A New Impedance-based Relative Stability Criterion for DC Power Systems

The growing need to support high transient loads has led to a necessary push towards power electronic-based DC distribution. However, these electronics are becoming more likely to cause destabilizing behaviors at their source interfaces due to the potential for negative impedance instability. The most common technique for assessing the small signal stability at a converter interface has been the impedance-based Nyquist Criterion, where input and output impedances are used to classify absolute stability. Unfortunately, this traditional method does not enforce any desired transient performance of the integrated power system and therefore does not completely account for hazardous oscillatory behavior. This paper proposes a new method of ensuring not only absolute stability of a power system interface but also a desired performance behavior. Through a redefined s-plane contour, the traditional Nyquist Criterion is modified to become the Relative Stability Criterion (RSC) for DC power systems. As numerically demonstrated in this paper, this novel technique can use black-box extracted port characteristics to enforce a transient time-constant for an integrated system and therefore ensure reliably safe system operation.