Low Voltage Ride Research Articles

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.

A New Method to Enhance the Low Voltage Ride Through Capability of Doubly Fed Induction Generator Using Resistive Type Superconducting Fault Current Limiter

A New Method to Enhance the Low Voltage Ride Through Capability of Doubly Fed Induction Generator Using Resistive Type Superconducting Fault Current Limiter

An Enhanced Control Procedure for that DVR to accomplish both LVRT and HVRT in the DFIG Wind Turbine

In general, Double Fed Induction Generator DFIG-driven wind turbines are extremely sensitive to fluctuations in the grid voltage. For enhancing DFIG wind turbines, this paper proposes an improved procedure for controlling Dynamic Voltage Restorer (DVR) to simultaneously perform both Low Voltage Ride Through (LVRT) and High Voltage Ride Through (HVRT) operations. Consequently, both LVRT and HVRT capabilities are used to increase DFIG performance during grid disturbances. In this study, the Dynamic Voltage Restorer (DVR) has been presented to enhance the capabilities of LVRT and HVRT. MATLAB simulations show that a proposed strategy works as expected.

Enhancing LVRT capability of DFIG using cooperative control of BTFCL and RPC

ABSTRACT To integrate the high penetration of power from wind farms into a grid, one of the key requirements posed by new grid codes is Low Voltage Ride Through (LVRT) capability. This paper studies voltage compensation-based methods to improve fault ride-through capability of the grid-connected Doubly Fed Induction Generator (DFIG). Bridge Type Fault Current Limiter (BTFCL) and Reactive Power Control (RPC), which is acting as an active voltage compensator, are cooperatively controlled in this study to achieve better LVRT capability of DFIG. Additionally, the design considerations to select shunt impedance of BTFCL are described to get optimal performance of the system under consideration. The test system was modelled and simulated in MATLAB/SIMULINK environment. The effectiveness of the proposed method is tested by comparing it with the conventional Crowbar resistance method. Simulation results show that the cooperative control of self-acting BTFCL and an intelligent RPC can effectively reduce the fault current, improves the stator voltage of DFIG for continuous operation and provides reactive power support to the grid during fault conditions.

Low Voltage Ride through Enhancement Using Grey Wolf Optimizer to Reduce Overshoot Current in the Grid-Connected PV System

In today’s world, the DG should not be disconnected in the event of a power outage but should instead remain linked to the grid and supported by reactive power. This can be accomplished by implementing the low voltage ride through (LVRT) with a proportional integral (PI) controller. As a result, the voltage profile can be enhanced. The PI controller, on the other hand, has drawbacks in that setting the gain takes a long time and results in an overshoot current on the grid, which could trigger the protection relay. To address this issue, this paper proposes employing a grey-wolf optimizer (GWO) to enhance the LVRT in a 5 MW three-phase grid-connected PV system. A MATLAB simulation was carried out then under a three-phase fault and load disturbance to verify the efficiency. It is found that, even with a 70% voltage sag, the PV system can remain connected to the electrical grid while minimising overshoot current on the grid side.

Power Quality and Low Voltage Ride Through Capability Enhancement in Wind Energy System Using Unified Power Quality Conditioner (UPQC)

The various approaches used to improve the Low Voltage Ride Through (LVRT) capabilities of DFIG-based wind turbine systems are investigated in this study (WT). The Type-III WT machine, which is primarily based on DFIG, is connected to the grid without a digital power interface, resulting in unmanageable terminal voltage or reactive electricity output. As a consequence, novel LVRT approaches based on the deployment of additional active interface technologies were given in this work. The problem of low voltage faults is now being addressed using a variety of approaches. By analyzing LVRT approaches for DFIG-based WECS, this research attempts to discover such working ways by bridging the gap in terms of overall adaptive performance, operative complexity of controllers, and cost-effectiveness. This study suggests ways to improve LVRT's ability to rely on the relationship arrangement in three major areas based on their grid integrations. The wind turbine system is connected to a DVR, STATCOM, and UPQC in this study for active and reactive power regulation throughout the fault detection procedure. Using UPQC with SRF theory offers improved reaction during faults to increase active power and maximum compensation in reactive power with synchronous reference frame and without synchronous reference frame operation presented in this paper.

