| High-bandwidth regulated converter loads, or constant-power loads (CPLs) exhibit a negative incremental input resistance within the regulation bandwidth of the power converter. Distributed power systems which include a large percentage of CPLs and contain energy storage devices may be susceptible to potentially destabilizing interactions of these elements. For the stand-alone dc-dc converter, and in distributed dc systems, design requirements that guarantee stability have been previously advanced and are extensively used in the design and specification of these systems. However, prior to this research, design-oriented stability criteria have not been developed for distributed ac and hybrid ac/dc systems with CPLs. In this research, a mathematical framework based on the generalized Nyquist criterion, reference frame theory, and multivariable control is set forth for dynamic stability assessment of distributed ac systems. Numerical and analytical techniques are established for determining the frequency-dependent impedance characteristics of representative sources and loads in the appropriate frame of reference. Moreover, design-oriented stability criteria analogous to those used in dc systems are derived. The purpose of these criteria is to ensure a safe stability margin without imposing undue restrictions on component designers and system integrators. Finally, the advanced criteria are used to assess the stability of several example systems and to evaluate different stabilizing control strategies, including passive and active approaches. |
