Comparison of 3- and 9-phase brushless PM drive systems for aerospace actuation

Nearly all electric vehicles (EVs), hybrid electric vehicles (HEVs), more electric aircraft, electric ship propulsion and others power conversion industrial applications uses power electronic inverters to convert AC to DC or vis versa, as in the starter/generator machine system and generation/regeneration process of the traction motor. Also, it has become possible to integrate HEVs power electronics component in one package with one set of liquid cooling. Recently, compactness and reliability of the power conversion and generation system design in automotive, in particular, and in aerospace industries are growing with global necessity of shifting from conventional airborne emission vehicles and aircrafts to the green all electric ones. Therefore, an advanced technology in the area of energy storage, conversion and dc-link capacitors, which account for a major fraction of the volume, weight and also cost of the inverter, is demanded by the developer of HEVs and other industrial areas. In three-phase system a dc-link voltage source inverters (VSI) are fed via controlled or uncontrolled rectifier bridges from a main source. Here, a dc-link capacitor is usually used to maintain a stiff dc-link voltage across the VSI, and to perform other tasks, as in [1]. Such that, in this application, the dc-link capacitor deals with the main voltage fluctuation and provides a dc-link current ripple to suppress the generated electromagnetic interface (EMI) caused by pulsating current (ripple current) associated with the inverter switching. It is recognized in the literature [1-7] that for voltage stiff inverter the dc-link capacitor adequate selection, sizing and minimizing presents a major issue for improving electrical system compactness and utilization. Lai et al discusses the use of low-inductance high current film capacitor in a hi