On-Line Estimation of Aluminum Electrolytic-Capacitor Parameters Using a Modified Prony's Method

Aluminum electrolytic capacitors (AECs) are the most common capacitors used in power electronics. They are frequently used for filtering and storage functions because of their small size, large capacitance and low price. However, AECs also represent the major cause for power electronics equipment breakdown, mainly due to their wear out through the vaporization of the electrolyte, as a result of both aging and temperature effects. The aging of AECs is expressed by the increase of their equivalent series resistance (ESR) and the decrease of their capacitance (C). Therefore, estimating these two parameters can provide a good indicator for a potential capacitor failure. Additionally, these changes in C and ESR parameters strongly influence the ratio between the capacitors voltage ripple and their current ripple. This ratio is dominated by C at low frequencies and by the ESR in the high frequency range. Hence, this paper suggests a method for on-line estimating and tracking of both C and ESR using that ratio, which is computed starting from some always existing harmonics at low and high frequencies. The proposed method uses the Short Time Least Square Prony's (STLSP) technique to determine and track the amplitudes of the target harmonics. The STLSP technique is well suited for such application, since it has the ability to determine and track the amplitude and frequency of any spectral component, even for noisy and non-stationary signals, using a small number of data samples. This reduces a lot the calculation time and the storage requirements. Consequently, the proposed method is appropriate for online implementation. The method's effectiveness is proved by simulation and experimental tests using a boost DC-DC converter.