Symmetrical Voltage Dips Research Articles

Protection of rotor side converter of doubly fed induction generator based wind energy conversion system under symmetrical grid voltage fluctuations

This paper presents the protection of the rotor side converter in a grid-connected doubly fed induction generator (DFIG)-based wind energy conversion system (WECS) during a symmetrical voltage dip. In order to manage rotor current and regulate DC link voltage, an efficient active crowbar protection circuit is implemented in the rotor side converter (RSC). To improve the low-voltage ride-through capability for grid-connected wind turbine systems, an integrated DFIG-based WECS role is crucial because wind turbines must remain connected to the utility grid during faults to ensure continuity and reliability of power supply. This paper aims to design and implement an efficient active crowbar protection technique to protect the RSC and avoid excessive rotor current during a symmetrical voltage dip. Therefore, the efficient active crowbar protection circuit is designed using MATLAB-Simulink software, and its performance is validated using a real-time (RT) simulator. Finally, the existing methods are compared with the proposed work outcomes, and a conclusion is made.

Real-time Assessment of Ride-through Capability of Grid-tied Converter in Renewable Power Applications

This paper presents a comprehensive strategy for controlling grid-tied converters, with the primary goal of seamlessly integrating renewable power sources into the grid while ensuring stability and reliability. The control strategy is designed to achieve unity power factor operation under normal grid conditions, while also adhering to ride-through requirements to withstand voltage dips. Using the Typhoon HIL604 real-time simulation platform, extensive testing of the grid-tied converter is conducted to validate its performance. The results of the performance assessment are thoroughly analyzed and presented to exemplify the efficacy of the proposed control strategy. Notably, the paper emphasizes the converter's operation at unity power factor during normal grid conditions, indicating maximized active power delivery to the grid. Furthermore, the grid-tied converter demonstrates impressive ride-through capability during symmetrical voltage dip, achieved through the dynamic adjustment of grid current references to maintain grid stability. This research contributes to the advancement of grid-tied converter control strategies, offering insights into enhancing the integration of renewable power sources into the power grid while upholding system reliability and stability. Overall, this research offers valuable insights into the practical implementation of grid-tied converters for renewable power integration. It presents a comprehensive control strategy that not only enhances the integration of renewable power sources into the power grid but also prioritizes system reliability and stability.

Control of Battery Energy Storage System for Wind Turbine based on DFIG during Symmetrical Grid Fault

This paper presents a specific control strategy of Doubly Fed Induction Generator (DFIG) conceived for a wind turbine system operating under electrical grid disturbance. Two mains aspects related to DFIG behavior are studied: fluctuation of its output power and Low-Voltage Ride Trough capability (LVRT) of wind turbine generator system. In order to smooth the output power injected in the electrical grid and to improve dynamic behavior of a variable speed wind turbine generator system under symmetrical voltage dip, a control strategy of the Battery Energy Storage System (BESS) is proposed. Simulations have been carried out in Matlab environment, and the results validate the effectiveness of our control.

Low-voltage ride-through capability improvement of Type-3 wind turbine through active disturbance rejection feedback control-based dynamic voltage restorer

Abstract Disconnections due to voltage drops in the grid cannot be permitted if wind turbines (WTs) contribute significantly to electricity production, as this increases the risk of production loss and destabilizes the grid. To mitigate the negative effects of these occurrences, WTs must be able to ride through the low-voltage conditions and inject reactive current to provide dynamic voltage support. This paper investigates the low-voltage ride-through (LVRT) capability enhancement of a Type-3 WT utilizing a dynamic voltage restorer (DVR). During the grid voltage drop, the DVR quickly injects a compensating voltage to keep the stator voltage constant. This paper proposes an active disturbance rejection control (ADRC) scheme to control the rotor-side, grid-side and DVR-side converters in a wind–DVR integrated network. The performance of the Type-3 WT with DVR topology is evaluated under various test conditions using MATLAB®/Simulink®. These simulation results are also compared with the experimental results for the LVRT capability performed on a WT emulator equipped with a crowbar and direct current (DC) chopper. The simulation results demonstrate a favourable transient and steady-state response of the Type-3 wind turbine quantities defined by the LVRT codes, as well as improved reactive power support under balanced fault conditions. Under the most severe voltage drop of 95%, the stator currents, rotor currents and DC bus voltage are 1.25 pu, 1.40 pu and 1.09 UDC, respectively, conforming to the values of the LVRT codes. DVR controlled by the ADRC technique significantly increases the LVRT capabilities of a Type-3 doubly-fed induction generator-based WT under symmetrical voltage dip events. Although setting up ADRC controllers might be challenging, the proposed method has been shown to be extremely effective in reducing all kinds of internal and external disturbances.

