| 1. |
- Sun, Chenghao, et al.
(författare)
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Adaptive Synchronous Rectifier On-Time Control Within Dead-Time for Improving Light-Load Performance of LLC Resonant Converters
- 2024
-
Ingår i: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 39:8, s. 9382-9398
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Tidskriftsartikel (refereegranskat)abstract
- LLC resonant converter exhibits nonmonotonic voltage gain at light-load, which could lead to the malfunction of traditional pulse frequency modulation strategy and degraded efficiency due to excessive increase in switching frequency. To address this issue, an adaptive synchronous rectifier (SR) on-time control within dead-time is proposed for LLC resonant converters to normalize the voltage gain and enhance the light-load efficiency. First, the root cause of nonmonotonic voltage gain is analyzed and revealed as the energy accumulated in resonant inductor due to mismatched output capacitor discharge between primary and secondary side switches within dead-time. To suppress the energy accumulation, an adaptive SR on-time control within dead-time is developed to synchronize the output capacitor discharge processes of primary and secondary side switches, which is characterized as: 1) SR is turned on within dead-time to accelerate its output capacitor discharge; 2) the turn-on rate of SR is controlled by designing its gate resistor to match the output capacitor discharge rate of primary side switches; 3) the turn-on instant of SR is adaptively tuned according to the switching frequency. With the proposed SR control, the energy accumulation of resonant inductor during output capacitor discharge of switches is fully suppressed, resulting in a monotonic voltage gain at light-load, which facilitates voltage regulation and improves light-load efficiency. A 360-440-V input, 50-V/1-kW output LLC prototype is built to verify the effectiveness of proposed SR control.
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| 2. |
- Wang, Xiaoyu, et al.
(författare)
-
Guest Editorial: Modeling and Simulation Methods for Analysis and Design of Advanced Energy Conversion Systems
- 2020
-
Ingår i: IEEE Transactions on Energy Conversion. - 1558-0059 .- 0885-8969. ; 35:1, s. 309-311
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The papers in this special section examine modeling and simulation methods for the analysis and design of advanced energy conversion systems. Energy conversion lies aEnergyveral fronts including materials, conversion methods, power electronics, and controls have created new opportunities for efficient energy conversion from both the conventional and new sources of energy. Our urgent need to solve many critical problems with regards to the sustainability and security of our energy system as well as the ever-increasing environmental challenges facing humanity have further spurred unprecedented opportunities for creation of innovative solutions to address these challenges.
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| 3. |
- Duan, Jinpei, et al.
(författare)
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Dual-Circulant Modulation for Modular Multilevel DC/DC Converters With Inherent Balance Capability
- 2023
-
Ingår i: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 38:7, s. 7958-7963
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Tidskriftsartikel (refereegranskat)abstract
- Modular multilevel dc/dc converters (MMDC) have emerged recently for medium-voltage dc applications. Under single-circulant modulation, the submodule (SM) capacitor voltages in MMDC are found to be evenly divided only at some specific modulation coefficients. To obtain the inherent balance capability under all modulation coefficients and expand the application range of circulant modulation, a simple dual-circulant modulation is proposed in this letter. On the basis of single-circulant modulation, the self-balancing of the SM capacitor voltages is realized by using the additional switching patterns generated by a simple circulant permutation method. The theoretical analysis of the proposed method is presented, and the inherent balance capability of MMDC under the dual-circulant modulation method is verified by experiments.
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| 4. |
- Liao, Yicheng, et al.
(författare)
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Frequency-Domain Participation Analysis for Electronic Power Systems
- 2022
-
Ingår i: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 37:3, s. 2531-2537
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Tidskriftsartikel (refereegranskat)abstract
- This letter proposes a frequency-domain participation analysis approach to identifying the root cause of small-signal instability for electronic power systems. Differing from the participation analysis based on state-space analysis, the proposed approach is implemented based on impedance models, which is, thus, readily applicable for large-scale systems only with black-box models. The theoretical analysis is finally verified by the simulations and experiments.
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| 5. |
- Ojo, Olorunfemi, et al.
(författare)
-
Welcome From: Technical Program Chairs
- 2023
-
Ingår i: 2023 IEEE Energy Conversion Congress and Exposition, ECCE 2023. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)
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| 6. |
- Wang, Xinshuo, et al.
(författare)
-
Transient Overvoltage Analysis of Grid-Following VSCs during Fault Recovery
- 2023
-
Ingår i: ICPE 2023-ECCE Asia. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 2404-2409
-
Konferensbidrag (refereegranskat)abstract
- Current grid code has explicit requirement on the fault current injection profile of grid-following voltage-source converters (GFL-VSCs), i.e., the output reactive current of GFL-VSC needs to be proportional to voltage- magnitude deviation at the point of connection (PoC) until its current limitation is reached. This article points out that such way of injecting the fault current may result in transient overvoltage (TOV) at the PoC during fault recovery, and the rate of change of current reference of GFL-VSC is critical to the duration of TOV. Moreover, a method for estimating the maximum magnitude of TOV is presented, which provides an intuitive insight for the TOV phenomenon.
