutting sheets simultaneously applied to EV component production.

This paper proposes that laser cutting has potential as a viable alternative to stamping for mass manufacture of thin steel components such as stator and rotor components in the electric automotive sector. Current laser cutting processes are much less efficient than stamping. However, laser cutting is much more flexible and is used for small batches and one-off production. This paper assesses the potential of performing laser cutting operations of multiple sheets or layers simultaneously. This method is referred to herein as polystromata cutting. A numerical model is used to assess the manufacturing performance of stamping, traditional laser cutting and polystromata laser cutting. Polystromata laser cutting is shown to be capable of producing parts at 37% less cost than stamping. However, polystromata remains slower than stamping, taking 79% more time to produce each stator stack. Through this research it has been identified that optimisation of polystromata processes is more complex and performance efficiency varies wildly dependent on manufacturing set-up. This work aims to provide a best practice optimisation methodology for polystromata laser cutting by assessing results using different manufacturing objectives.

Effect of stator height change on bearing life in aircraft autopilot servos

PurposeThe purpose of this paper is to make a more precise prediction of the life of servo motors used in aircraft. The variation of the axial load created by the wave washer for bearing, which is one of the factors affecting the bearing life of the electric motors and servo motors used in aircraft, was analyzed.Design/methodology/approachIn electric motors and servo motors that body as stator, the height of the stator stack affects the compression amount of the wave washer spring. Working with electric motor and servo manufacturers, production-related variations in stator height were determined by making multiple measurements. The reaction forces resulting from these compression amounts were simulated by mathematical modeling with the finite element method, and also experimentally measured on real parts.FindingsResults obtained with finite element method and real experiments were compared. By adding the force differences to the general operating conditions, the effect on the bearing life was theoretically determined. In a servo motor with this type of construction, the difference in stator height created different axial loads on the motor shaft. The difference of these loads affected the motor bearing life.Research limitations/implicationsThe results implicated in terms of flight safety, maintenance operation and resource efficiency.Practical implicationsThe results of this study are effective in determining the maintenance intervals more clearly. This study can be used for the design criteria of aircraft servo motors. These servos, which are especially used to move the flight control surfaces, contribute to flight safety as the life expectancy will be clearer.Social implicationsThis study may be effective in preventing aviation accidents caused by servo motors. It can make maintenance management more efficient.Originality/valueThis study investigated the effect of aircraft servo motor design inputs on servo motor life, considering the production.

Pulsed laser welding of laminated electrical steels

Abstract Stator core is one of the parts in the magnetic circuit, which playing an important role in the performance of the electric machine. Commonly the non-oriented electrical steel laminations are assembled into a stator stack by welding to meet the demand of strength at high-speed rotation. However, the effects of residual stress, microstructure change and inter-conduction among laminations introduced during welding process result in a great deterioration in magnetic properties of stator core. The pulsed laser welding of ultra-thin electrical steel laminations is adopted to decrease the iron loss while ensuring sufficient strength simultaneously. As two important indicators of the stator core, peak load after welding determines the maximum load torque and iron loss affects the energy conversion efficiency. There is currently no model that can accurately predict peak load and iron loss of the stator core after pulsed laser welding, and the influence of peak power and duty cycle on peak load and iron loss also needs to be further studied. In this paper, the peak load of stator core is studied based on the tensile test of a novel rectangular specimen which has the same stress state with the ring ones subjected to torsional load. An empirical model of peak load is proposed by the two-step fitting method considering the effect of peak power and duty cycle. Then an analytical model of iron loss of welded laminations is developed considering eddy current circuit in weld seam caused by damage of insulation coating. All peak load and iron loss models with small relative errors can obtain accurate prediction results. Finally, the weld lobe for pulsed laser welding is drawn, whose left and right boundaries are determined by peak load and iron loss, respectively. By selecting the appropriate process parameters, iron loss of the stator core using pulsed laser welding decreases, compared with traditional continuous laser welding.

