Unified Modeling and Hierarchical Control Strategy for Different Distributed Generators in Active Distribution Networks

The growing penetration of renewable energy resources (RESs) increases uncertainties in active distribution networks (ADNs), leading the networks to suffer low inertia, bidirectional power flows, and rapid power changes. The frequency overshoots, overvoltage, and unbalance power sharing are prone to happen in ADNs. To address those issues, this paper proposes a novel unified modeling and a hierarchical control strategy for different distributed generators (DGs). First, to unify the control states of different DGs and separate control states of different control layers, a unified modeling method for grid-following and grid-forming DGs is proposed. Then, based on the unified model, a two-layer control strategy is designed. The robust controllers are locally configured to achieve rapid recovery control, avoiding the impact of communication delays. The collaborative power controller is centralized designed to prevent power circulation caused by the interaction of local controllers of DGs. Compared with other hierarchical control strategies, our strategy can make further use of the residual capacities of different DGs and can more rapidly suppress the unpredictable changes of RESs. The effectiveness of the proposed strategy is validated by several cases in MATLAB/Simulink.