Hierarchical Optimal Reactive Power Dispatch for Active Distribution Network with Multi-microgrids

The interconnection of active distribution network and multi-microgrids leads to the increase of variable dimension of optimal reactive power dispatch. The overall reactive power dispatch will face the problems of high dimension, slow convergence, and reduced accuracy. Meanwhile, the decomposition dispatch requires a large number of coordination iterations. Hence, this paper proposes a hierarchical optimal reactive power dispatch method for active distribution network with multi-microgrids based on differential evolution algorithm and the network loss sensitivity. In this method, the upper layer takes the minimum loss of the distribution network as the goal, regards each microgrid as a generator node, and formulates the interactive power between each microgrid and the distribution network. The lower layer aims to minimize the network loss of the microgrid, regards the point of common coupling as the balance node, and make the power of the lower layer meet the constraints of the upper layer in the form of penalty function. To minimize the network loss of the whole network, the sensitivity is calculated to correct the output of reactive power equipment for further optimization. The improved IEEE-33 bus distribution network system is used to verify the method, and the results are compared with the global optimization results. Due to the reduction of the network scale, the number of iterations of each system of hierarchical optimization is 1000, which is greatly reduced compared with 10,000 of the overall optimization. The results show that the proposed method improves the economy of active distribution network system with multi-microgrids and significantly shortens the running time.