Voltage Sag Detection in Grid-Connected Photovoltaic Power Plant for Low Voltage Ride-Through Control

2019 ◽  
Vol 12 (4) ◽  
pp. 384-392 ◽  
Author(s):  
Ali Qasem Al-Shetwi ◽  
Muhamad Zahim Sujod
Keyword(s):  
Reactive Power ◽  
Low Voltage ◽  
Detection Methods ◽  
Normal Operation ◽  
Positive Sequence ◽  
Voltage Sag ◽  
Good Precision ◽  
Grid Voltage ◽  
Low Voltage Ride Through ◽  
Photovoltaic Power

Background: Due to the high level of photovoltaic power plants (PVPPs) penetration into power grids, disconnections of these plants during faults are no longer possible as it may cause problems concerning stability, quality, and operation of the power system. Therefore, new grid codes have been established with low voltage ride-through (LVRT) capability standard requirements for grid-connected PVPPs that should be met. Therefore, for an efficient LVRT control, the fast and precise sag detection strategy is essential for the system to switch from normal operation to LVRT mode of operation. Methods: For this purpose, this paper presents a two automatic fault detection methods which are RMS-based (d-q) components of grid voltage and positive sequence voltage. These methods were utilized to determine the beginning and end of a voltage sag and to determine the sag depth to regulate the required reactive current that should be injected according to the LVRT standard requirements. The operating method depends on calculating present grid voltage under faults to the nominal voltage that identifies the sags’ depth and therefore inject the required amount of reactive power accordingly. Also, a comparison between the two proposed methods regarding response speed and accuracy was made. The effectiveness of these detection strategies is that it can be integrated into the voltage source inverter (VSI) without utilizing additional external hardware or software programming. Results: The simulation results demonstrated a good precision and how straightforward the proposed methods’ usage is, proving that the RMS method is faster and more accurate than positive sequence method. Conclusion: In conclusion, it was found that RMS detection algorithm is preferred for a more accurate and efficient LVRT control.

The Transient Characteristics Analysis of Doubly-Fed Induction Generator during the Asymmetric Voltage Sag

2014 ◽  
Vol 644-650 ◽  
pp. 3509-3514
Author(s):  
Jian Hua Zhang ◽  
Hao Ran Shen ◽  
Lei Ding ◽  
Chun Lei Dai
Keyword(s):  
Control Strategy ◽  
Reactive Power ◽  
Low Voltage ◽  
Voltage Drop ◽  
Voltage Sag ◽  
Grid Voltage ◽  
Low Voltage Ride Through ◽  
Double Frequency ◽  
Characteristics Analysis ◽  
Doubly Fed

In order to analyze the control strategy of the low voltage ride through (LVRT) of DFIG during the asymmetric voltage sag, it is necessary to analyze the transient performance of a DFIG during the asymmetric voltage sag. In this paper, analyzed the influence of the asymmetric grid voltage to DFIG and the analysis method of the asymmetric voltage sag, and on the basis of positive and negative sequence mathematical model, analyzed the composition of stator output active and reactive power under the condition of asymmetric grid voltage. And built a DFIG asymmetric voltage drop simulation model of 1.5MW in MATLAB/Simulink, the simulation results shows that the stator voltage, current, active power and reactive power all present a double frequency ripple during the asymmetric voltage sag, consistent with theoretical analysis. It can provide theoretical basis for double-fed motor control strategy of asymmetric LVRT.

scholarly journals An Enhanced Low Voltage Ride-Through Control Scheme of a DIFG based WTG Using Crowbar and Braking Chopper

2021 ◽  
Vol 16 (1) ◽  
pp. 61-67
Author(s):  
Kishan Jayasawal ◽  
Khagendra Thapa
Keyword(s):  
Reactive Power ◽  
Low Voltage ◽  
Turbine Generator ◽  
Grid Voltage ◽  
Low Voltage Ride Through ◽  
Control Scheme ◽  
Safe Limit ◽  
Grid Codes ◽  
Doubly Fed ◽  
Rotor Side Converter

