Probabilistic Power Flow Containing Distributed Generation In Distribution System

As the development of the power technology, the daily increasing load demand and the expansion of the generation size, the problems gradually emerge, such as the hard tracking of power system to the load's change, low system reliability, large line loss of transmission system and distribution system, serious environment pollution. The traditional centralized mode of power supply mainly using hydraulic and thermal power plants is more and more difficult to be accepted. Based on this, one kind of distributed generation technology with small size and low cost which can supply clear and reliable power was put forward and studied. They represent the newest worldwide development of the energy industry.Distributed generation has the advantages of low cost, low lost, high reliability, high efficiency and diversity of energy resources. So applying distributed generation to current power system is the development trend. But the interconnection of distributed generation to power grid can make large influence and the control and management of distribution system can be more complex. Based on this, this paper analyzes the influences of distributed generation to the distribution system operation and planning and introduces the solving strategy. And it also prospects the future of the distributed generation's development.At present, distributed generation based on photovoltaic systems (PVS) and wind energy system (WES) are developing quickly. At the same time, the probabilistic output power relied on natural conditions can also cause overvoltage and undervoltage problems. Based on these problems, this paper conducts study on the impacts of WES and PVS to the distribution system voltage quality. It put forward a probabilistic power flow method to evaluate the influence of distributed generation. The probabilistic model of WES is established which considers the relationship between output power of WES and wind velocity. In the same way, the probabilistic model of PVS is established which considers the relationship between output power of PVS and solar radiance. Applying this model into the IEEE 34 distribution system with distributed generation and conduct probabilistic power flow, we can get the probabilistic density function of node voltage and the expected hours which exceed voltage limits in a whole year. The probabilistic power flow uses the method of combined cumulants and Gram-Charlier expansion. This method can get the probabilistic distribution function of the variables and can reduce the calculation work of convolution. This paper also makes comparison between Wind/PV hybrid system and single WES and concludes that the former system can get better system voltage quality.