The Experts below are selected from a list of 6738 Experts worldwide ranked by ideXlab platform
Frede Blaabjerg - One of the best experts on this subject based on the ideXlab platform.
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individual channel design based precise analysis and design for three phase Grid tied inverter with lcl filter under unbalanced Grid Impedance
IEEE Transactions on Power Electronics, 2020Co-Authors: Jiahao Liu, Frede BlaabjergAbstract:Three-phase Grid-tied inverter with LCL filter is usually designed to operate under symmetric Grid Impedance. However, in actual operations, the equivalent three-phase Grid Impedance tends to be unbalanced, which turns the three-phase Grid-tied inverter with LCL filter into a highly coupled multiple-input-multiple-out system. Traditionally, the impact of the cross-coupling on the stability is directly overlooked, which may lead to imprecise stability analysis. To overcome this issue, this article proposes an analysis and design method for three-phase Grid-tied inverter with LCL filter under the unbalanced Grid Impedance based on the individual channel analysis and design. First, the effect of unbalanced Grid Impedance on the structural robustness is comprehensively evaluated. Then, the control system is simplified with no loss of structural information. Thus, the stability can be precisely analyzed and, simultaneously, the controller parameters can be easily tuned by applying Bode/Nyquist plots. Simulation and experimental results are provided to demonstrate the validity and effectiveness of the proposed method.
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Individual Channel Design-Based Modeling and Analysis of Three Phase Grid-Tied Inverter with Unbalanced Grid Impedance
2019Co-Authors: Jiahao Liu, Frede BlaabjergAbstract:Three-phase Grid-tied inverters are usually designed to operate in symmetric Grid Impedance. In actual operations, due to the imbalanced loads, three-phase systems with significant single-phase loads, imbalanced power line Impedance or the imbalanced short-circuit Impedance of the three Grid power transformer, the equivalent three-phase Grid Impedance is unbalanced. It is, consequently, important to develop an effective model and stability analysis method to address three-phase Grid-tied inverter with unbalanced Grid Impedance. Traditionally, the stability of unbalanced system can be analyzed by harmonic linearization technique, however, the model derivation is complex and the controller parameters need second designing. This paper develops the system model in a multivariable frequency domain, by using the individual channel analysis and design (ICAD), simplifying the stability analysis of the unbalanced system. The detailed study on the three-phase LCL filter-based Grid-tied inverter under the unbalanced Grid Impedance condition is presented. Simulation and experiment analysis are carried out on a 380 V/50 Hz/6 kW Grid-tied inverter prototype.
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Impact of Grid Impedance variations on harmonic emission of Grid-connected inverters
2017 IEEE Manchester PowerTech, 2017Co-Authors: Bakhtyar Hoseinzadeh, Claus Leth Bak, Frede BlaabjergAbstract:This paper addresses harmonic magnification due to resonance circuits resulting from interaction between uncertain Grid Impedance and converter. The source of harmonic may be either the Grid or inverter. It is demonstrated that unknown and unpredictable Grid Impedance may result in variable resonance frequency, which challenges robust design of LCL filter of inverter.
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Impedance based analysis and design of harmonic resonant controller for a wide range of Grid Impedance
2014 IEEE 5th International Symposium on Power Electronics for Distributed Generation Systems (PEDG), 2014Co-Authors: Junbum Kwon, Xiongfei Wang, Frede BlaabjergAbstract:This paper investigates the effect of Grid Impedance variation on harmonic resonant current controllers for Grid-connected voltage source converters by means of Impedance-based analysis. It reveals that the negative harmonic resistances tend to be derived from harmonic resonant controllers in the closed-loop output admittance of converter. Such negative resistances may interact with the Grid Impedance resulting in steady state error or unstable harmonic compensation. To deal with this problem, a design guideline for harmonic resonant controllers under a wide range of Grid Impedance is proposed, where the controller gain boundary region is derived based on the short circuit ratio. The nonlinear time domain simulations are presented to verify the theoretical analysis in the frequency domain, and the experimental results based on the analysis results are included.
