The Experts below are selected from a list of 4032 Experts worldwide ranked by ideXlab platform
Jian Sun - One of the best experts on this subject based on the ideXlab platform.
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Methods to aggregate turbine and network Impedance for wind farm resonance analysis
IET Renewable Power Generation, 2020Co-Authors: Haijiao Wang, Christoph Buchhagen, Jian SunAbstract:Small-signal Sequence Impedance models have been developed for different types of wind turbines and used in industry to study wind farm and high-voltage direct current (HVDC) system harmonics and resonances. Compared to other small-signal methods, a major advantage of system modelling and analysis based on Sequence Impedance is its scalability: an equivalent Impedance model can be easily built for any complex system by aggregating the Impedance of individual turbines and the network. A recent development in the small-signal Sequence Impedance theory is the modelling of frequency coupling to improve the accuracy of system analysis and explain a common characteristic of harmonics created by system resonance. In light of this new development, this study presents and compares different aggregation methods to build farm-level Impedance models in the presence of coupling in individual turbine responses. The objective is to identify practical methods that can meet the needs of different system analyses and are easily to use. Experiences of China State Grid and TenneT with the application of Sequence Impedance models in renewable energy and HVDC system resonance and harmonic analysis are also discussed, along with an overview of their ongoing efforts to develop new grid codes and system analysis tools based on Sequence Impedances.
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Sequence Impedance Modeling and Analysis of MMC in Single-Star Configuration
IEEE Transactions on Power Electronics, 2020Co-Authors: Yang Zhang, Xin Chen, Jian SunAbstract:This paper presents Sequence Impedance modeling and analysis of modular multilevel converters (MMCs) in a single-star configuration for static VAR compensation (STATCOM) application. Prior work on Impedance modeling of MMC is limited to the double-star configuration for high-voltage dc transmission applications. Compared to that, single-star configuration uses only a single arm of switching modules in each phase, eliminating the second-harmonic circulating current and the need for the associated circulating current control. On the other hand, the lack of connection to a stiff dc bus makes it essential to include module capacitor voltage control in the model. A special form of the multi-harmonic linearization method is applied to take advantage of the simpler harmonic spectra and to reduce the complexity of the resulting models. The developed models are verified by simulation and experiment, respectively, and used to understand the similarities and differences in the Impedance characteristics of the two configurations as well as the effects on stability. A representative wind power plant is presented as an example to demonstrate the application of STATCOM Impedance models on the system stability analysis.
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accurate measurement of converter Sequence Impedance by active cancellation of coupling over frequency
2019 4th IEEE Workshop on the Electronic Grid (eGRID), 2019Co-Authors: Tommi Reinikka, Tomi Roinila, Jian SunAbstract:Impedance-based analysis plays important role in assessing the stability and dynamics of grid-connected inverters and related systems. Measuring the inverter Impedance is, however, not straightforward due to the load effect caused by the power grid. The power grid interacts with the inverter and produces additional (mirrored) frequency harmonics thus distorting the Impedance measurements when applying conventional measurement techniques. This paper proposes an active-power filtering method to minimize the undesired load effect caused by the power grid in the measured Impedance. Applying the method, the inverter output Impedance can be reliably measured under non-ideal grid conditions.
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Refined Small-Signal Sequence Impedance Models of Type-III Wind Turbines
2018 IEEE Energy Conversion Congress and Exposition (ECCE), 2018Co-Authors: Ignacio Vieto, Jian SunAbstract:Refined Sequence Impedance models are presented for type-III wind turbines that use doubly-fed induction generators (DFIG). Previous small-signal Sequence Impedance models of DFIG did not consider the dynamics of the dc bus voltage connecting the stator- and rotor-side converters, and ignored small-signal responses at non-perturbation frequency. This work models the turbine in a new way by first modeling each converter independently and fully characterizing their ac/dc dynamics, and then combining these transfer functions to obtain the small-signal models of the whole turbine. These improved small-signal models consider dc bus dynamics as well as the current response at non-perturbation frequency that occurs due to the nonlinear nature of the converter and control. Turbine-grid system stability analysis that accounts for the coupled current responses is also presented. The transfer functions and small-signal models are validated against detailed simulation. The developed models are also compared against previous models to demonstrate the improved accuracy.
