Low-voltage Ride-through Capability Research Articles

Coordinated Control Scheme of Battery Storage System to Augment LVRT Capability of SCIG-Based Wind Turbines and Frequency Regulation of Hybrid Power System

Fixed speed wind turbine-squirrel cage induction generator (FSWT-SCIG)-based wind farms (WFs) are increasing significantly. However, FSWT-SCIGs have no low voltage ride-through (LVRT) and frequency control capabilities, which creates a significant problem on power system transient and steady-state stability. This paper presents a new operational strategy to control the voltage and frequency of the entire power system, including large-scale FSWT-SCIG-based WFs, by using a battery storage system (BSS). The proposed cascaded control of the BSS is designed to provide effective quantity of reactive power during transient periods, to augment LVRT capability and real power during steady-state periods in order to damp frequency fluctuations. The cascaded control technique is built on four proportional integral (PI) controllers. The droop control technique is also adopted to ensure frequency control capability. Practical grid code is taken to demonstrate the LVRT capability. To evaluate the validity of the proposed system, simulation studies are executed on a reformed IEEE nine-bus power system with three synchronous generators (SGs) and SCIG-based WF with BSS. Triple-line-to-ground (3LG) and real wind speed data are used to analyze the hybrid power grid’s transient and steady-state stability. The simulation results indicate that the proposed system can be an efficient solution to stabilize the power system both in transient and steady-state conditions.

Control of a BDFIG Based on Current and Sliding Mode Predictive Approaches

The Brushless Doubly Fed Induction Generator (BDFIG) is a great attraction nowadays thanks to its high reliability and high low voltage ride-through capability. In variable speed generation systems, the most used control techniques are the vector control, direct torque/power control. Vector control is highly sensitive to parameters variations, while the two others offer high amount of ripples reducing power quality. This paper therefore proposes a Sliding Mode Power Predictive Control (SMPPC) and an Indirect Model Power Predictive Control (I-MPPC) for a simple and efficient power control of the BDFIG. The SMPPC takes current components in the αβ frame as sliding surfaces derived from the I-MPPC based on current predictions to track the desired active and reactive powers in the BDFIG. A cost function defined as currents’ quadratic errors is used to choose the appropriate voltage vector for control winding supply, and the Particle Swarm Optimization algorithm is used to determine the optimal gain for the SMPPC. Simulations on MATLAB/Simulink are carried out to show the effectiveness of the control schemes as well as their robustness to some parameters variations. More so, power compensation is used to improve the capability of the control strategy to provide sinusoidal and balanced currents under unbalanced grid conditions. The proposed methods compared to direct power control show good performances in terms of total harmonic distortion reduction, low ripples and robustness, strengthening the idea of using the BDFIG as an alternative to new generation of wind energy conversion systems.

Enhancement of low-voltage ride-through capability of permanent magnet synchronous generator wind turbine by applying state-estimation technique

Purpose The purpose of this study is to propose a control scheme based on state estimation algorithm to improve zero or low-voltage ride-through capability of permanent magnet synchronous generator (PMSG) wind turbine. Design/methodology/approach Based on the updated grid codes, during and after faults, it is necessary to ensure wind energy generation in the network. PMSG is a type of wind energy technology that is growing rapidly in the network. The control scheme based on extended Kalman filter (EKF) is proposed to improve the low voltage ride-through (LVRT) capability of the PMSG. In the control scheme, because the state estimation algorithm is applied, the requirement of DC link voltage measurement device and generator speed sensor is removed. Furthermore, by applying this technique, the extent of possible noise on measurement tools is reduced. Findings In the proposed control scheme, zero or low-voltage ride-through capability of PMSG is enhanced. Furthermore, the requirement of DC link voltage measurement device and generator speed sensor is removed and the amount of possible noise on the measurement tools is minimized. To evaluate the ability of the proposed method, four different cases, including short and long duration short circuit fault close to PMSG in the presence and absence of measurement noise are studied. The results confirm the superiority of the proposed method. Originality/value This study introduces EKF to enhance LVRT capability of a PMSG wind turbine.

