Stabilization of constant-power loads by passive impedance damping

This paper addresses stability problems of power systems with actively controlled loads that exhibit constant-power behavior. Instability occurs in such systems due to the negative incremental resistance of the constant-power loads (CPL). Existing approaches to stabilizing such systems require modification of the source and/or the load control characteristics, or isolating the CPL from the rest of the system by additional active devices, which are difficult to implement and often conflict with other system requirements such as control bandwidth, size, weight, and cost. In this work, we propose passive damping as a general method to stabilize power systems with CPL. Using a representative system model consisting of a voltage source, an LC filter, and an ideal CPL, we demonstrate that a CPL system can always be stabilized by a simple passive damping circuit added to one of the filter elements, no matter how the original system behaves. Three different damping methods are considered and for each analytical models are developed to define their parameters required for stabilizing the system. The different damping methods are also compared in terms of their stabilization capabilities and impact on other system performances such as filter attenuation. Time- and frequency-domain measurements from an experimental system are presented to validate the proposed methods.