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Online Grid Impedance estimation for single-phase Grid-connected systems using PQ variations
2007 IEEE Power Electronics Specialists Conference, 2007Co-Authors: Mihai Ciobotaru, A.v. Timbus, Remus Teodorescu, Pedro Rodriguez, Frede BlaabjergAbstract:This paper presents an online Grid Impedance estimation method for single-phase Grid-connected systems, such as photovoltaic systems, small wind turbines, fuel-cells power systems. The method is based on producing a small perturbation on the output of the power converter that is in the form of periodical variations of active and reactive power (PQ variations). The main idea is to make the power converter working in two operation points in order to solve the equation of the equivalent Grid Impedance. During the perturbation, measurements of voltage and current are performed and signal processing algorithms are used in order to estimate the value of the Grid Impedance. The online Grid Impedance estimation method can be used for compliance with the anti-islanding standard requirements (IEEE1574, IEEE929 and VDE0126) and for adaptive control of the Grid-connected converters. The proposed method is embedded in the existing power converter control. The selected results validate the effectiveness of the proposed method.
Friedrich W. Fuchs - One of the best experts on this subject based on the ideXlab platform.
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Design of a wide-band low-voltage Grid Impedance analyzer
2016 18th European Conference on Power Electronics and Applications (EPE'16 ECCE Europe), 2016Co-Authors: Sandro Gunter, Friedrich W. FuchsAbstract:In this paper the design and measurement results of a Grid analysis and Grid Impedance measurement system are presented. The system is provided to measure the frequency dependent Grid Impedance in different PoCs to detect resonances and improve the power quality especially of Grids with high amount of DERs. Moreover Active Filtering (AF) and reactive power feed-in are possible. It comprises also measurement of the negative and zero sequence as well as of subharmonics. The design of the converter is discussed in detail, the chosen method of Impedance measurement is explained briefly, calculations for the selection of the converter topology and the selection of power semiconductor devices are made. A special hysteresis current control for 3-level Active Neutral Point Clamped (ANPC) converters is presented. Finally different measurement results are shown. These measurements of the Grid Impedance include subsynchronous frequencies in the range of 0.1 Hz to 30 Hz and frequencies in the range of 70 Hz to 10 kHz as well as measurements of the negative sequence and the zero sequence Impedance of different low voltage Grids.
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Investigation of renewable energy generation and load impact on the Grid Impedance at different points of connection in public low voltage Grids to support Grid integration of renewable energies
2016 18th European Conference on Power Electronics and Applications (EPE'16 ECCE Europe), 2016Co-Authors: Lars Jessen, Friedrich W. FuchsAbstract:Due to an increasing number of distributed energy generation systems connected to low voltage Grids, further investigations are required to ensure high power quality and power system stability. One important power system parameter is the frequency depending Grid Impedance at the points of connection referred to as Grid Impedance. This Impedance considerably affects power quality and system stability especially if remarkable resonances occur. In this paper, the Grid Impedance composition of different public low voltage distribution systems is measured and analyzed. The primary objective is to reveal the contribution of load and solar power generation to the Grid Impedance and especially to resonances. This case study shows that Grid Impedance resonance strongly depends on loads and inductance of the upstream network in low voltage power systems. However, if the load Impedance is very high or no load is present, solar power plants lead to remarkable Grid Impedance resonances especially during nighttime.
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minimal invasive equivalent Grid Impedance estimation in inductive resistive power networks using extended kalman filter
IEEE Transactions on Power Electronics, 2014Co-Authors: Nils Hoffmann, Friedrich W. FuchsAbstract:Real-time estimation of the equivalent Grid Impedance and the equivalent Grid voltage seen from a power converter connected to the public electric distribution network by means of extended Kalman filter is addressed. The theoretical background of the extended Kalman filter used for equivalent Grid Impedance estimation is introduced. Practical aspects like the use of the filter in an environment with highly distorted voltage waveforms, the tuning of the noise covariance matrices, and the implementation on a laboratory system are discussed. The theoretical analysis is verified on a 22-kW test-bench where a Grid Impedance emulator is used to simulate Grid Impedance steps in the laboratory environment. The proposed extended Kalman filter is designed to utilize the noise that is already present at the connection point of the power converter to overcome the need of active disturbance injection to estimate the equivalent Grid Impedance. Thus, electrical equipment connected close to the Grid-connected converter is only affected marginally by the equivalent Grid Impedance estimation technique.