A Low Voltage Ride Through Strategy of DFIG based on Explicit Model Predictive Control

In this paper, an improved demagnetization control, based on Explicit Model Predictive Control (E-MPC) is proposed to improve Low Voltage Ride Through (LVRT) capability of Doubly Fed Induction Generators (DFIGs). By injecting an additional rotor current component, the demagnetization control can efficiently eliminate the free and negative flux to avoid saturation of the rotor converter. The conventional demagnetization control is based on fixed scaling factors, whose control performance can’t be guaranteed for different fault conditions. The proposed E-MPC approach can fully explore the potential of rotor side converter. Besides, the control parameters of E-MPC are derived offline and very efficient for online control. In addition, the proposed E-MPC structure is simple and easy to be implemented. The mechanism of proposed E-MPC is presented in detail and verified in Matlab/Simulink. The results show that the proposed control scheme has a good performance and can improve the LVRT capability of DFIGs under various fault conditions, especially unbalanced faults.

Enhancement of Dynamic Modeling for LVRT Capability in DFIG-Based Wind Turbines

Low-voltage ride through (LVRT) is important for system compensation and reliable operation of the system during balance and unbalanced voltage dips. In this study, a new LVRT capability method was developed using active and passive compensator in doubly fed induction generator (DFIG)-based wind turbines. While the active compensator provides the control of the rotor-side converter and grid-side converters of DFIG, the passive compensator decreases the stator and rotor over currents and injects reactive power into the network to support the grid voltage DFIG. Besides, rotor electromotive force is developed to improve LVRT capability against not only symmetrical but also asymmetrical faults of DFIG. It was found that the system became stable in a short time and oscillations damped using active and passive compensator modeling.

A General Mathematical Model for LVRT Capability Assessment of DER-Penetrated Distribution Networks

Low voltage ride through (LVRT) is one of the indispensable issues of recent decade in the context of grid codes. LVRT stands for the ability of a generation facility to stay connected during the voltage dip. Despite the numerous discussions in recent works, but they mostly concentrate on the LVRT-based control of distributed energy resources (DERs) integrated into a microgrid and its improvement. However, what has been hidden and not addressed any more yet is an index to measure the LVRT capability of a DER-penetrated distribution network (DPDN) under different voltage sags. This takes precedence when we want to evaluate the LVRT capability of DPDNs with consideration of various LVRT categories of DERs mandated in IEEE 1547 standard. This paper introduces a general framework for LVRT assessment of a DPDN by solving a system of differential algebraic equations (DAEs). Then expected LVRT capability of a DPDN is evaluated by a proposed LVRT index through the implementation of Monte Carlo simulation technique.

An efficient crowbar to improve the low voltage ride-through capability of wind turbines based on DFIG excited by an indirect matrix converter

Due to numerous advantages, in this work, the traditional back-to-back converter is substituted with an indirect matrix converter (IMC) to control the doubly-fed induction generator (DFIG). The recent grid codes require that the wind turbines must have the low voltage ride-through (LVRT) capability. One of the main challenges of the IMC that slows down the industrial applications is the fault currents handling. In this paper, a new low cost, simple and reliable method is proposed to protect the IMC from large fault currents. This method is based on a novel crowbar structure. The PSIM simulation results confirm the efficiency of the proposed method in satisfying the new LVRT standards. Also, experimental results of a laboratory prototype verify the effectiveness of the proposed method.

Cause, Classification of Voltage Sag, and Voltage Sag Emulators and Applications: A Comprehensive Overview

The large-scale application of wind power and photovoltaic power solves the energy crisis and alleviates the environmental problems caused by the use of conventional energy. However, they are at risk of being randomly tripped from the network when faced to voltage sag and severe fault events, which will lead to a sudden reduction of active power output and also complicates fault recovery process of the whole system. Moreover, it may also aggravate failures and lead to large-scale power outages, which stimulates a growing interest in analyzing the low-voltage ride-through (LVRT) capabilities of the renewable energy systems (RES) and improving the performance through developing various mathematical models and analysis tools. In this paper, a systematical overview of cause, classification of voltage sag phenomena and voltage sag emulating techniques is presented, and four voltage sag generators (VSGs) are discussed and compared, which include generator based-VSG, shunt impedance based-VSG, transformer based-VSG and full converter based-VSG. Furthermore, a closed-loop detection platform based on real-time digital simulator (RTDS) for the converter controller of a permanent magnet synchronous generator (PWSG) set is introduced, to investigate the LVRT performance of the WT system under grid voltage sag conditions. Finally, the application of VSG in RES are presented and the future research directions are also discussed.

