Integration Of Doubly-fed Induction Generator Research Articles

Enhancing transient stability and dynamic response of wind-penetrated power systems through PSS and STATCOM cooperation

The large-scale integration of doubly-fed induction generator (DFIG) based wind power plants poses stability challenges for power system operation. This study investigates the transient stability and dynamic performance of a modified 3-machine, 9-bus Western System Coordinating Council (WSCC) system. The investigation was conducted by connecting the DFIG wind farm to the sixth bus via a low-impedance transmission line and installing power system stabilizers (PSSs) on all automatic voltage regulators (AVRs). A three-phase fault simulation was carried out to test the system, with and without power system stabilizers and a static synchronous compensator (STATCOM) device. Time-domain simulations demonstrate improved transient response with PSS-STATCOM control. A 50% reduction in settling time and 70% decrease in power angle undershoots at the slack bus are achieved following disturbances, even at minimum wind penetration levels. Load flow analysis shows the coordinated controllers maintain voltages within 0.5% of nominal at 60% wind penetration, while voltages at load buses can deviate up to 15% without control. Eigenvalue analysis indicates the PSS-STATCOM boosts damping ratios of critical oscillatory modes from nearly 0% to over 30% under high wind injection. Together, the present findings provide significant evidence that PSS and STATCOM cooperation enhances dynamic voltage regulation, angle stability, and damping across operating ranges, thereby maintaining secure operation in systems with high renewable integration.

Dynamic Performance Analysis of a Grid-Connected Doubly-Fed Induction Generator

In the field of wind energy, the doubly fed induction generator (DFIG) is commonly used in variable speed wind energy conversion systems (WECS). This paper presents a review of various topologies, configurations, power converters and control schemes used with the operation of the DFIG. The operation of DFIG based on both slip ring and brushless arrangement has been discussed. The grid integration of DFIG and its influence on system stability, system reliability, power quality and power transmission is reviewed.

Improving low-voltage ride-through capability of a multimegawatt DFIG based wind turbine under grid faults

Large integration of doubly-fed induction generator (DFIG) based wind turbines (WTs) into power networks can have significant consequences for power system operation and the quality of the energy supplied due to their excessive sensitivity towards grid disturbances. Under voltage dips, the resulting overcurrent and overvoltage in the rotor circuit and the DC link of a DFIG, could lead to the activation of the protection system and WT disconnection. This potentially results in sudden loss of several tens/hundreds of MWs of energy, and consequently intensifying the severity of the fault. This paper aims to combine the use of a crowbar protection circuit and a robust backstepping control strategy that takes into consideration of the dynamics of the magnetic flux, to improve DFIG’s Low-Voltage Ride Through capability and fulfill the latest grid code requirements. While the power electronic interfaces are protected, the WTs also provide large reactive power during the fault to assist system voltage recovery. Simulation results using Matlab/Simulink demonstrate the effectiveness of the proposed strategy in terms of dynamic response and robustness against parametric variations.

DFIG Active Damping Control Strategy Based on Remodeling of Multiple Energy Branches

Concerning subsynchronous oscillation caused by the integration of doubly-fed induction generator (DFIG) to power grid via series compensation line, an active damping control strategy based on remodeling of multiple energy branches in DFIG is proposed. First, according to the flow path of oscillation components, energy branches in DFIG are divided. Second, potential energy and dissipation energy are defined characterizing accumulation and consumption of energy during oscillation. Then, by analyzing the contribution of energy branches to potential energy and dissipation energy, key energy branches affecting the stability of system are screened. On this basis, the relations among stator voltage, potential energy, and dissipation energy are established, and frequency-dependent energy compensation functions in key branches are derived. By assessing their impact on low voltage ride through (LVRT) performance of DFIG, the compensation branch compatible with DFIG fundamental frequency characteristics are screened. Then, take sub/supersynchronous frequency stability coefficient ratio as the objective function, and the requirement on stability in sub/supersynchronous frequency band as the constraints. The compensation branch parameter optimization scheme is established. Finally, a test system is built in RT-LAB for verification. Simulation results demonstrate that, the proposed strategy can realize active damping control in multiple oscillation cases, and guarantee the stability of system in full frequency band. Besides, the strategy does not affect LVRT performance of DFIG and is well compatible with DFIG fundamental frequency characteristics.