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| 7. |
- Wang, Zhihao, et al.
(författare)
-
Current Reference Control Scheme of Voltage Source Converters to Ensure the Existence of Stable Equilibrium Points During Grid Fault
- 2023
-
Ingår i: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 38:9, s. 10750-10765
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Tidskriftsartikel (refereegranskat)abstract
- Maintaining synchronization with the grid during fault ride-through (FRT) is essential for grid-connected voltage source converters (VSCs). However, improper current references can lead to a loss of synchronization during FRT due to the nonexistence of stable equilibrium points (SEPs). While the mechanism of SEPs has been explained, the development of control schemes ensuring their existence remains challenging due to the difficulty of obtaining real-time grid parameters during FRT. To address this issue, this article proposes a novel current reference control scheme that only requires prefault grid parameters. By analyzing the changes in grid parameters caused by faults and characterizing the correspondence between the during-fault and prefault grid parameters, a voltage-dependent current reference control scheme is proposed. Since no real-time grid parameter estimation is needed during FRT, the proposed control scheme is practical and easy to implement. Simulation studies using DIgSILENT PowerFactory demonstrate that the proposed control scheme enables the VSC to maintain synchronization with the grid under the conditions of short-circuit ratio equaling 1.3 and grid voltage dropping to 0.1 p.u. Moreover, experiments further verify the effectiveness and feasibility of the proposed control scheme.
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| 8. |
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| 9. |
- Zhan, Changjiang, et al.
(författare)
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An Overview of Stability Studies of Grid-forming Voltage Source Converters
- 2023
-
Ingår i: Zhongguo Dianji Gongcheng Xuebao/Proceedings of the Chinese Society of Electrical Engineering. - : Chinese Society for Electrical Engineering. - 0258-8013. ; 43:6, s. 2339-2358
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Tidskriftsartikel (refereegranskat)abstract
- Unlike grid-following converters, the grid-forming converter is operated as a synchronous voltage source, which can effectively improve the stability of power-electronics-dominated power systems, and hence, has attracted much research attention in recent years. As a basis of the large-scale implementation of grid-forming converters, there should be an in-depth understanding of its stability under different grid strengths as well as different grid disturbances. This article performs a comprehensive overview of the stability studies of grid-forming converters from the perspective of existence of equilibrium points, small-signal stability, and transient stability. On top of this, stabilization control solutions of grid-forming converters are also summarized. In the end, perspectives on the prospects and challenges of stability analysis of grid-forming converters are shared.
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| 10. |
- Bessegato, Luca, 1989-
(författare)
-
Modeling of Modular Multilevel Converters for Stability Analysis
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Modular multilevel converters (MMCs) have recently become the state-of-the-art solution for various grid-connected applications, such as high-voltage direct current (HVDC) systems and flexible alternating current transmission systems (FACTS). Modularity, scalability, low power losses, and low harmonic distortion are the outstanding properties that make MMCs a key technology for a sustainable future. The main objective of this thesis is the modeling of grid-connected MMCs for stability analysis. The stability of the interconnected system, formed by the converter and the ac grid, can be assessed by analyzing the converter ac-side admittance in relation to the grid impedance. Therefore, a method for the calculation of the ac-side admittance of MMCs is developed. This method overcomes the nonlinearities of the converter dynamics and it can be easily adapted to different applications. Moreover, the effects of different control schemes on the MMC ac-side admittance are studied, showing how the converter admittance can be reshaped. This is a useful tool for system design, because it shows how control parameters can be selected to avoid undesired grid-converter interactions. This thesis also studies ac/ac MMCs for railway power supplies, which are used in countries with a low-frequency railway grid, such as Germany (16.7 Hz) and Sweden (16 2/3 Hz). A hierarchical control scheme for these converters is devised and evaluated, considering the requirements and the operating conditions specific to this application. Furthermore, admittance models of the ac/ac MMC are developed, showing how the suggested hierarchical control scheme affects the three-phase and the single-phase side admittances of the converter. For computing the insertion indices, an open-loop scheme with sum capacitor voltage estimation is applied to the ac/ac MMC. Lyapunov stability theory is used to prove the asymptotic stability of the converter operated with the proposed control method. This specific open-loop scheme is also adapted to a modular multilevel matrix converter, which performs three-to-three phase direct conversion. Finally, this thesis presents the design of a down-scaled MMC prototype for experimental verification, rated at 10 kW with 30 full-bridge submodules. The hardware and the software are designed to be easily reconfigurable, which makes the converter suitable for different research projects focused on MMCs. Experiments on this down-scaled MMC are used to support and validate the key results presented throughout the thesis.
