Characteristics Of Doubly Fed Induction Generator Research Articles

Enhancing FRT capability of DFIG based on RC-crowbar considering the resonance and matching control strategies for different fault degrees

This paper compares the problems existing in the current fault ride-through (FRT) schemes of the doubly-fed induction generator (DFIG), and deeply analyzes the transient characteristics of DFIG during FRT. A comprehensive FRT scheme is proposed to improve the FRT capability by using an RC-crowbar and matching control strategy switching. The main innovation of this scheme lies in the consideration of resonance and other factors in the capacitance design of the RC-crowbar. To ensure that the DFIG still has good FRT capability after the RC-crowbar is cut off in advance in the later stage of FRT, an improved rotor side converter (RSC) control strategy is proposed for this situation. At the same time, to balance the reactive power on the stator side and accelerate the recovery of stator voltage throughout the entire FRT period, the control strategy of the grid side converter (GSC) is also improved. The comprehensive FRT scheme proposed in this paper can dynamically switch based on the degree of fault so that it still has good FRT ability when applied to different degrees of faults. Finally, the correctness and effectiveness of the proposed comprehensive FRT scheme were verified through simulation experiments.

Research on harmonic impedance characteristics of doubly-fed induction generator

Research on harmonic impedance characteristics of doubly-fed induction generator

Implementation and analysis of mono inverter-battery configuration for wind driven doubly fed induction generator

ABSTRACT This paper investigates the controller implementation and analysis of Doubly Fed Induction Generator (DFIG) for powering isolated loads in rural electrification. A simple speed sensorless algorithm-assisted controller for isolated power supply of DFIG has been proposed using a digital controller and voltage source converter at the rotor terminals of the generator. The controller can automatically correct the voltage and frequency of the rotor side inverter pulse to obtain a desired voltage and frequency at stator side despite the variations in the wind speed and load. A hardware prototype of the system has been built and tested on a prototype machine, which is driven by an emulated wind turbine under sub-synchronous and super-synchronous speed operations. The detailed results of both simulated and hardware waveforms are provided in the paper to demonstrate the working of the proposed topology and embedded control scheme. Further, the performance characteristics of DFIG are modeled and verified experimentally. A good agreement exists between theoretical and experimental results.

Influence of doubly-fed induction generator on power system oscillation center migration

With the proposal of the goals of carbon peaking and carbon neutrality, China’s power grid is moving towards low-carbon transformation. As a result, the power grid is increasingly affected by the dynamic response characteristics of renewable energy. This paper analyzes the Out-of-step Oscillation center characteristics of wind power connected to the power grid. And it establishes the equivalent model of three-machine system. Then we connects the equivalent model of Doubly-fed induction generator to the system. Based on the dynamic response characteristics of Doubly-fed induction generator, we study the expression of oscillation center position when the power system is in oscillation state. And we explore the influence on the migration of Out-of-step Oscillation center when the wind turbine is connected to the system. Finally, the conclusion is verified in IEEE-9 system.

Impact of Actual Wind Speed Distribution on the Fault Characteristic of DFIG Rotor Winding Asymmetry

Studies show that in industrial wind turbines (WTs), the wind speed may significantly vary across the rotor disk area. This variation may originate from different parameters, including wind shear (WS) and tower shadow (TS), which affect the mechanical load and the generated electrical power. However, the influence of wind speed variation on the fault characteristics of WTs has rarely been investigated so far. As an improvement, this study made an attempt to investigate the impact of spatiotemporal distribution (STD) of wind speed on the fault characteristic of the doubly fed induction generator (DFIG). The primary contribution of this article lies in two aspects: 1) establishment of a new equivalent wind speed (EWS) model comprehensively considering the affecting parameters, including WS, TS, and turbulence, and 2) reanalysis of the rotor winding asymmetry (RWA) fault characteristics under EWS, and thus new characteristics of fault were obtained. Simulations and experiments were also carried out to evaluate the accuracy of the theoretical analysis. The obtained results reveal that in addition to the original characteristic frequency, which is correlated with RWA fault, other modulation frequencies are also correlated with wind speed distribution. It is concluded that the RWA fault characteristics of DFIG are different from those of the ordinary induction generator considering the STD of the wind speed. Importantly, the obtained results are expected to improve the fault diagnosis of DFIG.

