Improved Spice models of aluminum electrolytic capacitors for inverter applications

Impedance modeling of aluminum electrolytic capacitors presents a challenge to design engineers, due to the complex nature of the capacitor construction. Unlike an electrostatic capacitor, an electrolytic capacitor behaves like a lossy coaxial distributed RC circuit element whose series and distributed resistances are strong functions of temperature and frequency. This behavior gives rise to values of capacitance, ESR (effective series resistance), and impedance that vary by several orders of magnitude over the typical frequency and temperature range of power inverter applications. Existing public-domain Spice models do not accurately account for this behavior. In this paper, a physics-based approach is used to develop an improved impedance model that is interpreted both in pure Spice circuit models and in math functions.