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| 11. |
- Bhadoria, Shubhangi, et al.
(författare)
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Enablers for Overcurrent Capability of Silicon-Carbide-Based Power Converters : An Overview
- 2023
-
Ingår i: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers Inc.. - 0885-8993 .- 1941-0107. ; 38:3, s. 3569-3589
-
Tidskriftsartikel (refereegranskat)abstract
- With the increase in penetration of power electronic converters in the power systems, a demand for overcurrent/ overloading capability has risen for the fault clearance duration. This article gives an overview of the limiting factors and the recent technologies for the overcurrent performance of SiC power modules in power electronics converters. It presents the limitations produced at the power module level by packaging materials, which include semiconductor chips, substrates, metallization, bonding techniques, die attach, and encapsulation materials. Specifically, technologies for overcurrent related temperatures in excess of 200°C are discussed. This article also discusses potential technologies, which have been proven or may be potential candidates for improving the safe operating area. The discussed technologies are use of phase-change materials below the semiconductor chip, Peltier elements, new layouts of the power modules, control and modulation techniques for converters. Special attention has been given to an overview of various potential phase-change materials, which can be considered for high-temperature operations.
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| 12. |
- Busatto, Tatiano
(författare)
-
On Waveform Distortion in Modern Low-Voltage Installations with Multiple Nonlinear Devices
- 2020
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The continuing society quest for more comfort combined with the need to minimize global environmental impacts is constantly introducing new technologies into our daily lives. Among the recent developments, the advances in energy-efficient lighting and renewable energy technologies have enabled a maturity level in cleaner electricity production and efficient use of energy. Aligned with these trends, more recently we are experiencing faster progress towards the electrification of the transport system. All these developments have been largely driven by advancements in power electronic technologies which ultimately introduces a significant number of nonlinear loads in the form of power converters into the low-voltage (LV) installations and networks for electricity distribution.The overall aim of this thesis is to investigate how these nonlinear loads (individually and together) impact the current waveform distortion in modern LV installations. The work addresses several issues related to the electrical interactions between the distribution grid and different nonlinear loads, such as LED lamps, power factor correction (PFC) converters, PV inverters, and electric vehicle chargers.As a first part, the influence of the network impedance is examined. A method combining analytical impedance network modelling with a probabilistic approach for the customer side equipment was developed to address the uncertainties associated with harmonic resonances in public LV networks. It was found that the main resonance is mainly due to the transformer inductance and the total customer capacitance, while cable capacitances and customer inductances have a small impact. Additionally, it was found that increasing PV penetration shifts the harmonic resonances to lower frequencies, but also decreases the impedance magnitude.The second part includes the examination of the so-called nonlinear interaction phenomenon. A methodology has been developed and applied to quantify the extent of nonlinear interaction between devices in the same LV installation. It was observed that the interaction of different power electronic devices creates nonlinearity deviation, changing the current harmonics emission mainly for low order harmonics. The harmonic phase angle is the most affected harmonic characteristic. Additionally, linked to the first part, it was observed that changes in the network impedance and voltage source waveform have a significant impact on the nonlinear interaction.As a third part, the current zero-crossing waveform distortion has been analysed with a focus on control instabilities. Prior measurements of multiple devices fitted with power-factor controller were compared with a simulation model and instabilities were evaluated. Results from this work have confirmed that zero-crossing distortion increases proportionally with the number of devices. In addition, it was found that the network impedance plays an important role in defining the stability-criteria of these devices.Results shown in this thesis have revealed the harmonic interdependency and its consequences in different frequency ranges: harmonics and supraharmonics. Understanding the details of these new scenarios becomes of fundamental importance to mitigate future power quality issues and ensure the functioning of equipment in modern LV installations. This work presents several findings and a comprehensive discussion serving as a guideline for future work on interaction analysis and its consequences for devices in the LV network.
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| 13. |
- Chen, Feifan, et al.
(författare)
-
Dynamics Enhancement for Power Synchronization Control with Asymmetric AC Voltage Controller in Strong Grids
- 2023
-
Ingår i: 2023 IEEE Conference on Control Technology and Applications, CCTA 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 1066-1070
-
Konferensbidrag (refereegranskat)abstract
- Power synchronization control (PSC) is designed for weak grid connections originally and its performance is weakened when connected to a strong grid. In this paper, an asymmetric AC voltage controller (AVC) is proposed to improve the performance of PSC in strong grids. The improvement is achieved by adding a coupling from d-axis to q-axis to the voltage control part. The effect of this d-to-q coupling is explained by small signal modeling. It is found that the asymmetric AVC gives an effective improvement in damping the low-frequency oscillation and stability robustness against the grid strengths. Theoretical analysis and experiments verify the effectiveness of the proposed asymmetric AVC.