Modeling and Analysis of Transient Reactive Power Characteristics of DFIG Considering Crowbar Circuit under Ultra HVDC Commutation Failure

Ultra high voltage direct current (UHVDC) transmission is an effective means of long-distance transmission of renewable power generation, which has obtained a lot of research and practical applications. The commutation failure is a common DC transmission fault, which will cause the voltage amplitude of the sending ac grid in UHVDC system to first decrease then increase. The existing transient mathematical models of the wind power generation system (WPGS) are difficult to apply to scenarios where the grid voltage changes continuously. A mathematical model suitable for commutation failure is established to analyze the transient reactive power characteristics of the doubly fed induction generator (DFIG)-based WPGS with the consideration of the crowbar circuit trigger. The correctness of the mathematical model is validated by an experiment based on the control hardware-in-loop (CHIL) platform. Based on the proposed mathematical model, the influence of the crowbar parameters on the reactive power output of the DFIG is analyzed, and the selection of crowbar parameters to suppress the overvoltage of the sending ac grid is investigated. A simulation model is built based on Matlab/Simulink to verify the overvoltage suppression effect of the proposed selection scheme.

Analysis of the influence of different control modes on the transient power characteristics of DFIG

In the event of failure, the doubly-fed Induction Generator (DFIG) with low voltage ride through (LVRT) ability will have different effects on the parallel network characteristics due to the different control mode. In order to analyze the influence of different control modes on the transient power characteristics of DFIG, three kinds of transient response states of wind power system under grid fault are modeled by using power superposition principle based on RSC / GSC controller sampling link and PWM small inertia link, and the accurate transient power response models of different control modes are obtained. The accuracy of the model is verified by simulation with PSCAD/EMTDC, and the influence of control mode on system frequency stability is analyzed.

An Electromagnetic Transient Analysis Model for DFIG Considering LVRT Hardware Protection

Crowbar protection and chopper protection (CCP) are commonly used hardware protection measures in the process of low voltage ride through (LVRT) of doubly-fed induction generator (DFIG). The protections operating states during fault have an important influence on the electromagnetic transient (EMT) process of DFIG. Therefore, different from only considering the influence of single protection, the coordinated control of crowbar protection and chopper protection are further considered in this paper, and a novel analysis method of CCP operation criterion is proposed by analyzing the relationship between rotor current, DC-link voltage and post-fault terminal voltage (PFTV) of DFIG. On this basis, the states of CCP under different voltage drop depths are analyzed. And an EMT analysis model of DFIG considering CCP is studied. The proposed method and EMT analysis model for DFIG are later validated through PSCAD/EMTDC-based simulation results. The results show that the method and model proposed in this paper have good accuracy and practicability, which provides more references for further study of the transient characteristics of DFIG.

A New Approach for Protecting TCSC Compensated Transmission Lines Connected to DFIG-Based Wind Farm

Thyristor-controlled series capacitor (TCSC) compensated transmission lines (TLs) are increasingly used in recent years for transmission of bulk power generated by doubly fed induction generator (DFIG) based large scale wind farms. However, the typical fault characteristics of DFIG and TCSC affect the performance of conventional distance relays. To solve the problem, in this article, a new relaying algorithm is proposed that utilizes sign of the half-cycle superimposed positive-sequence current for fault detection, empirical mode decomposition assisted random forest classifier for fault classification and modified impedance approach for fault location estimation. The performance of the proposed relaying algorithm is evaluated on various fault and nonfault cases generated on a test power system using MATLAB/Simulink and OPAL-RT (OP4510) manufactured real-time digital simulator environment. Also, compared with few existing approaches. The demonstrated results justify the merits of the proposed relaying algorithm for protecting the TCSC compensated TL connected with DFIG-based wind farm.

Impedance Modeling and Analysis for DFIG-Based Wind Farm in SSO Studies

Several models were developed in the literatures for studying the system impedance characteristics during sub-synchronous oscillations (SSO). However, the doubly-fed induction generator (DFIG) impedance presents a 2 × 2 matrix with the frequency coupling component at the off-diagonal position, which increases the difficulty for analyzing the impedance characteristics of DFIG. The coupling effect in this case is caused by the asymmetric impedance characteristics of controllers, which are composed of voltage source converters (VSCs). Accordingly, simplifications are often conducted to decouple the impedance matrix into single sequences. Outer loop controller and phase-locked loop (PLL), which are often neglected in simplifications, are the main causes of the asymmetry of impedance matrix. Such simplifications could also hamper proper system stability analyses. In this paper, a comprehensive impedance model is proposed in which the outer loop controller, PLL, and grid-side controller (GSC) are all considered. The proposed comprehensive impedance model can provide exact stability data, in which stable boundaries for compensation level and transmission distances are presented. Furthermore, the proposed model is converted to simplified models in which the impacts of outer loop controller, PLL, GSC and coupling components on boundary stability of SSO are analyzed. The results are validated by time domain simulations and eigenvalue analyses, and deviations of the simplified models are analyzed for different operating parameters and conditions leading to simplifications.

