Impedance Specifications for Stability Design of Grid-Connected DC Distribution Power Systems

In practical application, it is more expected that the impedance-based stability criteria can provide intuitive system design guidance. However, the existing stability criteria for the complicated systems always aggregate all equipment/subsystem impedances. As a result, it is difficult to determine the port impedance specification that each equipment/subsystem should meet to ensure the system stability and a certain stability margin. In this article, the impedance specifications for the stability design of grid-connected dc distribution power systems are proposed. First, the stability conditions for impedance specification design are presented based on the dc-side subsystem impedance ratio criterion. On this basis, the ac-side admittance specifications and dc-side impedance specifications are proposed to ensure system stability. The former is used to constrain the ac-side admittance of voltage-source converter (VSC), and the latter restricts the dc-side impedance of grid-connected VSC and the input impedance of each converter-based load. The proposed impedance specifications are mainly related to grid impedance, transmission power, dc-bus voltage, two specific frequencies, and the required stability margin. As long as the proposed impedance specifications are met, the whole system must be stable and has sufficient stability margin. Finally, the case studies and experiments validate the proposed impedance specifications.