Power Flow Algorithm For Distribution Network With Photovoltaic Forecasting

Power flow algorithm is the basis of the power system analysis. Power flow of distribution network provide important basis for distribution network reasonable planning, design, security and stability of operation. At present, under the dual pressure of energy crisis and environmental pollution, the distributed generation of solar, wind and others developed rapidly on distribution network. Their fluctuations will clearly affect the power grid when distributed generation reaches for a certain percentage of the total capacity to the grid. So this paper focused on the research and analysis of the power flow algorithm of distribution network with distributed generation, trying to ensure the power quality and facilitate the access of distributed generation.Above all, in order to optimize the configuration of distributed generation, clarify the research area, prepare for the power flow calculation of distribution network, this paper analyzes and describes the performance and potential development of distributed generation based on environmental protection, sustainable development, and economic efficiency. The domination of photovoltaic (PV) systems in the future distribution network was confirmed by the analysis of principle and HOMER simulation. In order to reduce the impact of PV fluctuations on the trend of distribution network, a PV prediction model based on cloud type information was established. By this model, the controlled PV load was converted into a predictable quantitative load. Moreover, the complexity of distribution network with distributed photovoltaic was reduced and power flow calculation was facilitated.Secondly, an algorithm containing the Newton-Raphson method and the back/forward sweep method was proposed for the power flow calculation. Newton-Raphson method converged fast when dealing with simple network, but its convergence rate decreased rapidly as the complexity of the network increased; Back/forward sweep method computed fast when dealing with radial distribution network, but it became slower when handling loop distribution network. Our algorithm described the distribution network as two parts:loop and radiation, which were respectively solved by Newton-Raphson and back/forward sweep methods. To calculate the power flow, two methods were used alternatively.Each iteration of Newton-Raphson method consumed roughly the same time. Reducing the number of iteration times of Newton-Raphson method effectively reduced the calculation time of the new method; the first iteration of the back/forward sweep method took longer time than the subsequent iterations, so that reducing the number of iteration times of back/forward sweep method only had little help on new method calculation speed. In order to ensure convergence and increase calculation speed, the variable convergence accuracy was introduced into the Newton-Raphson method part.At last, an example of weekly meshed distribution network with two distributed photovoltaic generations was demonstrated using aforementioned theories, with the comparison of Newton-Raphson method under several conditions with different impedance ratios. The results showed that the algorithm has advantages in computing speed as well as the speed of convergence.