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| 14. |
- Chen, Feifan, et al.
(författare)
-
Enhanced Q-Axis Voltage-Integral Damping Control for Fast PLL-Synchronized Inverters in Weak Grids
- 2024
-
Ingår i: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 39:1, s. 424-435
-
Tidskriftsartikel (refereegranskat)abstract
- The phase-locked loop (PLL) is a commonly used synchronization control method for grid-tied inverters. The PLL-synchronized inverters tend to have poor stability robustness with weak grid interconnections, especially when the PLL is designed with a high control bandwidth. To tackle this challenge, this article proposes an enhanced q-axis voltage-integral damping control, which not only stabilizes PLL-synchronized inverters in weak grids but also lifts the restriction on PLL bandwidth. This superior feature enables inverters to operate stably in ultraweak grids and with a superior transient response. The experimental tests confirm the performance of the method with 400-Hz PLL bandwidth under a short-circuit ratio of 1.28 of the grids.
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| 15. |
- Chen, Feifan, et al.
(författare)
-
Impedance Modeling for Quadrature-Axis Active Damping of PLL Dynamics
- 2022
-
Ingår i: 2022 IEEE 23RD WORKSHOP ON CONTROL AND MODELING FOR POWER ELECTRONICS (COMPEL 2022). - : IEEE.
-
Konferensbidrag (refereegranskat)abstract
- When grid-following voltage source converters (VSCs) operate in inverter mode, the phase-locked loop (PLL) dynamics introduce a negative-real-part impedance, which may lead to the instability of the closed-loop system, especially in a weak-grid connection. This undesirable property of the PLL may be offset by so-called active damping. Nevertheless, the interaction between the active damping and the adverse PLL impact is not fully understood. To this end, the properties of different active-damping methods are analyzed, with the focus on the q-to-q coupling of the input admittance. One important finding is that adding an integrator to the q-axis active damper can improve the system performance in a weak-grid connection. Simulations and experimental results verify the theoretical analysis.
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| 16. |
- Chen, Feifan, et al.
(författare)
-
Pitfalls of Using Passivity Index to Guide Grid-connected Inverter Control Design in Low-frequency Region
- 2023
-
Ingår i: 2023 IEEE Energy Conversion Congress and Exposition, ECCE 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 758-764
-
Konferensbidrag (refereegranskat)abstract
- The main purpose of this article is to elaborate on the pitfalls of using the frequency-domain passivity theories in grid-inverter interactions within the low-frequency range. It mainly covers the relationship between the passivity index and stability, considerations for control design guided by optimizing the passivity index, and issues with a negative infinite index. It is advised to exercise caution when applying passivity theory in the low-frequency range. These conclusions have been substantiated through numerical and experimental studies.
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| 17. |
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| 18. |
- Cheng, Li, et al.
(författare)
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Design of Neural Network for Adaptive Current Control with Different Short-Circuit Ratios
- 2022
-
Ingår i: Proceedings IECON 2022 - 48th Annual Conference of the IEEE Industrial Electronics Society. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)abstract
- Current control of grid-connected converters may result in harmonic instability when grid impedance changes. To prevent this issue, current controller parameters can be tuned adaptively according to different short-circuit ratios (SCRs). It is thus important to estimate the grid impedance in real-time. Unlike traditional FFT-based impedance measurement methods, a more efficient estimation approach based on neural networks is proposed in this paper. This method does not require a fixed and relatively long sampling window, making it possible for real-time impedance measurement. Further, a step-by-step design method of the feedforward neural network (FNN) used for grid impedance estimation is developed. Time-domain simulation results validate the effectiveness of the approach. Based on the designed FNN, adaptive current control is implemented and verified through simulation.
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| 19. |
- Cheng, Li, et al.
(författare)
-
Neural-Network-Based Impedance Estimation for Transmission Cables Considering Aging Effect
- 2023
-
Ingår i: 2023 8th IEEE Workshop on the Electronic Grid, eGRID 2023. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)abstract
- In power-electronic-based power systems like wind farms, conducting stability analysis necessitates a comprehensive understanding of the system impedance across a wide frequency range, from sub-harmonic frequencies up to the Nyquist frequency of control systems of power converters. The cable aging effect can significantly impact the cable impedance, while accurately estimating the degree of aging proves challenging. To avoid the requirement for precise aging prognostic, this paper proposes an approach based on Artificial Neural Networks (ANN) that enables the estimation of AC cable impedance in a wind farm solely through fundamental frequency measurements. The data used for training the ANN is obtained from the cable model in PSCAD, incorporating physical and geometrical parameters, which accurately approximates real cables within power systems. The training results of the ANN validate the accuracy of the proposed identification approach. As a result, the proposed approach effectively eliminates the potential misjudgment of system stability caused by the aging effect of power cables.