Direct speed fractional order controller for maximum power tracking on DFIG-based wind turbines during symmetrical voltage dips

Direct speed fractional order controller for maximum power tracking on DFIG-based wind turbines during symmetrical voltage dips

A Heuristic Approach to Optimal Crowbar Setting and Low Voltage Ride through of a Doubly Fed Induction Generator

In this paper, a heuristic approach to doubly fed induction generator (DFIG) protection and low voltage ride through (LVRT) is carried out. DFIG-based wind systems are rapidly penetrating the power generation section. Despite their advantages, their direct coupling grid makes them highly sensitive to symmetrical faults. A well-known solution to this is the crowbar method of DFIG protection. This paper provides a method to determine the optimal crowbar resistance value, to ensure a strong trade-off between the rotor current and DC voltage transients. Further, since the crowbar method requires disconnection from the grid, the linear quadratic regulator (LQR) is applied to the system. This is to ensure fault ride through compliance with recent grid code requirements. The well-known PSO, as well as the recently developed African vultures optimization algorithm (AVOA), was applied to the problem. The first set of results show that for severe symmetrical voltage dips, the AVOA provides a good option for crowbar magnitude optimization, whereas PSO performed better for moderately severe dips. Secondly, when the LQR was optimized via the AVOA, it exhibited superiority over the conventional PSO-based PI controller. This superiority was in terms of rotor current transient magnitude, DC voltage transient magnitude, and reactive power steady-state ripple and were in the order of 67.5%, 20.35%, and 37.55%, respectively. When comparing the crowbar method and the LQR, it was observed that despite the LQR exhibiting superiority in terms of transient performance, the crowbar method offered a unanimously superior settling time.

LVRT Fulfilment of the DFIG-based WECS During Symmetrical Grid Voltage Dips

The doubly fed induction generator (DFIG)-based wind energy conversion system (WECS) has seen rapid growth all over the world, resulting in a growing access of this source of energy into electrical grids. The low-voltage ride-through (LVRT) capability of the DFIG-based wind turbine must be improved to make it stay connected to the grid during the occurrence of grid faults. Because of its vulnerability to grid disruptions, careful arrangements must be made to the DFIG to keep it connected with the grid. Hence, this paper presents a modified control technique with crowbar protection for improving the LVRT of the WECS. This proposed scheme can be sufficient to meet the LVRT requirements as demanded by grid codes. The fault ride-through capability of the rotor side convertor (RSC) and grid side converter (GSC) is regulated in accordance with grid code requirements. During grid faults, the proposed scheme enhances device recovery by providing reactive power support through the GSC and the stator. The dynamic performance of the proposed scheme is investigated under symmetrical grid disturbances. The operation of the proposed system has been simulated in a MATLAB/Simulink environment for a 2.6 MW-grid-connected DFIG system.

