Present and Future of Fault Tolerant Drives Applied to Transport Applications

An electric drive is an electromechanical conversion device, consisting of an electrical machine, a power electronic inverter, which interfaces between the machine and the electrical supply, a set of sensors and a digital electronic controller. Drives of this sort are manufactured in high volumes at power levels ranging from less than 1W to many MW. Reliability of the complete system depends upon the local environment, levels of thermal cycling and predictive maintenance schedules. Overall the drive system has a typical reliability of the order of 10-5 failures per hour, making it much more reliable than, say, an internal combustion engine. As part of the “electrical revolution” electric drives are increasingly being developed for safety critical applications, where their reliability is several orders of magnitude below the application requirements. This is particularly the case in electrical propulsion and actuation systems in aircraft, leading to intensive research into fault tolerant electric drives. This paper will illustrate some of the most common failure mechanisms and the consequences of such failures. It will then progress to examine architectures which are fault tolerant through partitioning of the drive into several independent lanes and examine the penalties of adopting such an approach. The paper will discuss pros and cons of different fault tolerant architectures and suggests future research and development steps that are required to increase the overall safety of electric drives.