Multilevel cascaded three-phase inverter with low-voltage ride-through flexible control capability for photovoltaic systems

Multilevel cascaded three-phase inverter with low-voltage ride-through flexible control capability for photovoltaic systems

Enhancement of DFIG LVRT Capability During Extreme Short-Wind Gust Events Using SMES Technology

Wind energy is one of the premier renewable energy sources that have gained popularity during the last decade. Among the currently available wind energy conversion systems (WECS), doubly fed induction generator-based technology has been widely employed due to its superior advantageous. The key features of the DFIG-based WECS include its ability to capture more wind energy and support the grid with large reactive power during short disturbance events. On the other hand, DFIG is very sensitive to grid faults which affect its fault ride through (FRT) capability. Furthermore, extreme wind gust even for short durations may lead to the violation of the low voltage ride through (LVRT) threshold limits set by worldwide transmission line operators. This situation cannot be mitigated by the turbine blades pitch controller since the response of the pitch mechanical control is much slower than the rapid dynamic change in the wind speed during short duration of wind gust events. While DFIG FRT capability has been discussed in several papers in the literature, not much attention was given to the mitigation of the effects of extreme wind gust of short duration on the DFIG performance. In this paper, the effect of various levels of wind gust on the performance of a DFIG-based wind energy conversion grid-connected system is investigated and mitigated using a new controller for superconducting magnetic energy storage (SMES) unit. A combination of hysteresis current and fuzzy logic controllers is employed to control the voltage source converter and the DC-DC chopper interfacing the SMES coil with the investigated system. Simulation results reveal the effectiveness of the proposed SMES controller that can be easily implemented within existing as well as new WECS installations.

Positive-Negative Sequence Current Controller for LVRT Improvement of Wind Farms Integrated MMC-HVDC Network

Positive and negative sequence based current control strategy is developed for the modular multilevel converter (MMC), which complies with the grid code requirements during the balanced and unbalanced faults at the point of common coupling of AC grids. This research proposes an efficient and simplified current limiting technique to keep the inverter individual phase current at a predefined threshold during faults. In this work, the current controller of the MMC converter is designed based on stationary reference frame while positive sequence synchronous reference frame is used to design the current limiter. The proposed work considers the complete dynamics of permanent magnet synchronous generator (PMSG) and doubly fed induction generator (DFIG) based wind energy. The MMC aggregate model is developed and simulated in Matlab/Simulink. The MMC model is also developed using real-time digital simulation (RTDS). A comparative performance analysis between the proposed and the conventional current limiter is provided where the proposed sequence-based current controller with the current limiter shows promising performance under severe disturbances. Besides grid compliance, the results with the proposed control scheme demonstrate the improvement of low voltage ride-through capability without any violation of converter current and HVDC link voltage limits.

An efficient crowbar to improve the low voltage ride-through capability of wind turbines based on DFIG excited by an indirect matrix converter

An efficient crowbar to improve the low voltage ride-through capability of wind turbines based on DFIG excited by an indirect matrix converter

Improved Adaptive Robust Control for Low Voltage Ride-Through of Front-End Speed Regulation Wind Turbine

This paper proposes a low voltage ride-through (LVRT) control method for the front-end speed regulation (FESR) wind turbine based on an improved adaptive robust control (IARC) to find the solution of the generator parameter variation by grid voltage dip and enhance the LVRT capability of the FESR. First, the FESR system mathematical models and the control objective of LVRT are analyzed. Then, in the improved adaptive robust controller, the Lyapunov function for three sub-systems and the energy function of the system are constructed. The excitation control law and parameter replacement law of the system are obtained by the error compensation term and additional control variable. The method makes the energy function satisfy the dissipation inequalities to guarantee the stability and ability to suppress disturbance of the system. To verify the effectiveness of the proposed control method, the proposed IARC is compared with the predictive fuzzy PID (PFPID) by time-domain simulations under different fault conditions. The results show that the proposed IARC can not only realize the rapid regulation of reactive power and effective resistance to grid voltage fluctuations but also improve robustness and transient stability of the system and enhance the LVRT performance of the FESR during the grid voltage dip.

