Ride-through Research Articles

Marine Predator Algorithm-Based Optimal PI Controllers for LVRT Capability Enhancement of Grid-Connected PV Systems.

Photovoltaic (PV) systems are becoming essential to our energy landscape as renewable energy sources become more widely integrated into power networks. Preserving grid stability, especially during voltage sags, is one of the significant difficulties confronting the implementation of these technologies. This attribute is referred to as low-voltage ride-through (LVRT). To overcome this issue, adopting a Proportional-Integral (PI) controller, a control system standard, is proving to be an efficient solution. This paper provides a unique algorithm-based approach of the Marine Predator Algorithm (MPA) for optimized tuning of the used PI controller, mainly focusing on inverter control, to improve the LVRT of the grid, leading to improvements in the overshoot, undershoot, settling time, and steady-state response of the system. The fitness function is optimized using the MPA to determine the settings of the PI controller. This process helps to optimally design the controllers optimally, thus improving the inverter control and performance and enhancing the system's LVRT capability. The methodology is tested in case of a 3L-G fault. To test its validity, the proposed approach is compared with rival standard optimization-based PI controllers, namely Grey Wolf Optimization and Particle Swarm Optimization. The comparison shows that the used algorithm provides better results with a higher convergence rate with overshoot ranging from 14% to 40% less in the case of DC-Link Voltage and active power and also settling times in the case of MPA being less than PSO and GWO by 0.76 to 0.95 s.

Low‐voltage ride‐through control strategy for flywheel energy storage system

AbstractDue to its high energy storage density, high instantaneous power, quick charging and discharging speeds, and high energy conversion efficiency, flywheel energy storage technology has emerged as a new player in the field of novel energy storage. With the wide application of flywheel energy storage system (FESS) in power systems, especially under changing grid conditions, the low‐voltage ride‐through (LVRT) problem has become an important challenge limiting their performance. In this paper, we propose a machine‐grid side coordinated control strategy based on model predictive current control (MPCC) for the insufficient LVRT capability of traditional FESS during grid faults. Excellent dynamic properties are demonstrated by the technique, which allows the grid‐side converter output current to swiftly follow the reference current instruction. The FESS's LVRT capability is increased when the grid‐side converter uses the MPCC current inner loop rather than the proportional–integral current inner loop during grid voltage dips. This greatly increases the reactive power response speed and efficiently supports the quick recovery of grid voltage. According to simulation verification carried out by Matlab/Simulink, the suggested control approach can assure the long‐term dependable operation of the FESS during voltage dips. This study can also be used as a reference for improving the FESS's LVRT capabilities in the future.

The Implementation of the Low Voltage Ride-Through Curve on the Protection System of a Wind Power Plant

. This paper presents the implementation of the low voltage ride-through (LVRT) curve in two commercial numerical relays, assessing the features and limitations of each protection device. The LVRT curve is defined in grid codes of several countries, especially those who already have or are planning a high share of wind power in their electric power systems. The functionality of the wind turbine grid protection system is tested in a power system using the PSCAD/EMTDC simulation tool. The fault ride through capability curve applied in the test system is as defined in the Brazilian grid code and the protection system responses evaluated at the point of common coupling of the wind power plant when the power network is under symmetrical and unsymmetrical faults. The biggest challenge to adhere the system operator requirements is to ensure the highest conformity to the defined LVRT curve, because most relays only gives you the option of tuning in discrete time intervals.

