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The switched reluctance cycloconverter (SRC) is a power circuit for generating AC with a switched reluctance machine (SRM). It uses a single power electronic conversion step to achieve higher system efficiency compared to alternative approaches. The basic SRC system is described. Design results for a 400Hz, three phase, 60kVA (90kVA for 5 minutes and 120 kVA for 5 seconds) variable speed constant frequency (VSCF) system is presented. The machine and control designs are described. The unique design issues that exist for the SRC compared to a conventional DC SRM system are pointed out. Performance predictions for the final system design are presented.

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.

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.

The design results for a 250 kW switched reluctance aircraft engine starter/generator system power inverter are presented. The starter/generator employs a single switched reluctance machine and a generating system architecture that produces two separate 270 Vdc buses from that single switched reluctance machine. The machine has six phases with three of the phases connected to one inverter supplying 125 kW to one 270 Vdc bus while the other three phases are connected to a second inverter supplying 125kW to the other 270 Vdc bus. Each bus has its own EM1 filter and control in addition to its own inverter. Two types of inverters have been developed, one type employs MOS Controlled Thyristors (MCTs) for the controlled switches and the other type employs Insulated Gate Bipolar Transistors (IGBTs). High-current 500 A peak turn-off MCT modules were specifically developed for the MCT inverters. Two of these modules are placed in parallel to form the required 1000 A switches.

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.