Adaptive super-twisting terminal sliding mode control and LVRT capability for switched reluctance generator based wind energy conversion system

Wind Energy Conversion systems (WECS) based on the Switched Reluctance Generator (SRG) devoid of rotor windings and permanent magnets are becoming more and more an attractive generator in wind energy market. Currently, the applicability of this machine in the WECS is now possible thanks to the mitigation of its drawbacks, mainly its high torque fluctuations and its low power factor. In this paper, an Adaptive Super Twisting Terminal Sliding Mode (AST-TSM) control is proposed for SRG-based WECS interfaced to the grid via a full-scale back-to-back converter. The main purpose of the proposed scheme is controlling the generator speed in order to achieve a Maximum Power Point Tracking (MPPT) with better performances. The second issue addressed consists of exploring the Low Voltage Ride Through (LVRT) capability of SRG-based WECS for compliance with recent grid code requirements. In modern grid codes, wind farms are only allowed to be connected to the grid if they have the capacity to remain in service during a short grid disturbance. As a matter of fact, under grid faults, the main tasks of the LVRT method consist in feeding the required reactive power into the grid in order to facilitate the recovery of the grid voltage. In this work, the investigated LVRT scheme, classified as a software method, is responsible for swapping the back-to back converter duties without external devices under grid voltage sags. Thereby, the generated power is stored as kinetic form, preventing strong overvoltage on the DC-bus. The proposed AST-TSM control scheme and the adopted LVRT method are substantiated by simulation results. All simulation case studies show that the AST-TSM control achieves good performance and extreme robustness as compared with the Proportional Integral (PI) and Integral Backstepping (IBC) controllers. Furthermore, the proposed controller is able to improve the suppression of chattering effect when its parameters are adjusted carefully. Also, simulation under grid faults conditions has proven that the LVRT method is effective for SRG-based WECS.

Dynamic Phasor Model of Grid-Connected Photovoltaic System in MATLAB/Simulink Considering Low Voltage Ride through Characteristics for Voltage Stability Analysis of Power System

This paper proposes a model of grid-connected photovoltaic (PV) system with low voltage ride through (LVRT) characteristic in MATLAB/Simulink based on dynamic phasor approach. Unlike all PV system models available in MATLAB/Simulink using detailed model with small capacity, the proposed model focuses on control loops of PV system to simulate a large capacity system that is appropriate for voltage stability analysis of power system installing high penetration level of PV generation. An intuitive and convenient tool for adjusting the LVRT characteristics of the PV system is also developed. The effectiveness of dynamic phasor model and the impact of the LVRT characteristic of the PV system on voltage stability are examined through MATLAB/Simulink simulations conducted on IEEE 9-bus test system. The simulation results provide an insight of how the system integrated with a large PV generation behaves under the disturbances. It also points out that the LVRT of the PV system is very important to the power system voltage stability.

Simulation of a Low-Voltage Direct Current System Using T-SFCL to Enhance Low Voltage Ride through Capability

Owing to the increasing penetration level of distributed energy resources (DER) and direct current (DC) load, the usage of low-voltage direct current (LVDC) systems has expanded to achieve efficient operations. However, because the LVDC system reaches the peak fault current at a faster rate than the alternating current (AC) system, a solution that protects the system components is necessary to maintain system integrity. It is required by the low-voltage ride-through (LVRT) that the DERs maintain their interconnections with the LVDC system and support fault recovery. In this study, a method is proposed to allow the application of the superconducting fault current limiter (SFCL) to reduce the fault current and enhance the LVRT capability. However, when the DER maintain a connection to support fault recovery, the conventional resistive-type SFCL must withstand the burden of high-temperature superconducting (HTSC) operation during fault state dependence on LVRT. Therefore, this study proposes a trigger-type SFCL to reduce the burden of the HTSC element and enhance the LVRT capability. The voltage sag related to the LVRT was improved owing to the SFCL. The proposed solution was confirmed using PSCAD/EMTDC, which is a commercial software.

Modified Super Twisting algorithm based sliding mode control for LVRT enhancement of DFIG driven wind system

The grid-connected Doubly Fed Induction Generator (DFIG) system is exposed to severe grid faults. The DFIG is sensitive to grid disturbances, which lead to consideration in the controller design. This paper proposed the Modified Super Twisting (MST) algorithm for the Low Voltage Ride Through (LVRT) enhancement under voltage sag condition. This proposed algorithm is implemented using the 2nd Order Sliding Mode (SOSM) to control the DFIG based wind generator. The higher-order switching functions are introduced in the SOSM for sliding surface control. Moreover, the Lyapunov analysis for the MST algorithm brings down the chattering amplitude. The advantages of the proposed algorithm are that it reduces the system uncertainties, chattering effect and improves the settling period of the system parameters. The performance of the proposed algorithm is compared with existing algorithms in the literature with the help of MATLAB/SIMULINK. The Hardware-In-Loop (HIL) is used to validate the simulation results, which have been performed on the OPAL-RT setup. In addition, the proposed algorithm is also tested on an equivalent model of the practical Wind Farm (WF). Based on the studies, it is found that the proposed algorithm enhanced the LVRT performance of the single Wind Turbine (WT)-DFIG system as well as the practical WF under transient conditions.

