Four-Phase Switch Reluctance Machines for More Electric Aircraft Power Generation

The development of the more electric aircraft is in progress. An important part of more electric aircraft concept is the integral starter/generator (ISG) mounted on the shaft of the jet engine. The prime candidate technology for the ISG is a system based on the switched reluctance motor (SRM). Switched reluctance technology has been chosen for this application because the a single failure does not lead to a complete loss of electrical power. In fact, each phase of the SRM is essentially independent of every other phase. Thus it is possible to be able to loose a single phase as a result of a fault and still remain operational with all of the other phases. This characteristic of the SRM has been referred to as fault tolerance and it is a very important characteristic when there is only one generator per engine. Though the SRM is fundamentally capable of this kind of operation, the resulting power quality with a single phase fault is a concern as is the size and weight of the EMI filter required to achieve the desired power quality. This paper presents calculated power quality and EMI filter sizing results for faulted phase operation of three different SRM machines. The machines are the two phase, the three phase, and the four phase SRM. It is found, to meet Mil. Std. 704E with a single phase fault, that the four phase SRM requires an EMI filter that is substantially smaller and lighter than for any of the other SRMs considered.