Sukumar De

Low inductance axial flux BLDC motor drive for more electric aircraft

As the aircraft technology is moving towards more electric architecture, use of electric motors in aircraft is increasing.12 Axial-flux BLDC motors are becoming popular in aero application because of their ability to meet the demand of light weight, high power density, high efficiency and high reliability. Axial-flux BLDC motors in general and ironless axial flux BLDC motors in particular, come with very low inductance. Because of this they need special care to limit the magnitude of ripple current in motor winding. In most of the new more electric aircraft applications, BLDC motor needs to be driven from 300Vdc or 600Vdc bus. In such cases, particularly for operation from 600Vdc bus, IGBT based inverters are used for BLDC motor drive. IGBT based inverters have limitation on increasing the switching frequency, and hence they are not very suitable for driving BLDC motors with low winding inductance. In this paper, three-level NPC inverter is proposed to drive axial flux BLDC motors. Operation of BLDC motor driven from three-level NPC inverter is explained and experimental results are presented.

A front end switched rectifier DC source for neutral point balancing of a NPC three-level inverter for the full modulation range

A switched DC voltage three level NPC is proposed in this paper to eliminate capacitor balancing problems in conventional three-level neutral point clamped (NPC) inverter. The proposed configuration requires only one DC link with a voltage Vdc/2, where Vdc is the DC link voltage in a conventional NPC inverter. To get rated DC link voltage (Vdc), the voltage source is alternately connected in parallel to one of the two series capacitors using two switches and two diodes with device voltage rating of Vdc/2. The frequency at which the voltage source is switched is independent and will not affect the operation of NPC inverter. The switched voltage source in this configuration balances the capacitors automatically. The proposed configuration can also be used as a conventional two level inverter in lower modulation range, thereby increases the reliability of the drive system. A space vector based PWM scheme is used to verify this proposed topology.