Characteristics Of Doubly Fed Induction Generator Research Articles

Study on the Output Performance of DFIG under Unbalanced Grid Voltage

This paper uses dynamic equivalent circuits to study the impact of the unbalanced grid voltage on a Doubly Fed Induction Generator (DFIG) and draws the curves between the voltage unbalance factor (VUF) and the output characteristics of DFIG. A mathematical model of the grid and rotor side converters (GSC and RSC, respectively) is given in the stationary αβ reference frame under unbalanced network voltage conditions, which could be used in the coordinated control of the GSC and RSC. Finally, simulation studies on a 1.5MW DFIG can verify the feasibility of the proposed coordinated control strategy which can be used to improve the performance and stability of the whole wind power generation system.

Correlation among the transient characteristics of doubly fed induction generators under grid fault

Doubly fed induction generator (DFIG) under grid fault has increasingly gained attention among researchers for the better protection and control of power system. However, existing studies which focus on the single DFIG are incomplete, because other DFIGs can significantly affect the transient process of DFIG in the wind farm. Thus, this paper investigates the correlation among the transient characteristics of DFIGs when a three-phase fault occurs in power grids. A vector model of a DFIG is built with consideration for the excitation regulation. Transient processes of the DFIG when wind farm contains different numbers of DFIGs are mathematically deduced by dividing the fault process into two periods according to converter regulation. The analytic expressions indicate the relationship between the transient electrical variables of a DFIG and the number of DFIGs is proposed to acquire the varying pattern of the correlation. The correlation phenomenon is verified both through analysis and simulation, which provide positive implications for the operation of wind power integrated systems.

Research Doubly-fed Induction Generator Dynamic Characteristics Based on Time-varying Parameters

According to the dynamic characteristics of doubly-fed induction generator (DFIG) which is changing with the wind speed, the dynamic mathematical models of DFIG wind turbines major subsystems’ have been established, which includes the aerodynamic subsystem, drive train subsystem and generator subsystem. The whole nonlinear time-varying parameters dynamic mathematical model would be obtained to integrate the major subsystems’ dynamic mathematical models, and the whole linear time-varying parameters dynamic mathematical model can be obtained to linearize the whole linear time-varying parameters dynamic mathematical model. To take the 2MW DFIG wind turbine as example, the proposed model is validated by the study on the dynamic characteristics of DFIG with wind speed variation, and the results show that the proposed model could provide a theoretical support for optimal control of the DFIG wind turbines.

Study on Transient Characteristic of the DFIG LVRT

In order to analyze the operational capability of the low voltage ride through ( LVRT) of a gird-connected wind turbine with doubly fed induction generator (DFIG) effectively, it is necessary to evaluate operation characteristics of DFIG under a grid fault.By using the transient principle of the flux of stator and rotor, the expressions of transient currents of stator and rotor of DFIG are derived under the grid voltage sag. The transient process is analyzed by using the Matlab to derive the correctness of the expression. A control strategy is presented to eliminate harmonic currents by proposing the essential factors of over-current of stator and rotor. The output active power and reactive power are calculated by using the derived expression with different voltage sags. Based on the theoretical analysis, a DFIG is established to analysis the model of LVRT. Simulation results show that the control strategy is able to eliminate the harmonic currents and achieve the requirements of LVRT.

Analysis of LVRT Influence on the Neighboring Wind Farm and a New Protection Scheme for DFIG

Low voltage ride-through (LVRT) capability has become more important to the doubly-fed induction generator (DFIG) as the penetration of wind power increases. This paper analyses the LVRT influence on the neighboring wind farm, mainly considering the crowbar action during a fault. On the basis, a new protection scheme for the DFIG is proposed to prevent the negative influence, primarily based on a rotor series resistor and a reactive power compensation device. And the adaptive control strategy is presented. Through the simulation, characteristics of DFIG in the neighboring wind farm with and without the protection scheme are compared. The results show that the cascading crowbar action can be avoided by the protection scheme and it is advantageous for grid voltage restoration.

Integrated power characteristic study of DFIG and its frequency converter in wind power generation

A doubly fed induction generator (DFIG) is a variable speed induction machine. It is a standard, wound rotor induction machine with its stator windings directly connected to the grid and its rotor windings connected to the grid through a back-to-back AC/DC/AC PWM converter. The power generation of a DFIG includes power delivered from two paths, one from the stator to the grid and the other from the rotor, through the frequency converter, to the grid. The power production characteristics, therefore, depend not only on the induction machine but also on the two PWM converters as well as how they are controlled. This paper investigates power generation characteristics of a DFIG system through computer simulation. The specific features of the study are (1) a steady-state model of a DFIG system in d– q reference frame, (2) a simulation mechanism that reflects decoupled d– q control strategies, (3) power characteristic simulation for both generator and converter, and (4) an integrative study combining stator, rotor and converter together. An extensive analysis is conducted to examine integrated power generation characteristics of DFIG and its frequency converter under different wind and d– q control conditions so as to benefit the development of advanced DFIG control technology.