Doubly Fed Induction Generator Wind Turbine Research Articles

Artificial Intelligence-Based Fault Tolerant Control Strategy in Wind Turbine Systems

Power converters play an important role as an enabling technology in the electric power industry, especially in Wind Energy Systems (WESs). Where there ensure to regulate exchanging powers between the system and the grid. Therefore; any fault occurs in any parts of these converters for a limited time without eliminating, it may degrade the system stability and performance. This paper presents a new artificial intelligence-based detection method of open switch faults in power converters connecting doubly-fed induction (DFIG) generator wind turbine systems to the grid. The detection method combines a simple Fault Tolerant Control (FTC) strategy with fuzzy logic and uses rotor current average values to detect the faulty switch in a very short period of time. In addition, following a power switch failure, the FTC strategy activates the redundant leg and restores the operation of the converter. In order to improve the performance of the closed-loop system during transients and faulty conditions, current control is based on a PI (proportional-integral) controller optimized using genetic algorithms. The simulation model was developed in Matlab/Simulink environment and the simulation results demonstrate the effectiveness of the proposed FTC method and closed-loop current control scheme.

Calculation of current limiting reactance of hybrid SFCL for low voltage ride-through capability enhancement in DFIG wind farms

This paper presents a new approach for the low voltage ride-through capability enhancement of doubly-fed induction generator (DFIG) wind farms using a hybrid superconducting fault current limiter (SFCL) of the first peak current limiting type, which has the advantage of a fast recovery time. A design for the hybrid SFCL, focusing on current limiting reactor (CLR) reactance calculation, is proposed in this paper to determine an appropriate value for the CLR reactance that satisfies the grid code requirements of the DFIG wind turbines. High-temperature superconductors (HTS) such as Bi-2212, YBCO, Bi-2223, Ti-2223, and Hg-1223 are investigated for use in the hybrid SFCL. The recovery time and first peak current reduction effectiveness are the criteria for selecting the HTS. In the proposed method, a during-fault voltage from the grid code requirement is used as an input parameter to compute the reactance of the CLR. Based on the results of the base-case simulations conducted on the DIgSILENT PowerFactory software, the Bi-2223 HTS with the first peak of fault current less than 4.5 kA and recovery time of 2.5 s is selected for adoption in the hybrid SFCL. The calculated results of the proposed method are compared with the simulation results of the hybrid SFCL, in terms of the DFIG wind turbine fault ride-through capability enhancement, to demonstrate that the performance of the proposed method satisfies the grid code requirements.

A look-up table based approach for fault ride-through capability enhancement of a grid connected DFIG wind turbine

Abstract In wind power systems consisting of grid connected doubly fed induction generators (DFIGs), transient faults usually occur for a couple of milliseconds (typically between 100–700 ms) due to many reasons and cause voltage sags in different spots of wind power systems. During fault and after fault clearance, the parameters of DFIG such as produced active power, rotor speed, and rotor current profiles, experience disturbances for several seconds. The mean rate of wind speed and the kind of transient fault are two important factors which directly affect the duration and severity of disturbances. This paper described a new, simple approach for improving fault ride-through (FRT) capability of a grid connected DFIG wind turbine via using the look-up table (LUT) based procedure. The proposed method was based on the correction of the reference current value of the rotor current control in the rotor side converter (RSC) to smooth the reference current profile, which was destructed due to the occurrence of transient faults. Moreover, a speed damping loop was utilized by applying the other LUT for extracting the values of rotor reference speed to add the oscillations of the rotor speed to the improved reference current ( I r d 2 ∗ ) profile for compensation. Different simulations were carried out on the test system to validate the proposed method considering different mean wind speeds with various kinds of transient faults. The obtained results indicated that applying this approach could significantly improved DFIG performance in the case studies of symmetrical and asymmetrical transient faults, also oscillations on the produced active power, rotor speed and rotor current magnitude were significantly mitigated.

