Coordinated Damping Control Design for DFIG-Based Wind Generation Considering Power Output Variation

The power system small signal stability analysis considering wind generation intermittence is studied comprehensively in this paper. The modelling of doubly‐fed induction generator (DFIG) involving the converters with application of stator flux‐oriented vector control strategy is addressed briefly. In order to reveal how the intermittent nature of wind power affects the operating behaviour of an existing power system, a probabilistic small signal stability analysis method based on Monte Carlo simulation technique is proposed to explore and exploit the impact of intermittent grid‐connected wind power on small signal stability. The IEEE New England test system is applied as benchmark to verify the proposed model and approach. Total 3 scenarios are elaborately designed to figure out the potential relationship between the small signal stability indices and the wind generation intermittence. Finally, some preliminary conclusions and comments were drawn based on the numerical simulation results. Copyright © 2010 John Wiley & Sons, Ltd.

This paper focuses on developing a novel algorithm which dynamically optimizes the controllers of doubly fed induction generator (DFIG) driven by a wind turbine (WT) to increase DFIG transient performance in all wind speed conditions. Particle swarm optimization (PSO) is proposed to optimize parameters of PI controllers of DFIG's rotor side/grid side converters (RSC/GSC) at different wind speeds in order to maximize the damping ratios of the system eigenvalues in small signal stability analysis. Based on the optimal values and the wind speed data set, an artificial neural network (ANN) is designed, trained, and it has the ability to quickly forecast the optimal values of parameters. Adaptive PI controllers (including ANN) are designed which dynamically change PI gain values according to different wind speeds. Simulation is done via PSCAD software for a single machine connected to an infinite bus (SMIB) system. The results show that the DFIG of ANN-based adaptive PI control could significantly contribute in the transient performance improvement in a wide wind speed range.

The Vector controlled doubly fed induction generator (DFIG) wind energy system in a multi-machine power system is very sensitive to faults on transmission lines and thus affects the stability of the system. The performance of vector controlled DFIG highly depends on PI controller parameters. The objective of this paper is to optimize the performance of vector controlled DFIG in multi-machine power systems under faulty conditions by tuning the parameters using advanced differential evolution algorithm. An objective function is formulated, which drives the system with good voltage profile, reduced power oscillations under faulty conditions. The parameters of PI controller are tuned using Composite Differential Evolution algorithm. Simulations are performed on a two area benchmark problem in Matlab/Simulink. The simulation results of the optimized DFIG wind energy system are compared with the actual existed system. The simulation results show that the overall performance and stability of the optimized system are enhanced.

The increasing penetration of a renewable energy in the power system grid makes it one of the most important topics for generating electricity for the near future. Tidal currents energy is one of the most technologies growing rapidly for generating electric energy. This paper deals with the small signal stability analysis of the tidal current turbine using two different types of generators, doubly fed induction generator (DFIG) and direct drive permanent magnet synchronous generator (DDPMSG) for a single machine infinite bus system. DFIG and DDPMSG are tested for small signal stability analysis. The eigenvalues of the overall system show the advantages of using the DDPMSG over the DFIG.

Much attention has been continuously paid on the model development and stability analysis of the doubly fed induction generator (DFIG) widely applied in wind power generation. Similarly, this study develops the form-standardised state-space model in the dq reference frame of the DFIG with stator winding inter-turn fault (SWITF). Compared with those previously developed, it is definitely preferable for the simulation and stability analysis of the DFIG with SWITF due to its standard form. Moreover, for the DFIG with SWITF working in stator-voltage-oriented control frame, the small-signal stability analysis is conducted using MATLAB simulation, yielding the conclusion that SWITF will never eradicate the DFIG's small-signal stability but deteriorate it to some extent. This conclusion is further validated by means of the Lyapunov stability theory. As a kind of contribution of this study, the analytical expressions of the eigenvalues of the DFIG with SWITF are derived. Case study based on an MATLAB/Simulink demo routine is completed to demonstrate the validity of the model development and small-signal stability analysis of the DFIG with SWITF.

With the increase in penetration level of wind generation in modern electrical power systems, the accurate analysis of transient stability of wind turbine will become more crucial. For this purpose, an appropriate model of doubly fed induction generator (DFIG) for transient stability analysis is required. This paper focuses on the development of approximate model of DFIG for the determination of transient stability using transient energy functions (TEF). The transient stability of the wind turbine during three phase short circuit fault is simulated for a 2-machine test system to verify the effectiveness of TEF for determining the stability of the power system.

Small signal stability analysis and control of the wind turbine with the direct-drive permanent magnet generator integrated to the grid

This paper establishes a closed-loop interconnected dynamic model of a power system with a doubly fed induction generator (DFIG) for wind power generation, wherein, the DFIG and power system are modeled as two open-loop interconnected subsystems. The established model indicates that the impact of the dynamic interactions introduced by the DFIG on the power system's small-signal angular stability is the difference between the closed-loop and open-loop electromechanical oscillation modes (EOMs). The analysis conducted in this study reveals that when an open-loop DFIG oscillation mode (DOM) is close to an open-loop EOM on the complex plane, the modal coupling of the open-loop EOM and DOM can cause strong dynamic interactions between the DFIG and the power system; thus, the DFIG has a significant impact on the power system's small-signal angular stability. An example multimachine power system with grid-connected DFIGs is presented to demonstrate and validate the analysis and conclusions made in the paper.

