On the true maximum efficiency operations of synchronous motor drives

Energy efficient AC drives for synchronous machines are key components in modern mechatronic systems, including applications of renewable energy and transportation. It is possible that the next generation of synchronous motors may be of the reluctance-prevalent type, due to the ecological footprint and cost of permanent magnet materials. When a reluctance torque is available, the torque is usually regulated according to the maximum torque per ampere principle which minimises the copper losses for a given torque request. However, iron and additional losses also contribute to the total machine losses, although their influence on the best current vector trajectory for total loss minimisation is not clear yet. The aim of this paper is to discuss and quantitatively evaluate the effect of iron and additional losses on the efficiency of different synchronous machines, looking for the true maximum efficiency. An extended batch of measurements performed on different types of machines with low power rating are discussed in detail.