A condition monitoring system for an early warning of developing faults in wind turbine electrical systems

Electrical condition monitoring (CM) normally involves the collection of high-frequency, instantaneous data for feature extraction. This paper presents a novel development of an electrical condition monitoring system for wind turbines. The system is developed based upon a control and data acquisition system, for which hardware modules can be configured for a particular set of signals, thus tailoring the system to a specific range of monitoring tasks. A wavelet-based singularity detection method is proposed, which automatically calculates the Lipschitz exponent, a measure to describe the local transient activities in the measurement signal. The relationship between the Lipschitz exponent and the type and severity of faults occurring on the grid and in the power electronics is explored. The proposed algorithms are tested and validated using simulation data from computer simulations of a doubly-fed induction generator (DFIG) wind turbine with a grid connection. A field-programmable gate array (FPGA) embedded in the system has been utilised, allowing the signal processing tasks to be undertaken in real-time for monitoring purposes. The paper demonstrates that a fault signal of small magnitude generated at the early stage of a fault carries the same Lipschitz exponent as the signal of large magnitude generated at the late stage of the fault, thereby providing an early warning before the fault develops into a detrimental one.

Enhanced Control of DFIG Wind Turbine Based on Stator Flux Decay Compensation

For the doubly fed induction generator (DFIG)-based wind energy conversion system, the decaying flux and negative flux are the main reasons to cause the DFIG rotor overcurrent, during grid faults. The stator decaying flux characteristics versus the depth and instant of the stator voltage variation are analyzed first. On the basis of the stator flux performances, the enhanced control strategy is proposed to limit the decaying flux approximately into zero in half fundamental period by changing the stator voltage drop and recovery mode, and consequently the rotor transient current pulse is significantly reduced during grid faults. The experimental results based on the 7.5 kW DFIG setup are carried to validate the correctness and feasibility of the proposed strategy. Dynamic voltage restorer (DVR) can be one of the applications. With the proposed strategy, the DVR only works in a half fundamental period and its output voltage amplitude is half of the stator voltage variation, during the grid voltage drop and recovery, respectively. As a consequence, the DVR can be rated for lower power saving cost. The simulation results based on MATLAB/Simulink using a 2 MW DFIG and the experimental results based on the 7.5 kW DFIG validate the effectiveness and feasibility of the DVR-based low-voltage ride through strategy.

Reactive power control of DFIG wind turbines for power oscillation damping under a wide range of operating conditions

This study analyses the effect of replacing existing synchronous generators (SGs) equipped with power system stabilisers (PSS) by doubly fed induction generator (DFIG) based wind farms on the damping of power system oscillations in a multi-machine power system. A power system stabiliser was designed to enhance the capability of DFIG to damp power systems oscillations. The validity and effectiveness of the proposed controller are demonstrated on the widely used New England 10-machine 39-bus test system that combines conventional SGs and DFIG based wind farms using eigenvalue analysis and non-linear simulation. The non-linear simulation is used to demonstrate how the damping contribution of DFIG based wind farms is affected by different operating conditions within the same wind farm and stochastic wind speed behaviour. The results show that installing conventional fixed parameters PSS within reactive power control loop of DFIG rotor side converter has a positive damping contribution for a wide range of operating conditions. Furthermore, the results clearly show that DFIG based wind farms equipped with the proposed farm level PSS can damp power system oscillations more effectively than SGs PSS.

Effects of operational limits of DFIG wind turbines on long-term voltage stability studies

This paper investigates the effects of doubly fed induction generators (DFIGs) operational limits on long-term voltage stability. DFIG operational limits are defined based on wind generator's capability curve in terms of the actual terminal voltage and wind speed. Also, the limitations of the converter, machine and wind turbine are considered in DFIG control schemes. The evolution of different variables is examined using two models for DFIG operational limits: fixed limits and variable limits. Time domain simulations have been performed in three different cases: constant wind speed, ramp up event, and ramp down event. This study also considers the dynamic models of over excitation limiter (OEL) and on-load tap changers (OLTC) combined with static and dynamic loads. Some important conclusions can be extracted from the simulation results, which can help in choosing the appropriate model to represent the DFIG operational limits in long-term voltage stability studies.

