Low Voltage Ride Research Articles

Fault Tolerant Control of Grid Connected Inverters Based on Low-Voltage Ride Through

To enhance the reliability of new energy grid connected systems, a fault-tolerant model predictive control strategy with low-voltage ride-through capability for grid connected inverter bridge arms has been proposed. Firstly, the operational principles following a single-phase bridge arm fault in the grid-tied inverter are analyzed. Then, a fault-tolerant structure for the grid connected inverter is established by creating a virtual bridge arm using direct current-side capacitors. Subsequently, a current prediction model is established, and control is implemented using redundant vectors. Additionally, by dynamically adjusting reactive current compensation commands based on the relationship between grid voltage drops and reactive current commands, the system is ensured to maintain continuous and stable operation even during grid voltage fluctuations. Finally, experimental results demonstrate that this fault-tolerant control strategy can still maintain the continuous and stable operation of the system when bridge arm faults occur due to grid voltage drops at the inverter grid connection point.

An Oscillation Stability Analysis of a Direct-Driven Wind Power Grid-Connected System Considering Low Voltage Ride Though from an Energy Perspective

To solve the problem of the oscillation stability of direct-driven wind-powered grid-connected systems with a low-voltage crossing control, a method of oscillation stability analysis for these systems, based on interactive energy, is proposed in this paper. Firstly, a dynamic energy model of a direct-driven wind-powered grid-connected system is established, considering a low-voltage traverse control. Secondly, the energy is divided into four parts—the line parameter energy, current inner loop energy, PLL energy, and current inner loop–PLL interaction energy—and the conduction path of the energy during a low-voltage crossing is described. On this basis, the aperiodic components of each energy path are analyzed, the stability level of the system is quantified, the influence of the different control parameters on the interactive energy dissipation is deduced, the key interactive control links affecting the stability of the system are screened, and the influence rules of the parameters are expounded. Finally, a direct-driven wind-powered grid-connected system model is built on the Rt-lab platform, and it is verified by a simulation test. The results show that the interaction energy generated by the interaction of the current inner loop and phase-locked loop is a key factor affecting the stability of the direct-driven wind-powered grid-connected system. The simulation test parameters of the control group were adjusted as the current inner loop’s proportion parameter increased from 1.32 to 5.28, the current inner loop’s integral parameter increased from 4.48 to 6.42, the PLL’s proportion parameter decreased from 9.45 to 6.3, and the PLL’s integral parameter decreased from 50.25 to 40.2. Both the theoretical and experimental results show that increasing the current inner loop’s integral and proportion parameters can improve the stability level of the direct-driven wind-powered grid-connected system; reducing the phase-locked loop’s proportion and integral parameters can also improve the stability level of the grid-connected system.

Investigation of condition monitoring system for grid connected photovoltaic (GCPV) system with power electronics converters using machine learning techniques

Power systems protection has become more vital in recent years to ensure stability, reliability, security, and power quality due to the exponential growth of grid-connected photovoltaic (GCPV) systems. As a result, several nations have set new grid codes for the grid integration of PV plant installations to overcome these concerns. Investigating Fault Ride Through (FRT) capacity is one of the primary criteria for grid codes. For 3-phase GCPV systems, fault detection and classification approaches are proposed in this study. Firstly, different faults that occurred in the GCPV system are categorized and compared, with the critical and analytical evaluation of grid codes, particularly FRT requirements such as Low Voltage Ride Through (LVRT) and High Voltage Ride Through (HVRT) for different nations. Further, a detailed classification and a comparison of the existing FRT techniques are presented for better control methods based on system complexity, detection accuracy, and other evolutionary criteria. To ensure smooth grid operation, accurate fault detection and condition monitoring of the systems are required. This paper discusses a machine learning (ML) based technique for detecting faults in 3-phase GCPV systems. Multi-peak phenomena caused by FRT capabilities and anti-islanding detection are the main problems experienced while integrating a PV system into the local grid. The fault classification technique is developed using weighted K-nearest neighbor (WKNN) and fine Gaussian support vector machine (FGSVM) based ML approaches utilizing Wavelet Transform. The proposed ML-based findings show that the fault detection algorithm-based classification accuracy has significantly improved.

