Research On Power Flow Calculation Method For Distribution Network With Distributed Generation

With the increasing demand of power quality and fossil energy dying out, the distributed power has received more and more attention. In recent years, following the rapid development of distributed power grid technology, the research on the power flow algorithm in distribution network with distributed generation has become a hot issue.Firstly, this paper has analyzed the current states of power flow algorithm. Aiming at the shortcoming of complexity in programming, the forward and backward substitution method has introduced incidence matrix, and derived its own formula by the relationship between current and voltage in distribution network. With the formula, the k times of power flow results can be directly calculated from the k-1 iteration. Then, the correctness of the formula and the improved algorithm are verified by the example of IEEE33.Secondly, because the forward and backward substitution method cannot manage the distribution network with PV distributed power, so that the calculation formula of reactive power correction for PV node has been derived by the relationship between the current increment and the voltage increment of the PV node in this paper. The essence of this formula is to transform PV nodes into PQ nodes with the change of reactive power. By Comparing with the existing PV node processing methods in the case of IEEE33, the correctness and effectiveness of the PV node processing method are verified.Thirdly, in general, distribution network operating in open loop with closed loop designed, so in the situation of power grid equipment maintenance, accident exception handling and maximum demand control, but the forward and backward substitution method cannot manage the distribution network with loop. When calculating the power flow of distribution network with loop, the loop is opened in the middle of the contact line and adds two new virtual nodes in this paper. With the injection current can be carried out by voltage difference of the virtual nodes and Thevenin equivalent resistance, so that the improved network will be completely equivalent to the original loop network. From this theaccuracy of the virtual node voltage difference is not required, so that the time of power flow calculation can be reduced. Because of using the ring network processing method and PV nodes processing method to actual elbow line 115, the effectiveness of improved forward and backward substitution method is verified.Fourthly, the existing research on the power flow algorithm of distribution network with distributed generation is in the stage of theory, and assumes that the output of the distributed power supply and the load in the distribution network are constant. But, the load in the actual distribution network is always changing, for example, the output of photovoltaic power generation system is changing with the intensity of the sun, and the output of the wind power generation system is changing with the wind speed. So, if only for a certain time of distributed power distribution network in power flow calculation, the flow calculation results are not convincing. In this paper, the dynamic model of photovoltaic power generation system and wind power generation system are established, and accessed these distributed power to the distribution network IEEE36 with load changing follow time and the actual elbow line 115. From the calculating of their power flow, it is concluded that the Multi distributed system as different nodes in the distribution network can provides high quality electric energy to users.