Total Artificial Heart Incorporating Novel Stacked Motor; First In Vivo Results

The latest version of the continuous flow total artificial heart (CFTAH), which incorporates a novel stacked motor to improve passive self-regulation of pressure difference between the left and right atria, and reduce pump rotor over-excursion, was tested in vivo in a calf model to assess operational performance. The CFTAH was implanted in a calf and run at various pump operating conditions including mean pump speeds from 2400 to 3600 RPM, sinusoidal speed modulations from 0 to 25%, and speed modulation rates from 80 to 120 B.M. It was also tested under various combinations of simulated high and low systemic vascular resistance and pulmonary vascular resistance via outlet graft clamping and administration of a Nitroprusside respectively. The CFTAH responded to all control inputs and ran as expected during the experiment. The head curves of the right and left pumps generated from measured pressures, measured right flow and calculated left flow, were consistent with in vitro data on this pump. The passive atrial pressure regulation performed well in the normal operating range, and there were no signs of excessive rotor axial displacement during extreme pressure excursions as had been seen in the previous versions of the pump. The left atrial pressure was unusually low throughout most of the experiment and we believe that this may have been due to partial blockage of the of the left inflow cuff proximal to the pressure line tap. This led to several left inlet suction conditions and extreme pressure conditions. The replacement of the standard, single stack stator motor with the new dual stator stack motor resulted in better passive regulation of the pressure difference between the left and right atria. Also, the extreme pressure conditions resulting from left inlet suction events did not cause the pump's rotor to rub against the volute housing as had been seen in previous versions of the pump. Even though the self-regulation was acceptable, shifting of the regulation characteristic to increase the nominal LAP-RAP value will improve the regulation further, and this modification will be implemented prior to the next in vivo experiment.

Traction Synchronous Homopolar Motor: Simplified Computation Technique and Experimental Validation

Synchronous homopolar motors (SHMs) have been attracting the attention of researchers for many decades. Various mathematical models of SHM have been proposed to deal with its complicated magnetic circuit. Among them, there are time-consuming 3D finite element models (FEM), equivalent circuit models neglecting some significant features of the machine design, and 2D FEM models with virtual excitation winding distorting its magnetic field picture. This paper proposes a novel 2D FEM of SHM and shows that since there are no sources of excitation in the cross-sections of the rotor and stator stacks, no virtual elements are required. This model uses the general solution of the Gauss’s law for magnetism containing excitation flux. The model is based on a set of magnetostatic boundary value problems for various rotor positions. The set of boundary problems is completed with the excitation equivalent circuit. The losses in the armature and field windings and the stator and rotor magnetic cores are computed in postprocessing. All these computations are carried out for a single combination of stator and rotor stack. A symmetrization algorithm is proposed to extend the obtained results to the whole SHM. A comparison of the theoretical and experimental data for a nine-phase three-section 320 kW SHM is carried out. These SHMs were used in a mining truck with a carrying capacity of 90 tons.

Basic Design Method for SPMSM Based on Air‐Gap Magnetic Flux Density Distribution Focusing on Image Magnetic Pole

SUMMARYThis paper presents a basic design method for the surface‐mounted permanent magnet synchronous motor (SPMSM) for both distributed and concentrated windings. The design is based on the air‐gap magnetic flux density distribution focusing on the image magnetic pole. The calculus equation of the air‐gap magnetic flux density distribution is analytically derived by supposing the magnetic pole is located on the magnet surface and image planes. In this study, a three‐phase and double‐layer stator winding SPMSM that has a linear demagnetizing characteristic magnet, such as a ferrite or rare‐earth magnet is considered. From the required specifications and design conditions, the design target values of the parameters that appear in the voltages equations of the d–q axis coordinate system are calculated. Then, the relational equations for the torque constant, d‐axis inductance, copper loss, and the maximum current density are presented as a function of three design parameters under id = 0 control. They are the stator stack length, the number of coil turns in series in a phase, and the slot bottom length. Hence, this approach reduces the SPMSM basic design to the problem with these design parameters has to be solved. The proposed method makes it possible to address the concentrated winding as a special case of the distributed winding. The FEA results confirm the validity of the proposed basic design method for both distributed and concentrated windings.

