# US 8,786,232 B2 · Thermal stress reduction in aircraft motor controllers > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 8,786,232 B2 - Document ID: US8786232B2 - Status: Granted - Kind: B2 - Application number: 13/451,644 - Filed: 2012-04-20 - Published: 2013-10-24 - Granted: 2014-07-22 - Earliest claimed: 2012-04-20 - Assignees: Hamilton Sundstrand Corporation - Applicants: Huazhen Chai; Adam M. White; Mustansir Kheraluwala - Inventors: Huazhen Chai; Adam M. White; Mustansir Kheraluwala - Web page: https://patentgrep.com/patent/US8786232B2 ## CPC - F02C 7/26: Starting; Ignition - H02M 1/327: {against abnormal temperatures} - H02M 7/487: Neutral point clamped inverters - H02P 9/08: Control of generator circuit during starting or stopping of driving means, e.g. for initiating excitation - F02C: GAS-TURBINE PLANTS; AIR INTAKES FOR JET-PROPULSION PLANTS; CONTROLLING FUEL SUPPLY IN AIR-BREATHING JET-PROPULSION PLANTS (construction of turbines F01D; jet-propulsion plants F02K; construction of compressors or fans F04; generating combustion products of high pressure or high velocity F23R; using gas turbines in compression refrigeration plants F25B11/00) - H02M: APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF (transformers H01F; dynamo-electric converters H02K47/00; controlling transformers, reactors or choke coils, control or regulation of electric motors, generators or dynamo-electric converters H02P) - H02P: CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS ## Abstract A thermal stress reduction method includes ramping an electric power generator to start an aircraft engine, for a time period associated with the aircraft engine start sequence toggling a three-level inverter switch array to a three-level pulse width modulation mode, determining if a first time interval in the three-level pulse width modulation mode exceeded a predetermined three-level pulse width modulation mode interval, in response to the first time interval exceeding the three-level pulse width modulation mode interval, toggling the three-level inverter switch array to a two-level pulse width modulation mode, determining if a second time interval in the two-level pulse width modulation mode exceeded a predetermined two-level pulse width modulation mode interval and in response to the second time interval exceeding the two-level pulse width modulation mode interval, toggling the three-level inverter switch array to the three-level pulse width modulation mode. ## Claims ### Claim 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 an aircraft engine; during a time period associated with an aircraft engine start sequence: 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 three-level PWM mode 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, the 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. ### Claim 2 (depends on 1) The method as claimed in claim 1 wherein during the three-level PWM mode, the first and fourth switches dissipate a greater amount of thermal energy relative to the second and third switches. ### Claim 3 (depends on 2) The method as claimed in claim 2 wherein during the two-level PWM mode, the second and third switches dissipate a greater amount of thermal energy relative to the first and fourth switches. ### Claim 4 (depends on 1) The method as claimed in claim 1 wherein a ratio of three-level PWM mode interval to the two-level PWM mode internal is inversely proportional to a ratio of a three-level PWM mode thermal loss to a two-level PWM mode thermal loss. ### Claim 5 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, 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 three-level PWM mode 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, the 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. ### Claim 6 (depends on 5) The system as claimed in claim 5 wherein during the three-level PWM mode, the first and fourth switches dissipate a greater amount of thermal energy relative to the second and third switches. ### Claim 7 (depends on 6) The system as claimed in claim 6 wherein during the two-level PWM mode, the second and third switches dissipate a greater amount of thermal energy relative to the first and fourth switches. ### Claim 8 (depends on 5) The system as claimed in claim 5 wherein a ratio of three-level PWM mode interval to the two-level PWM mode internal is inversely proportional to a ratio of a three-level PWM mode thermal loss to a two-level PWM mode thermal loss. ### Claim 9 (depends on 1) The method of claim 1, wherein the predetermined three-level PWM mode interval is less than a semiconductor switch thermal time constant of the three-level inverter switch array. ### Claim 10 (depends on 5) The engine start system of claim 5, wherein the predetermined three-level PWM mode interval is less than a semiconductor switch thermal time constant of the three-level inverter switch array.