Steady State and Transient Analysis of FSIG and DFIG Integration to Grid for Different Penetration Levels using VSC-HVDC

Among all the Renewable Energy Sources Wind energy is the fastest growing energy source over the last decade mainly due to crucial developments of technology in wind energy. Nowadays, the penetration of wind energy is increasing in many countries in the world including India. The power system stability with large penetration of wind power is a concern for many electrical utilities. The common technical issues with increased penetration of wind energy are voltage and reactive power control, frequency control and Low Voltage Ride Through (LVRT) capability. The VSC-HVDC system with its benefit of independent control of active and reactive power promises to enhance the system stability at high penetration levels. The maximum wind penetration levels in to the grid is analysed for Fixed Speed Induction Generator (FSIG) & Doubly Fed Induction Generator (DFIG). The penetration levels are further enhanced by considering the evacuation of wind power with VSC-HVDC system without losing system stability. Different controllers for VSC-HVDC system are used to improve the stability and LVRT capability. Standard Benchmark System is considered, and the simulations are performed by using power system simulation software SIMPOW. Results shows that wind power evacuated through VSC-HVDC system has better stability and LVRT Capability compared to AC system at high wind penetration levels.

Equipment-Level Locating of Low Frequency Oscillating Source in Power System With DFIG Integration Based on Dynamic Energy Flow

In view of the complex correlation between Doubly Fed Induction Generator (DFIG) internal components and control links which makes it difficult to locate the oscillating source in the equipment level, a DFIG equipment-level oscillating source locating method based on dynamic energy flow is proposed. Firstly, the energy correlation topology network of DFIG internal components and control links is constructed. On this basis, the analytical expressions of dynamic energy flows of DFIG internal components and control links are derived. And then, through Partial Directional Coherence (PDC) analysis, the values of causality between dynamic energy flows of DFIG internal components and control links are calculated, and the diagram of DFIG internal oscillation transmission causality is depicted. Thus according to the distribution pattern of causality values in the causality diagram, the oscillation transmission route is identified and the oscillating source is located. Finally, simulation tests in Real Time Digital Simulator (RTDS) of IEEE 10-machine 39-bus system verify that, the proposed method can quantitatively describe the intensity of interaction between dynamic energy flows of DFIG internal components and accurately identify the oscillation transmission route and the oscillating source in the equipment level. The proposed method can accurately track the original control link/physical component that causes the system to oscillate. Therefore, this paper will facilitate research on DFIG parameter tuning and oscillation suppression measures for low-frequency oscillation in power system.

Stability Assessment of DFIG Subsynchronous Oscillation Based on Energy Dissipation Intensity Analysis

Concerning the subsynchronous oscillation caused by the integration of doubly-fed induction generator (DFIG) to the power grid via the series compensation circuit, a method to assess the stability of subsynchronous oscillation based on the dissipation intensity is proposed in this article. First, the transient energy that DFIG generates in one oscillation period is defined as the dynamic energy of DFIG, and the model of DFIG dynamic energy containing internal control and external networks is constructed. And then, according to the Lyapunov stability theory, the negative gradient of dynamic energy is defined as the dissipation intensity, which reflects the dissipation effect of DFIG on the energy generated during oscillation. On this basis, the effect of the series compensation degree, phase-locked loop, and converter control parameters on subsynchronous oscillation is assessed, and real-time assessment of the stability level of DFIG-integrated power system is realized. Finally, a simulation model is built in RT-LAB to verify the proposed method. Simulation results demonstrate that the stability level of the system can be assessed accurately according to the value of dissipation intensity. When the value of dissipation intensity is positive, system oscillation converges. When the dissipation intensity is zero, the system oscillates with constant-amplitude oscillation. When the value of dissipation intensity is negative, system oscillation diverges.

