Negative Impedance Characteristics in Passive Inductors

Inductors, known as basic passive components, are the essential devices in power electronics converters. The high frequency characteristics, including parasitic capacitance, in inductors can introduce significant capacitive current to the system due to the fast-switching transitions facilitated by wide-bandgap (WBG) devices. To represent these important parasitic capacitance behaviors, equivalent-circuit representations using capacitors have been proposed, where the capacitor values are usually assumed to be positive resulting in positive impedance characteristics. In this paper, the authors share an interesting finding of the negative impedance characteristics and equivalent negative capacitance in passive inductors, which are measured by an accurate impedance analyzer with factory-approved calibrations. Besides, two different measurement methods are also implemented to measure the negative impedance behaviors as cross validations for ensuring correct measured results. The experimental results also reveal that the negative impedance characteristics of inductors can be compensated by paralleling multiple ceramic capacitors. Perspectives, future work, and conclusions are addressed at the end of this paper.