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Sequence Impedance Modeling and Analysis of Type-III Wind Turbines
IEEE Transactions on Energy Conversion, 2018Co-Authors: Ignacio Vieto, Jian SunAbstract:Sequence Impedance models are presented for type-III wind turbines that use doubly fed induction generators and back-to-back voltage source converters. The models, presented in analytical form for both positive- and negative-Sequence Impedances, include the effects of the induction machine, both the stator- and rotor-side converters as well as their controls, and the phase-locked loop used for synchronizing converter control with the grid voltage. The models are valid from subsynchronous frequency up to one-third of the switching frequency of the converter, making them useful for the analysis and mitigation of both subsynchronous and supersynchronous resonances and control interactions of type-III turbines with different types of grid.
Yandong Chen - One of the best experts on this subject based on the ideXlab platform.
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Sequence Impedance Modeling and Stability Analysis for Load Converters With Inertial Support
IEEE Transactions on Power Electronics, 2020Co-Authors: Liu Yifeng, Yandong Chen, Zhou Xiaoping, Zhou Leming, Lei Wang, Wu WenhuaAbstract:Load converters with inertial support are used to enhance the system inertia. However, these converters may fail to operate stably in the weak grid. In this article, Sequence Impedance modeling and stability comparison analysis are proposed for the load virtual synchronous machine (LVSM) and the load converter with virtual inertia control (LCVIC). First, the universal Sequence Impedance formulas are derived by considering dc-link voltage dynamics and frequency-coupling effects. Then, the precise Sequence Impedance models are built for Impedance characteristics analysis of LVSM and LCVIC. The analysis shows that the positive-Sequence Impedance of LVSM is generally inductive in the middle-frequency band, which is basically consistent with the grid Impedance. In contrast, the positive-Sequence Impedance of LCVIC is negative-resistive-capacitive (i.e., phase angle is between −180° and −90°) in the middle-frequency band, which may lead to harmonic oscillation in the weak grid. Furthermore, the effects of grid Impedance, load power, and other control parameters on the stability are analyzed for the two load converters based on the derived model and Nyquist stability criterion. The analysis results reveal that LVSM has better stability than LCVIC in the weak grid. Finally, the experimental results validate the correctness of the theoretical analyses.
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Analysis and suppression of high-frequency oscillation between converter-based source and loads in an island power system
International Journal of Electrical Power & Energy Systems, 2020Co-Authors: Wu Wenhua, Yandong Chen, Xu Yuancan, Xie Zhiwei, Liu Jinming, Guo Jian, Wang Haining, An LuoAbstract:Abstract In island power system with strong mutual interaction of power electronic devices, stability problems such as high-frequency oscillation are prone to occur. Firstly, a small-signal Sequence Impedance model of an island power system is built by harmonic linearization method. It is found that the output Sequence Impedance of the source PWM inverter in the system is not affected by the stable operating point, but the input Sequence Impedance of the load PWM rectifier will decrease with the increase of power. Then, based on the Sequence Impedance model and Nyquist stability criterion, the influence of load type and load power on stability of the island power system is analyzed, which can reveal that high-frequency oscillation occurs when the source PWM inverter interacts with the load PWM rectifier. The essential reason of the high-frequency oscillation is that the capacitive output Impedance of the source PWM inverter does not match the inductive output Impedance of the load PWM rectifier at high-frequency areas. Aiming at this issue, an Impedance reconstruction control for the source PWM inverter is proposed, which improves the phase of the output Sequence Impedance of the source PWM inverter at high-frequency areas to effectively suppress the high-frequency oscillation of the system. Finally, experiment results verify the correctness of analysis and effectiveness of the proposed control strategy.
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Sequence-Impedance-Based Stability Comparison Between VSGs and Traditional Grid-Connected Inverters
IEEE Transactions on Power Electronics, 2019Co-Authors: Wenhua Wu, Leming Zhou, Yandong Chen, Yanting Dong, Xiaoping Zhou, Qianming Xu, Ling Yang, Josep M. GuerreroAbstract:Traditional grid-connected inverters (TGCI) could suffer from small-signal instability owing to the dynamic interactions among inverters and a weak grid. In this letter, the small-signal Sequence Impedance model of the virtual synchronous generator (VSG) is built, and the Sequence Impedance characteristics of the VSG and the TGCI are compared and analyzed. The Sequence Impedance of the TGCI is mainly capacitive in the middle-frequency area, and the Impedance amplitude is quite high. By contrast, the Sequence Impedance of the VSG, being consistent with the grid Impedance characteristics, is generally inductive, and the Impedance amplitude is quite low. Based on the Sequence Impedance model and the Nyquist stability criterion, the influence of the grid stiffness, the number of paralleled inverters, and the phase-locked loop (PLL) bandwidth on the stability of the VSG and the TGCI systems is analyzed. The stability analysis results show that the TGCI loses stability easily, whereas the VSG still works well without PLL restrictions under an ultraweak grid or with a large number of inverters connected to the grid. Therefore, the VSG is more suitable than the TGCI for achieving high penetration of renewable energy generation in an ultraweak grid from a system stability viewpoint. Finally, the experimental results validate the Sequence Impedance model and the stability analysis.
