Power Converter-Based Impedance Spectroscopy for Supercapacitors: Theory, Simulation and Experimental Verification

This paper addresses the need for cost-effective and integrated impedance spectroscopy (IS) techniques for supercapacitors (SCs), particularly in applications where conventional frequency response analyzers (FRAs) are impractical due to their high cost and lack of portability. A power converter-based methodology is proposed to perform IS using a power electronics interface, enabling in situ characterization of SCs. The approach is based on an analytical formulation that relates the amplitude of the duty-cycle perturbation introduced into the converter with the excitation frequency and the desired sinusoidal current amplitude, allowing the direct generation of frequency-dependent excitation signals using the power converter. The proposed methodology is first validated using circuital simulations, demonstrating accurate impedance estimation with a Range-Average Absolute Error (RAAE) of 0.30% in magnitude and 1.94% in phase compared with a reference simulation. Experimental validation is then conducted using a synchronous converter controlled by a digital signal processor, and those results are benchmarked against a commercial FRA, obtaining an experimental RAAE of 4.88% in magnitude and 2.41% in phase. These discrepancies are mainly attributed to limitations in the excitation and measurement stages. In addition to its accuracy, the proposed approach significantly reduces implementation cost. The converter-based setup relies on standard power electronics hardware and conventional laboratory instrumentation, with an estimated cost of approximately $2000 USD, which is much cheaper than commercial FRA-based systems (up to $60,000 USD). These results demonstrate that the proposed methodology provides a practical and scalable alternative for impedance spectroscopy of supercapacitors, enabling embedded and in situ diagnostics of energy storage systems.