Doubly fed induction generator (DFIG) based variable speed wind generator is vulnerable to any sort of grid fault, as the stator of the DFIG is directly connected to the grid. Likewise the symmetrical faults, the asymmetrical faults also may cause the DFIG face high mechanical stress which may lead to mechanical damage. Therefore, it is very important to investigate the fault ride through (FRT) capability of the DFIG system during the asymmetrical fault situations. In this work, in order to enhance the FRT capability of the DFIG based wind generation system, a DC resistive superconducting fault current limiter (SFCL) is proposed. The performance of the DC resistive SFCL is compared to that of the bridge type fault current limiter (BFCL). Simulations are accomplished by using the Matlab/Simulink software. Simulation results clearly indicate that the proposed DC resistive SFCL improves the FRT ability of the DFIG based variable speed wind generator system during any type of asymmetrical faults in the power network. Also, the performance of the proposed method is better than that of the BFCL.

This paper proposes an advanced control strategy for DFIG based Wind Turbine. The designed method is based on a combination of Particle Swarm Optimization (PSO) and Artificial Neural Network (ANN). PSO combined ANN is suggested to track the available maximum power point (MPPT) at varying wind speeds. Thus, PSO is used to improve the dynamic performance of Doubly Fed Induction Generator (DFIG) by optimizing its Proportional Integral (PI) controller gains. This work highlights the performance of the PSO optimized PI controller against classical one. The proposed control strategy is verified via 2 MW DFIG-WT using the MATLAB/Simulink environment. The obtained results validate the proposed PSO-PI as an effective tool for improving the dynamic behavior of DFIGWT, it reveals that the overshoots are reduced by 50 % compared to the classical PI. In addition, a faster transient response is achieved using the proposed control strategy.

Modelling Analysis in Power System Small Signal Stability with Grid-Connected Wind Farms of DFIG Type

Large-scale integration of Wind Generators (WGs) with distribution systems is underway right across the globe in a drive to harness green energy. The Doubly Fed Induction Generator (DFIG) is an important type of WG due to its robustness and versatility. Its accurate and efficient modeling is very important in distribution systems planning and analysis studies, as the older approximate representation method (the constant PQ model) is no longer sufficient given the scale of integration of WGs. This thesis proposes a new three-phase model for the DFIG, compatible with unbalanced three-phase distribution systems, by deriving an analytical representation of its three major components, namely the wind turbine, the voltage source converter, and the wound-rotor induction machine. The proposed model has a set of nonlinear equations that yields the total three-phase active and reactive powers injected into the grid by the DFIG as a function of the grid voltage and wind turbine parameters. This proposed model is integrated with a three-phased unbalanced power flow method and reported in this thesis. The proposed method opens up a new way to conduct power flow studies on unbalanced distribution systems with WGs. The proposed DFIG model is verified using Matlab-Simulink. IEEE 37-bus test system data from the IEEE Distribution System sub-committee is used to benchmark the results of the power flow method.

Background: With the large-scale Doubly Fed Induction Generator (DFIG) wind turbine integrated into the power system, the DFIG inertia response of the wind turbine should be provided. Also, the frequency response should be similar to the conventional generation technologies. This paper investigated the influence of frequency response term and wind speed conditions on system frequency control. Methods: The specific operating conditions of four control strategies, including inertia control, droop control, over speed control and pitch angle control were researched in this paper. Multi-factor coordinated frequency control strategy of DFIG wind turbine was established based on the above researches. The strategy was composed of wind speed ranging from low to high. Results: According to the simulation results, the DFIG wind turbine, which was based on multifactor coordinated frequency control strategy, could respond to the system’s frequency change of power grid, effectively. Conclusion: It helps system frequency return to stable states better and faster than DFIG wind turbine and also could reduce the fluctuation of system frequency.

Wind farm grid codes require wind generators to ride through voltage sags, which means that normal power production should be re-initiated once the nominal grid voltage has been recovered. Doubly Fed Induction Generator (DFIG) based wind farm is gaining popularity these days because of its inherent advantages like variable speed operation and independent controllability of active and reactive power over conventional Induction Generator (IG). This paper proposes a new control strategy using DFIGs for stabilizing a wind farm composed of DFIGs and IGs. Simulation analysis by using PSCAD/EMTDC shows that the DFIGs can effectively stabilize the IGs and hence the entire wind farm through the proposed control scheme by providing sufficient reactive power to the system.

A quick post fault recovery of wind generator system could be achieved with the help of a series dynamic braking resistor (SDBR). This paper investigates the dynamics, size, optimal location of a series dynamic braking resistor in the doubly fed induction generator (DFIG) structure based on different switching strategy of the braking resistor. Three signals were investigated in switching the SDBR during transient conditions of the DFIG wind generator; the DC-link voltage, rotor current and grid voltage, respectively. Also, three locations were considered in connecting the SDBR in the DFIG system; the stator, rotor and grid side converter, respectively. Furthermore, the optimum size and best insertion time of the SDBR were investigated based on the most effective performance of the SDBR scheme considering its switching signal and position in the DFIG system. Simulations were run in power system computer-aided design and electromagnetic transient including DC (PSCAD/EMTDC). The results show that when the SDBR is connected to the DFIG, improved performance was achieved; however, the stator based SDBR topology in conjunction with a grid voltage actuating signal, fast insertion time and short duration of operation quickly recovered the DFIG wind generator variables during transient conditions.