Linear synchronous machine performance improvement with flux barriers

Linear synchronous motors can be used for large scale electromagnetic launch. The machines are short time rated and can therefore use substantial values of stator current loading. This leads to high values of armature flux and the risk of demagnetising the excitation magnets. In order to mitigate this risk by reducing the armature flux, quadrature axis flux barriers can be positioned in the permanent magnet backing iron. These reduce the armature field but leave the permanent magnet excitation field largely unchanged. In addition to improving the force due to the larger usable stator current loading, the barriers are beneficial in reducing the synchronous reactance and hence improving the power factor and reducing the Volt Amps per Newton of useful force (VA/N) of a linear motor. The paper explores the use of these barriers for a typical configuration and shows the performance improvements that can be obtained.