Harmonic Probabilistic Power Flow Of Distribution Network With Distributed Generation

Traditional power grid needs long construction periods, high investments, and complex reliability technologies. Power load has a sustained growth. As a result, the grid-connected distributed generations such as wind power generations and photovoltaic power generations attract people’s attention. Wind power and solar power are clean, non-polluting, and renewable energy. Such kinds of distributed generations provide a strong support for dealing with energy shortages and promoting economic development. Due to the random fluctuations of wind and light intensity, the output power of the distributed generation is a random variation. When connected to the grid, a series of power quality problems would be caused. Such as voltage fluctuations and flicker, unbalance of three-phase voltage and harmonic distortion. Harmonic distortion in the network connected with distributed generation will be analyzed and calculated in this paper. Harmonics generated by the distributed generation are not constants because of the random characteristics of distributed generation. Harmonics generated by non-liner loads in the network are also changing along with the load changes. The network structure may change because of the device failure and other factors. As a result, certain calculation of harmonics is not enough. Harmonic probabilistic power flow is studied in this paper. In order to avoid complicated convolution operation, Gram-Charier series is used to approximate the probability function of random variables. Firstly, relationship of harmonic distortion with the known variables is built by linearized harmonic equations and the harmonic distortion calculating equations. Then each order cumulant of harmonic distortion is calculated. Finally, probabilistic function as well as the expectations and95%probability values of harmonic voltage distortion of every node can be obtained.On the basis of theoretical research, Delphi7software is used for programming and software design. Certain regional network connected with actual wind power project or photovoltaic project is calculated by the designed software. PSASP software is used to verify the result of the designed software. Harmonic distortion is evaluated according to its expectants and95%probability values.