A Transient-Modeling-Based Grey-Box Method for Online Monitoring of DC-Link Capacitors

This article proposes a suitable grey-box method for online monitoring of dc-link capacitors. It is found that the transient behavior of dc-link voltage in ac/dc and dc/dc converters is similar to the zero-state response of a parallel resistor-inductor-capacitor (
RLC
) circuit. Moreover, the damping factor
α
(related to capacitance) of the large-signal transient trajectories of converters can be chosen as a new health indicator of capacitors. Based on this, a nonintrusive transient equivalent circuit model based grey-box method is presented, which can realize the condition monitoring of dc-link capacitors with minimum dependency on the detailed topology and control information. Besides, it has features of relatively high applicability and extreme low sampling frequency requirement. Taking an ac/dc system and a dc/dc system as case studies, simulation results demonstrate the proposed method is suitable for converters with different load types. Moreover, a commercial power supply is chosen as an experimental case. Experimental results illustrate that the estimation errors of the damping factor
α
and dc-link capacitance are less than 1%. Furthermore, two typical application cases for a white-box system and a grey-box system are given to further illustrate the implementation of the proposed method.