Condition Monitoring Approach for DC Link Capacitors in MW-Scale Power Converters

This paper presents a condition monitoring approach for monitoring the DC link impedance of power converters using a reduced form of impedance spectroscopy. As degradation sensitive parameters, the phase shift and the amplitude of the voltage response resulting from the impedance change are analyzed utilizing precise measurements. This has the advantage of not requiring high-resolution analogto- digital converter sampling, makes system integration easier and simplifies data processing. The condition monitoring concept offers the advantage of DC link monitoring in the presence of the DC link voltage, which enables voltage-dependent effects in the capacitors to be taken into account. In the present paper, we introduce the monitoring concept and a first prototype. We present a sensitivity study to assess the dependency of the performance of the degradation detection on properties of the monitoring system and the DC link. In order to ensure the investigations are based on realistic capacitor aging behavior, comprehensive aging experiments of capacitors under High Voltage High Humidity High Temperature Reverse Bias (HV-H(exp 3)TRB) test conditions are presented. Measurements with the monitoringcircuit prototype and a comparison with a commercial reference system confirm the high precision of measurements achieved with the prototype under laboratory conditions.