With the automotive industry’s increasing focus on electromobility and the growing share of electric cars, new challenges are arising for the development of electric motors. The requirements for torque and power of traction motors are constantly growing, while installation space, costs and weight are increasingly becoming limiting factors. Moreover, there is an inherent conflict in the design between power density and efficiency of an electric motor. Thus, a main focus in today’s development lies on space-saving and yet effective and innovative cooling systems. This paper presents an approach for a multi-physical optimization that combines the domains of electromagnetics and thermodynamics. Based on a reference machine, this simulative study examins a total of nine different stator cooling concepts varying the cooling duct positions and end-winding cooling concepts. To ensure the highest possible comparability, the rotor geometry as well as the overall dimensions in terms of outer diameter and length of the electric machine remain unchanged. The stator design is slightly adjusted to achieve same maximum torque and winding cross-section. Initially, the electromagnetic effects of various cooling slot positions are investigated and compared with respect to efficiency and individual loss distribution. Subsequently, the thermal performance is analyzed by means of fluid-dynamical simulations to quantify the heat transfer and assess the cooling effectivity. Eventually, these results are merged in a lumped parameter thermal network model. Accounting for both the distinguished electromagnetic and thermal benefits and disadvantages, a final study is presented evaluating the continuous power capability of the different concepts at equal boundary conditions.

This contribution investigates the effect of a rotor step skew on the demagnetization ratio of internal permanent magnet synchronous machines. During the design of an electrical machine for an automotive traction drive different requirements such as torque ripple, cost targets, torque and power density need to be considered. Beyond this the reduction of heavy rare earth content is a current challenge to reduce the environmental footprint. A promising way to achieve the goals, is to reduce the magnetic field load on the permanent magnets and therefore the necessary coercivity, which is linked to the heavy rare earth content. To prevent partial demagnetization and decrease additional margins on the coercivity the consideration of side effects and local phenomena inside the electrical machine is essential. This paper shows that in case of a rotor step skew the effects in the transition area between the segments are important for the local demagnetization behavior of the permanent magnets. In a case study different skew variants are investigated and it is shown that 3-D finite element simulations are inevitable to consider these effects.

Riding grid sags has been a challenging issue for traditional doubly fed induction generator-based wind turbine systems. Multiphase wind turbine generators have been taken rarely into account as potential ones to increase the reliability especially in the offshore area. There is a lack of investigating the dynamic behavior of multiphase wind turbine generators in the literature. By considering the effect of the full grid voltage dip, this paper investigates thus different fault ride through measures on a six-phase doubly fed induction generator. Among well-known software-based solutions such as demagnetizing current injection and stator current feedback methods, a new voltage perturbation system is presented.

This work proposes a methodology to characterize a thermal finite element analysis model. The aim is to obtain an efficient calculation model with a high spatial resolution at the same time. The method is based on the superposition principle, which is valid for linear thermal networks. The procedure is applied on a permanent magnet synchronous machine for an automotive use case. Validation with different test cases is presented for an error estimation between the characterized and the finite element analysis model. Finally, the model is used to derive the thermal behavior respectively the continuous performance of the machine.

This article presents an electrodynamic converter with competitive operating characteristics compared to conventional electric machines, good scalability, and inexpensive manufacturing. The converter is suitable for being used in a variety of applications as an efficient and effective generator or motor. The introduced prototypical converter is a two-phase ex-ternal tooth pole machine with a permanently excited rotor and toroidal coils on the stator. The machine is based on the claw pole principle and has tooth pole pairs. The two subsystems have an electrical offset of 90 degrees to one another, and each of them generates a torque that pulsates over time. The rows of rotor teeth in each system have an electrical offset of 180 degrees to one another. A soft magnetic composite material is used to guide the magnetic flux in all three directions. The prototype generates a voltage of 30 V per coil at a speed of 1500 rpm and produces an extrapolated power of 350 W.

