Study On Voltage Stability Of Wind Farms With STATCOM

Due to the increasingly serious problem of the environment and resources, renewable resource development and utilization have been paid more attention to. The use of wind energy for electricity generation as a mature technology of renewable energy use patterns have developed rapidly. The installed capacity of wind power increased constantly year by year. The integration of lots of wind power and grid changed original load flow of the power system. Moreover, wind energy is random and wind farm is composed of large number of induction generators which are different from synchronous machine. Therefore, wind power will influence the stability of power system. With the increasing size of single wind farm and the increasing share of wind power in power system, the effect of wind power to power system is more and more serious. Researching on wind power integration has become a problem demanding prompt solution in the development of wind power. Because it is easy to connect to the power grid, and also simple structure, low price and high reliability, asynchronous generator is used widely in network as wind power generation units. But when the asynchronous generators generate the active power, they have to absorb the lagging reactive power, in other words, they have to absorb the lagging reactive current, so that they make the reactive load become much heavier. The reactive current absorbed by the asynchronous generator is used as excitation current. The excitation current of most asynchronous generator with medium or large size is about 20% to 25% of its rated current. If so great reactive power absorption is connected to power grid without compensation, the power factor will reduce sharply. It will not only pollute the power grid or impact the output of active power, but also increase the line loss, leading to the end-user's voltage dropping, and reducing the stability of power grid. Compensation of reactive power and increase of the power factor, are helpful to improve equipment utilization, transmission efficiency and power quality. Voltage stability issues about wind power integration are investigated in this paper. Mathematic model of fixed-speed wind turbine equipped with induction generator (IG) and variable-speed wind turbine equipped with doubly-fed induction generator (DFIG) are also studied. A method is put forward to treat different wind farms node in load flow calculation power systems.In recent years, a new technology which is called Flexible AC Transmission System (FACTS), which is an effective instrument for modern power system operating safely, reliably and economically, has appeared to improve the quality of power network. Static Synchronous Compensator (STATCOM) which is the important part of FACTS becomes the global research focus in virtue of control predominant characteristic and distinguished compensation effect. STATCOM is a voltage source inverter connected to the system by transformer or reactor, dynamic reactive power compensation is achieved by regulating and amplitude of the voltage or the current injected into power system. Comparing with the traditional reactive power compensation equipments, STATCOM has the advantages of faster regulation speed and higher control accuracy.The characteristics of wind power generation and the problems of its grid-connected operation are introduced. This paper also describes the importance of reactive compensation for induction generators and the whole system. Then it reviews the development of reactive compensation devices, the advantages of STATCOM, the research status at home and abroad, its working principle and simulation model. In PSASP environment, the power system, wind farms and STATCOM are simulated. The contribution of STATCOM for voltage stability of wind generators and whole grid is proved. Then simulation studies are carried out to examination the stability of system with and without STATCOM. And the results are shown that STATCOM can enhance the transient stability of induction and synchronous generators when a symmetrical network disturbance occurs in the power system.