Using Parallel Capacitor-based BFCL with MOV for Enhancing the LVRT Performance of SEIG-Based Wind Power Plants

Fulfilment the low-voltage ride-through (LVRT) is one of the important requirements of the grid codes (GCs) for connecting wind power plants (WPPs) to the power system. This study proposes a parallel capacitor-based bridge-type fault current limiter (PCBFCL) with metal oxide visitor (MOV) to comply the LVRT requirement of WPPs. The configuration of conventional BFCL in three steps is modified and developed to comply the WPP environment requirements. Extended time domain simulations are carried out in PSCAD/EMTDC environment to prove the efficiency of the PCBFCL under symmetrical and unsymmetrical faults. Also, the series dynamic resistor (SDR) is considered to compare its capability with the proposed PCBFCL. The aggregated self-excited induction generator (SEIG) is utilized to WPP model. Consideration simulation results, the PCBFCL provides the most effective series device to satisfy the LVRT capability of SEIG-based WPPs and has superior performance than the SDR.

Enhancement of the Dynamic Behavior of Grid-Connected DFIG Based Wind Turbines by using Fuzzy Logic Controller under LVRT Conditions

In recent years, due to the interconnection of large capacity wind turbines to the power grid lead, there are serious issues in the stability of Grid and generation of electrical power. Also, it is showing effect on the dynamic performance of the electrical power systems. To maintain stability during sudden changes in the grid, the LVRT (Low Voltage Ride Through) capability of the Wind Turbines is one of the prime requirements. Wind turbines attached to DFIG (Doubly Fed Induction Generators) are advantageous which have LVRT capability at limited extent. In this paper, the elaborated discussion of the LVRT of Wind turbines shafted to DFIG's in the Grid. It also presents the complete description of the sudden changes in the systems like transient characteristics and the Doubly Fed Induction Generators dynamic response at the time of grid voltage faults (Symmetrical and Asymmetrical). The latest rotor side control technology is displayed in this paper for DFIG and wind turbines with improved capacity of low voltage ride through at the time of severe grid voltage sags. A Fuzzy Logic controller-based control technology is introduced in this paper which performs the balancing the rotor-side voltage and short circuits during the disturbances in the Grid. The advantage in this proposed control scheme is that it reduces the additional cost and reliability issues. So, the DFIG is efficient and usability company norms are satisfied with the proposed Fuzzy logic controller compared to regular controller like PI controller. The performance of the proposed system is simulated and verified in the computer. The results are displayed and it conclude that the control strategy of LVRT capability for Grid connected DFIG based wind turbine systems with Fuzzy Logic Controller are more effective than the conventional control Methods.

Fuzzy Logic Control for Low-Voltage Ride-Through Single-Phase Grid-Connected PV Inverter

This paper presents a control scheme for a photovoltaic (PV) system that uses a single-phase grid-connected inverter with low-voltage ride-through (LVRT) capability. In this scheme, two PI regulators are used to adjust the power angle and voltage modulation index of the inverter; therefore, controlling the inverter’s active and reactive output power, respectively. A fuzzy logic controller (FLC) is also implemented to manage the inverter’s operation during the LVRT operation. The FLC adjusts (or de-rates) the inverter’s reference active and reactive power commands based on the grid voltage sag and the power available from the PV system. Therefore, the inverter operation has been divided into two modes: (i) Maximum power point tracking (MPPT) during the normal operating conditions of the grid, and (ii) LVRT support when the grid is operating under faulty conditions. In the LVRT mode, the de-rating of the inverter active output power allows for injection of some reactive power, hence providing voltage support to the grid and enhancing the utilization factor of the inverter’s capacity. The proposed system was modelled and simulated using MATLAB Simulink. The simulation results showed good system performance in response to changes in reference power command, and in adjusting the amount of active and reactive power injected into the grid.