High-Speed BLDC Motor Design for Suction Fan and Impact on the Loss caused by Core Welding

This paper deals with the effects of welding, which is done to fix the stator stack, on a motor in case of fabricating a prototype motor that is manufactured in a small quantity. In the case of a small motor, the stator is designed and fabricated with the segmented core as a way to raise the fill factor of winding wire to the utmost within a limited size. In case of fabrication by welding both inside and outside of the stator in order to fix the segmented-core stator, the effects of stack are ignored, and the eddy current loss occurs. This paper performed the no-load test on an IPM-type BLDC motor for driving the suction fan of a vacuum cleaner, which was manufactured by using a segmented-core stator. As a result of the test, it was found that input power more than expected was supplied. To analyze the effects of welding by using the finite element analysis method and verify them experimentally, a stator was re-manufactured by bonding, and input power supplied during the no-load test was compared.

Reducing Losses Due to Fringing Flux in an Axial-Flux Permanent-Magnet Synchronous Machine

This paper deals with iron losses caused by fringing fluxes generated by the concentrated stator windings of an axial-flux permanent-magnet synchronous machine. Fringing fluxes enter the laminated stator stack perpendicularly to the plane of the laminated silicon steel sheets. They cause additional eddy currents and losses in the sheets. Three approaches for reducing these losses are compared experimentally with a dedicated setup. The setup has no moving parts and makes accurate iron loss measurement possible. The first method directly restricts the eddy-current losses by segmenting the lamination surface. The second method deflects the fringing flux by using soft magnetic composite. The third method magnetically short circuits the fringing flux using ferromagnetic wires. The first method gives the best results, with a reduction of 6% of the total iron loss at an induction level of 0.6 T and a frequency of 200 Hz.

Analysis of the stator topology impact on cogging torque for surface permanent magnet motor

Purpose – The purpose of this paper is to investigate the impact of the stator core design for a surface permanent magnet motor (SPMM) on the cogging torque profile. The objective is to show how the cogging torque of this type of motor can be significantly reduced by implementing an original compound technique by skewing stator slots and inserting wedges in the slot openings. Design/methodology/approach – At the beginning generic model of a SPMM is studied. By using FEA, for this idealised assembly, characteristics of cogging and electromagnetic torque are simulated and determined for one period of their change. Afterwards, actual stator design of the original SPMM is described. It is thoroughly investigated and the torque characteristics are compared with the generic ones. While the static torque is slightly decreased, the peak cogging torque is almost doubled and the curve exhibits an uneven profile. The first method for cogging torque reduction is skewing the stator stack. The second technique is to insert wedges of SMC in the slot openings. By using 2D and 2 1/2D numerical experiment cogging curves are calculated and compared. The best results are achieved by combining the two techniques. The comparative analyses of the motor models show the advantages of the proposed novel stator topology. Findings – It is presented how the peak cogging torque can be substantially decreased due to changes in the stator topology. The constraint is to keep the same stator lamination. By skewing stator stack for one slot pitch 10° the peak cogging torque is threefold reduced. The SMC wedges in slot opening decrease the peak cogging almost four times. The novel stator topology, a combination of the former ones, leads to peak cogging of respectable 0.182 Nm, which is reduced for 7.45 times. Originality/value – The paper presents an original compound technique for cogging torque reduction, by combining the stator stack skewing and inserting SMC wedges in the slot openings.

Heat-transfer improvements in an axial-flux permanent-magnet synchronous machine

Axial-flux machines tend to have cooling difficulties since it is difficult to arrange continuous heat path between the stator stack and the frame. One important reason for this is that no shrink fitting of the stator is possible in an axial-flux machine. Using of liquid-cooled end shields does not alone solve this issue. Cooling of the rotor and the end windings may also be difficult at least in case of two-stator-single-rotor construction where air circulation in the rotor and in the end-winding areas may be difficult to arrange. If the rotor has significant losses air circulation via the rotor and behind the stator yokes should be arranged which, again, weakens the stator cooling. In this paper we study a novel way of using copper bars as extra heat transfer paths between the stator teeth and liquid cooling pools in the end shields. After this the end windings still suffer of low thermal conductivity and means for improving this by high-heat-conductance material was also studied. The design principle of each cooling system is presented in details. Thermal models based on Computational Fluid Dynamics (CFD) are used to analyse the temperature distribution in the machine. Measurement results are provided from different versions of the machine. The results show that significant improvements in the cooling can be gained by these steps.

