Study On Probabilistic Power Flow Calculation Method For Active Distribution Network With Distributed Generation

In recent years, with the development of distributed generation technologies, more and more distributed generation such as solar photovoltaic power generation and wind power generation, and electric vehicles access to the distribution system. Due to the random variation of wind speed and sunlight radiation, the distributed generation output power is random variation, thus causing the problem that the system voltage beyond limit has become increasingly prominent. At present the distribution network power flow calculation method used by most is the forward and backward substitution method, which is a deterministic load flow calculation method. However, with many random fluctuation distributed generation access in the distribution system, the power flow calculation of active distribution network becomes in essence into a probabilistic load flow calculation, which must give grid state, such as the probability distribution of node voltage and branch power.The thesis based on the present research status of distributed generation, focuses on the effect of the random output of wind power generation and photovoltaic power generation on the voltage quality of distribution system, proposes a method to evaluate the influence of distributed generation on the voltage of the active power distribution network by using the probabilistic power flow. The probability model of wind power generation, photovoltaic power generation and electric vehicles have been built, the models have considered the relationship between the active power output of wind power generator and wind speed, solar power and light intensity, the electric vehicle charging power demand and daily mileage and start charging time, the model is introduced into the IEEE37 node distribution system to calculated the probabilistic load flow. The probabilistic load flow is calculated by the Monte Carlo simulation method, there is a large scale sampling of random variables in distributed generation which is subject to various distribution functions, then the deterministic power flow calculation is carried out for each group of samples to obtain the voltage distribution and statistical indicators.The simulation results of three access form, photovoltaic power generation, wind and solar hybrid power generation and wind and solar hybrid power generation with the distribution network contains electric vehicles, were compared, to obtain the maximum penetration rate of distributed generation. The maximum system voltage, the probability index of voltage beyond limit and the index of voltage qualified rate are summarized, when the distributed generation are in different types of distributed generation, different access capacity and different access locations. This thesis puts forward the method of improving the permeability of distributed generation in distribution network, analyzes the influence of the voltage when the distributed generation connected, and provides reference for the distributed generation access to distribution system.