MIMO Analysis of Port-Coupling Induced Destabilization of Interlinking DC-DC Converters

Stability of large power electronics systems is often studied via impedance-based approach. Thereby, the admittance passivity criterion is widely used to predict the potential destabilizing interactions between the converter and the grid. It involves evaluating, in the frequency range critical for stability, passivity properties of the converter’s admittance at a connection port. However, this approach requires assumptions about termination at all other converter’s ports, which may not be known a priori, or may change, especially when the considered converter is inter-connecting multiple buses. Consequently, as demonstrated in this article, the port-coupling induced instability is difficult to be predicted by the standardly used single-input single-output (SISO) admittance passivity criterion. To overcome these limitations, this article proposes the use of multiple-input multiple-output (MIMO) admittance passivity properties as a novel tool to analyze stability and develop stabilization methods for dc-dc converters. Analytical MIMO admittance frequency responses are validated using experimentally measured ones, obtained for a current-controlled buck converter prototype. Stability implications from the resulting MIMO passivity properties are verified by time domain test results, thus demonstrating the capability of the proposed method to easily predict port-coupling destabilization.