A Detailed Power Inverter Design for a 250 kW Switched Reluctance Aircraft Engine Starter/Generator

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. Safe operating area issues and special considerations related to employing the MCT switches are described. The IGBT inverters use two commercial 400 A 600 V IGBT modules for each switch. The link capacitor bank for each inverter employs multilayer ceramic capacitors to meet the starter/generators temperature requirements. These same multilayer ceramic capacitors are also used in the EMI filters. Performance predictions and results for both inverters are presented.