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H. Ertl, K. Edelmoser, F. Zach, J.W. Kolar:
"A Novel Method for On-Line Monitoring and Managing of Electrolytic Capacitors of DC Voltage Link PWM Converters";
Talk: International Conference on Power Conversion and Intelligent Motion (PCIM), Nürnberg, Germany; 2006-05-30 - 2006-06-01; in: "Proceedings of the International Conference Power Electronics Intelligent Motion Power Quality", (2006), ISBN: 3-928643-43-6; 295 - 302.

The paper presents a novel concept for monitoring and
managing the DC link electrolytic capacitors of PWM converters,
especially for drive applications. The unit performs on-line
identification of the equivalent series resis-tance (ESR) of the
capacitor in order to detect the end-of-life cycle to permit a
preventive maintenance of the conver-ter prior to a capacitor failure.
The ESR detection scheme is based on the determination of the capacitor
AC losses calculated from voltage/current measure-ments using a simple
single-chip microcontroller. The unit is designed as a small printed
circuit board located between the capacitors screw terminals and the
converter busbars. This also opens the possibility to easily detect the
capacitor's operating temperature which is important for the evaluation
of the identified ESR values. The intention is, furthermore, that the
monitoring unit operates without a separate power supply and draws its
supply current out of the power capacitor. The measurement results of
the individual con-verter capacitors are gathered by an opto-isolated
three-wire bus. Finally, besides the ESR detection the moni-toring unit
further allows an energy efficient capacitor voltage balan-cing in case
a series array of capacitors is used. As opposed to conventional
resistor voltage divider networks this method reduces the balancing
losses to a very large extent by avoiding high quiescent currents.
The paper gives a short introduction into the life cycle problems of
electrolytic capacitors, presents a survey of known monitoring concepts
and describes a novel concept based on capacitor power loss
determination. Subsequently, a laboratory prototype of the proposed
monitoring and managing system based on a single chip microprocessor
is demonstrated.

http://aleph.ub.tuwien.ac.at/F?base=tuw01&func=find-c&ccl_term=AC06586101