Abstract: Aiming at the problem that it is hard to realize operational optimization of hybrid AC/DC distribution network with only local control, this paper proposes a hierarchical control strategy with different time scales to combine local control with optimal dispatch. In a short-term scale, the first layer control enables to regulate DC voltage balance by means of coordinated control between converter stations. At the second layer, secondary voltage recovery in harsh operating condition is achieved by changing the control strategy of converter stations. As the third layer control, targeting minimum network loss and voltage offset, optimal energy dispatch system provides operation instructions for the lower control by optimal power flow calculation in a longer-term scale. Operating condition of network is improved by coordinated control between different layers. Simulation results in Matlab/Simulink show that this control strategy can realize operational optimization of network in various conditions and it does not rely on optimal energy dispatch system absolutely to remain distribution networks balance, which improves system reliability.

Key words: hybrid AC/DC distribution network, multi-objective optimization, hierarchical control, coordinated control