Doubly Fed Induction Generator Rotor Research Articles

Research on Mathematical Model of Energy Storage Assisted Wind Turbine Frequency Regulation Control Strategy

Abstract This paper proposes an improved frequency regulation strategy for the Doubly-Fed Induction Generator (DFIG) to mitigate the impact of wind power integration on system frequency. An energy storage system is used on the wind side to participate in the frequency regulation. The influence of wind power integration on the power system frequency is analyzed and an improved frequency control strategy for the DFIG is proposed. A control strategy for energy storage devices to support wind turbine frequency control is proposed. An energy storage device model is established that considers power correction based on the state of charge to avoid excessive charging and discharging. According to the operating state of the DFIG, a control strategy for the frequency regulation of the energy storage device is proposed. According to different wind speeds, a control strategy is proposed for the participation of the joint wind storage system in the frequency regulation. This control strategy can provide frequency support to the system when the wind turbine cannot participate in frequency regulation according to the different operating conditions of the wind turbine. After the wind turbine uses the improved frequency control strategy, it accelerates the recovery of the DFIG rotor speed while avoiding a secondary drop in the system frequency. In addition, when the energy storage device has a poor state of charge and the system frequency is good, it charges to restore the state of charge.

The wind turbine's direct power control of the doubly-fed induction generator

The study suggests a comprehensive approach to modeling and controlling variable-speed wind turbine systems that utilize doubly fed induction generators (DFIGs). To make sure that energy is transferred efficiently between the DFIG rotor and the grid, a two-level inverter with perfect bidirectional switches is used. Using the tip speed ratio algorithm and taking into consideration the randomness in wind speed, the maximum power at the wind turbine is optimized. Then, the control strategy utilizes direct power control (DPC) due to its various advantages. The advantages of employing this control technique are manifold. Firstly, it eliminates the necessity for rotor current control loops. Secondly, it obviates the need for controllers such as PI controllers to manage torque and flux. Furthermore, it has yielded exceptional simulation results when implementing direct power control (DPC) within the MATLAB/Simulink environment, specifically in the context of a doubly fed induction generator (DFIG) wind power system.

A Three-Level Neutral-Point-Clamped Converter Based Standalone Wind Energy Conversion System Controlled with a New Simplified Line-to-Line Space Vector Modulation

Wind power systems, which are currently being constructed for the electricity worldwide market, are mostly based on Doubly Fed Induction Generators (DFIGs). To control such systems, multilevel converters are increasingly preferred due to the well-known benefits they provide. This paper deals with the control of a standalone DFIG-based Wind Energy Conversion System (WECS) by using a three-level Neutral-Point-Clamped (NPC) converter. The frequency and magnitude of the stator output voltage of the DFIG are controlled and fixed at nominal values despite the variable rotor speed, ensuring a continuous AC supply for three-phase loads. This task is achieved by controlling the DFIG rotor currents via a PI controller combined with a new Simplified Direct Space Vector Modulation strategy (SDSVM), which is applied to the three-level NPC converter. This strategy is based on the use of a line-to-line three-level converter space vector diagram without using Park transformation and then simplifying it to that of a two-level converter. The performance of the proposed SDSVM technique in terms of controlling the three-level NPC-converter-based standalone WECS is demonstrated through simulation results. The whole WECS control and the SDSVM strategy are implemented on a dSPACE DS 1104 board that drives a DFIG-based wind system test bench. The obtained experimental results confirm the validity and performance in terms of control.

Coordinated Control for Seamless Integration of Wind Energy Conversion System With Small Hydrogenerator Through Modified Notch Filters

This paper deals with the seamless integration of doubly fed induction generator (DFIG) based wind energy conversion system (WECS) with local grid constituted by a permanent magnet based small hydrogenerator (PMHG). The seamless integration is carried out using a solid state static transfer switch (SSSTS). The WECS-PMHG system is operated using a coordinated control strategy based on modified notch filters. The modified notch filters are adopted for the computation of (a) sensorless speed and position of the DFIG rotor, (b) fundamental constituents of unbalanced/nonlinear load current and (c) filtered DFIG stator voltages and phase angle. Moreover, the notch filters are also used for mitigating the effects of unbalance/nonlinearity in load currents on the stator and rotor currents of DFIG as well as PMHG currents. Additionally, the control methodology ensures no power interaction between the WECS and the PMHG during the synchronization process. This enables transient-free WECS and PMHG currents. Further, the coordinated control regulates the amplitude and frequency of system voltages even amidst wide variations in wind speed and load. The DFIG stator and wind currents are injected at unity power factor with the system voltages, while the excitation requirement of the DFIG is met by its machine side converter. The validness of the control is demonstrated experimentally through a developed laboratory-scale test bench.