Voltage-Coupled Cascading Trip-off within Permanent Magnet Synchronous Generator Based Wind Farm during Low Voltage Ride Through

Abstract With the increasing penetration of renewable energy, power electronic interfaced devices have become dominant in power system. It is necessary to investigate the dynamic process of the power grid in a smaller time scale. In case of failing in low voltage ride through (LVRT), the traditional method that treats the response of permanent magnet synchronous generator (PMSG) based wind farm as a one-time trip-off cannot accurately model the cascading failures in such a new-type power system. This paper focuses on this issue and conducts a detailed study of the dynamic process in a PMSG wind farm during LVRT. Firstly, we reveal an evolution mechanism of voltage-coupled cascading trip-offs in PMSG wind farm. Then, the wind farm based on PMSG is modeled in DIgSILENT/PowerFactory. The model takes into account the voltage losses on the power collection line inside the wind farm, and each wind turbine includes an independent control model. Finally, by simulation, we obtain the principle on cascading failures of internal wind turbines in the wind farm, and confirm the interaction mechanism between turbines as well as the detailed process of cascading failures.

FRT capability improvement of a wind power system using support vector regression and deep neural network models

ABSTRACT The increasing energy demand and environmental conditions have led many countries to favor renewable energy,such as wind and solar,over conventional power plants. As per the Central Electricity Authority (CEA), India’s wind power capacity has grown substantially, reaching 45,154 MW in 2023, from 22,465 MW in 2013. However, integrating wind generators to an existing power system network can reduce transient stability during faults. To prevent wind turbine disconnection during faults, Indian grid code authorities mandate Fault Ride Through (FRT) or Low Voltage Ride Through (LVRT) capability for wind turbines. This paper proposes Dynamic Voltage Restorer (DVR) for enhancing the FRT capability of a constant speed wind turbine. Analysis and simulation are done on a fixed speed wind turbine employing Squirrel Cage Induction Generator (SCIG) under balanced and unbalanced voltage sags. Performance of DVR with two Artificial Intelligence-based controllers, Support Vector Machines(SVM) Regression Model Based Supervised Machine Learning algorithm, and Deep Neural Network (DNN) controller, is analysed and compared. The SVM Regression algorithm, achieves 100% voltage sag compensation under unbalanced voltage sags, reduces torque pulsations to 25% and maintains rotor speed at rated values, enabling the turbine to remain connected to the grid. Additionally it reduces Total Harmonic Distortion to 2%.

Low Voltage Ride Through Control Strategy for a Two-Stage Grid-Tied Solar Photovoltaic System with Grid Faults

This paper investigates a low voltage ride-through (LVRT) control strategy for a two-stage grid-tied solar photovoltaic (SPV) system with line-to-ground (L-G) and double line-to-ground (L-L-G) faults. A proportional resonant (PR) controller controls the SPV inverter based on classical and reactive power oscillation-based reference current generating techniques. The proposed method injects reactive power as an ancillary service to provide voltage support and prevent power outages, reduces the DC component injection into the grid currents, and finally injects sinusoidal currents into the grid, avoid voltage oscillations in the DC-link and limit the inverter current by operating the boost converter in non-MPPT mode during L-G & L-LG faults. Experimental results for reference current generation using classical method and proposed method are compared to highlight the proposed controller’s ability to maintain power quality during faults.

Bifurcation Analysis and Criterion of Voltage Oscillation Induced by Low Voltage Ride Through Control in Renewable Energy Stations

Bifurcation Analysis and Criterion of Voltage Oscillation Induced by Low Voltage Ride Through Control in Renewable Energy Stations

Impact of Corrective Switching in Wind Farms Operation

Eventually, limits violations of bus voltages or of admissible loadings of transmission lines and/or power transformers may occur by the power system operation. If violations are detected, corrective measures may be carried out aiming their elimination or to reduce their intensity. Loading shedding is an extreme solution and should only be adopted as the last control action. The control tool adopted in this work is Corrective Switching. It controls power flows in electrical networks by changing their topologies, without requiring any additional cost. Due to the large potential of wind energy in Brazil, using the technique of Corrective Switching may result in disconnection of wind farms, whose machines are not equipped with Low Voltage Ride Through function, since its wind generators are turned off when submitted to voltage sags for a short time. Thus, this works aims to verify if Corrective Switching actions, that could eliminate operational violations in electrical energy systems, can cause disconnections of wind farms, contributing to degrade power quality.

