# US 2024/0201284 A1 · Process for detecting ageing of a dc bus capacitor of a power converter > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2024/0201284 A1 - Document ID: US20240201284A1 - Status: Published application - Kind: A1 - Application number: 18/534,897 - Filed: 2023-12-11 - Published: 2024-06-20 - Earliest claimed: 2022-12-15 - Assignees: Schneider Toshiba Inverter Europe SAS - Applicants: Schneider Toshiba Inverter Europe SAS - Inventors: Alain Dutrey; Mohamad Koteich - Web page: https://patentgrep.com/patent/US20240201284A1 ## CPC - G01R 31/64: Testing of capacitors - H02M 7/48: using discharge tubes with control electrode or semiconductor devices with control electrode - H02M 1/14: Arrangements for reducing ripples from DC input or output - H02M 1/32: Means for protecting converters other than automatic disconnection - G01R 31/42: AC power supplies - H02M 1/327: {against abnormal temperatures} - H02M 7/53873: {with digital control} - G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12) - 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) ## Abstract A method to estimate a remaining of useful life of a DC link capacitor of a converter through determination of a minimum value Clim of its capacitance C under which performances of the converter are considered as insufficient. The method includes implementing a real time model including a motor drive model and a capacitor model using decreasing capacitor values to calculate a forecasted minimum capacitance Clim sufficient for keeping at least one of DC voltage ripple, motor current ripple, speed ripple or torque ripple under a specified value. The method further includes calculating a time difference between a time Tactual, for which the capacitor has an estimated capacitance based on an ageing curve Ccurve, and a time Tlim for which the capacitor will have the forecasted minimum capacitance Clim, with the use of an ageing curve Ccurve of the capacitor and estimating the remaining useful life of the capacitor Tactual-Tlim. ## Claims ### Claim 1 A method to estimate a remaining of useful life of a DC link capacitor of a converter through determination of a minimum value Clim of its capacitance C under which performances of the converter are considered as insufficient comprising: implementing a real time model comprising a motor drive model and a capacitor model using decreasing capacitor values to calculate a forecasted minimum capacitance Clim sufficient for keeping at least one of DC voltage ripple, motor current ripple, speed ripple or torque ripple under a specified value; calculating a time difference between a time Tactual, for which the capacitor has an estimated capacitance based on an ageing curve Ccurve, and a time Tlim for which the capacitor will have the forecasted minimum capacitance Clim, with the use of an ageing curve Ccurve of said capacitor and estimating the remaining useful life of said capacitor Tactual−Tlim. ### Claim 2 (depends on 1) The method according to claim 1 comprising initializing said ageing curve through capacitance calculation of estimated values of said DC link capacitor during an initialization phase to provide an initial part of said ageing curve Ccurve and calculating a remainder of said ageing curve Ccurve using ageing characteristics of said capacitor. ### Claim 3 (depends on 2) The method according to claim 2 wherein said capacitance calculation comprises: measuring of a voltage vsrc and a current isrc at a voltage source upstream of the DC link capacitor; measuring a voltage vdc downstream from said DC link capacitor and either measuring a current idc or measuring an output power Pout and calculating an input power Pdc, which is equal to an output power Pout plus converter losses Ploss, downstream from said DC link capacitor; calculating an estimation of a capacitance value Ĉ of said capacitor based on said voltage vdc downstream from said DC link capacitor, current idc or input power Pdc. ### Claim 4 (depends on 3) The method according to claim 3, wherein Ploss is identified through a known function Ploss=f(Pout). ### Claim 5 (depends on 1) The method according to claim 1, wherein said motor drive model comprises performance criterion Pc, including, but not limited to, dc voltage oscillation amplitude and motor control quality and wherein said motor drive model is simulated for different system conditions, system parameters and system input power supply and load to evaluate such performance criterion continuously according to decreasing capacitance values and define said minimum acceptable capacitance Clim. ### Claim 6 (depends on 5) The method according to claim 5 wherein said different conditions comprise grid impedance values Rdc, Ldc which are pre-defined in the drive model or predefined by the user and based on the application load profile and history. ### Claim 7 (depends on 6) The method according to claim 6, wherein said different conditions comprise grid impedance Rdc, Ldc, corresponding to a usual loading or grid impedance Rdc, Ldc of a worst-case scenario, with maximum rated grid impedance and maximum loading. ### Claim 8 (depends on 1) The method according to claim 1, comprising further comprising: calculating an ESR of said DC link capacitor based on said measurements, implementing a modified motor drive model and capacitor model considering said ESR of said DC link capacitor to calculate the minimum capacitance Clim and the minimum ESR ESRlim allowing controlled system stability, determining an ESR curve ESRcurve of said capacitor, and calculating the time difference between the actual capacitance and the forecasted minimum capacitance Clim together with the difference between the actual ESR and the forecasted minimum ESR ESRlim, to estimate the remaining useful life of said capacitor considering the first occurrence of one of said minimum capacitance and minimum ESR. ### Claim 9 (depends on 1) The method according to claim 1, wherein said ageing curve Ccurve is based on a capacitor ageing model of the form Ca(t)=eαt+β. ### Claim 10 (depends on 2) The method according to claim 2, further comprising tracking a capacitance value Cactual through a capacitance observer activated during transient conditions of the operation of the converter. ### Claim 11 (depends on 10) The method according to claim 10 comprising calculating temperature of said capacitor using a comparison of said capacitance value Cactual and a capacitor Cageing resulting of the capacitor curve Ccurve obtained after the curve initialization. ### Claim 12 (depends on 1) The method according to claim 1, further comprising tracking a capacitance value Cactual through a capacitance observer activated during transient conditions of the operation of the converter.