The grid codes define low voltage ride-through (LVRT) as capability of wind turbine generator (WTG) to support the grid voltage by injecting reactive power and suppress the rise of DC-link voltage and inrush rotor current in the rotor side converter (RSC) of the doubly fed induction generator (DFIG) during a fault. Moreover, the rotor current increases significantly during severe disturbances if any protection schemes are not employed. Therefore, the protection schemes must be used to avoid the damage to the converter during a fault. This paper proposes an enhanced LVRT control scheme of a DFIG employing a crowbar in the RSC side and braking chopper across the DC-link capacitor. The DFIG is highly delicate to grid voltage fluctuation during a fault because the DFIG is directly linked to the grid via stator. During severe fault the crowbar regulates the rotor current within an acceptable range and the braking chopper discharges the DC-link capacitor via resistor within a safe limit. The proposed LVRT control scheme is performed for a 2.4-MW DFIG using a MATLAB/SIMULINK simulator. The results delineate that the proposed control scheme is able to rapidly decrease the rotor current and repress the escalation in DC-link voltage during a grid fault.

scholarly journals A novel low voltage ride through strategy for cascaded power electronic transformer

2019 ◽  
Vol 4 (1) ◽  
Author(s):  
Jiexiang Han ◽  
Xiangping Kong ◽  
Peng Li ◽  
Zhe Zhang ◽  
Xianggen Yin
Keyword(s):  
Low Voltage ◽  
System Stability ◽  
Positive Sequence ◽  
Voltage Sag ◽  
Power Electronic ◽  
Operating Characteristics ◽  
Electronic Transformer ◽  
Low Voltage Ride Through ◽  
Power Electronic Transformer ◽  
Voltage Recovery

Abstract In view of the operating characteristics for voltage sags of AC side of the power electronic transformer(PET), a low-voltage ride through(LVRT) strategy adapted to bidirectional power exchange of PET is proposed for the purposes of maintaining the system stability, assisting the system voltage recovery and protecting PET safety. During the asymmetric voltage sag, the negative sequence current of PET is eliminated to ensure the symmetry of the injected current. According to the degree of positive sequence voltage sag, the reactive current injection is provided to assist in voltage recovery. According to the PET active power condition before the voltage sag, the level and direction of which are maintained as far as possible without exceeding the limit, for which the disturbance to the AC and DC grids is reduced. Finally, the effectiveness of the proposed LVRT strategy is verified by simulation model.

The Control of Low Voltage Ride through Based on STATCOM and Crowbar Circuit

2014 ◽  
Vol 986-987 ◽  
pp. 1296-1299
Author(s):  
Li Juan Chen ◽  
Zhi Jie Wang ◽  
Xin Xia Su
Keyword(s):  
Power System ◽  
Transient Stability ◽  
Reactive Power ◽  
Low Voltage ◽  
Reactive Power Compensation ◽  
Grid Voltage ◽  
Low Voltage Ride Through ◽  
Voltage Dips

When the grid voltage dips, in order to keep DFIG connected to grid and accelerate the recovery of grid voltage, reactive power compensation STATCOM is adapted to provide reactive power for grid, and crowbar circuit is installed to protect the converter of DIFG. Transient stability of power system is improved and the low voltage ride through is realized.

Dual current control strategy to fulfill LVRT requirements in WECS

2014 ◽  
Vol 33 (5) ◽  
pp. 1665-1677 ◽  
Author(s):  
Matías Díaz ◽  
Roberto Cárdenas-Dobson
Keyword(s):  
Control Strategy ◽  
Reactive Power ◽  
Low Voltage ◽  
Current Control ◽  
Power Delivery ◽  
Positive Sequence ◽  
Content Type ◽  
Grid Voltage ◽  
Signal Cancellation ◽  
Laboratory Prototype

Purpose – The purpose of this paper is to investigate a control strategy to fulfill low-voltage ride through (LVRT) requirements in wind energy conversion system (WECS). Design/methodology/approach – This paper considers an active front-end converter of a grid connected WECS working under grid fault conditions. Two strategies based on symmetrical components are studied and proposed: the first one considers control only for positive sequence control (PSC); the second one considered a dual controller for positive and negative sequence controller (PNSC). The performance of each strategy is studied on LVRT requirements fulfillment. Findings – This paper shows presents a control strategy based on symmetrical component to keep the operation of grid-connected WECS under unsymmetrical grid fault conditions. Research limitations/implications – This work is being applied to a 2 kVA laboratory prototype. The lab prototype emulates a grid connected WECS. Originality/value – This paper validate the PNSC strategy to LVRT requirements fulfillment by experimental results obtained for a 2 kVA laboratory prototype. PNSC strategy allows constant active power delivery through grid-voltage dips. In addition, the proposed strategy is able to grid-voltage support by injection of reactive power. Additional features are incorporated to PNSC: sequence separation method using delay signal cancellation and grid frequency identification using phase locked loop.

scholarly journals Control Strategy of Three-Phase Photovoltaic Inverter under Low-Voltage Ride-Through Condition