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Sequence Impedance Modeling and Stability Comparative Analysis of Voltage-Controlled VSGs and Current-Controlled VSGs
IEEE Transactions on Industrial Electronics, 2019Co-Authors: Wenhua Wu, Leming Zhou, Yandong Chen, Xiaoping Zhou, Ling Yang, Zhixing He, Mingmin ZhangAbstract:The premise that the virtual synchronous generator (VSG) can actively support the weak grid is that the VSG can operate stably. In this paper, the small-signal Sequence Impedance models of the voltage-controlled VSG and the current-controlled VSG are built and the Sequence Impedance characteristics of these two types of VSGs are compared and analyzed. The Sequence Impedance of the voltage-controlled VSG, being consistent with the grid Impedance characteristics, is generally inductive. By contrast, the Sequence Impedance of the current-controlled VSG is mainly negative Impedance in the middle- and high-frequency area and the Impedance amplitude is quite low. Based on the built Sequence Impedance models and the Impedance stability criterion, the influence of the weakness of the grid on the stability of these two types of VSG grid-connected system is analyzed. The results of stability analysis show that the current-controlled VSG is prone to instability while the voltage-controlled VSG remains stable. Therefore, the voltage-controlled VSG is more suitable than the current-controlled VSG for grid-connected renewable energy generation in an ultraweak grid from the point of view of system stability. Finally, experiment results validate the stability analysis.
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Sequence Impedance Modeling and Stability Analysis for Renewable Energy Power Station
2018 IEEE International Power Electronics and Application Conference and Exposition (PEAC), 2018Co-Authors: Yandong Chen, Xu Yuancan, Wu WenhuaAbstract:The accessibility of renewable energy power station to weak energy grids is prone to harmonic disturbances and other small disturbance stability problems. Considering the influence of phase locked loop (PLL) and distributed transformer Impedance, a harmonic linearization Impedance modeling method is adopted to establish a system Sequence Impedance model for renewable energy power station in the frequency domain; equivalent principle is used to simplify the Impedance model of the system to the simplest one-port network; based on the criterion of Impedance stability, analyze the stability of the system by considering and investigating the dynamic interaction between the renewable energy power station and the grid; verify the number of parallel inverters and the impact of the bandwidth of the PLL on the stability of the system. The investigation shows that as the bandwidth of the PLL and the number of parallel connected inverters increase, the system stability will gradually deteriorate. The simulation results are also presented to validate the model and Impedance stability analysis method.
Ignacio Vieto - One of the best experts on this subject based on the ideXlab platform.
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Refined Small-Signal Sequence Impedance Models of Type-III Wind Turbines
2018 IEEE Energy Conversion Congress and Exposition (ECCE), 2018Co-Authors: Ignacio Vieto, Jian SunAbstract:Refined Sequence Impedance models are presented for type-III wind turbines that use doubly-fed induction generators (DFIG). Previous small-signal Sequence Impedance models of DFIG did not consider the dynamics of the dc bus voltage connecting the stator- and rotor-side converters, and ignored small-signal responses at non-perturbation frequency. This work models the turbine in a new way by first modeling each converter independently and fully characterizing their ac/dc dynamics, and then combining these transfer functions to obtain the small-signal models of the whole turbine. These improved small-signal models consider dc bus dynamics as well as the current response at non-perturbation frequency that occurs due to the nonlinear nature of the converter and control. Turbine-grid system stability analysis that accounts for the coupled current responses is also presented. The transfer functions and small-signal models are validated against detailed simulation. The developed models are also compared against previous models to demonstrate the improved accuracy.