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Minimal Invasive Equivalent Grid Impedance Estimation in Inductive–Resistive Power Networks Using Extended Kalman Filter
IEEE Transactions on Power Electronics, 2014Co-Authors: Nils Hoffmann, Friedrich W. FuchsAbstract:Real-time estimation of the equivalent Grid Impedance and the equivalent Grid voltage seen from a power converter connected to the public electric distribution network by means of extended Kalman filter is addressed. The theoretical background of the extended Kalman filter used for equivalent Grid Impedance estimation is introduced. Practical aspects like the use of the filter in an environment with highly distorted voltage waveforms, the tuning of the noise covariance matrices, and the implementation on a laboratory system are discussed. The theoretical analysis is verified on a 22-kW test-bench where a Grid Impedance emulator is used to simulate Grid Impedance steps in the laboratory environment. The proposed extended Kalman filter is designed to utilize the noise that is already present at the connection point of the power converter to overcome the need of active disturbance injection to estimate the equivalent Grid Impedance. Thus, electrical equipment connected close to the Grid-connected converter is only affected marginally by the equivalent Grid Impedance estimation technique.
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Online Grid Impedance estimation for the control of Grid connected converters in inductive-resistive distributed power-networks using extended kalman-filter
2012 IEEE Energy Conversion Congress and Exposition (ECCE), 2012Co-Authors: Nils Hoffmann, Friedrich W. FuchsAbstract:Real-time estimation of the equivalent Grid Impedance and the equivalent Grid voltage seen from a power converter connected to the public electric distribution network by means of Extended Kalman-Filter is addressed. The theoretical background of the Extended Kalman-Filter used for equivalent Grid Impedance estimation is introduced. Practical aspects like the use of the filter in an environment with highly distorted voltage waveforms, the tuning of the noise covariance matrices and the implementation on a laboratory system are discussed. The theoretical analysis is verified on a 22 kW test-bench where a Grid Impedance emulator is used to simulate Grid Impedance steps in the laboratory environment. The proposed Extended Kalman-Filter is designed to utilize the noise that is already present at the connection point of the power converter to overcome the need of active disturbance injection to estimate the equivalent Grid Impedance.
Tomi Roinila - One of the best experts on this subject based on the ideXlab platform.
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Identification of Three-Phase Grid Impedance in the Presence of Parallel Converters
Energies, 2019Co-Authors: Roni Luhtala, Tomi Roinila, Tuomas Messo, Henrik Alenius, Erik De Jong, Andrew Burstein, Alejandra FabianAbstract:Grid Impedance is an important parameter which affects the control performance of Grid-connected power converters. Several methods already exist for optimizing the converter control system based on knowledge of Grid Impedance value. Grid Impedance may change rapidly due to fault or disconnection of a transmission line. Therefore, online Grid identification methods have been recently proposed to have up-to-date information about the Grid Impedance value. This is usually done by perturbing the converter output current and measuring the response in output voltage. However, any parallel converters connected to the same interface point will cause errors, since the measured current differs from the current that is flowing through the Grid interface point. This paper points out challenges and errors in Grid Impedance identification, caused by parallel converters and their internal control functions, such as Grid-voltage support. Experimental Grid-Impedance measurements are shown from the power hardware-in-the-loop setup developed at DNV-GL Flexible Power Grid Lab.
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online Grid Impedance measurement using ternary sequence injection
IEEE Transactions on Industry Applications, 2018Co-Authors: Tomi Roinila, Tuomas MessoAbstract:Grid Impedance affects the stability and control performance of Grid-connected power-electronics devices, such as inverters, used to integrate wind and solar energy. Adaptive control of such inverters, to guarantee stability under different Grid conditions, requires online measurement of the Grid Impedance performed in real time. Wideband frequency-response-measurement techniques based on the pseudo-random binary sequence (PRBS) or impulse injection have been often applied for Grid-Impedance measurements. However, while using the PRBS or impulse, it is assumed that the system under study is linear. Because such an assumption does not typically hold for Grid-connected systems, the measured Impedances are usually prone to distortions caused by nonlinearities. This paper proposes the use of periodic ternary sequences for online Grid-Impedance measurements. Using appropriately designed periodic ternary signals, the linear component of the Grid Impedance can be identified, eliminating errors from even-order nonlinear distortions. In addition, the ternary sequences can be designed for a much wider range of sequence length compared to the conventional PRBS, enabling more efficient optimization of computing power and frequency resolution. Experimental measurements are shown from a Grid-connected photovoltaic inverter.