2015 ◽  
Vol 2015 ◽  
pp. 1-23 ◽  
Author(s):  
Xianbo Wang ◽  
Zhixin Yang ◽  
Bo Fan ◽  
Wei Xu
Keyword(s):  
Control Strategy ◽  
Reactive Power ◽  
Low Voltage ◽  
Voltage Drop ◽  
Stable Operation ◽  
Power Fluctuation ◽  
Negative Sequence ◽  
Grid Voltage ◽  
Low Voltage Ride Through ◽  
Grid Side

The new energy promoting community has recently witnessed a surge of developments in photovoltaic power generation technologies. To fulfill the grid code requirement of photovoltaic inverter under low-voltage ride-through (LVRT) condition, by utilizing the asymmetry feature of grid voltage, this paper aims to control both restraining negative sequence current and reactive power fluctuation on grid side to maintain balanced output of inverter. Two mathematical inverter models of grid-connected inverter containing LCL grid-side filter under both symmetrical and asymmetric grid are proposed. PR controller method is put forward based on inverter model under asymmetric grid. To ensure the stable operation of the inverter, grid voltage feedforward method is introduced to restrain current shock at the moment of voltage drop. Stable grid-connected operation and LVRT ability at grid drop have been achieved via a combination of rapid positive and negative sequence component extraction of accurate grid voltage synchronizing signals. Simulation and experimental results have verified the superior effectiveness of our proposed control strategy.

Study on Transient Characteristic of the DFIG LVRT

2013 ◽  
Vol 791-793 ◽  
pp. 1832-1836
Author(s):  
Jian Hua Zhang ◽  
Rong Luan ◽  
Hao Ran Shen
Keyword(s):  
Control Strategy ◽  
Reactive Power ◽  
Low Voltage ◽  
Voltage Sag ◽  
Voltage Sags ◽  
Doubly Fed Induction Generator ◽  
Low Voltage Ride Through ◽  
Harmonic Currents ◽  
Doubly Fed ◽  
Operation Characteristics

In order to analyze the operational capability of the low voltage ride through ( LVRT) of a gird-connected wind turbine with doubly fed induction generator (DFIG) effectively, it is necessary to evaluate operation characteristics of DFIG under a grid fault.By using the transient principle of the flux of stator and rotor, the expressions of transient currents of stator and rotor of DFIG are derived under the grid voltage sag. The transient process is analyzed by using the Matlab to derive the correctness of the expression. A control strategy is presented to eliminate harmonic currents by proposing the essential factors of over-current of stator and rotor. The output active power and reactive power are calculated by using the derived expression with different voltage sags. Based on the theoretical analysis, a DFIG is established to analysis the model of LVRT. Simulation results show that the control strategy is able to eliminate the harmonic currents and achieve the requirements of LVRT.

scholarly journals Modeling and Design of the Vector Control for a Three-Phase Single-Stage Grid-Connected PV System with LVRT Capability according to the Spanish Grid Code

Energies ◽  
2019 ◽  
Vol 12 (15) ◽  
pp. 2899 ◽  
Author(s):  
Alexis B. Rey-Boué ◽  
N. F. Guerrero-Rodríguez ◽  
Johannes Stöckl ◽  
Thomas I. Strasser
Keyword(s):  
Vector Control ◽  
Reactive Power ◽  
Low Voltage ◽  
Single Stage ◽  
Photovoltaic System ◽  
Lookup Table ◽  
Voltage Sags ◽  
Pv System ◽  
Low Voltage Ride Through ◽  
Three Phase

This article deals with the vector control in dq axes of a three-phase grid-connected photovoltaic system with single-stage topology and low-voltage-ride-through capability. The photovoltaic generator is built using an array of several series-parallel Suntech PV modules and is modeled as a Lookup Table (two-dimensional; 2-D). The requirements adopted when grid voltage sags occur are based in both the IEC 61400-21 European normative and the allowed amount of reactive power to be delivered according to the Spanish grid code, which avoids the disconnection of the inverter under grid faults by a limitation in the magnitude of the three-phase output inverter currents. For this, the calculation of the positive- and negative-sequences of the grid voltages is made and a conventional three-phase Phase-Locked Loop is used for the inverter-grid synchronization, allowing the control of the active and reactive powers solely with the dq components of the inverter currents. A detailed enhanced flowchart of the control algorithm with low-voltage-ride-through capability is presented and several simulations and experiments using Matlab/SIMULINK and the Controller Hardware-in-the-Loop simulation technique, respectively, are run for several types of one- and three-phase voltage sags in order to validate its behavior.

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