Dynamic analysis and oscillation elimination of brushless doubly fed wind power generation system during symmetrical voltage dips

Dynamic analysis and oscillation elimination of brushless doubly fed wind power generation system during symmetrical voltage dips

A Common Capacitor Based Three Level STATCOM and Design of DFIG Converter for a Zero-Voltage Fault Ride-Through Capability

To meet the augmented load power demand, the doubly-fed induction generator (DFIG) based wind electrical power conversion system (WECS) is a better alternative. Further, to enhance the power flow capability and raise security margin in the power system, the STATCOM type FACTS devices can be adopted as an external reactive power source. In this paper, a three-level STATCOM coordinates the system with its dc terminal voltage is connected to the common back-to-back converters. Hence, a lookup table-based control scheme in the outer control loops is adopted in the Rotor Side Converter (RSC) and the grid side converter (GSC) of DFIG to improve power flow transfer and better dynamic as well as transient stability. Moreover, the DC capacitor bank of the STATCOM and DFIG converters connected to a common dc point. The main objectives of the work are to improve voltage mitigation, operation of DFIG during symmetrical and asymmetrical faults, and limit surge currents. The DFIG parameters like winding currents, torque, rotor speed are examined at 50%, 80% and 100% comparing with earlier works. Further, we studied the DFIG system performance at 30%, 60%, and 80% symmetrical voltage dip. Zero-voltage fault ride through is investigated with proposed technique under symmetrical and asymmetrical LG fault for super-synchronous (1.2 p.u.) speed and sub-synchronous (0.8 p.u.) rotor speed. Finally, the DFIG system performance is studied with different phases to ground faults with and without a three-level STATCOM.

A direct power control of a DFIG based-WECS during symmetrical voltage dips

The Wind Energy Conversion System (WECS) based Doubly Fed Induction Generator (DFIG) has experienced a rapid development in the world, which leads to an increasing insertion of this source of energy in the electrical grids. The sudden and temporary drop of voltage at the network can affect the operation of the DFIG; the voltage dips produce high peak currents on the stator and rotor circuits, without protection, the rotor side converter (RSC) will suffer also from over-current limit, consequently, the RSC may even be destroyed and the generator be damaged. In this paper a new Direct Power Control (DPC) method was developed, in order to control the stator powers and help the operation of the aero-generator during the faults grid; by injecting the reactive power into the network to contribute to the return of voltage, and set the active power to the optimum value to suppress the high peak currents. The DPC method was designed using the nonlinear Backstepping (BS) controller associated with the Lyapunov function to ensure the stability and robustness of the system. A comparison study was undertaken to verify the robustness and effectiveness of the DPC-BS to that of the classical vector control (VC) using Proportional-Integral (PI) correctors. All were simulated under the Simulink® software.

A DFIG-based Wind Turbine Operation under Balanced and Unbalanced Grid Voltage Conditions

This paper presents a case study of a Doubly Fed Induction Generator (DFIG) wind turbine in operation subject to balanced and unbalanced grid voltage conditions. Three scenarios are addressed: balanced grid, symmetrical and asymmetrical voltage dips. We describe the DFIG model and the control strategies adopted to stabilize the system during voltage faults, in order to protect the converters. Several simulation experiments are presented to illustrate the performance and effectiveness of the described control strategies.

Full Converter Control for Variable-Speed Wind Turbines Without Integral Controller or PLL

This article addresses a controller for a full converter of variable-speed wind generators composed of permanent magnet synchronous generators. Conventionally, several proportional–integral (PI) controllers and a phase-locked loop (PLL) are used in the full converter for voltage-oriented control. The use of cascaded control loops with PI controllers degrades the control performance due to the windup of the integrators and complicates the tuning task. In this article, we propose a new full converter control scheme based on predictive control and a single P-controller in the $\alpha \beta$ stationary frame to replace the integrators and the PLL. The proposed controller can reduce the parameter tuning effort, is free from integrator windup, and is robust to symmetrical and asymmetrical voltage dips. The effectiveness of the proposed method is verified through simulations.

