Thermal stress reduction in aircraft motor controllers

An engine start system, comprising:

• an electric power generator having a three-level inverter switch array;
• an aircraft engine coupled to the electric power generator;
• an aircraft motor controller coupled to the electric power generator, the aircraft motor controller configured to:
• ramp the electric power generator to start the aircraft engine;
• during a time period associated with the aircraft engine start sequence:
• toggle the three-level inverter switch array to a three-level pulse width modulation (PWM) mode;
• determine if a first time interval in the three-level PWM mode exceeded a predetermined three-level PWM mode interval;
• toggle 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;
• determine if a second time interval in the two-level PWM mode exceeded a predetermined two-level PWM mode interval;
• and
• toggle 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.

An engine start system, comprising:

• an electric power generator having a three-level inverter switch;
• an aircraft engine coupled to the electric power generator;
• an aircraft motor controller coupled to the electric power generator, wherein the motor controller configured for:
• ramp the electric power generator to start the aircraft engine;
• and
• during a time period associated with the 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.

An engine start system, comprising:

• an electric power generator having a three-level inverter switch;
• an aircraft engine coupled to the electric power generator;
• an aircraft motor controller coupled to the electric power generator;
• a thermal stress reduction process residing on the motor controller and configured to:
• ramp the electric power generator to start the aircraft engine;
• and
• for a time period associated with the aircraft engine start sequence, ramping an output frequency of the motor controller from an initial frequency, controlling the output frequency to reduce the thermal dissipation in the three-level inverter switch.