Three-phase Power Flow For The Distribution Network With The Distributed Generation

China is developing the smart grid currently. The smart grid includes generation, transmission, substation, distribution, scheduling and other links. Nowadays, the shortage of energy in the world, exploration of generation technology of new power energy and the advantages of DG have drawn more and more experts'attention. How to realize DG access to the distribution network flexibly is the focus of the experts' study also is one of the goals of the development of smart grid. All above mentioned are based on the flow calculation.There are many kinds of distribute generation, including wind power, solar photovoltaic power, fuel cells, micro turbines, batteries, etc. During the current calculation, all the DG can not only be seen as PQ nodes, PV nodes or balanced nodes. Depending on the different characteristics of the DG, four models are presented and their respective features and treatments in the flow calculation were mentioned in details. As the three-phase is unbalanced and the line parameter R/X is very large in the distribution system, the traditional methods for power flow calculation are no longer applicable. Three-phase power flow calculation is needed and three-phase model is established. Considering all the advantages and disadvantages of various methods for flow calculation, the improved backward-forward sweep is presented. But the backward-forward sweep can not calculate the ring network and PV nodes, a new method is mentioned. The weak ring structure of the distribution system can be equivalent to a ring network and a pure radiation. Results can be obtained through the superposition principle. In the processing of PV nodes, the law of reactive power compensation and injection current is used to adjust its voltage. In the scheme of node numbering, new method is used. All the nodes do not need to be renumbered, so the operation is very simple. After the DG access to the distribution system, the structure of distribution system is changed. A single power supply system is changed to have more power supply. Flow calculation models with different DG in the distribution network are established in the power flow calculation. The method for flow calculation of distribution system with DG is verified in an example. DG accessing to the distribution system will influence the voltage of the system. The impact of voltage depends on the DG, so the reasonable choice of access location and power will be helpful. The example shows the accuracy and convergence of the algorithm.