Crowbarless Symmetrical Low-Voltage Ride Through Based on Flux Linkage Tracking For Brushless Doubly Fed Induction Generators

The significant benefits of brushless doubly fed induction generators (BDFIGs) are higher reliability and lower maintenance cost due to the lack of a brush gear. Recent studies on BDFIGs have shown promising applications in wind power generation. The low-voltage ride-through (LVRT) capability of wind turbines is one of the most important properties specified in the grid codes of many countries. A crowbarless LVRT control strategy based on flux linkage tracking for a BDFIG under symmetrical voltage dips is proposed in this article. A novel and simple controller in static reference frame is presented to implement flux linkage tracking. To both suppress the control winding (CW) current and increase power winding (PW) reactive current, a time-sharing control and CW current-first control solution is proposed. In the most severe case, where the BDFIG rotor speed is 100% of the maximum rotor speed and under 100% symmetrical voltage dips, the experimental results show that the CW current peak can be limited to 2.01 p.u. of the CW current rating and the torque ripple is small during the fault. The experimental results also show the possibility of the BDFIG to ride through the severest voltage dips without extra hardware, such as a crowbar.

Voltage-Dip Analysis of Brushless Doubly Fed Induction Generator Using Reduced T-Model

This paper presents the performance analysis of brushless doubly fed induction generator (BDFIG) during symmetrical voltage dips. The equivalent circuit consists of resistances and dependent voltage sources in its rotor loop; thus, its voltage-dip analysis becomes more challenging. To overcome such difficulty, a reduced full-order model of the BDFIG into a new T-model is presented. A detailed mathematical analysis is performed subject to voltage-dip conditions. The time variation for the machines fluxes, electromotive forces, voltages, currents, and active and reactive powers are analyzed and their analytical approaches are derived. The current/voltage stress of power converter during voltage dip is discussed. The accuracy of the proposed T-model and the theoretical voltage dip is confirmed via experimental tests on a 3-kW BDFIG, and simulation results of a 2-MW BDFIG.

A New Type-2 PLL Based on Unit Delay Phase Angle Error Compensation During the Frequency Ramp

This letter introduces a unit delay compensation scheme for Type-2 phase locked loop (Type-2 PLL) to eliminate the steady state phase angle error during the frequency ramp. The proposed PLL (ZPLL) uses an adaptive delayed signal cancellation (DSC) filter, along with a compensation scheme, to ensure effective operation under unbalanced grid. The proposed compensation scheme acts as an open-loop compensator, hence, ZPLL functions as Type-3 PLL with Type-2 dynamics features while preserving its second order characteristics. The proposed scheme is mathematically and experimentally validated under different scenarios of grid disturbances. The obtained results demonstrate the capability of the proposed compensation scheme to obtain a zero steady state phase angle error during the frequency ramp while employing symmetrical and asymmetrical voltage dip.

Dynamic behavior analysis under a grid fault scenario of a 2 MW double fed induction generator-based wind turbine: comparative study of the reference frame orientation approach

This paper investigates a comprehensive analysis of the dynamic behavior of a typical 2 mw grid-connected double fed induction generator-based wind turbine during a symmetrical grid voltage dip scenario. The stator flux dynamics and the induced rotor electromotive force have been investigated aiming to undertake an accurate assessment of the DFIG behavior. Furthermore, without any complication of the DFIG vector control scheme, the paper offers a comparative study between the use of the stator flux reference frame orientation approach and the grid voltage reference frame orientation approach, this, in order to accurately assess the appropriate choice regarding the stability of the vector control scheme and hence, to have a good background about the LVRT capability of the DFIG during the studied grid fault. The simulation results have been performed through Matlab/Simulink environment.

A Flexible Active and Reactive Power Control Strategy of a LV Grid Connected PV System

The aim of this paper is to present a command approach of a typical double-stage grid-connected PV system functioning under normal conditions and Symmetrical Grid Voltage Dips (SGVD). In Normal Operation Mode (NOM), the command developed rises the relatively low solar voltage to a suitable level corresponds to the Maximal Power Point Tracking (MPPT) and regulates, respectively, the dc-link voltage and the output inverter currents. It permits to inject energy into the grid at unity power factor and a current with low harmonic distortion. Under SGVD, the control strategy approach should ensure a stable connection as long as possible and inject some reactive power to support the grid faults. This command calculates dynamically active and reactive powers that inverter can deliver according to the level of voltage dips and inverter rating currents. Those values are used as reference to control output inverter currents, the dc-link voltage and to deactivate the MPPT command. To validate and to prove the effectiveness of the control strategy, some experimental results are also presented.