Reactive power control of micro-grids using FOSMC for grid code compliance during asymmetrical voltage sags

Application of micro-grids (MGs) as a solution for future energy systems are significantly increasing in recent years. On the other hand, more stringent requirements are added to grid codes (GCs) of low-voltage distribution networks. Accordingly, this paper proposes a low-voltage ride-through (LVRT) control scheme for four-wire multi-source MGs. The novel strategy is composed of two layers for controlling each phase of the grid-connected sources independently. The primary layer contains a reverse-droop function for each phase and fractional-order sliding-mode-control (FOSMC). The secondary layer determines the total requested reactive power for each phase during symmetrical and asymmetrical voltage drops. Then, the mentioned power is shared among the phases of each inverter based on the reactive power-sharing strategy and GC requirements. Based on the proposed grid-following controller, the voltage of faulty phases is compensated by reactive power injection. In addition, power quality indexes are kept in acceptable ranges during abnormalities, and the FOSMC performs better than the conventional methods. The effectiveness of the proposed scheme is verified through offline simulations in MATLAB/Simulink as well as validation by real-time results.

A Coordinated Voltage-Frequency Support Method for VSC-MTDC Integrated Offshore Wind Farms System

Voltage and frequency stability is one of the major concerns with the continuously increasing penetration of offshore wind farms (OWFs) integrated into onshore grid via VSC-MTDC system, and it is a challenge to coordinate its low voltage ride-through (LVRT) and frequency regulation (FR) control when a local fault or large disturbance occurs in onshore grid. To address this challenge, a coordinated voltage-frequency support (CVFS) method for the VSC-MTDC integrated OWFs system is proposed in three parts: 1) an adaptive maximum power point tracking (MPPT) strategy is developed for wind turbines (WTs) to satisfy the power demands for LVRT and FR; 2) an active and reactive power quantification strategy, which firstly considers the static load characteristics of nodes nearest the grid side VSC (GSVSC) stations, is proposed for GSVSC stations to support LVRT and FR respectively; 3) an adaptive power allocation strategy, which considers the capacity constraint and the coordination factor with deviation and rate of change of voltage and frequency of different GSVSC stations, is conducted to achieve differential power distribution between LVRT and FR. Extensive test results have validated the effectiveness and performance of the proposed CVFS method.

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.

Current‐Limiting Strategy for Unbalanced Low‐Voltage Ride Through of the SMSI‐MG Based on Coordinated Control of the Generator Subunits

Unlike the inverters in the traditional alternating‐current (AC) microgrid, those in a microgrid with series microsource inverters (SMSI‐MG) are connected to the power grid after being cascaded. The authors of this study first divide the control sections according to the degree of grid voltage dips and formulate a coordinated scheme to suppress fluctuations in the output powers of the SMSI‐MG. For the section in which the degree of unbalanced grid voltage dips is relatively low, a current‐limiting strategy that reduces the output power of the SMSI‐MG through the coordinated control of the generator subunits (CCGU) is proposed. More active power can be provided by the SMSI‐MG when the proposed strategy is used, than in the strategy that is based on changing the reference power, and the output reactive power of the SMSI‐MG can be automatically changed with the degrees of dip and unbalance of the grid voltage. The Light Gradient‐Boosting Machine (LightGBM) is used to establish a mapping relationship between the parameters characterizing overcurrent and the reduction quantity in output active power of the SMSI‐MG to implement the CCGU‐based current‐limiting strategy. The complex collaborative control is simplified to improve the low‐voltage ride through (LVRT) capability of the SMSI‐MG.

Optimizing Low-Voltage Ride-Through (LVRT) Curves for Wind Farms using Genetic Algorithms: A Case Study of Taiwan Power System

Optimizing Low-Voltage Ride-Through (LVRT) Curves for Wind Farms using Genetic Algorithms: A Case Study of Taiwan Power System

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 Enhanced Low-voltage Ride-through for PMVG-based WTS with Unified Super-capacitor and Rotor Speed Control

An Enhanced Low-voltage Ride-through for PMVG-based WTS with Unified Super-capacitor and Rotor Speed Control

Three-stage dynamic equivalent modeling approach for wind farm using accurate crowbar status identification and voltage differences among wind turbines