Most of the short circuit faults begin with an interturn fault caused by an insulation failure between winding turns. This can cause large circulating currents, which lead to high power losses, heating, and consequently further short circuits in the system. In mathematical modeling, this adds another dimension for the shorted turn to the system. Modelling a system with an interturn fault is the first step for the necessary diagnosis, prevention, and correction measures. This paper develops a mathematical dynamic model for a multiphase multi-circuit induction generator with 6 stator phases and 3 rotor phases for the application in the wind turbine systems.

Carbon-based conductors (CBCs) have the potential to overcome the physical properties of conventional metallic conductor materials and hence improve the key performance indicators of electric machines such as power (torque) density and efficiency. In comparison to copper, CBCs feature lower mass density, higher electrical conductivity and extremely high thermal conductivity. In this article differ...

The article deals with optimal design of surface-mounted permanent-magnet machines with carbon-based conductors. Owing to its high electrical and thermal conductivity, as well as low mass density, carbon-based conductors could be a break-through technology in achieving more power-dense electric machines. Authors analytically optimize machines with different winding parameters for maximum torque and specific torque taking into account both electromagnetic and thermal phenomena. The optimized machines are compared to machines with copper winding and improvements of up to 50% in torque density are obtained.

For the purpose of increasing the availability and redundancy of wind turbine systems especially offshore ones, this paper investigates dynamic modelling and control of a new multiphase doubly fed induction generator. The six-phase asymmetric winding with one neutral point has been considered, due to its advantages in the faulty conditions and less harmonic content compared to the symmetric 6-phase windings. The field-oriented control strategy is adopted to study the behavior of active and reactive power in the normal generating condition.

In home appliance applications, spoke-type synchronous motors with ferrite magnets are gaining more attention, because of the advantages of lower cost and wider speed range compared to conventional synchronous motors with rare-earth magnets. However, ferrite magnets have lower magnetic energy product and higher risk when a demagnetizing current is applied. In this case, it is necessary to pay more attention to torque density and performance against irreversible demagnetization. In this paper, a 10-pole/12-slot spoke-type synchronous motor with ferrite magnets are designed. Configurations with single- and double-layer windings are discussed in aspects of torque density, torque ripple, efficiency, and irreversible demagnetization resistance. The results indicate that double-layer windings are superior to single-layer windings in this case, especially in aspects of irreversible demagnetization.

In this contribution, a multidisciplinary analysis is performed on a permanent magnet synchronous machine for electric vehicle applications by studying its electromagnetic and thermal performance. The influence of the magnet depth on both the electromagnetic losses and the temperature distribution in the machine is investigated for a given cooling concept. Moreover, the thermal contact resistance, which is rarely considered for rotor thermal analysis in literature, is taken into account. To avoid critical conditions of the magnet that could lead to demagnetization, each parameter that influences the thermal behavior has to be included in simulation. The study underlines the importance to calculate magnet temperatures already during the early development stage, since significant differences in maximum magnet temperature are found for the different designs. A rotor-field analysis proposed in this paper is used to identify rotor topologies that are expected to be critical in terms of magnet temperature. Furthermore, by considering different combinations of loss implementation, magnet position and thermal contact resistance, the influencing parameters of the magnet position on temperature distribution is discussed. The presented work demonstrates how the proposed method allows to identify whether or not the thermal contact resistance has a relevant influence and needs to be investigated further for a given rotor topology.

Electrical machines for hybrid and electric vehicles are subjected to high requirements regarding power density and efficiency. One promising technology, which offers several advantages, are form-wound windings (e.g. hairpin- and i-pin-winding). These kind of windings usually consist of preformed, rectangular bars which are inserted into the stator during manufacturing. In contrary to conventional windings the combination of comparatively large cross-sectional area and high fundamental frequencies - usually exceeding 1kHz - can lead to high additional copper losses due to eddy currents that may not be neglected during design stage. The goal of this publication is to show eddy current’s influence on copper losses within form-wound windings and to identify the impact factors. It is shown, that the additional copper losses due to eddy currents can exhibit many times its equivalent DC-losses. Certain numbers of layers should be avoided due to an extraordinary increase in copper losses. In some cases material with lower electrical conductivity can be advantageous.