Improved Direct Torque Control for a DFIG under Symmetrical Voltage Dip With Transient Flux Damping

This paper proposes a new reference-generation-strategy for direct torque control (DTC) of doubly fed induction generator (DFIG), under symmetrical voltage-dips. Since DTC has no current-control loop, it cannot prevent overcurrent during voltage-dips. The proposed method prevents overcurrent in the rotor side converter, by damping the transient-flux and modifying the references of rotor-flux and torque, during voltage dip and recovery. The analysis of DTC for DFIG is presented by a λ-i equivalent circuit, which is decomposed into forced and natural circuits. Based on the natural λ-i circuit, the method adds a transient compensation term to the rotor-flux reference, which is obtained by multiplying the stator-natural-flux with a proposed decaying-ramp function. Moreover, this method reduces the forced component of rotor-flux proportional to the grid voltage. As a result, this method adjusts the transient-flux damping time and ensures overcurrent prevention in the rotor and stator windings. The torque reference is modified to maintain the torque-angle (between rotor and stator flux vectors) constant, which results in stable control of the DFIG during grid faults. The effectiveness of the proposed method is confirmed by experimental results of a 3-kW test set-up and simulation results of a 2-MW DFIG.

Влияние провалов напряжения на асинхронную электрическую машину двойного питания в системе генерации ветроэнергетической установки

Renewable Energy Sources (like wind energy) minimize the demand for other types of power. Wind energy generation has become a major power in some countries, covering the essential share in the Energy Balance in Holland, Spain, Brazil, Germany, China and others. The construction of new Wind Power causes new challenges for the transmission distribution infrastructure. However, environmentally friendly Renewable Energy has recently become an important part of generation in industrial applications, worth for distributed lines expansion. A significant part of electric machines used in Wind Industry are doubly fed induction motors (DFIM) used as electric generators. They earned the leading market position over the recent decade and continue their run. The machines of this type offer operation stability along with affordable costs. The out­standing technical benefits include the ability for variable speed operation and independent control of reactive and active power. To protect the rotor side converter (RSC) from transient overcurrent during voltage dips, the crowbar circuit protection is usually used. The paper analyzes and investigates the dynamic behavior of the doubly-fed induction motor, back-to-back converter, and the rotor side converter during symmetrical voltage dips using the crowbar protection system with MATLAB/Simulink simulation. In addition, it studies the crowbar circuit affects the diodes, switches, and resistances at the low voltage ride through (LVRT) capability enhancement.

Efficient Approach to LVRT Capability of DFIG-Based Wind Turbines under Symmetrical and Asymmetrical Voltage Dips Using Dynamic Voltage Restorer

<span>The capability of low-voltage ride-through (LVRT) of doubly fed induction generator (DFIG) has been considered as an essence for grid code requirements. Any unbalance on the grid side causes the rotor current of the generator to rise which leads to saturate the dc-link of the back-to-back converter or even destroy it. To meet this requirement, a dynamic voltage restorer (DVR) without dc-link energy storage elements is utilized to compensate any disturbance imposed to the DFIG wind turbine system. On the time of any disturbance or fault, DFIG and DVR are properly controlled in order to compensate the specified faulty phase uninterruptedly. DVR is connected in series to the grid and by injecting instantaneous compensating voltage, prevents the stator voltage from rapid changing; consequently, the rotor side converter can accomplish its normal operation. As voltage dips are the most common grid faults subjected to DFIGs, this paper investigates both symmetrical and asymmetrical voltage dips caused by grid faults. The independent and instantaneous phase voltage compensation, less volume, weight, and cost are the merits to utilize the proposed DVR along with DFIG wind turbines. PSCAD/EMTDC based simulations verifies the capabilities of the proposed technique for the LVRT capability of DFIG.</span>