With increasing wind farm scale, dynamic modeling and simulating the low-voltage ride-through (LVRT) process of wind farms are time- and source-consuming. Thus, a dynamic equivalent model of a wind farm considering the LVRT process is necessary and vital for power system analysis. However, the crowbar status of each doubly-fed induction generator (DFIG), voltage, and wind speed differences among will influence the LVRT process and equivalent results. To consider these three factors comprehensively and eliminate the error, this paper proposes a three-stage dynamic equivalent modeling approach, using accurate crowbar identification and voltage differences among DFIGs. Stage I: DFIGs are divided by crowbar status. A new accurate crowbar identification method is proposed to consider the interference from other DFIGs, using the experimental two-machine system and several dynamic simulations to correct fault voltage. Stage II: The often-overlooked voltage differences are considered, and DFIGs are divided into different clusters for accurate fault dynamics. Stage III: To eliminate errors resulting from wind speed differences, the DFIG active power reference is corrected based on the analytical function of the wind farm LVRT process. The proposed model can accurately identify crowbar status and consider the voltage and wind speed differences without detailed model simulation results, improving the accuracy. Case studies are undertaken on a wind farm with fifty DFIGs. Simulation results indicated that the proposed model can match the detailed model under different wind scenarios and fault voltages, and it also increases simulation efficiency, which is suitable for studying the effect of LVRT on power systems.

An implementation of inertia control strategy for grid-connected solar system using moth-flame optimization algorithm

As the solar power system power system grows rapidly, inertia control strategy (ICS) becomes crucial to enable stable grid integration. However, the existing ICS lacks of dynamic weather analysis with maximum power point tracking (MPPT) and fault-ride through (FRT) capabilities such as low voltage ride-through (LVRT) and high voltage ride-through (HVRT). In this work, an inertia weighting strategy and the Cauchy mutation operator are introduced to improve the moth-flame optimization (MFO) algorithm to support vector machine prediction of photovoltaic power generation. In this paper, the proposed adaptive VICS with variable moment of inertia (J) and damping factor ( D P ) demonstrates its effectiveness with faster frequency recovery, less overshooting and continuous stable operation under grid fault and dynamic weather. The MFO algorithm is used to implement inertia control strategies for grid-connected solar systems. Accurate simulation results confirm the inertia control of the emulsion and the control of the solar system. The results of the simulation show a significant improvement in frequency with the designed MFO and compared to Horse Herd Optimization (HHO). The proposed method contributes to improve photovoltaic energy prediction, reduces the impact of photovoltaic power penetration into the grid and maintains the system reliability.

Pilot protection scheme for transmission line of wind-storage combined system based on one-mode current similarity

With the gradual growth of the scale of energy storage devices for wind power generation, a large-scale grid-connected wind-storage combined system (WSCS) has been formed. When the external transmission line fails, its control strategy will lead to problems such as limited output short-circuit current amplitude, frequency deviation from power frequency, and uncertain phase angle, which makes the traditional pilot protection possible to malfunction and refuse to operate. In order to solve this problem, this paper first analyzes the fault current output characteristics of the WSCS during low voltage ride through (LVRT), and its impact on the traditional pilot protection scheme. Secondly, considering the difference of fault current amplitude and phase change at both sides of the transmission line, the similarity relationship of one-mode current is verified. Finally, a pilot protection scheme based on one-mode current similarity is proposed in this paper. The simulation results conducted using PSCAD/EMTDC demonstrate that the proposed scheme exhibits robust anti-interference capability, capable of withstanding significant transitional resistance and noise, while maintaining good selectivity and reliability.

A Current Differential Protection Scheme for Distribution Networks with Inverter-Interfaced Distributed Generators Considering Delay Behaviors of Sequence Component Extractors