A Wideband Equivalent Model of Type-3 Wind Power Plants for EMT Studies

This paper presents the development and validation of an accurate and computationally efficient wideband reduced-order dynamic equivalent model for the Type-3-based wind power plant (WPP). The proposed Type-3 WPP equivalent model reproduces the dynamic behavior of the WPP in response to an electromagnetic transient in the host power system and is composed of two parts: 1) a static frequency-dependent network equivalent model which represents the response of all passive components of the WPP in a wideband frequency range, and 2) a dynamic low-frequency equivalent model that represents the aggregated dynamic model of the doubly-fed asynchronous generator (which is also referred to as doubly-fed induction generator) wind turbine generators, their local controls, and the WPP supervisory control. The proposed model significantly reduces the hardware/software computational burden and the computation time, as compared to the WPP detailed models, without compromising the accuracy of the simulation results. The proposed model is incorporated as a software module in the PSCAD/EMTDC environment and its computational efficiency and accuracy are verified based on comparing the results with those of a detailed model.

Optimization of SMES-FCL for Augmenting FRT Performance and Smoothing Output Power of Grid-Connected DFIG Wind Turbine

Fault-ride-through (FRT) performance and output power variation are crucial issues of the grid-connected wind turbine with the doubly fed induction generator (DFIG). To overcome these problems, the optimal parameters tuning of the superconducting magnetic energy storage and the fault-current limiter (SMES-FCL) with the common part of the superconducting coil (SC) is proposed. In addition to the alleviation of the DFIG output power, the SC behaves as the short-circuit current limiter to enhance the FRT capability. The tuning of the SC inductance and the controller parameters of converters is optimally conducted, so that the DFIG terminal voltage deviation and the power fluctuation during faults are at their minimum. By simulation study, the utilized power and energy of the SC for the grid stabilization are curtailed, whereas the dynamic performance of the SMES-FCL is higher than a single SMES unit.

Reactive Power Dispatch Method in Wind Farms to Improve the Lifetime of Power Converter Considering Wake Effect

In wind farms (WF), the most popular and commonly implemented active power control method is the maximum power point tracking (MPPT). Due to the wake effect, the upstream wind turbine (WT) in WFs has more active power generation than the downstream WT at the wind directions and wind speeds that the WF has wake loss. In the case that WTs support the voltage control by reactive power, the upstream WT's power converter may have shorter lifetime even below the industrial standard. In this paper, based on the analysis of the wake effect, the reactive power capability of the doubly fed induction generator (DFIG) WT, and the lifetime of the DFIG WT's power converter, a reactive power dispatch method is proposed in the WF with DFIG WTs to improve the lifetime of the upstream WT's power converter. The proposed reactive power dispatch method is analyzed and demonstrated by the simulation on a WF with 80 DFIG WTs. It can be concluded that, compared with the traditional reactive power dispatch method, the proposed method can increase the lifetime of the upstream WT's power converter.

Active and reactive power control of the doubly fed induction generator based on wind energy conversion system

Abstract This paper presents a dynamic modeling and control of doubly fed induction-generator (DFIG) based on the wind turbine systems. Active and reactive power control of the DFIG are based on the feedback technique by using the suitable voltage vectors on the rotor side. The rotor flux has no impact on the changes of the stator active and reactive power. The proposed controller is based on the feedback technique in order to reduce the oscillation of the generator. The control approach is estimated through the simulation result of the feedback controller assembled with DFIG wind turbines. It is applied by the feedback control based techniques in order to control the power flowing of DFIG and the power grid. Hence, an improved feedback control technique is adopted to get a better power flow transfer and to improve the dynamic system and transient stability. In stable condition, the improved performance of the controller, the proposed method is verified for the effectiveness of the control method is done in stable conditions.

