Norman Borchardt

Design of a wheel-hub motor with air gap winding and simultaneous utilization of all magnetic poles

This paper presents a new structure of BLDC motor applied for a wheel-hub motor for an electric vehicle. Today the physical structure of BLDC motors is dominated by a massive stator with salient poles as a framework for the windings. This construction results in high weight and in significant energy losses caused by eddy currents and hysteresis losses in the stator material. Furthermore, a huge amount of conductor material is needed, mostly with limited cross-section areas, so that resistive losses occur. In this paper a new approach to a permanent excited electrical motor is presented that allows for stator constructions with reduced weight, size, resistive and magnetic losses in combination with a very compact and high efficient air gap winding that allows for simultaneous utilization of all permanent magnets to generate very high torque. The design of a wheel-hub motor useful to drive a 4WD electric vehicle is presented.

Mechatronic model of a novel slotless permanent magnet DC-motor with air gap winding design

This paper presents a mechatronic model of a novel slotless permanent magnet DC-motor with air gap winding. Besides technical advantages of this type of motor like high power density, high torque, very low weight and high efficiency, the motor design allows a very precise and efficient modelling with limited effort. A nonlinear model of magnetic field density can be extracted from a detailed nonlinear FE-model build in ANSYS/Maxwell, approximated by Fourier series and then used to model driving torque and back EMF, representing the coupling between electrical and mechanical subsystems. Analytically founded numerical models for driving torque and back EMF will be given. Real geometry of the phase winding is taken into account to improve model accuracy. The electrical subsystem will be described as coupled three phase system, whose parameters can also be extracted from the nonlinear FE-model with high accuracy. Together with a mechanical model of the rotor a MATLAB/Simulink model is build and extended by models of the hall sensors to detect rotor position and commutation logic to control the HEX-Bridge during operation. Finally, results of a complex simulation model, based on the parameters of the prototype of a wheel-hub motor, implementing the new motor design, are getting shown. Simulation results compare very well to measured data. Simulation time is very short due to the efficient approximation of magnetic flux density.

Nonlinear design optimization of electric machines by using parametric Fourier coefficients of air gap flux density

Weight and efficiency are conflicting top requirements for all kind of mobile applications of electrical machines. Utilizing the design freedom of a novel machine design, based on a slotless air gap winding while providing high torque and efficient cooling, this paper presents a design optimization approach that allows for precise and fast design of that type of machine. Design speed is achieved by building a simplified parametric model of the electrical machine that combines very well with a nonlinear optimization formulation of the design problem, where machine mass and losses are balanced out to find a Pareto optimal design set. Additional design requirements are treated via constraints. The parametric machine model was built upon a numerical finite elements method analysis of magnetic flux density in the air gap with ANSYS Maxwell, which is used to formulate parametric Fourier series based models of flux acting on a phase, flux acting on a six-step commutated winding and effective flux useful to define machine torque constant. Except the numerical optimization procedure, all model and design equations can be formulated analytically exploiting Maples symbolic computation features, thus simplifying analysis and speeding up design. Finally, an optimal motor design study for a 15-inch rim wheel-hub drive is presented. The range of a tradeoff between demands for weight and efficiency while delivering the required torque at nominal speed is shown.

Winding Machine for Automated Production of an Innovative Air-Gap Winding for Lightweight Electric Machines

This paper presents a newly developed winding machine, which enables an automated production of stator-mounted air-gap windings with meander structure. This structure has very high accuracy requirements. Therefore, automation is realized by the interaction of 15 actuators and a compound construction with 13 degrees of freedom. The programming works with discrete open-loop motion control to generate the kinematics. Above all, a flexible prototype of the winding machine is developed, manufactured, and tested for a motor with external rotor. Finally, experimental results of the developed automation for air-gap windings with meander structure are presented.

Analytical magnetic circuit design optimization of electrical machines with air gap winding using a Halbach array

This paper aims to analyze the influence of a Halbach array by using a semi analytical design optimization approach on a novel electrical machine design with slotless air gap winding. The useable magnetic flux density caused by the Halbach array magnetization is studied and compared to conventional radial magnetization systems. First, several discrete magnetic flux densities are analyzed for an infinitesimal wire size in an air gap range from 0.1 mm to 5 mm by the finite element method in Ansys Maxwell. Fourier analysis is used to approximate continuous functions for each magnetic flux density characteristic for each air gap height. Then, using a six-step commutation control, the magnetic flux acting on a certain phase geometry is considered for a parametric machine model. The design optimization approach utilizes the design freedom of the magnetic flux density shape in air gap as well as the heights and depths of all magnetic circuit components, which are stator and rotor cores, permanent magnets, air gap, and air gap winding. Use of a nonlinear optimization formulation, allows for fast and precise analytical calculation of objective function. In this way the influence of both magnetizations on Pareto optimal machine design sets, when mass and efficiency are weighted, are compared. Other design requirements, such as torque, current, air gap and wire height, are considered via constraints on this optimization. Finally, an optimal motor design study for the Halbach array magnetization pattern is compared to the conventional radial magnetization. As a reference design, an existing 15-inch rim wheel-hub motor with air gap winding is used.

Parametric model of electric machines based on exponential Fourier approximations of magnetic air gap flux density and inductance

Purpose This study aims to present a parametric model of a novel electrical machine, based on a slotless air gap winding, allowing for fast and precise magnetic circuit calculations. Design/methodology/approach Approximations of Fourier coefficients through an exponential function deliver the required nonlinear air gap flux density and inductance. Accordingly, major machine characteristics, such as back-EMF and torque, can be calculated analytically with high speed and precision. A physical model of the electrical machine with air gap windings is given. It is based on a finite element analysis of the air gap magnetic flux density and inductance. The air gap height and the permanent magnetic height are considered as magnetic circuit parameters. Findings In total, 11 Fourier coefficient matrixes with 65 sampling points each were generated. From each, matrix a two-dimensional surface function was approximated by using exponentials. Optimal parameters were calculated by the least-squares method. Comparison with the finite element model demonstrates a very low error of the analytical approximation for all Fourier coefficients considered. Finally, the dynamics of an electrical machine, modeled using the preceding magnetic flux density approximation, are analyzed in MATLAB Simulink. Required approximations of the phase self-inductance and mutual inductance were given. Accordingly, the effects of the two magnetic circuit parameters on the dynamics of electrical machine current as well as the electrical machine torque are explained. Originality/value The presented model offers high accuracy comparable to FE-models, needing only very limited computational complexity.