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Aggregated Modeling and Power Hardware-in-the-Loop Emulation of Grid Impedance
2018 IEEE Energy Conversion Congress and Exposition (ECCE), 2018Co-Authors: Henrik Alenius, Tuomas Messo, Tommi Reinikka, Tomi RoinilaAbstract:The rapid growth of renewable energy production increases the number of Grid-connected inverters in the power system. The interface between the inverter and the Grid may face stability issues, which can be assessed using Impedance-based stability criterion. The frequency-dependent Grid Impedance is often an unknown parameter, and vastly simplified Grid Impedance models are widely used. Most common modeling approach is to use series-connected inductor as the Grid Impedance. However, measurements on real Grids have shown the Grid to be more complex, resonant, and time-variant. This paper introduces a Grid-Impedance model based on aggregation of sub-models, which drastically simplifies complex Grid modeling, while still accurately captures resonances and possible time-variant behavior. Numerical sensitivity analysis is carried out for Grid parameters to illustrate the significance of separate Grid elements. Lastly, Impedance measurements are shown for emulated full-order and aggregated Impedance models in an experimental power hardware-in-the-loop setup.
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online Grid Impedance measurement using discrete interval binary sequence injection
IEEE Journal of Emerging and Selected Topics in Power Electronics, 2014Co-Authors: Tomi Roinila, Matti Vilkko, Jian SunAbstract:Grid Impedance affects the stability and control performance of Grid-connected power electronic devices, such as inverters used to integrate wind and solar energy. Adaptive control of such inverters, to guarantee stability under different Grid conditions, requires online measurement of the Grid Impedance performed in real time. Such online measurement can be performed by injecting a current perturbation from the inverter into the Grid and by reading the Grid voltage responses. To minimize the impact on the inverter operation, the injection must be kept as small as possible while producing enough voltage perturbation that can be reliably measured and processed to extract its various frequency components. This paper proposes the use of a discrete-interval binary sequence (DIBS) for this application to minimize the injection. The DIBS is a computer-optimized binary sequence, where the energy is maximized at specified harmonic frequencies based on the expected Grid-Impedance characteristics. Experimental results based on a three-phase Grid-connected inverter are presented to demonstrate the effectiveness of the proposed methods.
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broadband methods for online Grid Impedance measurement
Energy Conversion Congress and Exposition, 2013Co-Authors: Tomi Roinila, Matti VilkkoAbstract:Grid Impedance is an important parameter for the operation and control of Grid-connected inverters used for the integration of solar, wind, and other distributed generation resources. Since the Grid Impedance usually varies over time and with Grid operation conditions, online measurement is required for adaptive control of Grid-connected inverters. Existing online measurement methods based on impulse perturbation and Fourier analysis require large current or voltage injection that may interfere with normal operation of the inverter. This paper proposes the use of maximum-length binary sequence (MLBS) injection and averaging Fourier techniques to overcome the drawbacks of impulse injection. Experimental results based on a three-phase Grid-connected inverter are presented and used to demonstrate the effectiveness of the proposed methods.
Thiago De Oliveira Alves Rocha - One of the best experts on this subject based on the ideXlab platform.
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Real-Time Wavelet-Based Grid Impedance Estimation Method
IEEE Transactions on Industrial Electronics, 2019Co-Authors: Denis Keuton Alves, R. L. A. Ribeiro, Flavio Bezerra Costa, Thiago De Oliveira Alves RochaAbstract:This letter presents a novel method to estimate the Grid Impedance based on stationary discrete wavelet packet transform (SDWPT). The proposed method uses a steady-state technique, by injecting an interharmonic current into the Grid and measuring the voltage response at the point of common coupling to estimate the Grid Impedance. The proposed method employed a standard three-phase photovoltaic system interconnected to the Grid to validate its effectiveness experimentally. Comparisons with a discrete Fourier transform- and continuous wavelet transform-based Impedance estimation approaches demonstrate the performance of proposed method. Besides, the proposed SDWPT-based Impedance estimation provided accurate experimental results, which make it viable for real-time applications.
