Understanding rotor losses in high-speed permanent magnet rotor with copper shield under variable frequency drive supply

Surface mounted permanent magnet (PM) machines are the most common in high-speed applications. Heat in the rotor is among the critical challenges for such high-speed PM machines. Using a sine filter is often the adopted solutions at the expense of cost and overall layout of the variable frequency drive (VFD) cabinet. Another approach is to use a copper shield on the rotor together with magnet segmentation. This paper evaluates the appropriate placement of the copper shield, on the shaft, the magnets, or the carbon fibre reinforced polymer (CFRP) composite. After a qualitative analysis allowing to understand the mechanisms in play on the rotor losses, simulations have been performed to quantify the losses in the different layers and materials. Experimental tests have been carried out on two machines, each with a different copper shield configuration. The influence of the DC bus supply and the switching frequency have been studied and the temperature in the magnets and the rotor measured, showing the trend.