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| 20. |
- Cheng, Li, et al.
(författare)
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Online Identification of Wind Farm Wide Frequency Admittance with Power Cables Using the Artificial Neural Network
- 2023
-
Ingår i: 2023 IEEE Energy Conversion Congress and Exposition, ECCE 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 1530-1535
-
Konferensbidrag (refereegranskat)abstract
- In power-electronic-based power systems like wind farms, stability analysis requires knowledge of system impedance across a wide frequency range, from sub-harmonic frequencies to the Nyquist frequency. Although it is feasible to take the fundamental frequency measurement during power system operation, obtaining a wide-frequency impedance curve in real time is very challenging. This paper proposed an ANN-based approach to estimate wide-frequency system admittance of wind farms with power cables, through fundamental frequency measurements. Real-life uncertainties are considered, including shunt capacitor injection, filter inductance variance, cable aging, errors in voltage and current measurements, and the variance of other system parameters. The generalization ability of the ANN is validated on a new dataset with different uncertainty distributions, and the error sensitivity to the potential system parameter variance is evaluated. These results can be referenced in the data acquisition step in future neural-network-based applications.
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| 21. |
- Ciftci, Baris, et al.
(författare)
-
Wireless Communication in Modular Multilevel Converters and Electromagnetic Interference Characterization
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- The wireless control of modular multilevel converter (MMC) submodules was recently proposed. The success of the control depends on specialized control methods suitable for wireless communication and a properly designed wireless communication network in the MMC valve hall while aiming for low latency and high reliability. The wireless communication in the hall can be affected by the electromagnetic interference (EMI) of MMC submodules, voltage and current transients. In this article, firstly, a wireless communication network based on 5G New Radio is designed for an example full-scale MMC valve hall. After that, radiated EMI characteristics of MMC submodules with different voltage and current ratings and two dc circuit breakers are measured. The effects of EMI on wireless communication in the multi-GHz frequency band are tested. The interference from the components is confined below 500 MHz, and the wireless communication with 5825 MHz center frequency is not affected by the interference.
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| 22. |
- Ciftci, Baris, 1987-, et al.
(författare)
-
Wireless Communication in Modular Multilevel Converters and Electromagnetic Interference Characterization
- 2022
-
Ingår i: IEEE Access. - : Institute of Electrical and Electronics Engineers (IEEE). - 2169-3536. ; , s. 38189-38201
-
Tidskriftsartikel (refereegranskat)abstract
- The wireless control of modular multilevel converter (MMC) submodules was recently proposed. The success of the control depends on specialized control methods suitable for wireless communication and a properly designed wireless communication network in the MMC valve hall while aiming for low latency and high reliability. The wireless communication in the hall can be affected by the electromagnetic interference (EMI) of MMC submodules, voltage and current transients. In this article, firstly, a wireless communication network based on 5G New Radio is designed for an example full-scale MMC valve hall. After that, the radiated EMI characteristics of the MMC submodules with different voltage and current ratings and two dc circuit breakers are measured. The effects of EMI on wireless communication in the multi-GHz frequency band are tested. The interference from the components is confined below 500 MHz, and the wireless communication with 5825 MHz center frequency is not affected by the interference.
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| 23. |
- Ciftci, Baris, et al.
(författare)
-
Wireless control of modular multilevel converter autonomous submodules : 23rd European Conference on Power Electronics and Applications
- 2021
-
Ingår i: Proceedings 23rd European Conference on Power Electronics and Applications. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)abstract
- The wireless control of modular multilevel converter (MMC) submodules might offer advantages for MMCs with a high number of submodules. However, the control system should tolerate the stochastic nature of the wireless communication, continue the operation flawlessly or, at least, avoid overcurrents, overvoltages, and component failures. The previously proposed control methods enabled to control the submodules wirelessly with consecutive communication errors up to hundreds of control cycles. The submodule control method in this paper facilitates the MMC to safely overcome communication errors that last longer and when the MMC experiences significant electrical disturbances during the errors. The submodules are proposed to operate autonomously by implementing a replica of the central controller in the submodules and drive the replicas based on the local variables and the previously received data. The simulation and experimental results verify the proposed control method.
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| 24. |
- Ciftci, Baris, et al.
(författare)
-
Wireless control of modular multilevel converter submodules under ac-side faults
- 2021
-
Konferensbidrag (refereegranskat)abstract
- Wireless control of modular multilevel converter (MMC) submodules has been offered recently with potentially lower cost and higher availability advantages for the converter station. In this paper, the wireless control of MMC submodules under ac-side faults is investigated. The central controller of the MMC is equipped for the unbalanced grid conditions. Local current controllers in the submodules are operated autonomously in case of loss of wireless communication during the fault. A set of simulations with single line-to-ground, line-to-line, and three-phase-to-ground faults reveal that the MMC rides through the faults in all the cases with the expected communication conditions or when the communication is lost before or after the fault instant.