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Sequence Impedance Modeling and Analysis of Type-III Wind Turbines
IEEE Transactions on Energy Conversion, 2018Co-Authors: Ignacio Vieto, Jian SunAbstract:Sequence Impedance models are presented for type-III wind turbines that use doubly fed induction generators and back-to-back voltage source converters. The models, presented in analytical form for both positive- and negative-Sequence Impedances, include the effects of the induction machine, both the stator- and rotor-side converters as well as their controls, and the phase-locked loop used for synchronizing converter control with the grid voltage. The models are valid from subsynchronous frequency up to one-third of the switching frequency of the converter, making them useful for the analysis and mitigation of both subsynchronous and supersynchronous resonances and control interactions of type-III turbines with different types of grid.
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Sequence Impedance Modeling and Converter-Grid Resonance Analysis Considering DC Bus Dynamics and Mirrored Harmonics
2018 IEEE 19th Workshop on Control and Modeling for Power Electronics (COMPEL), 2018Co-Authors: Ignacio Vieto, Jian SunAbstract:Sequence Impedance models have been developed for two-level voltage source converters by assuming constant dc bus voltage and ignoring coupling over frequency effects. There have been efforts to overcome these limitations but the resulting models are very complex and the formulated system models require generalized Nyquist criterion for stability analysis. This paper presents a new modeling and system analysis method that solves these problems. The method starts by modeling the converter current response at different frequencies to a perturbation in the ac terminal voltage while keeping the dc bus voltage constant, and to a perturbation in the dc terminal voltage while keeping the ac terminal voltage constant. The individual transfer functions are then connected to build the overall converter models that include both the effects of dc bus dynamics and coupling over frequency. For converter-grid system stability analysis, the effects of coupling over frequency are shown to be equivalent to an additional Impedance in parallel with the Sequence Impedance. The developed models are validated individually as well as in system resonance analysis.
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automated Sequence Impedance modeling of three phase converters based on computer algebra
Conference of the Industrial Electronics Society, 2017Co-Authors: Talha Anwar, Ignacio Vieto, Jian SunAbstract:Sequence Impedance models have been accepted as an effective method for resonance and stability analysis of renewable energy, high-voltage dc transmission and other three-phase power electronics systems. While such Impedance models can be obtained in numerical form by simulation or measurement, the analytical models such as those presented in [2, 3] provide invaluable insight into how Impedance behavior relates to circuit and control design. Developing such analytical models, however, requires special skills and has been limited to few specialists. To facilitate the application of the method, this paper presents automated generation of Sequence Impedance models using computer algebra. The preliminary program that is capable of performing this function is developed based on a new matrix formulation of the underlying harmonic linearization method [7] and is implemented in Mathematica. Applications in two-level voltage-source converter and modular multilevel converters are presented to demonstrate the feasibility of the method.
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IECON - Automated Sequence Impedance modeling of three-phase converters based on computer algebra
IECON 2017 - 43rd Annual Conference of the IEEE Industrial Electronics Society, 2017Co-Authors: Talha Anwar, Ignacio Vieto, Jian SunAbstract:Sequence Impedance models have been accepted as an effective method for resonance and stability analysis of renewable energy, high-voltage dc transmission and other three-phase power electronics systems. While such Impedance models can be obtained in numerical form by simulation or measurement, the analytical models such as those presented in [2, 3] provide invaluable insight into how Impedance behavior relates to circuit and control design. Developing such analytical models, however, requires special skills and has been limited to few specialists. To facilitate the application of the method, this paper presents automated generation of Sequence Impedance models using computer algebra. The preliminary program that is capable of performing this function is developed based on a new matrix formulation of the underlying harmonic linearization method [7] and is implemented in Mathematica. Applications in two-level voltage-source converter and modular multilevel converters are presented to demonstrate the feasibility of the method.
Josep M. Guerrero - One of the best experts on this subject based on the ideXlab platform.
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Sequence-Impedance-Based Stability Comparison Between VSGs and Traditional Grid-Connected Inverters
IEEE Transactions on Power Electronics, 2019Co-Authors: Wenhua Wu, Leming Zhou, Yandong Chen, Yanting Dong, Xiaoping Zhou, Qianming Xu, Ling Yang, Josep M. GuerreroAbstract:Traditional grid-connected inverters (TGCI) could suffer from small-signal instability owing to the dynamic interactions among inverters and a weak grid. In this letter, the small-signal Sequence Impedance model of the virtual synchronous generator (VSG) is built, and the Sequence Impedance characteristics of the VSG and the TGCI are compared and analyzed. The Sequence Impedance of the TGCI is mainly capacitive in the middle-frequency area, and the Impedance amplitude is quite high. By contrast, the Sequence Impedance of the VSG, being consistent with the grid Impedance characteristics, is generally inductive, and the Impedance amplitude is quite low. Based on the Sequence Impedance model and the Nyquist stability criterion, the influence of the grid stiffness, the number of paralleled inverters, and the phase-locked loop (PLL) bandwidth on the stability of the VSG and the TGCI systems is analyzed. The stability analysis results show that the TGCI loses stability easily, whereas the VSG still works well without PLL restrictions under an ultraweak grid or with a large number of inverters connected to the grid. Therefore, the VSG is more suitable than the TGCI for achieving high penetration of renewable energy generation in an ultraweak grid from a system stability viewpoint. Finally, the experimental results validate the Sequence Impedance model and the stability analysis.
