Impedance-Based Stability Evaluation for Multibus DC Microgrid Without Constraints on Subsystems

Multibus dc microgrids, which combine renewable energy sources, energy storage systems, and loads, have voltage stability requirement, which solicits increasing research attention in practice. Potentially complex architectures of the multibus dc microgrids make it difficult to evaluate the stability using the conventional stability criteria. In this article, some constraints related to the conventional stability criteria, such as right-half-plane (RHP) poles or zeros in the subsystems are discussed. Further, an impedance-based stability criterion is proposed in the light of generalized bode plots for multibus dc microgrids. The configuration of the multibus dc microgrid is simplified by adopting generalized voltage source, generalized current source, and two-port model. Then, impedances or admittances for each bus port can be derived, which are helpful for assessing the stability of the system. Using the proposed stability criterion, the stability of each bus port in the multibus dc microgrid can be evaluated separately. The proposed stability method considers the number of RHP pole of the open-loop transfer function for the system so the stability of the system consists of subsystems with RHP pole and zero can be analyzed correctly. Moreover, the intermittent bus converter connected with neighboring dc microgrid can be regarded as an extension unit. Then, the proposed method can be easily extended and is acting as a generalized approach for different configurations, i.e., single-bus dc mirogrid or a cluster of dc microgrids. Experiments are done to validate the effectiveness of the proposed criterion.