계통 연계형 3레벨 TNPC 인버터의 LVRT & HVRT

With the increase in renewable power generation facilities, strict regulations on grid connection standards are being presented. The standards of Low Voltage Ride Through(LVRT) and High Voltage Ride Through(HVRT), which are representative grid connection standards to improve grid stability by maintaining grid connection in low and high voltage situations when a grid failure occurs, are gradually being subdivided. In this paper, the LVRT and HVRT control algorithms suggested in the transmission and distribution system connection regulations of KEPCO(Korea Electric Power Corporation) are applied to the grid-connected 3-level TNPC(T-Type Neutral Point Clamped) inverter. And in the VRT situation, the active and reactive current injection strategies were applied to the grid connected inverter algorithm. In addition, various simulation cases were analyzed, such as LVRT & HVRT conditions of transmission and distribution system. In the distribution system LVRT simulation, the grid voltage operated at 150ms and 1500ms, respectively, within 0.5p.u. and 0.75p.u. In the transmission system simulation, the LVRT operation and the HVRT operation were also simulated. By analyzing various simulation cases, the characteristics of the VRT cases was analyzed in detail and VRT control performance of the designed TNPC inverter was verified.

IEEE1547-2018 Category3 대응을 위한 연료전지 시스템의 인버터 제어 전략

This paper presents an inverter control scheme for fuel cell systems in IEEE1547-2018 Category3. The current configuration of Grid-Connected fuel cell system has limitations Category3’s LVRT (Low Voltage Ride Through) reponse, additional inverter are needed. The inverter operates in an abnormal state where the grid voltage is unstable, and normally supplies the voltage to BOP (Balance of Plant) of the fuel cell system. Simulated verification of the inverter control scheme was performed to change the voltage source to the BOP from grid to inverter during abnormal conditions.

Research on Low Voltage Ride through Control of a Marine Photovoltaic Grid-Connected System Based on a Super Capacitor

With the increase of photovoltaic penetration rate, the fluctuation of photovoltaic power generation affects the reliability of ship power grids. Marine PV grid-connected systems with high penetration rates should generally have a low voltage ride-through capability. In the present paper, a strategy in which super capacitors are applied for energy storage in a marine photovoltaic grid-connected system is proposed, and an inverter adopts independent decoupling control of active and reactive currents to improve the LVRT capability of photovoltaic grid-connected systems. In addition, a comprehensive control strategy is also designed to control the supercapacitor, to regulate the active power through the control method of the voltage outer loop and the current inner loop, in order to maintain the DC bus voltage stability. At the same time, the inverter can increase the reactive power output to support the grid voltage. The advantage of this system is in smoothing the power imbalance in a short time, enhancing the low voltage ride-through capability of the photovoltaic grid-connected system, improving the power quality, and ensuring the safety and stability of the ship’s power grid. MATLAB/Simulink were employed to establish a ro-ro ship super capacitor–marine photovoltaic grid-connected power system model and to carry out simulation experiments by setting the grid voltage drop. The results show that when the grid voltage drops, the inverter adjusts the distribution of active and reactive power. The power factor drops from 1 to 0.77, and the effective value of the voltage drop increases from 150 V to 156 V, which proves that this strategy effectively reduces the depth of the grid voltage drop and improves the low voltage ride-through capability of the photovoltaic grid-connected system.

Experimental Study on Low Voltage Ride-Through of DFIG-Based Wind Turbine

This paper presents an architecture of the Doubly-Fed Induction Generator based on Wind Energy Conversion System (DFIG-WECS) to study with the Low Voltage Ride Through (LVRT) capability. The proposed architecture consists of three main parts namely the wind turbine, electric generator, control systems. The wind turbine and gearbox are modeled by a servo motor driven by using an inverter system. The electric generator uses the Wound Rotor Induction Generator (WRIG). The control system composes of the rotor-side converter (RSC) and the grid-side converter (GSC). The integration of the digital signal processor (DSP) with the Simulink/Matlab software of the vector control scheme is implemented to control both RSC and GSC. Besides, to protect the overcurrent of the generator’s rotor and overvoltage of the DC-link, the crowbar and chopper circuits and the logical scheme between the crowbar and the RSC are also proposed. To approve the control algorithms implemented in DSP as hardware in the loops, the proposed 0.8kW DFIG-WESC system has been performed under the experimental environment considering LVRT requirement in German grid code.

