Integrating Load Flow And Fault Calculation For Asymmetrical Three-phase Weakly Meshed Distribution Systems Containing Distributed Generations

With the supply of energy sources becomes emergency and more emphasis on the environmental protection, global industrial competition is already and the energy revolution is the core of the competition. Developing smart grid is the inevitable trend of our country and the other countries, so the distributed generation technology attracts great recognition and gets rapid development. The development of distributed generation has brought new advantages to traditional power systems, it has also brought challenges. Traditional distribution power flow will not meet the requirement of distributed generation systems. This paper focuses on load flow and short-circuits current calculation for distribution systems containing DGs. The main works of this paper include as below:At first, 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the line parameter r/X is very large in the distribution system, the traditional methods for power flow calculation are no longer applicable.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.Secondly, based on the improved backward-forward sweep, an efficient method for calculating the load flow solution of distribution system is presented. In this algorithm, by using path matrix of the distribution network, the incident matrix of node voltages an load injection currents is established based on circuit fundamental laws.Based on network branch equation, according to the weakly meshed structure characteristic of a distribution network, the nodal impedance matrices are calculated directly by line impedance matrices, avoiding constitute the nodal impedance matrices of the networks. The method can be adaptable to network changes in topology.There are many kinds of distribute generation, all the DG can not only be seen as PQ 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. The essence of the method is to transform all kinds of nodes into PQ node. At last, By using a uniform compensation, circuit model given for all kind of faults, the algorithm can be applied in both normal and short circuit conditions, and their computation formulas and iteration steps are basically the same. Finally, this paper presents a uniform approach for power flow and fault analysis of asymmetrical three-phase, as well as weakly meshed distribution system with DGs.An example of33-node system is used to test the method proposed. Test result verifies the feasibility of the proposed algorithm.