Research On The Modern Distribution Network Controlled By UPFC

With the development of national economy, distribution system in China is undergoing profound changes. As the world's rapid economic development, making the international and domestic demand for electricity has increased dramatically. Energy and environment is the urgent problem for human to survival and development today to solve. Conventional energy resources dominated by coal, oil, natural gas are not only limited, but also caused serious pollution. Therefore, the development and utilization of renewable energy, has been has been paid much attention by the whole world in recent years. Wind power, solar power and other distributed power generation systems are gradually incorporated into the traditional distribution network to improve the power supply reliability.In distributed power generation technologies, wind power is one of the most mature technologies. Wind power generation operating with the traditional distribution network, as a supplement centralized power can not only solve the shortage of resources, but also can improve the centralized power generation's some disadvantages. However, due to the randomness of wind speed, wind power has the characteristics of instability, especially with the large-scale wind power connected to the distribution network, caused a great deal of pressure to the security and stability of the entire power grid. How to ensure the power system run stable and reliable after large-scale wind power connected to it has become a subject to study by electricity researchers.FACTS (Flexibility AC Transmission Technology System) technology is the power electronics technology, which combine with modern control technology and computer technology and power system. it can adjust the active and reactive power flow fast through controlling the transmission system bus voltage, transmission line reactance and phase angle, Rational distribution of transmission power flow can reduce the power consumption and power generation costs and improve the stability and transfer capability of traditional AC transmission system, meet the target of the power system's security, reliability and economic operation.Unified Power Controller UPFC (United Power Flow Controller) is the most powerful one in FACTS family, has the characteristics of powerful multi-function control ability and flexibility. It can adjust the system of active and reactive power quickly and flexibility. In 1998 the world's first UPFC device commission and operate successfully in the United States Inez substation, which not only proved the correctness in theory and the feasibility in practice, but also proved that UPFC can give a huge economic benefit to power system.From the development trend of international wind power technology, wind turbine unit capacity increases, the stability of wind farm wind power as a key factor to constraint the development of wind power. To prevent the dramatic changes of system voltage in the export of wind power generation due to short-circuit or the change of wind speed, and even cause the distribution network voltage collapse, we must reduce the fluctuation of wind farm's voltage, so the exchange reactive power between wind power generation system and network must be reduced, and also ensure the balance of active power in the entire distribution network. The paper put UPFC into the distribution network with wind power in order to provide continuous voltage control and power flow control, reduce the absorption reactive power of wind power generation system from the system, can solve the power fluctuations, voltage flicker, instability and other issues in distribution network. The paper using PSCAD/EMTDC software to establish the simulation model of UPFC connected into the distribution network with wind power system, verify that UPFC can stable the bus voltage of wind turbine's export, maintain distribution system's power to balance, and can protect the safe operation of wind power system when there is a failure in the system.