In this paper, a scalable thermal model of a permanent magnet electric machine is presented. The model is designed to simulate the temperature development of active machine parts during different driving cycles depending on the machine diameter, the length, and the turns per coil. The impact of the various parameters is demonstrated by means of a sensitivity analysis. The sensitivity analysis is performed for two different driving cycles and two different vehicle types in order to outline the dependence of the general vehicle layout and the use case on the thermal machine behavior. Only machines that are able to perform the respective duty cycle are considered. It shows that despite the increase in thermal heat capacity, big machines do not always experience the lowest temperature during transient operation. The method demonstrated in this paper allows a thermal assessment in an early development stage, when machine scaling is used for a first estimation of the required volume of the PMSM.

A variable magnetic permeability is introduced to the skin effect coefficient to reflect the influence of flux density variation on eddy current losses. The evaluation results show that the new iron loss model can cover a wide range of frequencies without using piecewise functions. Two types of punched edges are defined and the additional iron losses are tested, separated, and modeled, so that the punching and burrs' connection effects on iron losses can be considered more accurately. The iron loss model proposed in this article is very useful for a more accurate design of high-speed motors including the punching effects.

Due to relatively lower price of ferrite magnets, and the flux concentration effects, spoke-type synchronous motors with ferrite magnets become more and more attractive, especially for applications with a wide speed range. In this paper, several topologies of spoke-type rotor for home appliance applications are investigated and compared with each other. Mechanical performance and irreversible demagnetization resistance are taken into consideration, as well as mass production convenience. After that, the final design is selected. The results show that the final design has a sufficient performance for home appliance applications.

This research aims to quantify the measurability of permanent magnet quality for Internal-Permanent-Magnet (IPM) rotors in a production line. The focus lies on the determination of the coercive characteristics of those permanent magnets based on an opposing field treatment using the present magnetization coil and a subsequent flux density measurement around the rotor circumference. Furthermore, simulation results will be presented to determine the predictability of this measurement.

Over the past decades, the performance of ferrite magnets has been significantly improved, which causes an increasing interest in using ferrite magnets for high power density motor applications. This paper compares two different ferrite magnet grades in a spoke-type permanent-magnet synchronous machine (PMSM) concerning machine performance, which includes output torque, irreversible demagnetization resistance, and efficiency using the finite element method (FEM). The results of this analysis show that the machine with advanced ferrite magnets provides larger output torque and higher demagnetization resistance at low temperature, which make the usage of the machine with ferrite magnets in the traction application, such as electric vehicle (EV), more attractive.

The spoke-type permanent magnet motors with ferrite magnets provide relatively high torque density and high efficiency at a low cost compared to conventional structures and are widely applied in different drive systems. In this paper, a parametric finite element model of a spoke-type permanent magnet motor for washing machines is built up. Operating points at low speed and high speed are calculated respectively. An optimization process by using genetic method is then conducted, with the goal to find an optimal design that satisfies a list of constraints and has lowest cost. A fitness function is specially defined to deal with the object together with the constraints. The results show the feasibility of the proposed approach combining genetic method with finite element method.

this paper presents an overview of recent LVRT solutions for Doubly Fed Induction Generators (DFIG) based on hardware and software or a combination of both. The transient behavior of the system under three-phase grid fault is therefore simulated. Among the software solutions, the stator current feedback and demagnetizing current injection strategies are analyzed and simulated, and a coordinated crowbar, rotor side and grid side converter control is provided as the hardware software combination.

The main advantage of the doubly fed induction generators (DFIG) over the synchronous generators is the small size converter which is located in the rotor circuit. However, this advantage can cause a problem during grid faults, because the over voltages and currents that will occur on the rotor circuit can damage the rotor side converter (RSC), if it is not over-dimensioned or protected for such high voltages and currents. Crowbar protection is a quite common solution of the grid faults for DFIG, the crowbar connects small resistances to the rotor terminals of the generator in order to limit voltage and current peaks; the RSC is disconnected as long as the crowbar is active. In this situation the DFIG is still connected to the grid and support it with a reactive power to fulfill the grid codes. A simulation study of different types of grid faults will be carried out in MATLAB/SIMULINK environment.