Online Capacitance Estimation Method in Buck Converters with Characteristic Frequency Injection for Optimal Sensitivity

Accurate capacitance estimation for aluminum electrolytic capacitor is vital for parametric fault diagnosis and fault prognosis of switching power converters. This paper proposes an online capacitance estimation method based on characteristic frequency injection. First, the paper analyzes the key challenges of capacitance estimation methods using the switching frequency information: the parameter sensitivity is insufficient. Next, to ensure optimal sensitivity, the analytical expression of characteristic frequency is derived, to provide guidance on the selection of the injection frequency. Finally, the capacitance is estimated via the equivalent circuit at the inj ection frequency. Simulation and hardware experiments verify that the characteristic frequency injection results in optimal parameter sensitivity, and the proposed method can accurately estimate the varying capacitances.