Advanced PLL structures for grid synchronization in distributed generation

The actual grid code requirements include specific demands for grid connected wind power generation facilities. The Transmission System Operators are specially concerned about the Low Voltage Ride Through requirements which are becoming more restrictive in terms of the admissible disconnection conditions, but also in the active/reactive power that wind farms should inject to the network under fault conditions to support the grid. Solutions based on the installation of STATCOMs and DVRs, as well as on advanced control functionalities for the existing power converters of wind power plants, have contributed to enhance their response under faulty and distorted scenarios, and hence to fulfill these requirements. However, in order to achieve satisfactory results with such systems it is necessary to count on accurate and fast grid voltage synchronization algorithms, able to work under unbalanced and distorted conditions. This paper analyzes the synchronization capability of three advanced synchronization systems: the DDSRF-PLL, the DSOGI-PLL and the 3phEPLL, designed to work under such conditions. In the following the different algorithms will be presented and discretized and finally their performance, as well as its computational cost, will be tested in an experimental setup controlled by a means of a TMS28335 floating point DSP.

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.

Optimizing the power quality of the MV distribution network in fault condition based on D-STATCOM in accordance with the Moroccan Grid Code requirements

In this work, we present a novel method concerning a D-STATCOM integration to the Moroccan electrical distribution network, which is not yet adopted by national DSO’s (Distribution system Operator), the device is implemented at the PCC (Point of common Coupling) of a grid connected PV power plant, which is a typical case of the increasing penetration of renewable generators in the national electrical network. The device is proposed to compensate for voltage fluctuation and the dynamic support of grid voltage in the event of disturbances or the failure of renewable generators especially in context of the increasing integration of these sources. The control strategy is tuned to achieve performance constraints imposed by the national Grid Code. The proposed system overcomes network uncertainties and grid disturbances and significantly improves the power quality at the point of common connection PCC while absorbing and providing reactive power to the network in an acceptable reversing time due to voltage sags and swells and mitigating voltage flicker. The considered D-STATCOM (Distribution Static Compensator) was able to ride through grid faults in most cases which is necessary to achieve LVRT (Low voltage Ride through) and dynamic voltage support requirements. The results of the simulation are compared to the technical requirements according to the Moroccan Grid code and show good results in simulation while respecting the technical limits imposed by local regulations.

An Improved Grid-Forming Control Strategy for Microgrid Stability in Modern Power System

Permanent Magnet Synchronous Generator-Wind Turbines (PMSG-WTs) are becoming increasingly popular, which is contributing to significant issues concerning the stability of modern power. One crucial aspect is the Low Voltage Ride Through (LVRT) capability, especially in interconnected networks. To address this issue, this study presents a novel control strategy for Grid-Forming Inverters (GFMIs) using Droop Control in modern power systems. The proposed strategy, termed the De-loaded Technique enhanced by Three-Dimensional Fuzzy Logic Control and Supplementary Control Loop (DT-3D FLC-SCL), aims to enhance the stability and performance of five microgrids (MGs) by controlling both, machine-side and grid-side of the WTs. To evaluate the behavior of PMSG-WTs during low voltage conditions, simulation tests are conducted using the IEEE 14-bus modified test system in MATLAB/Simulink environment.

Comparative Analysis of Low Voltage Ride Through Techniques of DFIG Connected to Grid using AI Techniques

The requirement for clean and eco-friendly energy initiated the production of renewable energy. Wind energy promises attractive features such as bulk power production and reduced maintenance cost. Advancement of technologies in the field of wind turbines and generators made the gates open for attractive investments. Adjustable-speed wind turbines tied to Doubly Fed Induction Generators (DFIG) became the most excellent choice of power utilities due to their low-cost power converters and four-quadrant control of useful and wattless powers. The ability to extract a high amount of power for a specified wind speed is a major advantage of DFIG which attracted Power system Operators (PSOs). Low voltage ride-through and wattless Spower support to the grid are estimated and compared using conventional PI controllers, Artificial Neural Network (ANN), and Random Forest Optimization (RFO) algorithm.

