Low-Frequency Impedance Monitoring and Corresponding Failure Criteria for Aluminum Electrolytic Capacitors

Condition monitoring of aluminum electrolytic capacitors (AECs) is essential for predictive maintenance of power electronic converters. The AEC is considered at the end of its life when its capacitance or equivalent series resistance (ESR) reaches corresponding critical values. In the literature, it is found that either of these parameters may reach its critical limit depending on the operating conditions and applications. However, most of the existing health monitoring techniques of the AEC in dc-dc converters are based on the estimation of ESR. To address the aforementioned issue, this paper proposes to estimate the low-frequency impedance of the AEC, which is dominated by its capacitance value, thereby allowing health monitoring based on the capacitance value. The technique is based on injection of a low-frequency current ripple into the AEC using duty ratio control of the dc-dc converter. The parameters of new and aged capacitors are experimentally obtained at various temperatures and are used to establish the failure criteria. Furthermore, the proposed method is applicable for both the continuous conduction mode and the discontinuous conduction mode (DCM) of operation. For DCM operation, a sampling instant to recover a low-frequency waveform is suggested based on mathematical analysis. Detailed simulation studies are performed and results are included in this paper. Experimentation is carried out on a dc-dc boost converter integrating solar photovoltaic with the dc system. Experimental results are found to be in agreement with simulation results.