Single Doubly Fed Induction Generator Research Articles

Modeling of wind turbine based on dual DFIG generators

In order to investigate a viable approach to fully exploit the wind speed, the present work investigates the application of a novel wind turbine consisting of dual doubly-fed induction generators (DFIG). The model can be further used to apply in areas where the winds are high to achieve high conversion efficiency in order to produce large electric power and increase the wind turbine capacity with an economy of hardware on the one hand, and to reduce the installation cost on the other. Furthermore, this model is always guarantees the continuity of power production because if one generator fails, the second generator will keep working until the broken one is repaired. The proposed model of the wind turbine based on dual doubly-fed induction generators (WT-dual-DFIG) were using the indirect field-oriented control (IFOC) was validated by wind turbine based on single doubly-fed induction generator (WT-single-DFIG) in MATLAB/Simulink. The results of simulation show that the simulated responses of the WT-dual-DFIG increased the power by a factor of about 14.3% compared to a WT-single-DFIG due to the use of a variable speed dual-DFIG. Finally, we can say that the WT-dual-DFIG model is strongly developed and could be applied in the coming years.

A reduced-order model for representing the reactive power response of a doubly fed wind turbine during ZVRT

Zero-voltage ride through (ZVRT) is the worst-case scenario of low-voltage ride through (LVRT), which indicates the optimal fault-response capability of wind turbines (WTs). The reactive response during ZVRT shows the dynamic performance of WTs during extreme grid faults, which greatly improves the flexibility and robustness of renewable-rich grids. The reactive response of a doubly fed (type-3) WT during ZVRT depends on the control strategy of the converter and the steady-state and transient-state performance of the doubly fed induction generator (DFIG). This paper proposes a reduced-order model for representing the reactive response of a type-3 WT during ZVRT including the control strategy of the converter and the equivalent electric circuit of the DFIG, which simplifies some complicated equations but is practical for modeling a renewable-rich power system in most cases. Some simplified expressions between the reactive energy and a single DFIG parameter are presented, which could satisfy the demands of designing a DFIG. Finally, the method of model consistency verification, the influence analysis of DFIG parameters on the reactive response, the reasonable ranges of DFIG parameters and the fault-response performance of the WT in the theoretically longest ZVRT period are also obtained for reference.

Voltage Control and Braking System of a DFIG during a Fault

This paper describes a voltage control scheme of a doubly fed induction generator (DFIG) wind turbine that can inject more reactive power to the grid during a fault so as to support the grid voltage. To achieve this, the coordinated control scheme using both rotor side converter (RSC) and grid side converters (GSC) controllers of the DFIG are employed simultaneously. The RSC and GSC controllers employ PI controller to operate smoothly. In the voltage control mode, the RSC and GSC are operated. During a fault, both RSC and GSC are used simultaneously to supply the reactive power into the grid (main line) depending on voltage dip condition to support the grid voltage. The proposed system is implemented for single DFIG wind turbine using MATLAB simulation software. The results illustrate that the control strategy injects the reactive power to support the voltage stability during a fault rapidly. Also, the braking system is designed to protect the wind turbine system from over speed. For this purpose, the braking resistors are being used.

A Practical Short-Circuit Current Calculation Method for DFIG-Based Wind Farm Considering Voltage Distribution

This paper presents a calculation method of short-circuit current (SCC) for doubly fed induction generator (DFIG)-based wind farm considering the voltage distribution characteristics. When a short-circuit fault occurs in a wind farm, a large SCC will be contributed by the dozens or even hundreds of DFIGs in the wind farm. And the security and stability of the wind farm will be affected by the SCC. The SCC characteristics of the DFIG are closely related to its post-fault terminal voltage (PFTV). Therefore, a practical calculation model of SCC in single DFIG is proposed in this paper, based on the electromagnetic transient analysis. And according to a correction method of the topological matrix for a post-fault wind farm proposed in this paper, the relationship model between voltages and currents under short-circuit faults is established. Then, the PFTVs and SCCs of the DFIGs in the wind farm can be obtained by solving the model equation. Finally, the proposed method is validated through MATLAB/Simulink-based simulation results, and a comparison with the national standard calculation method is analyzed. The results show that this method has better accuracy, which provides a more accurate basis for the electrical safety design of wind farms.