Direct Power Control Optimization for Doubly Fed Induction Generator Based Wind Turbine Systems

This study presents an intelligent metaheuristics-based design procedure for the Proportional-Integral (PI) controllers tuning in the direct power control scheme for 1.5 MW Doubly Fed Induction Generator (DFIG) based Wind Turbine (WT) systems. The PI controllers’ gains tuning is formulated as a constrained optimization problem under nonlinear and non-smooth operational constraints. Such a formulated tuning problem is efficiently solved by means of the proposed Thermal Exchange Optimization (TEO) algorithm. To evaluate the effectiveness of the introduced TEO metaheuristic, an empirical comparison study with the homologous particle swarm optimization, genetic algorithm, harmony search algorithm, water cycle algorithm, and grasshopper optimization algorithm is achieved. The proposed TEO algorithm is ensured to perform several desired operational characteristics of DFIG for the active/reactive power and DC-link voltage simultaneously. This is performed by solving a multi-objective function optimization problem through a weighted-sum approach. The proposed control strategy is investigated in MATLAB/environment and the results proved the capabilities of the proposed control system in tracking and control under different scenarios. Moreover, a statistical analysis using non-parametric Friedman and Bonferroni–Dunn’s tests demonstrates that the TEO algorithm gives very competitive results in solving global optimization problems in comparison to the other reported metaheuristic algorithms.

Fault ride through strategy of DFIG using rotor voltage direct compensation control under voltage phase angle jump

Wind power has developed rapidly in recent years, and large-scale wind power facilities connected to power grids will bring many new challenges. Some new operation characteristics of power grids with doubly-fed induction generator (DFIG) may exhibit, for example voltage phase angle jumps (VPAJ). VPAJ can negatively impact the fault ride through (FRT) performance of DFIG. This paper firstly investigates the physical mechanism and the operation characteristics of DFIG with VPAJ. It is noted that the current control strategies designed for voltage amplitude changes are not suitable for VPAJ. Secondly, the paper develops an FRT optimization control strategy under VPAJ which optimizes the DFIG operation characteristics. Finally, simulations of a 250 MW wind farm are presented which validate the proposed FRT strategy.

Fault Overload Control Method for High-Proportion Wind Power Transmission Systems Based on Emergency Acceleration of Doubly-Fed Induction Generator

With a high proportion of wind power being transmitted through ac and dc lines, a new power grid pattern has gradually emerged. A dc inverter is prone to commutation failure, which may lead to cascading trip of ac lines for overload, resulting in serious consequences. However, existing control methods have problems of over- or under-shedding and are unsuitable for high-proportion wind power transmission systems. Accordingly, a new fault overload control method based on emergency acceleration of doubly fed induction generator (DFIG) is proposed. The fast power control capability of DFIG is fully utilized; the active power of power grid could be rapidly balanced. First, the fault characteristics of a wind power ac/dc transmission system under the fault of dc receiving-end grid are analyzed, and the power flow transfer after self-recovery from the dc commutation failure is derived. Second, by analyzing the power characteristics of DFIG, a fault overload control idea of the wind power transmission system is proposed based on emergency acceleration of DFIG. At last, the maximum controllable capacity of a wind farm is analyzed, and a fault overload control strategy of the wind power transmission system is proposed. The simulation results prove that the proposed method can rapidly reduce the output of wind farms and prevent the overload of ac lines.

Effect of PLL on transient performance of wind turbines generator under voltage phase jump

With the increasing proportion of wind power installed capacity, the influences of transient characteristics of wind turbines generator on safety and stability of power grid is becoming more and more important. The rotor side of doubly fed induction generator (DFIG) is connected to the grid through a back-to-back inverter, and vector control based on phase-locking synchronisation is used generally. Phase-locked loop (PLL) drive internal potential phase changes to achieve synchronous operation with the grid. Therefore, PLL has great influence on transient characteristics of DFIG. A dynamic model of PLL is built in this study. Phase-locking performance of PLL under voltage phase jump is studied by changing its parameters, and its impact mechanism on transient characteristics of DFIG is proposed. Simulation models are built with DIgSILENT/PowerFactory. The influence of parameters of PLL on phase-locking performance of DFIG under voltage phase jump is simulated.

Mechanism Research on the Influence of Large Scale Wind Power Integration on Power System Angle Stability

Base on the equivalent external characteristics of doubly-fed induction generator (DFIG) during the period of the fault and the power characteristic equation of delivery system, a novel method of eliminating equivalent mutual impedance is proposed to research the influence mechanism of different wind power penetration rate, the SG dispatch pattern and siting of wind farms on system transient power angle stability (TPAS) under fault condition are researched. The results show that system power angle characteristics are improved with the increase of the wind power scale. However, when the wind power scale reaches a certain level, the power angle stability promptly deteriorates. The distance of wind farms siting away from a SG group with leading power angle, as well as the generation reduction of the SG group, plays an important role in the improvement of TPAS. The effectiveness of the proposed method is verified by the numerical simulations of the two-machine power system.