The high-level proliferation of inverter-interfaced distributed generators (IIDGs) in modern distribution networks (DNs) has changed system topologies and fault current signatures, which compromises the protective relays in DNs. Investigating IIDG fault behaviors-based protection scheme will benefit the grid’s safety and stability. This paper proposes a novel current differential protection (CDP) scheme that considers the delay behaviors of positive- and negative-sequence component extractors for IIDGs in DNs. A frequency-domain analytical model of the fault current for a grid-connected IIDG with the PQ control strategy and a low-voltage ride-through (LVRT) capability is investigated. The dynamic behavior of the IIDGs considering the sequence-component extractor based on the Pade approximation is presented, where the T/4 delay extractor of the IIDGs causes a two-stage behavior in the fault transient process. It is found that a 5 ms error between the measured and actual values after the fault will affect the transient characteristics of the IIDGs. The transient current generated by the IIDGs during grid faults contains a large number of low-order harmonic components within the range of 0–200 Hz, which is significantly different to the current provided by the power grid. Therefore, the proposed CDP scheme uses protective relays at both terminals to obtain the required transient electric quantity using the Prony method. By constructing the frequency-characteristics ratio (FCR) and the exchanging FCR between two terminal relays, the developed protection criteria are implemented. The accuracy of the fault analysis method, whose maximum computational error is below 0.1%, and the feasibility of the proposed protection scheme are demonstrated by using a 10 kV DN in a PSCAD/EMTDC simulation, which can be applied to various fault conditions and traditional DNs without IIDGs.

Analysis of the impact of transient overvoltage on grid-connected PMSG-based wind turbine systems

The annual increase in installation capacity and electrical production of renewable energy sources, primarily wind turbine generators (WTG), is shaping a renewable energy dominated power system. WTGs are susceptible to the temporary overvoltage caused by reactive power surplus following low-voltage ride through (LVRT). This can lead to the large-scale trip-off of WTGs and pose significant risks to the secure and stable operation of power systems. An insightful elaboration of the underlying mechanisms determining the occurrence of temporary overvoltage, and an analysis of influencing factors, is pivotal to ensure the reliable integration of WTGs. This paper investigates the temporary overvoltage in the AC systems integrated with multiple renewable energy stations. A temporary overvoltage model that accounts for various types of equipment has been derived. Resorting to the model, the influence of LVRT parameters of WTGs, SCR and IR of the AC system on the maximum terminal overvoltage has been quantitatively assessed. Simulations and semi-physical validations have been conducted to verify the effectiveness and accuracy of the theoretical analysis.

Transient Behavior Analysis of Microgrids in Grid-Connected and Islanded Modes: A Comparative Study of LVRT and HVRT Capabilities

Microgrids, with integrated PV systems and nonlinear loads, have grown significantly in popularity in recent years, making the evaluation of their transient behaviors in grid-connected and islanded operations paramount. This study examines a microgrid’s low-voltage ride-through (LVRT) and high-voltage ride-through (HVRT) capabilities in these operational scenarios. The microgrid’s behavior was analyzed using both electromagnetic transient (EMT) and RMS simulation methods. Two operational modes, grid-connected and islanded, were considered. A three-phase diesel generator acted as a reference machine in islanded mode. Findings highlighted distinct behaviors in the two operational modes. The EMT simulation revealed in-depth characteristics of electrical parameters, showing high-frequency oscillations more precisely than the RMS simulation. Additionally, the transient recovery times were longer in islanded mode compared to grid-connected mode. The EMT simulation offers a more detailed portrayal of transient behaviors than the RMS simulation, especially in capturing high-frequency disturbances. However, its completion time becomes significantly extended with longer simulation durations. Microgrids showcase distinct transient behaviors in grid-connected versus islanded modes, especially in LVRT and HVRT scenarios. These findings are critical for the design and operation of modern microgrids.

