Fault tolerant, variable frequency, unity power factor converters for safety critical PM drives

The aerospace industry is currently considering a constant voltage, variable frequency supply for aircraft power systems. This variable frequency system is based on a generator directly driven from the aero-engine, in which the frequency is dependent on engine speed. A number of safety critical loads are placed on this system, and it is essential that failure of any one load does not affect the operation of another. The paper develops the concept of fault tolerant input converters for an electric fuel pump. The converters always act as a unity power-factor load, and can tolerate a range of failures, whilst maintaining both the operation of the pump and minimal impact on the electrical supply. Two converter types are proposed and compared for this application. The operation of these two unity power factor converters from a variable frequency supply is demonstrated. The effect of faults in the selected converters on converter operation and the supply itself is then discussed.