Patent ID: 9435263
Filing Date: 2016-09-06
CPC Classification: F02C,H02M,H02P

Claim Text:
1. A thermal stress reduction method for an aircraft motor controller having a three-level inverter switch array, and configured to control an electric power generator coupled to an aircraft engine, the method comprising: ramping the electric power generator to start the aircraft engine; and during a time period associated with an aircraft engine start sequence, applying a current profile to the current from the electric power generator to the aircraft engine, the current profile controlling the current to reduce the thermal dissipation in the three-level inverter switch; toggling the three-level inverter switch array to a three-level pulse width modulation (PWM) mode; determining if a first time interval in the three-level PWM mode exceeds a predetermined three-level PWM mode interval; toggling the three-level inverter switch array to a two-level PWM mode, in response to the first time interval exceeding the three-level PWM mode interval; determining if a second time interval in the two-level PWM mode exceeds a predetermined two-level PWM mode interval; and toggling the three-level inverter switch array to the three-level PWM mode, in response to the second time interval exceeding the two-level PWM mode interval; wherein the three-level inverter switch array includes a first switch, a second switch, a third switch and a fourth switch, wherein the first switch, the second switch, the third switch and the fourth switch are configured in a serial arrangement, the array including: a three-level PWM mode that includes alternating between switching on the first switch and the third switch while applying a PWM signal to the second switch and the fourth switch, and switching on the second switch and the fourth switch while applying a PWM signal to the first switch and the third switch, a two-level PWM mode includes turning on the first switch and the fourth switch while applying a PWM signal to the second switch and the third switch, and a carrier frequency in the two-level PWM mode is greater than a carrier frequency in the three-level PWM mode.