Inertia-enhanced method for active distribution network based on hierarchical control structure

•A VSG-based hierarchical control scheme is proposed for DGs in active distribution network.•Multiple VSG-based distributed generators can enhance the inertia of system through regulating the equivalent output power.•In order to minimize the voltage deviation and power loss, we adopt model predictive control to cooperate DGs. With the increasing penetration of renewable energy, converters need to help enhance the stability and rigidity of the power system. This paper proposes an inertia-enhanced method with the hierarchical control scheme for active distribution network to support inertia for the utility grid. The paper first analyzes the mechanism and influence of inertia in power systems and quantifies the inertia which an active distribution network can supply. Then, two-layer control structure is designed for favorable control performance. At the primary control layer, a virtual synchronous generator control strategy is adopted for instant inertia support under frequency fluctuation. The objective of primary control is to track the control references rapidly and accurately. At the secondary control layer, the objective is to coordinate the active and reactive power output of distributed generators to keep voltage deviations and power loss of internal distribution network operating at a comparatively appropriate level. The secondary control strategy is based on model predictive control method, which can consider the physical and control constraints of distributed generators and find the optimal reference signals for all the primary controllers to track. The inertia of power system is apparently enhanced with the hierarchical inertia-enhanced scheme. Finally, simulation based on Matlab/Simulink is carried out, and the feasibility and validity of proposed control strategy are verified.