A Device for the Study of Electrical Steel Losses in Stator Lamination Stacks

A new electromagnetic device to measure the electrical losses in stator lamination stacks, along with its associated test procedure, is presented. This procedure provides the ability to distinguish between stators made of different types of materials and can be employed to evaluate finished stator stacks prior to motor assembly. The design and simulation - using both ordinary differential equation solvers in the preliminary phase and detailed finite-element analyses following that - of the aforementioned device are documented, along with experimental data supporting our conclusions.

Local Heat Flux Measurement in a Permanent Magnet Motor at No Load

Heat transfer is a limiting factor in the performance of electrical machines. Measuring the heat flux in an electrical machine is traditionally carried out indirectly with temperature measurements as there are only a few sensors for heat flux measurements. This paper describes a new experimental method to measure the local heat flux inside an electrical machine. The measurement was proven successful in the air gap of the permanent magnet machine, 37 kW 2400 min-1, under an influence of the air gap magnetic flux. The heat flux was measured by using sensors based on the transverse Seebeck effect. The test machine was an axial flux permanent magnet machine with two stator stacks and one internal, ironless rotor disc. A gradient heat flux sensor was installed in the air gap on the stator side. Local Nusselt and Reynolds numbers were calculated according to the measured heat flux results and compared with the results given by traditional methods to verify the new measurement method.

Temperature Influence of NiFe Steel Laminations on the Characteristics of Small Slotless Permanent Magnet Machines

High performance electrical machines can operate at temperatures of 100°C and beyond in rotor and stator cores. However, magnetic properties are generally measured at room temperatures around 23°C to 25°C according to the standards, even if it is known that the magnetization of some materials is substantially influenced by increasing temperatures. This paper investigates the thermal influence on the magnetic properties and iron losses in the stator cores of small slotless permanent magnet synchronous machines (PMSMs). The stator stack is made of thin nickel iron (NiFe) lamination sheets. Magnetic measurements of the stator core are conducted for different frequencies and flux densities at several temperatures between 25°C and 105°C. The obtained measurement data is afterwards used in finite element method (FEM) simulations to investigate the influence of the magnetic property change on the machine performance. For the PMSM in consideration, the FEM simulations show that an increased stator core temperature reduces the electromagnetic torque considerably; approximately 1/3 of the torque reduction due to increased rotor magnet and stator core temperatures (from 25°C to 100°C) can be attributed to the increased stator core temperature.

3-D Finite Element Method Analysis of Additional Load Losses in the End Region of Permanent-Magnet Generators

Machine design typically concentrates on the main magnetic and electric circuits while various additional losses are evaluated only by simple empirical equations. The objective of this paper is to examine the importance of the additional losses in the stator end region and in the housing of a 3.1 MW permanent-magnet wind generator. Stator stack clamping ring and finger plate losses are investigated using a 3-D finite element method. 2-D FEM analysis of the stator supporting housing losses is also performed. Two common mechanical component materials are analyzed in the 3-D studies; construction steel and stainless steel. The results show that failure to consider stator end areas and stator supporting constructions at the design stage can result in unwanted additional losses and affect machine efficiency. Indirect verification of the results is provided by efficiency measurements of different versions of the real 3.1 MW machine.

Development and Control of an Integrated and Distributed Inverter for a Fault Tolerant Five-Phase Switched Reluctance Traction Drive

A concept of an integrated and distributed inverter for switched reluctance machines is introduced. The application at hand is an outer-rotor direct drive designed for railway traction applications. A five-phase switched reluctance machine was developed and is used to demonstrate the function of the integrated and distributed inverter. The distribution is achieved by supplying each phase coil with its own modular inverter. Each inverter module is placed evenly around the end of the stator stack next to its dedicated coil. This increases the redundancy of the drive significantly. The likelihood of phase-to-phase faults is reduced, because no overlapping end-turns are necessary. Also, the integration of machine and inverter is simplified, because the semiconductors can be evenly distributed around the machine. The concept reduces the amount of terminals between drive and vehicle to communication, power supply, and cooling, independent of the number of machine phases. With the integrated and distributed inverter new control strategies can be developed to influence machine vibration and radiated noise. In this paper, the design of the prototype, the direct torque control of the five-phase machine, and the behavior in the case of a fault inside a module is analyzed.

