| The rapid development of economy in China increases the demand for energy, therefore, developing renewable energy is a basic way to solve this problem. As a renewable energy, wind power has the unique advantage of abundance is deposits, renewability, widely distribution, no pollution, thereby, developing and utilizing wind power is paid more and more attention.Utilizing wind energy is to convert the kinetic energy of atmosphere movement to other forms of energy, the specific usages include: wind power, aiding navigation, pumping water with windmill, etc. At present, the main form of application is to generate electricity.As the rapid progress of wind power generation technology, wind power is more and more widely used, and the proportion of wind power in electrical energy becomes larger and larger. But since the disadvantage of randomness and uncontrollability, there are many technical problems for wind power to connect to power system in practical, such as poor ability to regulate active power, and bad quality of electrical energy, etc, which is the main problem to restrict large-scale development of wind power. According to"Technical Rule for Connecting Wind Farm into power grid"by State Grid, wind farm should not only be able to regulate active power, reactive power, voltage, and frequency, but also the power quality should satisfy the state standard.To follow as a result, depending on the development of power electronic technology Doubly-Fed Induction Generator(DFIG)is used more and more in wind power generation. Thus, establishing the model of doubly-fed wind generator has a special importance for further research of active power-frequency regulation, reactive power-voltage regulation.This paper introduces mathematical model of doubly-fed wind generator and principle of vector control in detail, on the basis of which transient characteristics and dynamic characteristics are studied further, meanwhile, reasons of all phenomenons are analyzed and solutions are raised, meanwhile, the control strategy of regulating frequency is raised and proved to effective through simulation. The details are as follows:(1)The basic principle of doubly-fed wind generator is studied, and models of control system of grid-side and rotor-side converters are established on the basis of stator and rotor voltage equation, flux equation, adopting stator-flux oriented control method, which makes active power decouple from reactive power, thereby, active power and reactive power can be controlled independently.(2)Mathematical model of gust wind, ramp wind and random wind are studied and the simulation models are established, then the response of doubly-fed wind generator under every kind of wind is analyzed. Simulation results demonstrate that the models established can embody the typical features of power quality variation with the wind; according to the principle of conversion from wind to electricity in doubly-fed wind generator, then the conversion from wind to electricity is realized by establishing the model of doubly-fed wind generator.(3)On the basis of studying the pitch angle control strategy, the model is established to realize constant power control under high wind speed and constant voltage control under low wind speed, the relationship between rotor speed, torque and active power is analyzed, a measure for wind farm to reserve active power by reducing wind power coefficient is raised. By analyzing the effect of doubly-fed wind generator on power system, a method for wind farm to participate in frequency regulation is raised, and the simulation results demonstrate that the wind power coefficient can be increased against the need of active power, and finally the frequency will return normal.(4)A system with 3 generators is taken as a research object, and simulations under fault on the connection point and load sudden change are carried out, during which the effect on the operation of wind turbine generators and power system stability is analyzed. The effect of wind turbine generator on system frequency and voltage is studied under every kind of wind. According to the simulation results, wind farm can participate frequency regulation by adjusting rotor speed and wind power coefficient, which can compensate active power and maintain system frequency when the system is short of active power.This paper improves the operating characteristics of connecting wind farm into power system, through researching control strategy of doubly-fed wind generator in-depth, and the improved operating characteristics satisfies the demand of State Grid, which provides technical support for further utilizing wind power... |
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