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| 25. |
- Ciftci, Baris, et al.
(författare)
-
Wireless Control of Modular Multilevel Converter Submodules With Communication Errors
- 2022
-
Ingår i: IEEE Transactions on Industrial Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0278-0046 .- 1557-9948. ; 69:11, s. 11644-11653
-
Tidskriftsartikel (refereegranskat)abstract
- Wireless control of modular multilevel converter (MMC) submodules can benefit from different points of view, such as lower converter cost and shorter installation time. In return for the advantages, the stochastic performance of wireless communication networks necessitates an advanced converter control system immune to the losses and delays of the wirelessly transmitted data. This paper proposes an advancement to the distributed control of MMCs to utilize in wireless submodule control. Using the proposed method, the operation of the MMC continues smoothly and uninterruptedly during wireless communication errors. The previously proposed submodule wireless control concept relies on implementing the modulation and individual submodule-capacitor-voltage control in the submodules using the insertion indices transmitted from a central controller. This paper takes the concept as a basis and introduces to synthesize the indices autonomously in the submodules during the communication errors. This new approach allows the MMC continue its operation when one, some, or all submodules suffer from communication errors for a limited time. The proposal is validated experimentally on a laboratory-scale MMC.
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| 26. |
- Dimitropoulos, Dimitrios, et al.
(författare)
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Impact of Synchronous Condensers' Ratings on Mitigating Subsynchronous Oscillations in Wind Farms
- 2024
-
Ingår i: Energies. - : MDPI AG. - 1996-1073. ; 17:7
-
Tidskriftsartikel (refereegranskat)abstract
- Subsynchronous oscillations have occurred in wind farms due to the high penetration of converter-based technology in power systems and may potentially lead to grid instability. As an effective solution, synchronous condensers, with their ability to control voltage and inject reactive power in the power system, are increasingly being adopted, as they can lead to the mitigation of such oscillations in weak grid conditions. However, the impact of synchronous condensers' power ratings on system stability is a topic that requires further investigation. In fact, an improper selection of a synchronous condenser's rating will not extinguish existing subsynchronous oscillations and may even cause the emergence of new oscillatory phenomena. This paper presents a novel examination of the impact that the synchronous condenser's power rating has on the small-signal stability of a wind farm with existing subsynchronous oscillations while being connected to a weak grid. The wind farm's model is developed using state-space modeling, centering on grid interconnection and incorporating the state-space submodel of a synchronous condenser to show its impact on subsynchronous oscillation mitigation. The stability analysis determines the optimal synchronous condenser's power ratings for suppressing these oscillations in the wind farm model. The findings are corroborated through time domain simulations and fast-Fourier transformation (FFT) analysis, which further validate the stability effects of a synchronous condenser's rating.
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| 27. |
- Dimitropoulos, Dimitrios, et al.
(författare)
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Stability Analysis in Multi-VSC (Voltage Source Converter) Systems of Wind Turbines
- 2024
-
Ingår i: Applied Sciences. - : MDPI AG. - 2076-3417. ; 14:8
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a holistic nonlinear state-space model of a system with multiple converters is developed, where the converters correspond to the wind turbines in a wind farm and are equipped with grid-following control. A novel generalized methodology is developed, based on the number of the system's converters, to compute the equilibrium points around which the model is linearized. This is a more solid approach compared with selecting operating points for linearizing the model or utilizing EMT simulation tools to estimate the system's steady state. The dynamics of both the inner and outer control loops of the power converters are included, as well as the dynamics of the electrical elements of the system and the digital time delay, in order to study the dynamic issues in both high- and low-frequency ranges. The system's stability is assessed through an eigenvalue-based stability analysis. A participation factor analysis is also used to give an insight into the interactions caused by the control topology of the converters. Time domain simulations and the corresponding frequency analysis are performed in order to validate the model for all the control interactions under study.
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| 28. |
- Fan, Bo, et al.
(författare)
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A Review of Current-Limiting Control of Grid-Forming Inverters Under Symmetrical Disturbances
- 2022
-
Ingår i: IEEE OPEN JOURNAL OF POWER ELECTRONICS. - : Institute of Electrical and Electronics Engineers (IEEE). - 2644-1314. ; 3, s. 955-969
-
Forskningsöversikt (refereegranskat)abstract
- Grid-forming (GFM) inverters are recognized as a viable solution to increase the penetration of renewable energy in bulk power systems. However, they are physically different from synchronous generators in terms of overcurrent capability. To protect the power semiconductor devices and support the power grid under severe symmetrical disturbances, the GFM control systems should be able to achieve the following requirements: current magnitude limitation, fault current contribution, and fault recovery capability. Various current-limiting control methods are reported in the literature to fulfill these goals, including current limiters, virtual impedance, and voltage limiters. This paper presents an overview of those methods. Emerging challenges that need to be addressed, including temporary overcurrent, unspecified output current vector angle, undesired current saturation, and transient overvoltage, are pointed out. Comparative simulations are conducted to demonstrate the performance of different methods under grid voltage drops and phase jumps. Finally, open issues of current-limiting control methods for GFM inverters, including transient stability assessment, voltage source behavior under overcurrent conditions, and windup of voltage controllers, are shared.