Evaluating Reactive Power-Based Voltage Support for the Low Voltage Ride Through Capability of the Distributed Energy Resource

Most of the grid codes generally require the Distributed Energy Resources (DERs) in order to remain connected throughout short-circuit grid faults and to provide the grid voltage support through reactive power-based regulation via additional Reactive Current Injection (aRCI) during the Low Voltage Ride Through (LVRT). It has been found out that the X/R ratio of the DER connection affects the effectiveness of the voltage support in improving the voltage sags. In this paper, the theoretical analysis of the system's X/R ratio impact on the effectiveness of the investigated voltage support is given. Furthermore, with the help of a MATLAB Simulink-based simulation study, the theoretical analysis is verified. The research is meant to substantiate a clear understanding of the effect of low X/R ratio to the voltage support in improving voltage sag. Finally, the rising number of the DERs on the distribution grid has been linked to the weakening of the grid strength, which often causes the system instability following the post-LVRT state. From the simulation, it has been found out that on a weak grid, the instability during the post-LVRT period could be prevented through correctly adjusted reactive power-based voltage regulation.

Low voltage ride through enhancement in DFIG based WECS by hybrid method

ABSTRACT This paper proposes a hybrid technique for the enhancement of Low Voltage Ride Through (LVRT) capacity in a Doubly Fed Induction Generator (DFIG) based Wind Energy Conversion System (WECS). The proposed hybrid technique is the joint execution of S-shaped binary version of Whale Optimisation Algorithm (S-bWOA) and Random Decision Forest (RDF), hence it called S-bWOA-RDF method. The major objective is to ensure the LVRT capacity in the WECS at voltage drop including failure stages. S-bWOA model is used to identify the optimal solutions for offline mode as an available search location under objective function and generates the training dataset. In light of proficient dataset, RDF performs and predicts better feasible machine side with grid side converter control signals. The proposed technique is activated in MATLAB/Simulink site, and the efficiency of the proposed S-bWORDF method is compared with the existing methods, such as Random Decision Forest and Whale Optimisation Algorithm. The IAE and ITAE of the proposed and existing methods are also analysed. The IAE and ITAE of the proposed hybrid technique are identified as 5.0071 and 54.0475. The comparison results demonstrate the efficiency of the S-bWORDF method and confirm its potential for enhancing the LVRT of DFIG based WECS.

Enhanced TVI for Grid Forming VSC under Unbalanced Faults

With an increasing capacity of inverter-based generation and with a 100% renewable energy power system on the horizon, grid forming converters have the potential to become the prevalent control mode in the grid. Thus, the correct performance of these devices is going to be crucial for system stability and security of supply. Most research related to the grid-forming control is focused on normal operating conditions, although significant effort has been devoted to current limitation strategies to ensure Low Voltage Ride Through (LVRT) capability. However, most contributions usually consider only balanced faults. This paper, proposes a new current limiting method based on the well-known threshold virtual impedance (TVI) that keeps the voltage source behaviour associated to the grid forming (GFM) capability, even when the current limit is reached, while reducing the voltage unbalance according to user-defined settings.

Enhanced Low Voltage Ride Through Capability for Grid Connected Wind Energy Conversion System

It is obvious that the current era has received much attention in the fields of science and technology, besides the continuous endeavor to provide environmentally friendly and resource-saving alternatives for conventional energy conversion systems. The rapid development of Wind Energy Conversion Systems (WECS) has made Permanent Magnet Synchronous Generator (PMSG) a primer choice because of its advantages. The current trend on WECS necessitates wind turbines to maintain continuous operation during voltage drops, which is referred to as Low Voltage Ride Through (LVRT). The PMSG control technique is a widely used approach for improving conversion efficiency as well as LVRT capability. This paper provides LVRT and power enhancement for grid-connected PMSG based WECS using control techniques. The LVRT capability has been investigated by using PI and Residue controllers. The simulation results show improved active power delivery and better LVRT capability during voltage dips when the Residue controller is implemented.

계통 연계형 인버터의 LVRT 동작 성능 분석

The scale of renewable power generation facilities such as wind power and solar power generation is being enlarged. Due to the increased scale of renewable power generation facilities, the system stability has been significantly affected by the increased distributed power sources, and various countries such as Germany and the United States are enacting standards to prevent deterioration of system stability. In this paper, we analyze the LVRT (Low Voltage Ride Through) conditions and reactive current injection standards established by Germany and Korea Electric Power Corporation (KEPCO). And, the LVRT control algorithm is applied to the designed inverter, and the operation of the grid-connected inverter was confirmed through simulation based on the LVRT boundary. In addition, the injection characteristic algorithm1 of active and reactive current in LVRT situation was modeled, and the modeled algorithm was verified by checking the simulation performance.

A Fuzzy Based Improved Control Strategy of Dynamic Voltage Restorer for Low Voltage and High Voltage Ride Through Compensation for Variable Speed Hybrid Energy System

A Fuzzy Based Improved Control Strategy of Dynamic Voltage Restorer for Low Voltage and High Voltage Ride Through Compensation for Variable Speed Hybrid Energy System