Miniaturized claw-pole generators and motors with high power density

Energy harvesting systems converting kinetic energy to drive an electromagnetic generator either to power an electronic device directly or to charge a secondary battery may be used to substitute big size and heavy weight batteries of autonomous systems. The output voltage and current of the generator is mostly transient and discontinuous in nature and must be converted to a DC signal. This requires energy converters with small volume and low weight. We therefore present a novel topology for a claw-pole generator, which features an extremely compact design and high conversion efficiency. The design can be further miniaturized, still using conventional processes and technologies for manufacturing. In the development process analytical calculations applying reluctance network techniques were first carried out in order to determine the basic geometry of the magnetic circuit. A 3D-FE model was created to perform field calculations in order to optimize the alternator's output power. These investigations also allowed a substantial reduction of the cogging torque, which is typical for claw-pole machines. The 3D-FE model calculations are in good agreement with experimental results. However, it turned out that there is a high sensitivity of the cogging torque to geometrical variations of the claws. When extending the system to two electrical phases, the generator principle was applied to build a motor with a high torque density. In a comparison with the data of commercially available motors of similar size it turned out that this new machine is more than a match to them.