Experimental Investigation of DFIG-based Wind Energy Conversion System Using Fuzzy Logic Control

In this paper, an experimental study of a Wind Energy Conversion System (WECS) is performed. A test bench with a power of 1.5 kW is setup. The system consists of a Doubly-Fed Induction Generator (DFIG) and a wind emulator based on a DC motor associated with a Maximum Power Point Tracking (MPPT) control. The proposed emulator is driven by a four quadrants DC/DC converter to produce a real wind turbine behavior. The aim of this work is to improve the DIFG performances by using the fuzzy logic-based intelligent controller. This control technic is designed to monitor the stator reactive and active powers. This can be achieved by the DFIG rotor side converter (RSC) using the field-oriented control. The experimental setup uses a dSPACE DS1104 device, MATLAB/Simulink software and a ControlDesk interface. The paper shows that, the desired amount of active and reactive powers has been independently controlled and the implementation is successfully verified the effectiveness of the proposed control scheme achieved using the FLC strategy.

Optimal low voltage ride through of wind turbine doubly fed induction generator based on bonobo optimization algorithm

The large-scale wind energy conversion system (WECS) based on a doubly fed induction generator (DFIG) has gained popularity in recent years because of its various economic and technical merits. The fast integration of WECS with existing power grids has caused negative influence on the stability and reliability of power systems. Grid voltage sags produce a high overcurrent in the DFIG rotor circuit. Such these challenges emphasise the necessity of the low voltage ride through (LVRT) capability of a DFIG for ensuring power grid stability during voltage dips. To deal with these issues simultaneously, this paper aims to obtain the optimal values of injected rotor phase voltage for DFIG and wind turbine pitch angles for all operating wind speeds in order to achieve LVRT capability. Bonobo optimizer (BO) is a new optimization algorithm that is applied to crop the optimum values of injected rotor phase voltage for DFIG and wind turbine pitch angles. These optimal values provide the maximum possible DFIG mechanical power to guarantee rotor and stator currents do not exceed the rated values and also deliver the maximum reactive power for supporting grid voltage during faults. The ideal power curve of a 2.4 MW wind turbine has been estimated to get the allowable maximum wind power for all wind speeds. To validate the results accuracy, the BO results are compared to two other optimization algorithms: particle swarm optimizer and driving training optimizer. Adaptive neuro fuzzy inference system is employed as an adaptive controller for the prediction of the values of rotor voltage and wind turbine pitch angle for any stator voltage dip and any wind speed.

Blackstart and Fault Ride-Through Capability of DFIG-Based Wind Turbines

Grid-forming wind turbines must be able to re-energize transmission branches, motor loads, unbalanced loads, and power electronics loads following a blackout. Further, they must ride through faults that can arise during restoration. To tackle these challenges, this paper sets forth a grid-forming control strategy for wind turbines using doubly-fed induction generators (DFIGs). In particular, a special set of feedforward control loops are engineered to mitigate the impacts of restoration transients as well as symmetrical and asymmetrical faults on the regulation of DFIG rotor currents and stator voltages. This paper also leverages two-axis anti-windup regulators to bound two-axis voltage and current commands within ratings. The controller performance is demonstrated via a high-fidelity simulation model of a notional wind-dominant grid.

IMPROVED ADAPTIVE NONLINEAR CONTROL FOR VARIABLE SPEED WIND-TURBINE FED BY DIRECT MATRIX CONVERTER

This paper proposes a robust decoupling power algorithm based on a doubly fed induction generator (DFIG) for variable speed wind-turbine (WT). The DFIG rotor circuit is fed by the direct matrix converter (DMC), which presents several features such as no need to the dc-bus voltage, sinusoidal supply, rotor side waveforms, bidirectional power flow, and adjustable input power factor. The 18 bidirectional switches are controlled using the Venturini modulation technique. On the other hand, the DFIG stator circuit is connected directly to the grid. The nonlinear control strategy based on feedback linearization is applied to control the stator power (Ps and Qs) independently using the rotor quadrature and direct currents (irq and ird), which present the images of the previous stator powers. Some limitations appear in the power algorithm using the conventional pi controller, especially in power tracking, error, and quality. In this context, the model reference adaptive controller (MRAC) presents an alternative solution, a robust and efficient controller proposed instead of the pi controllers to control stator powers. Finally, the simulation results confirm that the proposed algorithm could work under hard conditions and demonstrate that the wind energy conversion system (WECS) provides enhanced dynamic responses in transient and steady states and good power quality delivered to the grid.

