The demand for electric machines has been rising steadily for several years—mainly due to the move away from the combustion engine. Synchronous motors with rare earth permanent magnets are widely used due to their high power densities. These magnets are cost-intensive, cost-sensitive and often environmentally harmful. In addition to dispensing with permanent magnets, electrically excited synchronous machines offer the advantage of an adjustable excitation and, thus, a higher efficiency in the partial load range in field weakening operation. Field weakening operation is relevant for the application of vehicle traction drive. The challenge of this machine type is the need for an electrical power transfer system, usually achieved with slip rings. Slip rings wear out, generate dust and are limited in power density and maximum speed due to vibrations. This article addresses an electrically excited synchronous machine with a wireless power transfer onto the rotor. From the outset, the machine is designed with a wireless power transfer system for use in a medium-sized electric vehicle. As an example, the requirements are derived from the BMW’s i3. The wireless power transfer system is integrated into the hollow shaft of the rotor. Unused space is thus utilized. The overall system is optimized for high efficiency, especially for partial load at medium speed, with an operation point-depending optimization method. The results are compared with the reference permanent magnet excited machine. A prototype of the machine is built and measured on the test bench. The measured efficiency of the inductive electrically excited synchronous machine is up to 4% higher than that of the reference machine of the BMW i3.

In order to increase torque and power density, novel electrical machines with a 3D magnetic flux path are used. One of them is the transverse flux machine, which offers high torque at low speed and therefore is predestined for use as near-wheel drive in an electrical vehicle or as a joint drive for a robot arm. In contrast to typical machines, such as a synchronous machine, the magnetic flux has a component transverse to the radial plane. Additionally, the materials are highly saturated to achieve the high power density. The aim, beside high power and torque density, is to reach high efficiency. This is especially necessary for mobile applications with batteries, such as an electrical vehicle or a mobile robot. Hence, the losses have to be calculated during the machine optimization process in finite element analysis. Beside, the copper losses the iron losses have to be considered. For these reasons this paper presents a method to calculate iron losses in electrical machines with 3D flux path. Alternating and rotational magnetic fields are considered, as well as the influence of saturation. The computation method of iron losses is performed exemplary on a transverse flux machine. The results are compared with the measurements of the transverse flux machine on the test bench.