A novel life-cycle monitoring and voltage-managing device for dc-link electrolytic capacitors in pulsewidth modulation converters is presented. The system performs online identification of the capacitor's equivalent series resistance (ESR) in order to detect the life-cycle status and permit preventive maintenance. The ESR detection is based on the capacitor's ac losses calculated from voltage/current measurements using a simple low-cost microcontroller. The unit is designed as small printed circuit board located directly at the capacitor's screw terminals in order to simplify the required temperature sensing and to minimize wiring effort. The minimized energy consumption allows a power supply taken out of the capacitor to be tested. Besides life-cycle monitoring, the unit further facilitates energy-efficient voltage balancing for capacitors in series arrangements avoiding any power resistors typically used in balancing circuits. Instead, the unit controls the capacitor voltage by influencing its power consumption. Each individual monitoring unit (one per each power capacitor of the converter) transfers the ESR results to the converter's main controller and receives control commands via a common optoisolated fieldbus. Alternatively, this data transfer is performed using wireless near-field communication leading to a completely autonomous monitoring unit without any wiring for power supply and data transmission.

Life-Cycle Monitoring and Voltage-Managing Unit for DC-Link Electrolytic Capacitors in PWM Converters

The objective of this paper is to propose a new method to detect the rise of equivalent series resistor in order to realize the online failure prediction of the electrolytic capacitor for LC filter of switching-mode power converter. Characteristics of electrolytic capacitors are introduced in this paper. Different experimental measurements are conducted and shown to illustrate the properties of electrolytic capacitors. The proposed online failure prediction method has the merits of low cost and circuit simplicity. It can be integrated within the package of the electrolytic capacitor to improve its reliability. Hardware experimental results are shown to verify the performance of the proposed method.

Online Failure Prediction of the Electrolytic Capacitor for LC Filter of Switching-Mode Power Converters

This paper presents a very simple technique to estimate the condition of aluminum-electrolytic-capacitors. The aging of aluminum-electrolytic-capacitors is expressed by the increase of their equivalent series resistance (ESR) and the reduction of their capacitance. Thus, the proposed technique is based on the estimation of both the ESR and capacitance values. To implement the proposed technique, the capacitor is fed by a sinusoidal voltage with the required power. The resultant impedance vector defined by the capacitor voltage and current gives enough information to estimate the condition of the capacitor.

A Simple Offline Technique for Evaluating the Condition of Aluminum–Electrolytic–Capacitors

Switched capacitor (SC) converters are gaining acceptance as alternatives to traditional, inductor-based switching power converters. Proper design of SC converters requires an understanding of all loss sources and their impacts on circuit operation. In the present work, an equivalent resistance method is developed for analysis, and equivalent resistance formulae are presented for various modes of operation. Quasiresonant converters are explored and compared to standard SC converters. Comparisons to inductor-based switching power converters are made. A number of capacitor technologies are evaluated and compared for applications to both SC converters and inductor-based converters. The resulting model can be used to accurately predict and optimize converter performance in the design phase.

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Modeling of capacitor impedance in switching converters

The aim of this study is to present a simple on-line fault detection technique that is able to prevent structural failures in aluminium electrolytic capacitors used in the output filter of step-down DC–DC converters. The aluminium electrolytic capacitors equivalent circuit consists of an ideal resistance in series with an ideal capacitor and an ideal inductor. The first two elements change with frequency, temperature and aging. Most manufacturers define the end of life limit of these capacitors when their internal resistance (equivalent series resistance (ESR)) doubles or their capacitance (C) reduces by 20%, when compared with the initial values. The proposed on-line fault detection technique is able to estimate the capacitor ESR value during converter operation. For that purpose, a simple relationship between the input current and the output voltage ripple is used. The measurement system is composed of a digital oscilloscope that is connected to a microcomputer with ‘Matlab’ software. Several simulation and experimental results are presented to validate the proposed fault detection technique.

On-line fault detection of aluminium electrolytic capacitors, in step-down DC-DC converters, using input current and output voltage ripple

Impedance modeling of aluminum electrolytic capacitors presents a challenge to design engineers, due to the complex nature of the capacitor construction Unlike an electrostatic capacitor, an electrolytic capacitor behaves like a lossy coaxial distributed RC circuit element whose series and distributed resistances are strong functions of temperature and frequency This behavior gives rise to values of capacitance, ESR (effective series resistance), and impedance that vary by several orders of magnitude over the typical frequency and temperature range of power inverter applications Existing public-domain Spice models do not accurately account for this behavior In this paper, a physics-based approach is used to develop an improved impedance model that is interpreted both in pure Spice circuit models and in math functions

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Jr. S.G. Parler

Papers

Improved Spice models of aluminum electrolytic capacitors for inverter applications