The Primary Frequency Control Method of Tidal Turbine Based on Pitch Control

Due to the increasing penetration level of tidal power in power system, the tidal turbines can provide less frequency support than conventional generators due to their small rotor mass. This makes the power system with low inertia and cause frequency problem. This paper presents a simulation model of a tidal power farm based on a MW-level variable speed tidal turbine with doubly-fed induction generator (DFIG) developed in the simulation tool of Matlab/Simulink. According to the reserve capacity required for primary frequency control, a de-loading control method is proposed in this paper to resolve the issue of primary frequency control via tidal power plant. Based on the analysis method of the frequency control characteristics of DFIGs, it is proposed by improved variable pitch control method. The control strategy, which is based on pitch control system of tidal turbine, is proposed in order to participate into primary frequency regulation of power system. Simulation results show that the proposed control strategy is effective means the tidal turbines with DFIG generators could providing frequency support for power system when they are working under the de-loading condition in this paper.

Research on Short Circuit Current Characteristics of Doubly-fed Wind Power Generator Considering Converter Regulation

When fault occurs in the grid, the short circuit characteristics of doubly-fed induction generator (DFIG) are more complicated due to the coupling influence of generator electromagnetic transient and converter regulation. In view of this problem, a DFIG stator/rotor short circuit current calculation method considering the transient regulation of both rotor-side and grid-side converters is proposed in this paper. First, DFIG fault equivalent network considering the rotor-side converter control is established, and the analytical expressions of stator/rotor currents in this network are derived. On this basis, considering the DC bus voltage fluctuation, the double-loop transient control process of the gird converter in the short circuit process is described quantitatively. Thus, the mechanism of the second harmonic in the stator short circuit current is revealed, and the expression of the harmonic component is derived. Finally, the analytical expressions of stator and rotor short circuit full currents are obtained. Simulation results verify the correctness and feasibility of the proposed method.

Adaptation virtual inertia control strategy of DFIG and assessment of equivalent virtual inertia time constant of connected power system

As the mechanical parts of doubly fed induction generator (DFIG) are decoupled from electrical part, the total equivalent rotary inertia of power system are decreased with growing continuously of wind power penetration, which will bring pressure to frequency stability of system. On the basis of analysing operation and control characteristics of DFIG, the equivalent virtual inertia time constant of DFIG, wind farms based on DFIG, and connected power system was calculated. A virtual inertia control strategy of DFIG using rotor current direct control based on equivalent virtual inertia time constant was proposed. The proposed virtual inertia control strategy of DFIG includes traditional control function module, status assessment module, and additional virtual inertia control module. The time domain simulation was carried out on the basis of theoretical analysis, the simulation results show that the proposed virtual inertia control strategy of DFIG can provide efficacious frequency support to the power grid at all kinds of operating conditions, and the frequency stability of power system with large-scale wind power was improved.

Improved Control Strategy of Wind Turbine with DFIG for Low Voltage Ride through Capability

As the number of doubly fed induction generator (DFIG)- based wind-turbine systems continues to increase, wind turbines are required to provide Low Voltage Ride-Through (LVRT) capability, especially under the condition of grid voltage dips. This paper, depending on the operating characteristics of doubly-fed induction generator during grid faults ,deals with a protection and control strategy on rotor-side converter (RSC) to enhance the low voltage ride through capability of a wind turbine driven doubly fed induction generator (DFIG). The simulation and experiment studies demonstrate the correctness of the developed model and the effectiveness of the control strategy for DFIG-based wind-turbine systems under such adverse grid conditions.

Study of Fault Current Characteristics of the DFIG Considering Dynamic Response of the RSC

During nonsevere fault conditions, the crowbar protection is not activated and the rotor windings of a doubly fed induction generator (DFIG) are still excited by the ac/dc/ac converter. In these cases, the dynamic response of a rotor-side converter (RSC) has a large influence on the fault current characteristics of the DFIG. In this paper, an analysis method for the fault current characteristics of the DFIG under nonsevere fault conditions is proposed. First, the dynamic response of the RSC is analyzed on condition that the external power control loop is shut down and the reference signals of the inner rotor current control loop are kept constant. Then, the simplified calculation models of the rotor fault current are established according to different design principles of the inner rotor current controller. Based on it, the fault characteristics of the stator current are studied and the analytical expressions of the stator fault current are obtained. Finally, digital simulation results validate the analytical results. The proposed analysis method is applicable for the study of fault current characteristics of DFIG with different control strategies for low-voltage ride through. The research results are helpful to the construction of adequate relaying protection for the power grid with penetration of DFIGs.