Spare parts management algorithm for wind farms using structural reliability model and production estimation

Doubly fed induction generators (DFIGs) are widely used in wind power systems; hence their reliability model is an important consideration for production assessment and economic analysis of wind energy conversion systems. However, to date mutual influences of reliability analysis, production estimations and economic assessments of wind farms have not been fully investigated. This study proposes a reliability model for DFIG wind turbines considering their subcomponent failure rates and downtimes. The proposed production estimation algorithm leads to an economic assessment for wind farms. A comprehensive spare parts management procedure is then presented in the study. As a case study, practical data from a prominent wind farm is used and the procedure of the study is verified.

Study of stabilty analysis of a grid connected Doubly fed induction generator based on wind energy Application

<p><em> </em><em> </em>The present paper formulates the state space modeling of doubly fed induction generator (DFIG) based wind turbine system for the purpose of the stability analysis. The objective of this study is to discuss the various modes of operation of the DFIG system under different operating conditions such as voltage sags with reference to variable wind speed and grid connection. The proposed control methodology exploits the potential of the DFIG scheme to avoid that grid voltage unbalances compromise the machine operation, and to compensate voltage unbalances at the point of common coupling (PCC), preventing adverse effects on loads connected next to the PCC. This methodology uses the rotor side converter (RSC) to control the stator current injected through the machine and the GSC to control the stator voltage to minimize the electromagnetic torque oscillations. Extensive simulation results on a 2MW DFIG wind turbine system illustrate the enhanced system performance and verify the effectiveness of the controller.</p>

Hierarchical Co-Ordinated Wide Area and Local Controls of DFIG Wind Turbine and PSS for Robust Power Oscillation Damping

In this paper, the two-level hierarchical scheme, which consists of wide area centralized and local controls of the power oscillation damper (POD) installed with the doubly-fed induction generator (DFIG) wind turbine and the power system stabilizer (PSS) has been proposed for robust power oscillation damping. In the wide area level, the centralized POD and PSS has received the input signals from synchronized phasor measurement units (PMUs). The geometric measures of controllability and observability have been applied to select the suitable DFIG and synchronous generator (SG) for stabilizing the target oscillation modes, the proper input signals of the centralized POD and PSS, and the location of PMUs. In the local level, the suitable DFIG and SG have been equipped with POD and PSS, respectively. In the parameters optimization of POD and PSS, the practical issues such as damping performance, controller structure, communication latency, and robustness against system uncertainties have been considered. The controller efficiency and resiliency of the proposed controller have been evaluated in comparison with other controllers by eigenvalue analysis and nonlinear simulation for a wide range of operating conditions, line outage contingencies, severe faults, and communication failure.

Enhancing DFIG wind turbine during three‐phase fault using parallel interleaved converters and dynamic resistor

Transient operations are very crucial for high power insulated-gate bipolar transistor modules, because high current and voltage are applied during this period for several microseconds. Therefore, the ability for doubly fed induction generator (DFIG) variable speed wind turbine power converters to withstand abnormal conditions is strictly imperative in order to achieve its lifetime specifications and also fulfil the grid codes. This study presents a new control scheme for DFIG wind turbine having parallel interleaved converters (PIC) configuration and a series dynamic braking resistor (SDBR) connected at its stator side. Interleaving the wind turbine converters in parallel configuration could help to increase the current capability, while the SDBR helps in post fault recovery of the wind turbine. The coordinated control analysis of the scheme was implemented in power system computer aided design and electromagnetic transient including DC simulation environment for a severe three-phase to ground fault. Results obtained were compared with the conventional DC chopper and crowbar rotor circuit protection scheme for the wind turbine. A better performance of the wind turbine variables were achieved using the proposed control scheme of the PIC and SDBR because the space vector modulation of the PIC results in maximum value of the change in common mode voltage, leading to improved switched output voltage of the voltage source converter leg.

