Electrolytic Capacitor Online Monitoring via Analog ESR Estimation

Resolve Bottlenecks,
Find Innovative SolutionsGenerate Solutions

Solution Overview

Problem

Electrolytic capacitors in power electronics are vulnerable and prone to failure, leading to out-of-service conditions, with existing condition monitoring technologies being costly, sensitive to disturbances, and requiring complex calculations or invasive system access.

Innovation Solution

A method and system for on-line monitoring of electrolytic capacitor condition using voltage ripple, current ripple, and temperature measurements, with a capacitor model comprising a solid-state adjustable resistor to estimate equivalent series resistance (ESR), allowing for low-cost, resilient, and accurate prediction of capacitor aging without interrupting device operation.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If existing condition monitoring technologies are used to detect electrolytic capacitor ageing, then ageing detection capability is improved, but system cost and complexity increase

Engineering Contradiction:

Improveageing detection capabilityVSAvoidsystem complexity

Core Design Contradiction:

Measurement precisionVSDevice complexity

Solution Approach 1:

The patent creates an analog copy of the capacitor's electrical behavior using operational amplifiers and resistors that replicate the voltage-ripple-to-current-ripple relationship. This analog model copy eliminates the need for complex digital signal processing while maintaining accurate ageing detection capability through the transfer function that relates voltage ripple across the capacitor to current ripple through it.

Inventive Principle:

Principle #26Copying

Solution Approach 2:

The patent replaces complex digital computational systems with an analog electrical system using operational amplifiers, resistors, and capacitors. The analog circuit directly computes the equivalent series resistance by exploiting electrical relationships rather than requiring microcontrollers, ADCs, and complex algorithms, thereby reducing system complexity while maintaining measurement precision.

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

2Measurement precision

If existing condition monitoring technologies are used to detect electrolytic capacitor ageing, then ageing detection capability is improved, but system cost increases

Engineering Contradiction:

Improveageing detection capabilityVSAvoidsystem cost

Core Design Contradiction:

Measurement precisionVSEase of manufacture

Solution Approach 1:

Inventive Principle:

Principle #26Copying

Solution Approach 2:

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

3Measurement precision

If complex calculations and invasive system access are required for monitoring, then measurement precision is improved, but ease of operation deteriorates

Engineering Contradiction:

Improveparameter estimation accuracyVSAvoidsystem accessibility

Core Design Contradiction:

Measurement precisionVSEase of operation

Solution Approach 1:

The patent enables the monitoring system to use the capacitor's own operational characteristics (voltage ripple and current ripple that already exist during normal operation) to perform self-diagnosis. The system extracts ageing information from the capacitor's natural electrical behavior without requiring external test signals or invasive access, making the capacitor essentially monitor itself during normal operation.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

Inventive Principle:

Principle #28Mechanics substitution (Replace mechanical system)

4Productivity

If on-line monitoring is implemented without interrupting operation, then productivity is improved, but measurement precision may deteriorate

Engineering Contradiction:

Improvecontinuous operation capabilityVSAvoidcondition monitoring accuracy

Core Design Contradiction:

ProductivityVSMeasurement precision

Solution Approach 1:

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent implements continuous monitoring by constantly analyzing the voltage ripple and current ripple that are present during normal capacitor operation. The analog circuit continuously computes the equivalent series resistance without interruption, allowing real-time ageing detection while the capacitor remains in service, thus maintaining both productivity and measurement precision.

Inventive Principle:

Principle #20Continuity of useful action

Data Source

PatentEP3109648B1Method and system for on-line monitoring an electrolytic capacitor condition

Publication Date: 2018.05.02 MITSUBISHI ELECTRIC R&D CENTRE EUROPE BV

Figure 1
Figure 2a~2b
Figure 3a~3c

AI summary

The present invention concerns a method for on-line monitoring an electrolytic capacitor condition. The method comprises the steps of: -measuring a voltage ripple across the electrolytic capacitor and the current ripple flowing through the electrolytic capacitor; -measuring the temperature of the electrolytic capacitor; -emulating the monitored electrolytic capacitor using a capacitor model comprising a capacitor and a solid state adjustable resistor, - applying one of the measured ripple to the capacitor model, -adjusting the solid state adjustable resistor to minimize the error between an estimated ripple provided by the capacitor model and the other measured ripple not applied to the capacitor model, - estimating an equivalent series resistance of the monitored electrolytic capacitor using value of the solid state adjustable resistor. -determining an end of life limit value as a function of the temperature of the electrolytic capacitor and an initial equivalent series resistance of the monitored electrolytic capacitor ; -comparing the estimation of the equivalent series resistance of the monitored electrolytic capacitor with the end of life limit value.