Fault-Tolerant Voltage Source Converter for Wind-Driven Doubly Fed Induction Generator Connected to a DC Load

This paper presents a fault-tolerant Voltage Source Converter (VSC) for Field Oriented Control (FOC) of a stand-alone Doubly Fed Induction Generator (DFIG) connected to a DC load. In the proposed topology, the stator of the DFIG is connected to a DC load through a diode rectifier, while the rotor is connected to the DC load through a VSC. This topology allows the integration of DFIG in the hybrid system with other sources of production and storage, such as photovoltaic system, connected to the same DC bus. The fault-tolerant VSC consists in incorporating a fourth leg to replace the faulted leg. A fault detection scheme for switch device open-circuit faults is proposed in this study. The novelty of this method consists in analyzing the rotor currents within normal and faulty operating modes. Simulation results are presented for a 3.7[Formula: see text]kW DFIG-DC system with single open-circuit faults that validate the methods presented in this study. The effectiveness of the proposed fault detection method has been validated experimentally by using dSpace DS1104 control board based on TMS320F240 real time Digital Signal Processor (DSP).

Model order reduction analysis of DFIG integration on the power system small‐signal stability considering the virtual inertia control

In view of the problem that the detailed model of doubly-fed induction generator (DFIG) considering virtual inertia control is high ordered and difficult to analyse, a reduced-order model for DFIG that is applicable to small-signal stability analysis is presented. First, according to the attenuating speed of each state variable, the dynamic characteristics of different components of DFIG are explored from the time scale perspective. On this basis, considering the electromechanical coupling characteristic of DFIG, the third-order simplified model retaining the dynamic of virtual inertia control and phase-locked loop is derived. Moreover then, the dynamic model of inter-connected system with reduced-order model integration is established. Finally, the attenuation time constant of each state variable of DFIG detailed model is calculated. Simulation tests on the New England 10-generator 39-bus test system verify that compared with detailed model of DFIG, the presented reduced-order model could reflect the dynamic characteristics of power system under small-signal disturbance more accurately, with greatly reduced computation amount.

Research on the Impact of DFIG Virtual Inertia Control on Power System Small-Signal Stability Considering the Phase-Locked Loop

Doubly fed induction generator (DFIG) wind turbines with virtual inertia control are coupled to power system in dynamic characteristics, and the control input of virtual inertia control is directly affected by the tracking ability of phase-locked loop (PLL). Thus, it is urgent to study the impact of DFIG wind turbines with virtual inertia control on power system small-signal stability considering the effects of PLL. First, based on DFIG operation characteristic and control strategy, a small-signal model of interconnected system with DFIG integration considering PLL and virtual inertial control is established. Second, the attenuation time constants of DFIG state variables are calculated, and according to the attenuation speeds of different state variables and the coupling between them, it is found out that PLL and virtual inertia are the main factors that affect the coupling between DFIG and synchronous generators. And then, considering that both PLL and virtual inertia control will affect the oscillation modes of synchronous generators, analytical method is used to reveal system small-signal stability under the joint effects of the two factors quantitatively. Analysis results show that, for DFIG wind turbines with virtual inertial control, PLL affects system damping mainly by affecting the participation of virtual inertia in the system. The smaller the PI parameters of PLL are, the smaller the participation factor of virtual inertia control state variables in the interarea oscillation mode is, and the bigger the electromechanical oscillation mode damping ratio is. Simulation results verify the reasonableness of the established model and the possibility that virtual inertia control may cause system small-signal stability to deteriorate in multimachine system.

Small signal stability region of power systems with DFIG in injection space

The modal analysis method is utilized to study the influence of doubly-fed induction generator (DFIG) on electromechanical oscillations. On this basis, the small signal stability region (SSSR) of power systems with DFIG in injection space is evaluated and the corresponding relationship between SSSR boundary and electromechanical oscillations is analyzed. The effects of the locations of DFIG on SSSR are considered. It is found that the boundary of SSSR consists of several smooth surfaces, which can be approximated with hyper-planes in engineering application. With the integration of DFIG, SSSR becomes smaller, thus indicating the deterioration of the small signal stability of the system. The 11-bus system with four generators is used to illustrate the proposed method.