# US 9,435,264 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 9,435,264 B2 - Document ID: US9435264B2 - Status: Granted - Kind: B2 - Application number: 14/282,312 - Filed: 2014-05-20 - Published: 2014-09-11 - Granted: 2016-09-06 - Earliest claimed: 2012-04-20 - Assignees: Hamilton Sundstrand Corporation - Applicants: Hamilton Sundstrand Corporation - Inventors: Huazhen Chai; Adam M. White; Mustansir Kheraluwala - Web page: https://patentgrep.com/patent/US9435264B2 ## 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 during an aircraft engine start sequence, the method comprising: ramping 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 array; 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 wherein 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 the initial frequency is a non-zero frequency. ### Claim 3 (depends on 2) The method as claimed in claim 2 wherein the non-zero frequency is selected as a percentage of a frequency of the electric power generator to start the aircraft engine. ### Claim 4 (depends on 3) The method as claimed in claim 3 wherein the percentage is between one and eight percent. ### Claim 5 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; 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 arrangements 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. ### Claim 6 (depends on 5) The system as claimed in claim 5 wherein the initial frequency is a non-zero frequency. ### Claim 7 (depends on 6) The system as claimed in claim 6 wherein the non-zero frequency is selected as a percentage of a frequency of the electric power generator to start the aircraft engine. ### Claim 8 (depends on 7) The system as claimed in claim 7 wherein the percentage is between one and eight percent.