DC Link Capacitor Ageing Detection Through Ripple-Based RUL Estimation
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Solution Overview
Problem
DC Bus capacitors in power converters age sensitively to operational voltage and temperature, leading to unpredictable instability and performance degradation before reaching critical failure, as existing empirical models fail to anticipate drifts caused by ageing precision errors, resulting in current and voltage ripples that degrade connected devices.
Innovation Solution
A method to estimate the Remaining Useful Life (RUL) of a DC link capacitor by implementing a real-time model combining a motor drive model and a capacitor model, calculating the minimum capacitance required to maintain specified voltage and current ripples, and using an ageing curve to determine the time difference between actual and forecasted capacitance values, thereby estimating the RUL.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If generic empirical models are used to predict capacitor end of life, then prediction simplicity is improved, but prediction accuracy deteriorates due to model precision errors and drifts
Solution Approach 1:
The patent implements a feedback mechanism by continuously monitoring actual capacitor performance parameters (capacitance value, ESR) during operation and comparing them against predicted values from the empirical model. When drifts or precision errors are detected, the system adjusts the prediction by calculating the time difference between actual and forecasted minimum capacitance, thereby correcting the end of life prediction to account for real-world deviations from the generic model.
2Measurement precision
If real-time modeling with decreasing capacitance values is implemented to calculate forecasted minimum capacitance, then prediction accuracy is improved, but computational complexity increases
Solution Approach 1:
The patent applies preliminary action by pre-calculating and storing the forecasted minimum capacitance values through real-time modeling before actual failure occurs. The system continuously simulates capacitor behavior with decreasing capacitance values to establish a performance baseline, which is then used to predict remaining useful life by comparing actual measurements against these pre-established forecasts, thereby simplifying the real-time decision-making process.
3Measurement precision
If continuous monitoring of capacitance and ESR is performed to detect ageing, then detection accuracy is improved, but measurement and processing requirements increase
Solution Approach 1:
The patent implements self-service by utilizing the power converter's existing operational data and control structures to automatically extract capacitance and ESR values without requiring separate dedicated measurement hardware. The system leverages available voltage and current measurements during normal operation, processing them through the embedded model to derive capacitor health parameters, thereby reducing additional measurement complexity while maintaining high detection accuracy.
Data Source
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AI summary
Method to estimate a remaining of useful life of a DC link capacitor (3) of a converter (1) 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 (130, 230) comprising a motor drive model and a capacitor model using decreasing capacitor values (140, 150, 240, 250) 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 (120).