Inverter-Embedded Detection of Rotor Winding Faults in Doubly Fed Induction Generators for Wind Energy Applications

Automated and remote testing of wind turbines is highly desirable since they are prone to failure with the harsh operating environment, and are difficult to test due to the remote location and limited accessibility. The turn insulation of the rotor winding is susceptible to failure due to operating stresses. Unlike turn faults in the stator, rotor turn faults do not cause immediate failure due to the low induced voltage in the shorted loop at low slip frequency, and therefore, are difficult to detect during operation. Although this fault progresses slowly, it must be detected to prevent performance degradation due to rotor asymmetry. In this article, a new concept for inverter-embedded testing of doubly fed induction generators (DFIG) used for wind energy applications is presented. The main idea is to inject test voltages into the DFIG rotor winding from the rotor side inverter whenever the wind turbine is stopped, to extract information on the rotor asymmetry. The proposed test concept is a simple off-line test that can be implemented in DFIGs without additional hardware to perform automated and sensitive detection of rotor faults. Experimental results show that faults in the rotor winding can be detected with higher sensitivity compared to on-line methods for improving the reliability of wind turbines.

Optimal maximum power point tracking of wind turbine doubly fed induction generator based on driving training algorithm

The operation of wind power system at optimum power point is a big challenge particularly under uncertainty of wind speed. As a result, it is necessary to install an effective maximum power point tracking (MPPT) controller for extracting the available maximal power from wind energy conversion system (WECS). Therefore, this paper aims to obtain the optimal values of injected rotor phase voltage for doubly fed induction generator (DFIG) to ensure the extraction of peak power from wind turbine under different wind speeds as well as to get the optimal performance of DFIG. A new metaheuristic optimization approach; Driving Training Algorithm (DTA) is used to crop the optimal DFIG rotor voltages. Three different scenarios are presented to have MPPT, the first one is the MPPT with unity stator power factor, the second one is the MPPT with minimum DFIG losses, and the third scenario is MPPT with minimum rotor current to reduce the rating of rotor inverter. The MATLAB environment is used to simulate and study the proposed controller with 2.4 MW wind turbine. The optimum power curve of wind turbine has been estimated to get the reference values of DFIG mechanical power. The results ensured the significance and robust of the proposed controller to have MPPT under different wind speeds. The DTA results are compared with other two well-known optimization algorithms; water cycle algorithm (WCA) and particle swarm optimizer (PSO) to verify the accuracy of results.

Investigation of Voltage Dip Problems during Faults on a Grid-Tied Doubly Fed Induction Generator in a Wind Energy System

A voltage dip is a sudden drop of voltages - generally between 10 and 90 % of the rated RMS value - during a period lasting from half a cycle to a few seconds on the phases of the power lines. It is one of the most important power quality problems affecting the stability of the Doubly Fed Induction Generator (DFIG) in Wind Energy Conversion System (WECS) and hence needs to be analyzed for a given machine for its performance analysis under grid disturbances. When a voltage dip problem happens in the given power as of faults, the magnitude of the rotor and stator currents of DFIG get increased, and hence disturbs steady state operation of the system. Therefore, in this paper, the worst voltage dip of 90 % is tested for grid faults on a 5 kW DFIG to validate its performance under this phenomenon. Based on the results of the simulation - along with its experimental validation - the machine is found to be robust for faults staying a shorter period without disconnecting it from the grid. On the other hand, operating a machine for a longer period while keeping it connected to a grid during a heavy dip, may result in its degradation as the rated limits are violated. To rectify and mitigate the aforesaid problems, a control system - with and without a crowbar - is developed for symmetrical faults to tackle such a problematic situation, and to discuss its fulfillment of the current grid code requirements. Finally, a complete model of the DFIG coupled with the grid is developed, modeled, analyzed and simulated using MATLAB/Simulink user-defined function toolbox block.