Impact of LVRT Control on Transient Synchronizing Stability of PLL-Based Wind Turbine Converter Connected to High Impedance AC Grid

With large scale of wind turbines connected to high impedance AC grid, transient synchronizing stability of PLL (phase locked loop) based WTC (wind turbine converter) during LVRT (low voltage ride through) is increasing concerned. However, the existing research is usually carried out at the assumption of constant current injection. The influence of dynamic current injection adjusted by LVRT control is neglected. Yet, in high impedance AC grid, the dynamic current injection significantly affects the terminal voltage tracked by PLL. Then LVRT control has much impact on the transient synchronizing stability, which is concerned especially in this paper. First, an novel equivalent motion model is developed, in which PLL is modelled in the form of rotor motion and LVRT control adjusts its equivalent driving force similar as governor in synchronous generator. Then based on the developed model, accelerating-decelerating area method is employed to reveal the transient stability mechanism from energy's transformation and dissipation. Transient stability region method is employed to present the visualized stability region. Furtherly, the influence of K-factor, grid impedance and grid voltage sag are studied from the influence of them on accelerating-decelerating area and stability region. Finally, simulated results are presented to verify the analytical results.

Low voltage protection method of DFIG based on rotor-side double current limiting circuit

A doubly fed induction generator (DFIG) configured for crowbar protection faces the following problems during low voltage ride through (LVRT): delayed input of crowbar protection and the difficulty in coordinating current limiting targets and DC voltage overrun with constant resistance rectification. A low voltage protection method of a DFIG based on a rotor-side double current limiting circuit is proposed. The rotor current characteristics during a fault are analyzed from a time domain perspective and used as a basis for resistance setting. The transient response characteristics of a resistive superconducting fault current limiter (RSFCL) are used for fast initial suppression of rotor currents. The adaptive crowbar resistance adjustment method is used to realize the coordinated consideration of current limiting and DC voltage non-overrun. The simulation results show that the proposed protection method effectively shortens the actual input time of the current limiting circuit and has good suppression ability for the rotor current at the early stage of fault. The adaptive and flexible resistance setting of the controllable crowbar circuit ensures that the DC voltage does not exceed the limit during the fault current limiting period, which helps improve the LVRT capability of doubly fed wind turbines.

A model predictive control strategy for enhancing fault ride through in PMSG wind turbines using SMES and improved GSC control

Wind energy has emerged as a prominent player in the realm of renewable energy sources, both in terms of capacity and technological adaptability. Among the various renewable energy technologies, wind turbine generators stand out as the most widely employed. Recently, gearless permanent magnet synchronous generators have gained traction in the wind energy sector due to their appealing features, such as reduced maintenance costs and the elimination of gearboxes. Nevertheless, challenges remain, particularly concerning the grid-friendly integration of wind turbines, specifically with regard to high voltage ride-through (HVRT) and low voltage ride-through (LVRT) improvements. These challenges pose a threat to grid stability, impede Wind Turbine Generator performance, and may lead to significant damage to wind turbines. To address these concerns, this research proposes an integrated strategy that combines a model predictive control (MPC) superconducting magnetic energy storage (SMES) device with a modified WTG grid-side converter control. By coupling SMES devices to the dc-link of Permanent Magnet Synchronous Generator WTGs, the proposed approach aims to achieve an overvoltage suppression effect during grid disturbances and provide support for grid reactive power. Through various test scenarios, the feasibility and practicality of this suggested technique are demonstrated.

Enabling LVRT Compliance of Electrolyzer Systems Using Energy Storage Technologies

This paper presents a comprehensive techno-economic analysis of different energy storage systems (ESSs) in providing low-voltage ride-through (LVRT) support for power electronics-based electrolyzer systems. A framework for analyzing the performance of a grid-integrated electrolyzer-ESS system is developed, taking into account realistic scenarios and accurate models. The system components consist of a 500 kW alkaline electrolyzer module integrated with a medium-voltage grid and three different commercially available ESSs based on Li-ion battery, Li-ion capacitor, and supercapacitor technology, respectively. The performance of these ESSs is extensively studied for three LVRT profiles, with a primary focus on the upcoming Danish grid code. In order to perform simulation studies, the system is implemented on the MATLAB®/Simulink®-PLECS® platform. The results demonstrate that all three energy storage technologies are capable of supporting the electrolyzer systems during low-voltage abnormalities in the distribution grid. The study also reveals that the supercapacitor-based technology seems to be more appropriate, from a techno-economic perspective, for fault ride-through (FRT) compliance.