Effect of Lamination Stack Ends and Radial Cooling Channels on No-Load Voltage and Inductances of Permanent-Magnet Synchronous Machines

The effect of lamination stack ends and radial cooling channels on the effective stator stack length, no-load voltage, and synchronous inductances of a permanent-magnet synchronous machine are studied using three-dimensional finite element analysis. The stack ends and the radial cooling channels decrease the equivalent electrical length of the machine, thus leading to the fact that a two-dimensional (2-D) approach overestimates the no-load voltage. The effect of stack ends and radial cooling channels on the electrical length of the machine can be compensated by making the rotor stack and permanent magnets longer than the corresponding stator stack. It is shown that in case of no radial cooling channels, synchronous inductances are typically overestimated with the 2-D approach. However, in the case of stator structure having several radial cooling channels, inductances are underestimated using the 2-D approach.

永久磁石発電機のＲＮＡモデルを用いた鉄損算定について

In a previous paper, we proposed a reluctance network analysis (RNA) model of a permanent magnet (PM) generator with a distributed winding and an overhang structure in which the permanent magnet is longer than the stator's stack in the axial direction. Using the RNA model, the basic characteristics of the PM generator were calculated accurately. A method for calculating the iron loss of the generator, however, was not discussed. In this paper, we estimate the iron loss on the basis of flux density waveforms calculated by using the RNA model. To verify the validity of the proposed method, the estimated values are compared with those given by a finite element method (FEM). In addition, we examine the accuracy of the flux and iron loss distribution obtained from the RNA model.

リラクタンスネットワーク解析による永久磁石発電機の特性算定

This paper presents a method for calculating the operating characteristics of permanent magnet (PM) generators based on the reluctance network analysis (RNA) method proposed by the authors. The PM generator used in the discussion has a distributed winding and an overhang structure in which the permanent magnet is longer than the stator's stack in the axial direction. In the analysis, the stator and rotor, gap, and the permanent magnet including the overhang are expressed as a simplified three-dimensional RNA model. The RNA model of the PM generator is combined with an external electric circuit and motion calculation blocks on a general-purpose circuit simulator called “SPICE.” We can readily calculate the characteristics of the PM generator using the combined model, including its transient state. The calculated values agree well with the measured ones.

Detent torque from the soft magnetic stator stack of a hybrid stepper motor

The residual magnetism present in the stator stack of a hybrid stepper motor, which will be of the last excited polarity, will develop a detent torque, similar to the static torque of the last excited phase, but with reduced excitation. The predominant component is fundamental. Even though this torque is the result of the stator excitation, it can be considered as a detent torque as it is available when the stator excitation is withdrawn. This detent torque is in addition to the inherent one due to the rotor permanent magnet, and it will be present until the next phase is switched ON. Once the excitation is removed from the second phase, because of the hysteresis the detent torque will be available, similar to the static torque profile for phase 2, but with less excitation. This means because of the hysteresis the detent torque follows the static torque of the phases. The magnitude of this detent torque will depend upon the level to which the phase was excited. Experiments have been carried out on a 0.5° hybrid stepper motor to study the effects of the excitation on the detent torque profiles. Harmonic analyses of the measured detent torque curves had been carried out and it is seen that the fundamental detent torque increases with the excitation and also follows the respective phases. Therefore, the residual flux density and the coercive force of the soft magnetic material used for the stator stack have to be as small as possible to get rid of this effect. Controlling a hybrid stepper motor by a suitable switching scheme for a given application requires the measured static torque profiles of the motor for all the phases at the exact working voltage (or voltages in case of a variable voltage supply) and detent torque profiles both before and after excitation. Harmonic spectrum of the measured static and detent torque profiles have to be accounted for while simulating stepping behavior of the motor, from which an appropriate switching scheme can be arrived at.

Homopolar variable reluctance machine incorporating an axial field coil

Switched reluctance drives have been shown to benefit from DC flux assistance from a coil arrangement that is mutually coupled to all its phase windings. This paper proposes an alternative way of providing this additional DC flux through the use of a toroidal, axially orientated coil. A reluctance machine is constructed and tested in which the stator comprises two stacks separated by a coil to give axial magnetic flux. This construction is similar to a homopolar inductor alternator. The paper describes and develops the complex magnetic structure of the machine and describes initial test results. The ideal angular orientation between the two stator stacks is presented.