Converter Control During Low Voltage Ride Through Operation for Grid-Interfaced Solar PV Battery Assisted System

The grid interfaced solar PV based distributed generation system (DGS) installations have increased tremendously. The penetration of DGS into the grid requires the DGS converter to pose the fault ride through capability. It demands the converter to remain connected during sags and to provide reactive power support to the grid. In this work, the grid interfaced solar PV-battery assisted system for balanced as well as unbalanced power generation along with low voltage ride through (LVRT) functioning is presented. An efficient and simple control technique is developed for the system, such that the DGS converter stays connected to the grid under fault conditions till the LVRT required standards are fulfilled. The DC link voltage variations and LVRT control are achieved by the battery energy storage (BES) bidirectional DC-DC converter (BDDC). The positive sequence grid current components are considered to meet the LVRT standards. The controller ensures the DGS converter currents are within the rated limits. The presented control strategy of DGS converter operation during voltage sags and unbalanced power generation is simulated and validated in MATLAB/Simulink. The developed topology and its control are validated through test results.

Enhancement of LVRT Capability in DFIG-Based Wind Turbines with STATCOM and Supercapacitor

Overvoltage and overcurrent resulting from various faults cause instability in Doubly Fed Induction Generator (DFIG)-based wind turbines connected to a grid. The grid code requirement must be met during faults to minimize the effect of these problems. Low Voltage Ride Through (LVRT) capability is used to meet the grid code requirement. It is important to use coordinate control for transient states in LVRT capability. This study aimed to improve the stator dynamics for ease of calculation and the rotor dynamic model by damping oscillations caused by balanced and unbalanced faults on the grid side. For this, electromotive force (emf) models were developed for stator and rotor dynamic modeling. Furthermore, for the coordinate control of the DFIG, models were developed for a lookup-table-based supercapacitor and a decoupled Static Synchronous Compensator (STATCOM). Using these models, analyses of three-phase and two-phase faults were conducted. Following different balanced and unbalanced faults within the grid, the system was stabilized in a short time, and the oscillations occurring during the faults were quickly damped using the LVRT models developed in this study.

A Novel Protection Method to Enhance the Grid-Connected Capability of DFIG based on Wind Turbines

This paper proposes a robust protection technology to enhance the grid-connected capability of the doubly fed induction generator (DFIG) based on wind turbines (WTs) under low voltage ride through (LVRT) conditions. The proposed method to control the rotor side converter (RSC) and grid side converter (GSC) uses proportional–integral (PI) controllers. The protection devices are the static compensator (STATCOM), crowbar, series dynamic resistor (SDR), and DC-chopper, with the proposed method to control STATCOM using proportional–integral (PI) controllers and the proposed method to control the rest of the protection devices based on the allowable threshold values of rotor current and DC-link voltage. The protection coordination strategy between them is proposed to avoid the disconnection between the rotor circuit and grid, maintain the DC-link at constant voltage, enhance the dynamic response of WT, and improve the voltage response at the point of common coupling (PCC) of WT. The DFIG-WT of 2 MW-575 V connecting to the 34-bus IEEE network is carried out to verify the effectiveness of the proposed method under the conditions of symmetrical and asymmetrical faults, and the LVRT requirements of the Spanish grid code are considered. The obtained simulation results using the PSCAD/EMTDC software show that the rotor current, DC-link voltage, voltage PCC, and power oscillation damping are significantly improved compared to not using it or applying the conventional method based on passivity theory. Therefore, the LVRT capability of the proposed DFIG-WT system is significantly enhanced, and it has enough ability to continue to provide electrical energy to the power network. Abbreviation DFIG, Doubly Fed Induction Generator; DVR, Dynamic Voltage Restorer; FACTS, Flexible AC Transmission System; FRT, Fault Ride Through; FS-WT, Fixed-Speed Wind Turbine; GSC, Grid Side Converter; LVRT, Low Voltage Ride Through; PCC, Point of Common Coupling; PI, Proportional–Integral; PMSG, Permanent Magnet Synchronous Generator; PWM, Pulse Width Modulated; RSC, Rotor Side Converter; SDR, Series Dynamic Resistor; STATCOM, Static Compensator; SVC, Static Var Compensator; UPFC, Unified Power Flow Controller; VS-WT, Variable-Speed Wind Turbine; SLG, Single Line-to-Ground; LL, Line-to-Line; LLG, Double Line-to-Ground; WT, Wind Turbine

SWRDFT Controller for Single Phase Grid Tied PV system with Low Voltage Ride through Capability

