Reduced-Order Symbolic Admittance Model and Stability Analysis of Grid-Connected Converters

With the penetration of power electronic devices in the power grid, their multi-time scale coupling characteristic with the power grid leads to a decrease in the power system stability. To study this issue, small-signal impedance modeling and stability analysis are necessary for interconnected power electronic devices. However, with the increasing complexity of the control structure and power grid structure, the order of small-signal model transfer functions of power electronic systems becomes higher. Especially for systems with high-proportion grid-connected converters, modeling complexity rises exponentially. Traditional numerical simplified models make it difficult to cover the general scenarios where grid-connected converters work under different operating conditions and parameters. On the other hand, these models lack generality and clear physical significance. To solve the above issue, this article proposes a novel symbolic order-reduction method for grid-connected converters in the wide frequency band (1 ∼ 5000 Hz), by decoupling and simplifying the control loops with different bandwidths in the full-order small-signal admittance model, which significantly reduces the order of the model with physical meanings retained. Based on the symbolic model, the corresponding RLC circuit model is subsequently provided, revealing a clearer system stability mechanism. Finally, the effectiveness of the method is demonstrated through theoretical analysis, simulation, and experimental verification.