Research On Grid Planning In Active Distribution Network

Environmental pollution and fossil energy shortage has become a growing topic of concern, while driving the rapid development of distributed generation technologies including renewable energy generation. The active distribution network is the key technical support to the wide access of distributed generation and is the advanced stage of the smart grid. The grid planning method for traditional distribution network has been unable to adapt to the access of distributed generation with high penetration. The adaptability of typical connection modes of the existing distribution network to the access of distributed generation is of big difference. The research on the grid planning model which can be used in active distribution network and the capability of the traditional grid to accept the access of distributed generation are hot issues in the field of distribution network planning, which have important theoretical and practical significance.Firstly, this paper does a study on power flow calculation considering the randomness of distributed generation output in distribution network. The stochastic models of wind turbine and photovoltaic power generation are introduced. The basic principles and procedures of the typical power flow calculation in distribution network are explained. It achieves the power flow calculation considering the factor of distributed generation by improving forward and backward substitution method program. It combines the Monte Carlo simulation method which is used for random sampling and the power flow calculation introduced before to conduct the random power flow calculation in distribution network. Secondly, a bi-layer planning model considering the randomness of distributed generation output which is used for grid planning in active distribution network is put forward. The objective of the upper layer function is the lowest annual comprehensive cost and the objective of the lower one is the minimum total of the network loss and the whole output power in power and voltage constrains. It optimizes the locations of distributed generations based on the initial network obtained by using the minimum spanning tree method. Then, the active distribution network grid plan which costs the minimum total investment is obtained. Finally, the adaptability of four typical connection modes to the access of distributed generation is analyzed by the maximum allowable access penetration and three evaluation index: the voltage change rate, the voltage sensitivity coefficient and the rate of active power loss change, which provides a theoretical basis for the further connection mode selection in active distribution network grid planning.