Reinforcement Learning Controllers for Enhancement of Low Voltage Ride Through Capability in Hybrid Power Systems

The present study applies reinforcement learning strategy for controller design to improve the low voltage ride through (LVRT) capability of a hybrid power system through convertible static compensator (CSC). This article considers different configurations of CSC such as static synchronous series compensator (SSSC), one static synchronous compensator (STATCOM), two STATCOMs, and unified power flow controller (UPFC). Both Q-learning and dynamic fuzzy Q-learning (DFQL)-based controllers are designed and their performances were compared with classical proportional-integral derivative (PID) controller considering a 3-machine system consisting of 2-synchronous and 1-wind energy systems. The results of simulation show that the performance of DFQL-based controller is better compared to other 2-controllers in improving the LVRT capability. Further, it is shown that the UPFC and two STATCOMs configurations of CSC provide higher voltage support compared to other configurations.

Development of improved direct current based saturated core fault current limiter in DFIG system for enhancing the low voltage ride‐through capability

With the increase of electrical energy consumption and associated power grid expansion the complexity in the grid network increases which tends to increase the fault occurrence possibilities. Low voltage ride-through capability helps the system to achieve the standard of grid code by remaining connected with the grid during fault occurrence. Direct current-based saturated core fault current limiter (DC-SCFCL) is a type of fault current limiter with superior influence in fault ride-through (FRT) capability. It has an arrangement of embedded alternating current coil and direct current (DC) coil across the side and centre of the core limb. However, being more effective in FRT, the ideal DC-SCFCL has some of its drawback such as development of high voltage across the DC coil and more current difference during fault occurrence. To limit these drawbacks a modified DC-SCFCL with shorted ring and also working with the coil below its critical temperature has been proposed in this study. The voltage profile, as well as the current profile, has been analysed which comprises its behaviour in all conditions. The proposed technique is applied to DFIG-based wind energy system to restrict the fault current and enhance the FRT capability.

An integrated reactive power control strategy for improving low voltage ride-through capability

Among all renewable energies, wind power is rapidly growing, whereby it has the most participation to supply power. Doubly fed induction generator (DFIG) is the most popular wind turbine, as it can play a very significant role to enhance low voltage ride through (LVRT) capability. Ancillary services such as voltage control and reactive power capability are the main topics in wind power control systems that should be handled profoundly and carefully. The lack of reactive power during fault period can result in instability in generators and/or disconnection of the wind turbine from the power system. The main aims of this study are to illustrate the most effective approaches subject to improve the efficiency, stability, and reliability of wind power plant associated with LVRT capability enhancement. This effectiveness and efficiency are demonstrated by, firstly, comparison between all types of wind turbines, focusing on the ancillary services, after the existing advanced control strategies. According to the literature, there is a consensus that modifying converter-based control topology is the most effective approach to enhance LVRT capability in DFIG-based wind turbine (WT). Therefore, an advanced integrated control strategy is designed by considering the effect of the rotor side converter (RSC) and the grid side converter (GSC). A model of the wind power plant is presented based on the control objectives. MATLAB/Simulink is also used to illustrate the effectiveness of the designed algorithm.

Multi-objective PSO applied to PI control of DFIG wind turbine under electrical fault conditions

Wind generation increase in electric power systems is a general trend in many countries. Variable speed wind turbines (WT) with doubly fed induction generators (DFIG) are commonly used for this purpose. In order to ensure stability and obtain the desired performance when WT are subject to transient disturbances, their control system needs to operate properly. This work aims at tuning the controllers comprising the DFIG control structure enhancing transient performance during electric faults and so contributing to the Low-Voltage Ride-Through (LVRT) capability. To do this, a multi-objective particle swarm optimization algorithm (MOPSO) is proposed applying to the complete dynamic model of the WT (electrical and mechanic parts) and minimizing a set of objective functions (OF) adapted to the electrical network fault problem. Tuning performance is compared with the classical symmetrical optimum method. Simulation results show that the MOPSO and penalization of both electrical and mechanical variables in the OF led to improved mechanical oscillations damping and voltage performance during a fault event, enhancing the LVRT capability even for the more critical condition of the flexible mechanical coupling. The results validate the proposed MOPSO as an effective tool capable of improving the behavior of this type of control for WT.