Voltage control and power quality (PQ) management are crucial aspects for the control of grid connected voltage source converters (VSC). In this paper, a novel control technique for solar photovoltaic (PV) tied single-phase grid is described based on a Sliding Window Recursive Discrete Fourier Transform (SWRDFT). This article considers a single-phase, double-staged PV interconnection. The major goal of control is to operate the VSC as per the standard grid codes and ensure quality power is delivered to the grid even under abnormal grid conditions. The system is designed to work at unity power factor during typical operation. Reactive power injection is mandated as per a country's grid code and helps to regulate the voltage profile and low voltage ride through (LVRT) during grid voltage fluctuations. Furthermore, the paper focuses on two important aspects viz. load compensation and LVRT operation carried out in the event of grid voltage sags. During night time operation, in the absence of PV, the VSC and dc link capacitor operate as a shunt compensator. The proposed controller completes both the tasks as demonstrated by simulation and hardware results. Additionally, a comparison study using state of the art fundamental extraction techniques based on Second / Third order generalized Integrator (SOGI/TOGI) is presented.

Analysis of Voltage Dip Impact on Doubly Fed Induction Generator under Dynamic Conditions

Doubly Fed Induction Generator (DFIG) is the most widely employed generator in the Wind Energy Conversion Systems (WECS) for the production of electricity. However, despite all of its various advantages, it is extremely vulnerable to grid faults such as voltage dip since its stator is directly coupled to the grid. A voltage dip problem is one the main issues among the power quality concerns. This fault causes the flow of excessive current across both the stator and the rotor terminals, which may lead to serious damage to the generator, power converters, and DC Link capacitor. On the other hand, the current Grid Codes (GC) requires the system to stay connected to the grid during this fault condition and support it in healing its nominal voltage. This capacity of the system is known as the Low Voltage Ride Through (LVRT) capacity. For the system to achieve such capacity, appropriate protection mechanisms or controlling strategies must be utilized. Therefore, in this paper, the crowbar protection technique, PI controller, and the Adaptive Neuro-Fuzzy Inference System (ANFIS) controller are employed. Furthermore, the performance of the system employing PI, crowbar, and ANFIS is analyzed and compared under grid fault conditions, i.e., a voltage dip with a magnitude of 0.1 pu (worst case) using MATLAB/Simulink software and based on actual data obtained from Adama II wind farm. The obtained results unveil that the settling time of ANFIS for controlling the rotor currents in d and q axes (idr and iqr) and DC link voltage is 3.6 s, 3.57 s, and 3.4 s, respectively. On the other hand, the settling times of the PI controller for controlling the rotor currents in d and q axes and the DC link voltage are found to be 4 s, 3.91 s, and 45.2 s, respectively, while the crowbar protection technique’s settling times are found to be 4 s, 6 s, and 4.9 s, respectively. It is evident from the aforesaid results that the ANFIS controller provides the best performance of the three strategies since it allows both the rotor currents and the DC link voltage to return to their steady state values faster than the other two techniques, employed in this investigation.

Sequential Dynamics in Photovoltaic Power Station Under Low Voltage Ride Through

Sequential Dynamics in Photovoltaic Power Station Under Low Voltage Ride Through

Control of a DFIG based wind turbine using modified Conditional Servo-compensator

This paper presents the control of a wind turbine composed by a doubly fed induction generator (DFIG), which provides power to the main grid through a feeder. The control algorithm is designed following the modified Conditional Servo-Compensator (mCS) theory. This control technique was recently developed to a broad class of nonlinear systems, and this paper brings the first result applied to wind turbines. The mCS theory has several advantages compared to others, as it is a robust nonlinear control scheme. First, it provides rigorous stability analysis, that allows explicit definition of performance and operating conditions. Secondly, it is a robust controller, and only needs lump values and bounds for parameters and dynamics. Finally it is very simple and easy to implement, and does not need heavy computer burden, it is only based on standard local measurements, and represents a promising solution for real applications. The theoretical results are verified by simulations using detailed Simpower models. These simulations show very good results facing a Low Voltage Ride Through scenario, which is one of the most severe tests used for practical applications. The proposed scheme could easily be adapted to the control of other applications based on power converters, as the control of the interconnection of a full wind farm to the main grid, or the control of a terminal in a DC grid.