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| 29. |
- Fan, Bo, et al.
(författare)
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Fault Recovery Analysis of Grid-Forming Inverters With Priority-Based Current Limiters
- 2023
-
Ingår i: IEEE Transactions on Power Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8950 .- 1558-0679. ; 38:6, s. 5102-5112
-
Tidskriftsartikel (refereegranskat)abstract
- Grid-forming (GFM) inverters are required to operate robustly against grid faults. However, due to the limited over-current capability of inverters, current-limiting controls are usually applied to protect these semiconductor devices, which may prevent GFM inverters from a successful fault recovery. To understand this phenomenon, this study analyzes the fault recovery process of a GFM inverter with a priority-based current limiter. According to whether the GFM inverter can ensure transient stability and exit the current-limiting mode after fault clearance, three post-fault scenarios are identified, including normal operation, current limitation, and oscillations. Further, the impacts of the short-circuit ratio and control parameters on the post-fault behavior of GFM inverters are demonstrated. To illustrate the implications of these theoretical results, typical numerical examples are presented. Finally, the theoretical findings are validated through experimental tests.
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| 30. |
- Gao, Guoqing, et al.
(författare)
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Fault current control of MMC in HVDC-connected offshore wind farm : A coordinated perspective with current differential protection
- 2023
-
Ingår i: International Journal of Electrical Power & Energy Systems. - : Elsevier BV. - 0142-0615 .- 1879-3517. ; 148, s. 108952-
-
Tidskriftsartikel (refereegranskat)abstract
- The modular multilevel converter (MMC) based high-voltage dc (HVDC)-connected offshore wind farm (OWF) is power electronic converter dominated power system, where the conventional current differential protection may not operate effectively. Based on the basic operation principle of the current differential relay, this paper points out that the phase difference ((fidiff) of fault currents from MMC and OWF should be limited within a specific range, i.e. (-(fidiffmax, (fidiffmax), to guarantee the reliable tripping of the current differential relay. Yet, the highly control-dependent fault currents from the MMC and OWF could yield an arbitrary (fidiff that might beyond (-(fidiffmax, (fidiffmax), which leads to the possible malfunction of the current differential relay. To tackle this challenge, the coordinated control method of MMC is proposed to align the phase angle of its fault current with that of the OWF, such that (fidiff is an element of (-(fidiffmax, (fidiffmax) can be always guaranteed, so as the reliable operation of the current differential relay. Finally, the proposed coordinated control is verified by the electromagnetic transient (EMT) simulations in PSCAD and the real-time digital simulator (RTDS).
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| 31. |
- Gao, Xiaonan, et al.
(författare)
-
Maximizing Current Contribution of Grid-Forming MMCs under Asymmetrical Grid Faults
- 2024
-
Ingår i: 2024 IEEE 10th International Power Electronics and Motion Control Conference, IPEMC 2024 ECCE Asia. - : Institute of Electrical and Electronics Engineers IEEE. ; , s. 2440-2445
-
Konferensbidrag (refereegranskat)abstract
- This paper explores the limitations of the fault current contribution of grid-forming modular multilevel converters (GFM-MMCs) under asymmetrical grid faults. Differing from the voltage source converters with a centralized dc-link capacitor, the arm current of MMCs comprises a circulating current for internal energy balancing, in addition to the dc-link current and ac output current. Under asymmetrical grid faults, the interaction between the positive- and negative-sequence components results in a power imbalance among the phases (or legs) of the MMC. This requires the presence of the dc circulating currents in each phase of MMC to eliminate this imbalance. The presence of this dc circulating current not only complicates the design of current limiting strategies but also constrains the fault current contribution of GFM-MMC. To address this issue, we propose a current limiting strategy ensuring that GFM-MMC can provide its allowable maximum fault current during asymmetrical grid faults.
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| 32. |
- Gong, Hong, et al.
(författare)
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Rethinking Current Controller Design for PLL-Synchronized VSCs in Weak Grids
- 2022
-
Ingår i: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 37:2, s. 1369-1381
-
Tidskriftsartikel (refereegranskat)abstract
- This article revisits the design of the current controller for grid-connected voltage-source converters (VSCs), considering the dynamic impacts of the phase-locked loop (PLL), weak grids, and of voltage feedforward (VFF) control. First, a single-input single-output transfer-function-based model is proposed to characterize the interactions of control loops. It is analytically found that the proportional gain of the current controller essentially aggravates the instability effect of PLL in weak grids, while the cutoff frequency of the low-pass filter used with the VFF loop has a nonmonotonic relationship with the PLL-induced instability. Then, based on these findings, a guideline for redesigning the current controller of PLL-synchronized VSCs is developed, which enables a codesign of the current controller and VFF controller. Finally, simulation and experimental results confirm the validity of theoretical analyses.