Normalized Maximum Correntropy Criterion Based Ripple Mitigation Strategy for Wind–Solar Hybrid Generation System Under Nonideal Grid Conditions

A doubly-fed induction generator (DFIG) integrated to a solar photovoltaic array for wind-solar hybrid power generation, exhibits large multiple-order ripples in DFIG torque as well as active and reactive grid powers, when subjected to a nonideal grid voltage scenario. In this context, this article aims to develop a ripple mitigation strategy based on a novel application of the normalized maximum correntropy criterion (NMCC). The NMCC-based strategy puts forth a comprehensive solution toward mitigating all the ripples emanating either due to voltage unbalance in the grid, or due to grid voltage distortions with both positive and negative sequences of any possible harmonic order. Additionally, the power ripples originating from unbalanced and nonlinear loads interfaced locally to the wind-solar hybrid system are also compensated. The strategy is devised to be parametrically robust and does not necessitate individual harmonics separation in either fluxes, voltages, or currents. Besides, need for inner loop PI, PR, or other complex regulators is also eliminated. Moreover, the control scheme is formulated as a modular structure to ensure distortion-less DFIG rotor currents and balanced-sinusoidal grid currents at nonideal voltages, even as the ripple mitigation loops are disabled. Experimental results from a laboratory test bench verify the effective operation of the NMCC-based control strategy.

Coordinated Control for Performance Enhancement of an Islanded AC/DC Microgrid With Uninterrupted Power and Seamless Transition Capabilities

This article presents a simplistic control approach and multimode operation of a wind-solar-based ac/dc microgrid. The islanded microgrid consists of a doubly-fed induction generator (DFIG) for wind energy conversion, and a solar photovoltaic array for solar energy conversion. In this configuration, the stator terminals of DFIG are connected at the point of common intersection (PCI) of ac loads via a stator-side solid-state transition switch ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SSTS</sub> ). The developed control strategy is designed to seamlessly disconnect and reconnect the DFIG stator from the PCI based on the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">SSTS</sub> operation, without interrupting power to ac and dc loads in the microgrid. The disconnection of stator terminals is required in the event of a prolonged period of no wind generation from the DFIG. The controller is synthesized to ensure no or low transient effect during the transition between the two operating modes, i.e., DFIG stator connected mode (SCM) and stator disconnected mode (SDM). Further, the power quality enhancement of stator voltages and currents amidst nonideal ac loads is ensured without need for computationally exhaustive approaches involving sequence decompositions, notch filters, resonant regulators, or load current sensors. Moreover, the power quality enhancement at the DFIG stator is achieved without injecting any undue harmonics in the DFIG rotor currents. The effectiveness of this islanded microgrid is verified through obtained results from a developed laboratory prototype.

Study on Suppression Strategy for Broadband Sub-Synchronous Oscillation in Doubly-Fed Wind Power Generation System

In the power transmission of doubly-fed induction generators (DFIGs), sub-synchronous oscillation (SSO) can occur due to the influence of series compensation capacitance and long-distance transmission. SSO not only affects the output of the DFIG but also leads to oscillation diffusion. In order to solve the problem of disturbance in the control of the DFIG rotor side converter (RSC) under SSO, an adaptive quasi-resonant controller is proposed for the suppression of SSO. This strategy focuses on the propagation path of and frequency change in the SSO in the RSC control system and suppresses the SSO current in the wideband through the cooperative control of the back-stepping controller and the adaptive quasi-resonant controller. In this way, the stator-side output of the DFIG will not be affected by SSO, thus avoiding the amplification of the sub-synchronous power of the line by the DFIG. A simulation model and experimental platform were built to verify the suppression effect of this control strategy on the DFIG stator sub-synchronous current at different SSO frequencies. The results show that the proposed strategy has a good suppression effect on broadband SSO.

Improving DFIG performance under fault scenarios through evolutionary reinforcement learning based control

The doubly fed induction generator (DFIG) usually experiences high rotor current and DC capacitor link voltage spikes during system fault events. In this paper, a novel data-driven approach is proposed to enhance DFIG performance under fault scenarios. An advanced reinforcement learning algorithm called guided surrogate-gradient-based evolution strategy (GSES) is used to control the DFIG power and capacitor DC-link voltage by adjusting the optimal reference signals. This controller is able to prevent the DFIG rotor from over-current risk and maintain grid-connected operation. The proposed GSES-based control algorithm was evaluated through simulations on a 3.6-MW DFIG in the PSCAD/EMTDC software. Results have validated the effectiveness of the proposed GSES-based control algorithm in improving DFIG performance under various fault scenarios.