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Wavelet-Based Monitor for Grid Impedance Estimation of Three-Phase Networks
IEEE Transactions on Industrial Electronics, 1Co-Authors: Denis Keuton Alves, R. L. A. Ribeiro, Flavio Bezerra Costa, Thiago De Oliveira Alves Rocha, Josep M. GuerreroAbstract:This article proposes a wavelet-based monitor (WBM) for Grid Impedance estimation, which combines a wavelet-based transient detection scheme (WB-TDS) and a wavelet-based Grid Impedance estimator (WB-GIE). The WB-TDS employs the analysis of the wavelet coefficients energy for detecting Grid Impedance changing, whereas the WB-GIE estimates the Grid Impedance by using the real-time stationary discrete wavelet packet transform associated with signal injection scheme. During a Grid Impedance changing, the WB-TDS triggers the WB-GIE for injecting an interharmonic into the power Grid to estimate its current Impedance. This method mitigates the total harmonic distortion generated by the continuous signal injection employed in the existing techniques. The WB-GIE identifies the phase Grid Impedance resistance and reactance accurately in balanced or unbalanced conditions. Due to its inherent characteristics, WBM is suitable to be inserted into the adaptive power flow control of distributed generation systems. Experimental results obtained from a Grid-connected photovoltaic generation laboratory setup validates the proposed method and demonstrates its effectiveness.
Denis Keuton Alves - One of the best experts on this subject based on the ideXlab platform.
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Real-Time Wavelet-Based Grid Impedance Estimation Method
IEEE Transactions on Industrial Electronics, 2019Co-Authors: Denis Keuton Alves, R. L. A. Ribeiro, Flavio Bezerra Costa, Thiago De Oliveira Alves RochaAbstract:This letter presents a novel method to estimate the Grid Impedance based on stationary discrete wavelet packet transform (SDWPT). The proposed method uses a steady-state technique, by injecting an interharmonic current into the Grid and measuring the voltage response at the point of common coupling to estimate the Grid Impedance. The proposed method employed a standard three-phase photovoltaic system interconnected to the Grid to validate its effectiveness experimentally. Comparisons with a discrete Fourier transform- and continuous wavelet transform-based Impedance estimation approaches demonstrate the performance of proposed method. Besides, the proposed SDWPT-based Impedance estimation provided accurate experimental results, which make it viable for real-time applications.
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Wavelet-Based Monitor for Grid Impedance Estimation of Three-Phase Networks
IEEE Transactions on Industrial Electronics, 1Co-Authors: Denis Keuton Alves, R. L. A. Ribeiro, Flavio Bezerra Costa, Thiago De Oliveira Alves Rocha, Josep M. GuerreroAbstract:This article proposes a wavelet-based monitor (WBM) for Grid Impedance estimation, which combines a wavelet-based transient detection scheme (WB-TDS) and a wavelet-based Grid Impedance estimator (WB-GIE). The WB-TDS employs the analysis of the wavelet coefficients energy for detecting Grid Impedance changing, whereas the WB-GIE estimates the Grid Impedance by using the real-time stationary discrete wavelet packet transform associated with signal injection scheme. During a Grid Impedance changing, the WB-TDS triggers the WB-GIE for injecting an interharmonic into the power Grid to estimate its current Impedance. This method mitigates the total harmonic distortion generated by the continuous signal injection employed in the existing techniques. The WB-GIE identifies the phase Grid Impedance resistance and reactance accurately in balanced or unbalanced conditions. Due to its inherent characteristics, WBM is suitable to be inserted into the adaptive power flow control of distributed generation systems. Experimental results obtained from a Grid-connected photovoltaic generation laboratory setup validates the proposed method and demonstrates its effectiveness.
