Martin Doppelbauer

A comparison of the transverse, axial and radial flux PM synchronous motors for electric vehicle

This paper presents the performance comparison among three different topologies of the permanent magnet synchronous machine, namely a transverse flux permanent magnet machine with flux concentration and claw pole structure, an axial flux machine with segmented armature torus structure and a conventional radial flux machine with embedded permanent magnets in the rotor. With the help of Finite Element Method, three electrical machines have been designed considering the required dimensions and permanent magnets mass. The complete results evaluation and comparisons are described in this paper. From the obtained results it can be concluded, the axial flux machine with segmented armature torus structure can be a competitive alternative compared with the conventional radial flux machine for applications with limited axial length, while the transverse flux machine is an attractive alternative for the high torque and low-speed applications due to its high pole number.

Development of a Yokeless and Segmented Armature Axial Flux Machine

This paper is about the mechanical design and analysis of a yokeless and segmented armature axial flux permanent-magnet (PM) synchronous machine, which consists of two external rotors and an inner stator. Although this new electrical machine has many advantages such as high torque density, shorter axial length, and high efficiency, its mechanical construction is yet challenging. This is mostly due to the high axial force between the stator and the two rotors, which can be further increased by the inevitable manufacturing and assembly tolerances. Based on the determined geometric dimensions of the electromagnetically relevant components, a reliable mechanical construction is developed in this paper. Subsequently, stress, deformation, thermal, and modal analyses are performed based on finite-element method (FEM). Finally, the first prototype is successfully manufactured and measured. It can be concluded that the proposed construction is reliable and the measured data match well with the results of the electromagnetic analysis.

Predictive Trajectory Control of Permanent-Magnet Synchronous Machines With Nonlinear Magnetics

High-performance permanent-magnet synchronous machines show nonlinear behavior due to saturation effects. Nonlinear differential equations describe these phenomena which makes feedback control challenging. This paper presents a unified approach based on the current, flux linkage and voltage plane to visualize the physics of machine dynamics. A predictive control method to precisely control arbitrary dynamic trajectories in all planes can then be developed. Four real-time strategies for dynamic trajectory identification are deduced: two straight trajectories, a strategy that yields a fast torque response, and a strategy that reaches the reference currents in minimal time. The performance of the four approaches is analyzed using simulations and test bench measurements. Advantages and disadvantages of specific trajectories are identified. It is thus shown how the dynamics of permanent-magnet synchronous machines with nonlinear magnetics can be controlled both precisely and optimally.

Multi-Objective Optimization of a Transverse Flux Machine With Claw-Pole and Flux-Concentrating Structure

This paper describes a new method aiming at the multi-objective optimization of a transverse flux machine with a claw-pole and flux-concentrating structure (CPTFM). Considering the 3-D main magnetic flux in the CPTFM, the time-consuming 3-D finite-element method (FEM) should be used to accurately analyze the performance of the machine. In order to reduce the calculation time for the optimization of the complex CPTFM, the Taguchi method is first applied to evaluate the importance of all the design parameters in the consideration of the predefined five objectives. Subsequently, a mathematical model is developed to replace the 3-D FEM, so that the objectives depending on the selected four critical parameters can be analytically calculated. With its help, the four parameters are further optimized with the multi-objective particle swarm optimization method and nondominated sorting genetic algorithm 2. Finally, the optimal design of the CPTFM is selected from all the searched Pareto solutions with the help of fuzzy logic. It can be concluded that the developed method is effective and efficient, which can make an appropriate compromise between the calculation time and the improvement of the machine performance.

Indirect slot cooling for high-power-density machines with concentrated winding

Electric machines with concentrated winding and single tooth design provide a cost effective way to use flat wires. Hereby high filling factors can be achieved, but due to geometric constraints and the influence of current displacements there remains unused space inside the slot. This space can be used for water cooling channels. As a result of the small thermal resistance between winding and cooling fluid this leads to an outstanding cooling performance. Compared to round wires efficiency is improved in wide parts of the operating area. The absence of the cooling jacket leads to comparable production costs but an even more compact machine design. Technological aspects are discussed and a particular high-power-density interior permanent magnet synchronous machine (IPMSM) with water jacket cooling and round wires is compared to a flat wire wound, slot cooled motor by the use of FEM and CFD simulations and measurements on single tooth specimen.

