The high speed axial flux disc generator-unlocking the potential of the automotive gas turbine

To enable an electric traction vehicle to have acceptable performance and range, a hybrid approach must be adopted whereby electrical power is generated on board by means of a combustion engine and generator in addition to the energy storage device. One approach is to couple a spark ignition or diesel engine to a conventional generator but an alternative solution of a gas turbine driving a high speed generator, denoted a turbogenerator, is considered superior for the following reasons: the power plant has a much lower weight and volume; toxic emissions are much lower due to steady flow combustion in the gas turbine; noise and vibration are reduced; and multifuel capability is inherent with the gas turbine. The most favoured design for the high speed generator is a permanent magnet synchronous machine but this may either have the disc or drum topology. The disc topology offers the following advantages over drum type machines: the magnet containment structure is not in the magnetic circuit; iron hysteresis and eddy currents are eliminated; the rotor has better rotor dynamics characteristics suitable for high speed operation; and the design lends itself to air cooling. (4 pages)