Rotor speed control of doubly fed induction generator wind turbines using adaptive maximum power point tracking

This paper proposes a new method for obtaining the maximum power output of a doubly fed induction generator (DFIG) wind turbine. This scheme does not require the precise parameters of the wind turbine or any information about the wind speed or wind sensor. The maximum power point tracking (MPPT) ability of the proposed method is theoretically proven under some certain assumptions. To obtain the required control performance, several control parameters may be adopted. Particularly, the control method is constructed on the basis of the Lyapunov function. The quality of the proposed method is verified by the numerical simulation of a 1.5-MW DFIG wind turbine. The simulation results show that the wind turbine implemented with the proposed method can track the optimal operation point. Furthermore, the energy output of the DFIG wind turbine using the proposed method is higher compared to conventional methods under the same conditions.

Simulation and Control of Doubly Fed Induction Generator (DFIG) Used in Wind Turbines by Using Genetic Algorithm

Wind energy is one of the extraordinary sources of renewable energy due to its clean character and free availability. With increase in wind power penetration, the wind farms are directly influencing the power systems. The majority of wind farms are using variable speed wind turbines equipped with doubly fed induction generators (DFIG) due to their advantages over other wind turbine generators (WTGs). Therefore, the analysis of wind power dynamics with the DFIG wind turbines has become a very important research issue, especially during transient faults. In this article, a controller is provided to control the active and reactive power of a wind system equipped with doubly fed induction generator. The generator is connected to the grid by a back to back converter that gets benefit from control system known as single periodic controller. Grid and generator side converters respectively control the generator speed and reactive power using proposed controller. In order to increase the accuracy of controller, we optimized its PI parameters using genetic optimization algorithm. Finally, simulation results conducted by the MATLAB software are shown. The results of simulation gained through this system, show the capability of proposed controller under error conditions for controlling active and reactive power and also elimination of harmonics caused by non-linear load.

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.

Two Layer Constant Power Control of DFIG Wind Turbines with Super Capacitor Energy Storage

To dynamically match the intermittency of wind energy, energy storage devices will be required. In this project a two-layer constant power control scheme for a wind farm equipped with doubly fed induction generator (DFIG) wind turbine is considered. In the two layer control, there is a high layer controller known as Wind farm supervisory control (WFSC), which generates Active power (P), Stator power (Ps), Energy storage power (Pe), DC voltage (Vdc) etc. references for the low layer Wind turbine generator (WTG) controllers, according to the power demand from the grid operator. The low layer wind turbine generator(WTG) controller consist of Rotor side converter control and Grid side converter control to regulate each Double fed induction generator (DFIG) wind turbine, to generate desired amount of active power, Where the deviations between the available wind energy input and desired active power output are compensated by Super capacitor Energy storage system. Simulation is carried out in a MATLAB/SIMULATION to evaluate the performance of wind farm equipped with 15 DFIG wind turbines with and without energy storage system to provide a constant active power of 36MW.

Critical Short Circuit Ratio Analysis on DFIG Wind Farm with Vector Power Control and Synchronized Control

The introduction of renewable energy sources into the AC grid can change and weaken the strength of the grid, which will in turn affect the stability and robustness of the doubly-fed induction generator (DFIG) wind farm. When integrated with weak grids, the DFIG wind turbine with vector power control often suffers from poor performance and robustness, while the DFIG wind turbine with synchronized control provides better stability. This paper investigates the critical short circuit ratios of DFIG wind turbine with vector power control and synchronized control, to analyze the stability boundary of the DFIG wind turbine. Frequency domain methods based on sensitivity and complementary sensitivity of transfer matrix are used to investigate the stability boundary conditions. The critical capacity of DFIG wind farm with conventional vector power control at a certain point of common coupling (PCC) is obtained and is further increased by employing synchronized control properly. The stability boundary is validated by electromagnetic transient simulation of an offshore wind farm connected to a real regional grid.