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control strategies for islanded microgrid using enhanced hierarchical control structure with multiple current loop damping schemes
IEEE Transactions on Smart Grid, 2017Co-Authors: Pan Shen, Xin Zhao, Josep M. GuerreroAbstract:In this paper, the modeling, controller design, and stability analysis of the islanded microgrid (MG) using enhanced hierarchical control structure with multiple current loop damping schemes is proposed. The islanded MG consists of the parallel-connected voltage source inverters using inductor-capacitor-inductor (LCL) output filters, and the proposed control structure includes the primary control with additional phase-shift loop, the secondary control for voltage amplitude and frequency restoration, the virtual Impedance loops which contain virtual positive- and negative-Sequence Impedance loops at fundamental frequency and virtual variable harmonic Impedance loop at harmonic frequencies, and the inner voltage and current loop controllers. A small-signal model for the primary and secondary controls with additional phase-shift loop is presented, which shows an over-damped feature from eigenvalue analysis of the state matrix. The moving average filter-based Sequence decomposition method is proposed to extract the fundamental positive and negative Sequences and harmonic components. The multiple inner current loop damping scheme is presented, including the virtual positive, virtual negative, and variable harmonic Sequence Impedance loops for reactive and harmonic power sharing purposes, and the proposed active damping scheme using capacitor current feedback loop of the LCL filter, which shows enhanced damping characteristics and improved inner-loop stability. Finally, the experimental results are provided to validate the feasibility of the proposed approach.
Fred Wang - One of the best experts on this subject based on the ideXlab platform.
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Sequence Impedance based harmonic stability analysis and controller parameter design of three phase inverter based multibus ac power systems
IEEE Transactions on Power Electronics, 2017Co-Authors: Fred WangAbstract:Three-phase inverter-based multibus ac power systems could suffer from the harmonic instability issue. The existing Impedance-based stability analysis method using the Nyquist stability criterion once requires the calculation of right-half-plane (RHP) poles of Impedance ratios, which would result in a heavy computation burden for complicated systems. In order to analyze the harmonic stability of multibus ac systems consisting of both voltage-controlled and current-controlled inverters without the need for RHP pole calculation, this paper proposes two Sequence-Impedance-based harmonic stability analysis methods. Based on the summary of all major connection types including mesh, the proposed Method 1 can analyze the harmonic stability of multibus ac systems by adding the components one by one from nodes in the lowest level to areas in the highest system level, and accordingly, applying the stability criteria multiple times in succession. The proposed Method 2 is a generalized extension of the Impedance-sum-type criterion to be used for the harmonic stability analysis of any multibus ac systems based on Cauchy's theorem. The inverter controller parameters can be designed in the forms of stability regions in the parameter space, by repetitively applying the proposed harmonic stability analysis methods. Experimental results of inverter-based multibus ac systems validate the effectiveness of the proposed harmonic stability analysis methods and parameter design approach.
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Sequence Impedance measurement of three-phase inverters using a parallel structure
2015 IEEE Applied Power Electronics Conference and Exposition (APEC), 2015Co-Authors: Wenchao Cao, Xuan Zhang, Fred WangAbstract:This paper proposes a method of Sequence Impedance measurement of three-phase inverters by using a parallel structure with another inverter as the measurement unit, in order to apply the Impedance-based stability analysis of power converter systems. The paralleled inverter not only injects smallsignal perturbations but also creates the desired operating conditions for the inverter under test. The measurement setup is simple, since no additional AC source or load banks are needed. First, the Sequence Impedance model of three-phase inverters is described. Then the measurement setup and injection method are presented. Zero-Sequence circulating current reduction and open-loop control with voltage compensation strategies guarantee the measurement accuracy. The agreement between the theoretical analysis and the measurement results in both simulation and experiments verifies the effectiveness of the proposed method.