A Short-Circuit Calculation Method for DFIG-Based Wind Farms

Short-circuit calculations for wind farms are crucial for determining equipment ratings and providing basic information for protection coordination. In this paper, a practical calculation method of short-circuit currents (SCCs) is proposed for doubly fed induction generator (DFIG)-based wind farms. The improved calculation method of the SCCs in single DFIG is developed based on electromagnetic transient analysis. Combined with the traditional method of calculating the SCCs of the power system, an equivalent model of the DFIG-based wind farm used for SCCs is studied. The equivalent model and expressions for SCCs are later validated through PSCAD/EMTDC-based simulation results, and a comparison with the national standard calculation method is analyzed. The results show that the calculation method proposed in this paper has better accuracy and practicability, which are important elements in the electrical design of DFIG-based wind farms.

Integration of DFIG-Based Wind Farms Into Series-Compensated Transmission Systems

Recent events have shown that doubly-fed induction generator (DFIG) wind turbines close to series capacitors are prone to subsynchronous oscillations (SSO). This paper analyzes these subsynchronous interactions (SSI) and a countermeasure to enable a reliable and secure integration of DFIG-based wind farms into series-compensated transmission systems. A case study based on a real power system is considered in this work. It has several transmission lines (many of them series compensated), various conventional and wind power plants, and a distributed load. This system allows to study the SSI among various wind farms and multiple subsynchronous modes, unlike previous studies which considered a single DFIG and one series-compensated line (i.e., one subsynchronous mode). An analytical investigation and development of fundamental concepts of the SSO are also discussed. A supplementary damping control (SDC) is designed to enhance the operating range and to damp the SSO of these series-compensated wind farms. A detailed analysis is carried out using eigenvalues and nonlinear time-domain simulations to evaluate the performance and robustness of the SDC. Besides the parameters usually studied, such as wind speed, series compensation level, control gains, the effects of conventional synchronous generation, type of load model, and system demand level on the SSI are also analyzed.

Equivalent Modeling of DFIG-Based Wind Power Plant Considering Crowbar Protection

Crowbar conduction has an impact on the transient characteristics of a doubly fed induction generator (DFIG) in the short-circuit fault condition. But crowbar protection is seldom considered in the aggregation method for equivalent modeling of DFIG-based wind power plants (WPPs). In this paper, the relationship between the growth of postfault rotor current and the amplitude of the terminal voltage dip is studied by analyzing the rotor current characteristics of a DFIG during the fault process. Then, a terminal voltage dip criterion which can identify crowbar conduction is proposed. Considering the different grid connection structures for single DFIG and WPP, the criterion is revised and the crowbar conduction is judged depending on the revised criterion. Furthermore, an aggregation model of the WPP is established based on the division principle of crowbar conduction. Finally, the proposed equivalent WPP is simulated on a DIgSILENT PowerFactory platform and the results are compared with those of the traditional equivalent WPPs and the detailed WPP. The simulation results show the effectiveness of the method for equivalent modeling of DFIG-based WPP when crowbar protection is also taken into account.

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.

Ride-Through Capability of Grid-Connected Brushless Cascade DFIG Wind Turbines in Faulty Grid Conditions—A Comparative Study

Doubly-fed induction generator (DFIG)-based wind turbines (WTs) are reported to suffer reliability problems due to the presence of slip-rings, brushes, and the gearbox. These disadvantages encouraged several research groups to investigate the viability of employing single or double-frame brushless cascade DFIGs (BCDFIGs) in grid-connected multimegawatt WTs especially offshore and in solar chimney power plants. In this regard, this paper tackles three main issues. Initially, the expected reduction in gear ratio when BCDFIGs are used instead of DFIGs is examined from a steady state perspective. A reduction would lead to less frequent maintenance and an improved return on investment. Next, a detailed comparison between DFIG-WTs and BCDFIG-WTs under unbalanced grid voltage is presented. Finally, the extent to which a multimegawatt BCDFIG-WT is grid code compliant in terms of fault ride-through capability is studied. This is illustrated by comparing and quantifying the response of a DFIG-WT and a BCDFIG-WT to a severe three-phase voltage dip. Simulation and experimental results indicate promising behavior for BCDFIGs during disturbances.

Equivalence of Large Scale Wind Farm Based on Per-Unit System on RTDS

The paper introduces per-unit system for single Doubly-fed induction generator (DFIG) and large scale wind farm (LSWF) equivalence, based on which their modeling, including main circuit, linkage equation, power equation and rotor motion equation, are built, and equivalence method of LSWF are present. The single DFIG wind farm system and LSWF are built respectively on Real time digital simulator (RTDS). Comparing simulating results of single DFIG with those of LSWF, conclusion shows per-unit value system is correct, equivalent method is feasible.