Effects of Interaction of Power Converters Coupled via Power Grid: A Design-Oriented Study

Voltage-source converters are commonly employed as rectifiers for providing a regulated dc voltage from an ac power source. In a typical microdistribution system, the power grid is nonideal and often presents itself as a voltage source with significant impedance. Thus, power converters connected to the grid interact with each other via the nonideal grid. In this paper, we study how stability can be compromised in a system of interacting grid-connected converters, which are used typically as rectifiers. Specifically, the stable operating regions in the selected parameter space may shrink when grid-connected converters interact under certain conditions. We consider the effect of both source (grid) impedance and transmission line impedance between converters, and derive bifurcation boundaries in the parameter space. A small-signal model in the dq-frame is adopted to analyze the interacting system using an impedance-based approach. It is shown that the system of interacting converters can become unstable. Moreover, results are presented in design-oriented forms so as to facilitate the identification of variation trends of stable operation boundaries. Experimental results verify the instability phenomenon.