New Investigator Award for FEMM researcher Dr Xiao Chen

His project ‘Bearing currents and associated high frequency effects in permanent magnet machines - improved computational and experimental methods’, has three key objectives:

• Develop an innovative analysis methodology based on models for the high-fidelity modelling of high frequency capacitive and inductive effects in PM machines, with a particular focus on bearing currents and winding voltage stress.

• Develop methods for well-founded a-priori parameter extraction to aid design and analysis.

• Provide robust verification of the developed methods through innovative and well-founded extensive experimental measurements on existing prototype machines.

With electrical machines becoming ever-more important in the transition to a zero-carbon society, particularly in the decarbonisation of transport, their use in electric and hybrid vehicles is already accelerating rapidly. Electrical machines are almost always used in conjunction with power electronic controllers which apply a high frequency voltage pulse train to the machine to control the current and hence the speed or torque.

In combination, the machine and its associated controller provide an efficient and highly controllable drive-train solution. However, the high frequency switching produced by the controller is not without its drawbacks, one of the most problematic being that high frequency parasitic currents can flow through the machine bearings unless precautions are taken in design and installation. 

These parasitic and unintended currents in the bearings lead to deterioration of the lubrication film and surface damage to the rolling parts of the bearings. This bearing damage could in turn cause catastrophic and unexpected failure of the electrical machine in service. 

The various phenomena which result in bearing currents are complex and, in many cases, poorly understood and the precautions which are adopted at present are rudimentary and compromise other aspects of performance. This research programme will investigate the high frequency capacitive and inductive effects in permanent magnet machines with a particular focus on innovative modelling and measurement approaches for high frequency bearing currents. 

This will lay the cornerstone for bearing current mitigation through improved design and simulation, enhancing reliability and safety and hence promote further electrification of transport. This is of particular importance in hybrid aerospace propulsion systems where the highest levels of reliability based on robust and rigorous understanding of physical phenomena is essential for the adoption of new technology.

Dr Chen said,

“I am grateful for receiving this award and the tremendous support provided by Professor Geraint Jewell for this funding application. The knowledge, skills and partnership gained from the research activities in the FEMM Hub has also been extremely helpful in getting me to this point.”