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Preliminary testing of a 125kW power inverter for a switched reluctance aircraft engine starter/generator system has been completed and system testing of the complete starter/generator system has been initiated. The starter/generator employs a single switched reluctance machine (SRM) and a generating system architecture that produces two separate 270Vdc buses from that single SRM The machine has six phases with three of the phases connected to one inverter supplying 125kW to one 270Vdc bus while the other three phases are connected to a second inverter supplying 125kW to the other 270Vdc bus. Each bus has its own EMI filter and controller in addition to its own inverter. Two types of inverters have been developed, one type employs MOS Controlled Thyristors for the controlled switches and the other type employs Insulated Gate Bipolar Transistors. The link capacitor bank for each inverter employs multilayer ceramic capacitors to meet the starter/generator's temperature requirements.

This paper describes the characteristics of the switched reluctance motor (SRM) used as a generator. In this mode of operation the SRM is unique in that it does not employ permanent magnets or a field winding on its rotor. Thus the SRM generator does not have the inherent problem of generating into a shorted winding like the permanent magnet machine (you cannot turn off the excitation), and the rotor structure is inherently simpler and more reliable than the wound field machine. Because the SRM generator does not use permanent magnets or a field winding, the nature of its excitation during generating is of particular interest. In fact, the SRM's lack of direct field excitation makes the SRM generator unstable when operating open loop in the square-wave mode and connected in the conventional manner. In this case, the generator's output voltage increases exponentially for loads less than a critical value and goes to zero for loads greater than this same critical value.