Ironless Rotor Research Articles

Impact of Manufacturing Tolerances on Axial Flux Permanent Magnet Machines with Ironless Rotor Core: A Statistical Approach

Axial Flux Permanent Magnet (AFPM) machines with ironless rotors are an attractive and recently studied solution in low-speed applications, due to their potentially high power/weight ratio, high aspect ratio, and high efficiency. Nevertheless, these machines are prone to be affected by manufacturing tolerance during its fabrication process and consequently, the magnets may move freely inside the rotor structure. This work presents a statistical analysis of manufacturing tolerances of an AFPM machine with an ironless rotor, considering several magnet fault types. A computationally efficient superposition method is developed and implemented to obtain both the cogging torque and rated torque considering several tolerance combinations with acceptable accuracy. The results obtained from a statistical analysis of 10,000 designs of a two-stator one rotor tooth coil winding AFPM (TCW-AFPM) machine allowed us to identify the parameters with the most impact on relevant performance indicators and disclosed a substantial increase in cogging and ripple torque when unavoidable combined tolerances are present.

Optimal Design of Axial Flux Permanent Magnet Motors for Ship RIM-Driven Thruster

This paper deals with the design and optimization of a 2.1 MW rim-driven electric thruster for ship propulsion. For this purpose, a double stator ironless rotor axial flux permanent magnet (AFPM) motor is considered as the propulsion motor. The analytical model of the selected AFPM motor is presented. The magnetic field in the AFPM machine is calculated using the 3D magnetic charge concept in combination with image theory and permeance functions to take into account the stator slotting effects, and a simple thermal model is used to evaluate the heat dissipation capabilities of the machine and the thermal dependence of the main electromagnetic losses. To optimally design the AFPM, an optimization process based on genetic algorithms is applied to minimize the cost of the active motor materials. An appropriate objective function has been constructed, and different constraints related to the main electrical, geometrical, and mechanical parameters have been taken into account. The achieved results are compared with the performance of a podded radial flux permanent magnet (RFPM) motor, which is considered a reference propulsion motor. The obtained results show a fairly satisfactory improvement in the cost and masses of the active motor materials. Finally, the accuracy of the obtained optimum solution is validated by performing 3D finite element analysis (3D-FEA) simulations.

Development and experimental validation of a fast and accurate field calculation tool for axial flux permanent magnet machines

A fast calculation method of magnetic flux density in axial flux permanent magnet (AFPM) machine is presented. This method is based on an original combination of magnetic charges concept, image theory, and relative permeance functions. Using this combined approach, significant 3D effects, which are present in axial flux machines such as curvature and edge effects as well as slotting effects due to stator slots, are considered. The main electromagnetic specifications of the AFPM machine such as cogging torque, Back Electromotive Force (EMF), and local air-gap flux density are calculated accurately in very short times. To validate this approach, an original prototype of double stator ironless rotor AFPM machine with adjustable air-gap is used. Experimental protocol including measurements of global characteristics (EMF, Torque) and measurements of local field density is presented. The obtained results are in good agreement with the experimental measurements which allows validating the proposed computation method.

A comparative study on the performance of SSDR coreless AFPM generators with conventional and Halbach magnet arrays

An axial flux permanent magnet (AFPM) generator is known to be a good candidate for both low- and high-speed applications. In this paper, a comprehensive comparison of four coreless AFPM generators is presented with conventional and Halbach magnet arrangement combined with iron and ironless rotor (epoxy). With the same coreless stator structure, four different AFPM generators with different rotor magnet arrangement and materials are compared in terms of voltage, current, power, machine weight, and power density. The analytical design approach is first presented and is subsequently validated using ANSYS Maxwell electromagnetic finite element analysis (FEA) software. Results show that AFPM machine with fully coreless topology using Halbach array with epoxy rotor can deliver similar power density but has a lower cost compared to conventional magnet array with iron rotor. Hence, this topology is favorable for low power low cost applications.

The Formula SAE Electric Vehicle Competition: A High-Torque Density Permanent Magnet Motor

The formula sae, or formula student, is an international vehicle design competition carried out by university students. This article deals with a fractional-slot synchronous permanent magnet (PM) machine designed to be mounted in the wheel hub of an electric vehicle (EV). By adopting an outer ironless rotor topology, a Halbach array magnet structure, and light materials, a low rotor inertia and a high-torque density are achieved. The results described in this article provide a quantitative assessment of the achievable torque density for small motors.

Two Phase Dual-Stator Axial-Flux PM BLDC Motor With Ironless Rotor Using Only-Pull Drive Technique

This paper proposes a two-phase dual-stator axial-flux permanent magnet brushless dc motor with an ironless rotor for higher torque per magnet volume using the only-pull drive technique. The advantage of the ironless rotor is that it reduces magnet volume by providing an effective flux linkage, while the only-pull drive technique, which involves only the pull process, benefits from the use of thin magnets that do not experience the irreversible demagnetization. The axial-flux configuration of the proposed dual-stator motor was adopted because of its capability of achieving the desired trapezoidal back electromotive force that maximizes the advantages of the only-pull drive technique. The thin magnets were fixed on the ironless rotor using a non-magnetic structure, and the stator was particularly designed to implement the only-pull drive technique. The performance of the motor was analyzed in terms of torque per magnet volume using the finite element analysis and validated by the experimental results.

Analysis of Halbach Permanent Magnet Synchronous Motor with Ironless Rotor Based on AYSYS

Modern motor needs high power density and low rotary inertia,which can improve its dynamic characteristics.Traditional permanent magnet motor shows its limitations.A new structure of ironless rotor motor is proposed. Finite element analysis based on ANSYS proves that the new design not only can increase the motor air gap flux density, but can make the use of ironless rotor rotor become reality. From the relationship curve between air gap flux density and ironless material width, can easily find the ideal width of ironless material of the motor.

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.

Semi-analytical study of 3 kinds of axial flux PM actuator

This paper deals with the study of discoidal Permanent Magnet machines using a method of field calculation based on the magnetic charges theory. This fast calculation method enables a systematic study of these devices. The presented method has been validated by a comparison with the classical FE method. Three kinds of discoidal machines are studied and compared. The first is a classical machine with axially magnetized magnets with iron stator and rotor cores. The second and third use simple Halbach array configurations for the magnets with iron and ironless rotor core. This study illustrates the interest of the Halbach structures for this type of device.

THEORY OF A SYNCHRONOUS MACHINE WITH A SELF-LEVITATED ROTOR

ABSTRACT The properties of an ironless rotor synchronous machine (SM) with null-flux windings on the stator and radial displacement of the rotor are considered. The system of the SM equations are derived. These equations are based on an analytic representation of a three-dimensional excitation field and on considering the SM as a dynamic system with three generalized coordinates, two of which are the coordinates of the Center of rotor mass and one is the angle coordinate which characterizes the rotation of the rotor on its own axis. On the basis of the solution of the equations we obtain the relations for all the basic quantities: radial and centering forces, radial suspension stiffness and parameters of the null-flux circuit. They characterize all the properties of the SM in the state when the rotating rotor undergoes a radial displacement.