A Hybrid H∞-MRAS Observer of Wind Turbines Conversion Systems based on DFIG

This study proposes the robust sensor-less advanced frequency control (robust H∞ control) of the system of wind turbine based on a doubly fed induction generator (DFIG), the power exchange between the machine stator and the network is achieved by applying the rotor of DFIG via a bidirectional converter. The purpose of the control is to regulate the stator active and reactive power produced by the DFIG using a robust H∞ controller. The Model reference and adaptive system (MRAS-Observer) uses the error between the actual and estimated values ​​(voltage/current) to construct the observed mechanical parameters (speed and position) value, this technique uses two separate models: the first is the reference model, the second is the adjustable mode. The error between these models is used by the adaptive mechanism. The adjustment mechanism is mostly a PI controller, to improve the performance and robustness of the classical MRAS observer, we replace the classical PI controller with a robust H∞ controller. The results simulations confirm the robustness of the sensorless robust H∞ control using the H∞-MRAS observer compared to conventional MRAS, which improves the quality and quantity of generated power.

Diagnosing multiple short circuit switches faults in wind turbine doubly-fed induction generator

In the current paper, the inverter feeding doubly fed induction generator (DFIG) in the case of short circuit switches fault is presented. Defects diagnosis is based on the so-called the Lissajous curves of DFIG rotor currents. For this purpose, the modeling of the variable speed wind energy conversion chain based on the DFIG, is firstly introduced, after that a description of the voltage source inverter operating mode is presented. Finally, rotor currents Lissajous curves are analyzed in case of a non-defective and defective inverter. Simulation results were achieved using MATLAB^®- SIMULINK^® package, thus confirming the efficiency of the proposed method.

Doubly Fed Induction Generator Low Voltage Ride Through Improvement Through Modular Multilevel Converter

This paper proposes a novel fault current suppression method for doubly fed induction generator (DFIG) low voltage ride through (LVRT) improvement employing modular multilevel converter (MMC). It is based on the inherent MMC arm impedance and the number of levels to provide transient damping of DFIG rotor and stator currents under severe grid faults, contributing effectively to maintaining the DFIG connection while ensuring controllability by avoiding the protection activation. Neither additional hardware nor control loops are necessary. DFIG dynamic equations under LVRT, including the contribution of the MMC, are presented, and a model is derived for control design. Performance assessment, including symmetrical and asymmetrical fault scenarios for MMC with 3, 21, 51, and 101 levels and comparison with existing and proposed controllers, highlighted that arm impedance and increased MMC level number contributed to DFIG stator and rotor fault current suppression, providing DFIG LVRT improvement under severe grid fault conditions.

Approach Control of DFIG Rotor Side Converter Based on Grid Frequency Coordinated Control

Abstract. This paper presents an approach frequency coordinated control of Doubly Fed Induction Generator (DFIG) applying in the Rotor Side Converter (RSC) using an order reference active power (Pref ). Pref is obtained from the frequency deviation, speed regulation and kinetic energy stored in the DIFG. The Pref is employed as a main controller parameter of the dq-axis currents in the RSC under two case studies. In case1 study, the Pref is used to regulate the q-axis reference current and the grid reactive power controlled d- axis reference current. Whilst in case2 study, the d- axis reference current is produced by Pref , and the rotormechanical speed responsible to generate the q-axis reference current. The modified vector control method is used to control the Grid Side Converter (GSC) in two case studies. The transient performance of two case studies is simulated by PSCAD/EMDTC program under constant, step and variable wind speeds. A comparative result between two case studies shown that the frequency coordinated control has an ability to control both rotor dq-axis currents, and it enhancing the system frequency as well as improved DFIG voltage stability.However, case2 study has a better response than case1 study during system operated under random wind speed.

Performance analysis and enhancement of direct power control of DFIG based wind system

&lt;span lang="EN-US"&gt;The paper proposes a complete modeling and control technique of variable speed wind turbine system (WTS) based on the doubly fed induction generator (DFIG). Two levels back-to-back converter is used to ensure the energy transfer between the DFIG rotor and the grid. The wind turbine to operate efficiently, a maximum power point tracking (MPPT) algorithm is implemented. Then, direct power control (DPC) strategy has been combined with the MPPT technique in order to guarantee the selection of the appropriate rotor voltage vectors and to minimize the active and reactive power errors. Finally, the simulation is performed by using MATLAB/simulink platform basing on 7.5KW DFIG wind generation system, and the results prove the effectiveness of our proposed control technique.&lt;/span&gt;