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DC microgrids are gaining high momentum under the smart grid environment. DC microgrid stability can be an issue under high penetration of tightly regulated power converters used to interface distributed resources and loads. This paper addresses dc microgrid stability under high penetration of tightly regulated power electronic converters; and proposes three simple and computationally efficient active damping solutions that can be implemented to stabilize a controlled voltage-source converter (VSC) interfacing a dc- microgrid to an ac system. The proposed active damping methods depend on reshaping the VSC impedance by injecting internal-model-based active damping signal at the outer, intermediate and inner control loops of the voltage-oriented VSC interface. Small signal analysis is conducted to assess the system stability under different compensation schemes. Moreover, the reshaped source impedance of the VSC interface and the modified voltage-tracking dynamics are derived under different compensation schemes. Sensitivity and robustness analyses are provided to assess the dynamic coupling among active damping and voltage tracking controllers. Evaluation results, based on a detailed model of a dc microgrid with multiple tightly regulated converter-interfaced loads, are provided to validate the developed models and demonstrate the effectiveness and robustness of proposed techniques.
Date of Publication: March 2012