Theoretical analysis of synchronous machines with displaced reluctance axis

This paper examines synchronous machines, whose excitation axis and reluctance axis can have an arbitrary angle. Basic equations for this machine type are set up and control strategies for maximum torque are derived. By using a normalized representation, it will be shown that machines with displacement angles of about 60° need up to 10% less permanent magnet material than conventional machines while yielding comparable motor performance.

Iron loss and parameter measurement of permanent magnet synchronous machines

In this paper a measurement technique for synchronous machines is presented that allows the experimental identification of stator flux linkage as well as iron and friction losses in each operation point. The technique can be applied to all kinds of synchronous electric machines, even to machines showing magnetic anisotropy, iron saturation and cross-coupling. Influences of spatial harmonics, inverter switching and temperature transients are considered. The method uses steady-state measurements at constant motor speed. It is based on a combined evaluation of two operation points with corresponding magnetic states, one being in the motor and the other in the generator mode. The method is demonstrated by characterization of an automotive permanent magnet synchronous traction motor.

Mechanical construction and analysis of an axial flux segmented armature torus machine

This paper deals with the mechanical construction and static strength analysis of an axial flux permanent magnet machine with segmented armature torus topology, which consists of two external rotors and an inner stator. In order to conduct the three dimensional magnetic flux, the soft magnetic composites is used to manufacture the stator segments and the rotor yoke. On the basis of the detailed electromagnetic analysis, the main geometric dimensions of the machine are determined, which is also the precondition of the mechanical construction. Through the application of epoxy with high thermal conductivity and high mechanical strength, the independent segments of the stator are bounded together with the liquid-cooling system, which makes a high electrical load possible. Due to the unavoidable errors in the manufacturing and montage, there might be large force between the rotors and the stator. Thus, the rotor is held with a rotor carrier made from aluminum alloy with high elastic modulus and the form of the rotor carrier is optimized, in order to reduce the axial deformation. In addition, the shell and the shaft are designed and the choice of bearings is discussed. Finally, the strain and deformation of different parts are analyzed with the help of finite element method to validate the mechanical construction.

Feasibility Study of a Superconducting DC Direct-Drive Wind Generator

Superconducting (SC) direct-drive wind generators are proposed as a possible approach for offshore wind energy application. A lot of studies showed their benefits and superior performances. Small demonstrators up to several hundreds of kilowatts have been built and laboratory tested. More demonstrators will come in the future, and the success of these projects is very important for the large-scale prototypes to be realized. For most studies, the SC direct-drive generators are a synchronous generator concept. As the offshore wind farms are located far away from the land mainly due to the overall economic benefit, direct current transmission has been put forward. Hence, employing SC dc wind generators would be a good option. This enables a highly efficient and compact generator and, in addition, a new and also very efficient generator connection scheme at dc. For this reason, this paper investigates the feasibility of the large-scale SC dc direct-drive wind generator, in terms of torque, weight, and efficiency. In addition, the tape cost and commutation are discussed.

Cascaded design methodology for switched reluctance motors considering optimum control

Switched reluctance motors (SRM) have a cheap and robust structure, which makes them interesting for electric vehicle applications. In this paper, a new optimization scheme for the design of SRM is proposed. The design methodology is then used to design a 127 kW high speed SRM for electric vehicles. The optimization procedure has a cascaded structure with a geometry optimization as the outer loop and a new control optimization as the inner loop. This new control scheme ensures maximum efficiency with the constraint of a minimum torque ripple by developing a current profile, which considers the non-linear behavior of the switched reluctance motor and the declining current dynamics with increasing speed. The control scheme is used to evaluate rated power and motor efficiency of the relevant operating points within the outer geometry optimization of the design methodology.