Permanent Magnet Linear Generators (PMLG) are currently studied as a main solution for the conversion of the energy contained in sea waves. Typically, a PMLG consists of an iron-made armature and a moving shaft. Magnets are usually installed on the shaft and the coils on the armature. The moving shaft generates an electromotive force in the coils. Such a machine suffers from a high level of cogging force due to the interfaces between air and iron impairing its overall performance. However, the function of iron in Permanent Magnet (PM) based machines is simply that of driving the flux along a predesigned path. No amplification of the magnetic flux is generated by iron because the flux is generated by the permanent magnet. As a result, a well-tailored design of a PM generator could avoid the use of iron avoiding any permeability difference along with its magnetic circuits and therefore cogging force is completely suppressed. Several questions remain open: how much is the performance of an ironless generator affected by the absence of iron? Which is the comparison between a traditional and an ironless generator? In this paper, we try to address experimentally these questions. We have built two prototypes of PM linear generators that share the same geometry: one of the two is a traditional generator the other is an ironless generator. At first, we have characterized the two machines by measuring the main electrical and mechanical parameters: resistance, reactance, mass, magnetic fields. Secondly, we have performed several open circuit measurements, by measuring cogging force, vibrations, electromotive force when the slider is moving at some given conditions. Finally, we have performed several load tests by measuring cogging force, vibrations, output voltage, current, and output power when the slider is moving at some given conditions. The comparison reported in the paper shows that the performance of the traditional machine is slightly superior in comparison with the ironless one, but an ironless machine does not present any cogging force and is lighter than the traditional one. These features can be a great advantage in the field of sea-wave energy conversion.

An Experimental Comparison Between an Ironless and a Traditional Permanent Magnet Linear Generator

**Session chair:** Amr Adly, Cairo University



JOC - Linear Motors, Energy Harvesting and Vibration Analysis

technical paper

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An Experimental Comparison Between an Ironless and a Traditional Permanent Magnet Linear Generator

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