I. Introduction
Electrical machine drives are an essential component of modern industrial systems and have found use in a variety of applications, ranging from industrial processes, to power generation and transport [1]–[4]. The current trends favour increased use of ac machine drives in the energy sector, where, for example, the ongoing global expanse of wind power generation is underpinned by effective use of ac machine drive technology at the core of modern multi MW size wind turbine systems. In addition, the imminent move to full ground transport electrification and plans for electrification of future air transport will see a much increased volume of ac machinery usage in critical applications, where reliability of operation is fundamental and expected to be enabled by effective real-time condition monitoring (CM) techniques [3], [4]. Furthermore, in high value areas such as off-shore wind power generation, the condition monitoring service of assets, largely aimed at the wind turbine (WT) ac generator drive/drive-train failure detection have been steadily gaining prominence in a competitive diagnostic service provision market, estimated to have the potential to form a high profit global industry [5], [6].