A New Online Continuous Stability Monitoring Method for DC Microgrids

As the penetration rate of renewable energy and electric vehicle keeps increasing, dc microgrids incorporating renewable energy, battery energy storage, and dc loads, such as electric vehicle chargers and electric buildings, are attracting more attention for their effectiveness of integrating zero-carbon-emission elements and reducing system costs. One key challenge in dc microgrids is the small-signal stability analysis and associated system design and operation. This article proposes a new online continuous small-signal stability monitoring method to address the challenge without adding hardware or interrupting the system operation. The proposed method evaluates stability continuously by measuring the crossover frequency and phase margin of the system impedance minor loop gain. Detailed system modeling and analysis and design of the stability monitoring method are presented in this article. Experimental results for a scaled-down system with three 2-kW power converters operating at 100 kHz are provided to validate the proposed method and demonstrate the effectiveness in monitoring the system stability margins under different conditions.