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| 33. |
- Harnefors, Lennart, 1968, et al.
(författare)
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Asymmetric Complex-Vector Models with Application to VSC-Grid Interaction
- 2020
-
Ingår i: IEEE Journal of Emerging and Selected Topics in Power Electronics. - 2168-6777 .- 2168-6785. ; 8:2, s. 1911-1921
-
Tidskriftsartikel (refereegranskat)abstract
- The properties of complex space-vector models for asymmetric three-phase systems are investigated in this article. Most importantly, three alternative methods for the stability analysis of the asymmetric closed-loop systems are presented. The end results avoid the usage of matrix manipulations. It is shown how the theory can be applied to modeling and stability analysis of a grid-connected voltage-source converter (VSC). The methods are compared using numerical examples.
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| 34. |
- Li, Helong, et al.
(författare)
-
Parallel Connection of Silicon Carbide MOSFETs - Challenges, Mechanism, and Solutions
- 2023
-
Ingår i: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 38:8, s. 9731-9749
-
Tidskriftsartikel (refereegranskat)abstract
- Power semiconductor devices are often connected in parallel to increase the current rating of the power conversion systems. However, due to mismatched circuit parameters or semiconductor fabrication discrepancies, the current of paralleled power semiconductor devices can be unbalanced, which potentially leads to accelerated aging and long-term reliability issues. The fast-switching speed of silicon carbide (SiC) devices aggravates this problem due to its higher sensitivity to parasitic parameters. Numerous efforts have been dedicated to analyzing and addressing the current imbalance issue of paralleling SiC devices. This article comprehensively summarizes and presents state-of-the-art research regarding the current imbalance in paralleled SiC devices. Degree of imbalance is proposed to comprehensively quantify the current mismatch. Starting with mechanism analysis, different types of current imbalance are categorized. Various device parameters and the package layout that impact the current distribution are investigated. The existing solutions including passive methods and active methods are concluded and categorized. This work also incorporates insight into the future development needs of high-power multichip SiC module packaging and driving technologies.
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| 35. |
- Li, Yifei, et al.
(författare)
-
Current Reference Generation of Inverter-Based Resources During Asymmetrical Faults
- 2023
-
Ingår i: 2023 IEEE Energy Conversion Congress and Exposition, ECCE 2023. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 1129-1136
-
Konferensbidrag (refereegranskat)abstract
- This paper analyzes the current reference generation of inverter-based resources (IBRs) during asymmetrical faults. It is revealed that the existing current generation methods are insufficient in maximizing the fault current contribution under different current priority modes. In this paper, a novel current reference generation approach is proposed to address this problem while simultaneously ensuring compliance with converter current limitations and grid codes. Electromagnetic transient (EMT) simulations are given to verify the proposed method.
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| 36. |
- Li, Yifei, et al.
(författare)
-
Impacts of Current Reference Generation on Phase Selection Element
- 2023
-
Ingår i: 2023 8th IEEE Workshop on the Electronic Grid, eGRID 2023. - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)abstract
- With the increasing integration of inverter-based resources (IBRs) into power systems, the fault characteristics of the power system can be altered, potentially affecting the performance of the traditional phase selection element (PSE). This paper first analyzes the fault characteristics of IBRs, then provides a theoretical examination of how these unique fault characteristics affect the performance of PSE. It is revealed current reference generation of IBRs will significantly impact the efficiency of PSE by altering the proportion of active current. Electromagnetic transient (EMT) simulations are given to verify the theoretical analysis.
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| 37. |
- Li, Yifei, et al.
(författare)
-
Impacts of inverter-based resources on directional elements during asymmetrical faults
- 2023
-
Ingår i: Proceedings 22nd Wind and Solar Integration Workshop, WIW 2023. - : Institution of Engineering and Technology (IET). ; , s. 400-405
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The large-scale integration of Inverter-Based Resources (IBRs) significantly alters the fault characteristics of synchronous generator-dominated power systems, posing a challenge to the conventional sequence component-based directional elements in the grid protection system. To reveal the impacts of IBRs on sequence component-based directional elements during asymmetrical faults, this paper first investigates the impacts of various priority modes of current reference generation. Subsequently, the impacts of control dynamics in the cases where the control scheme has not yet reached a steady state are investigated. It is found that the current reference generation and Phase-Locked Loop (PLL) dynamic can adversely affect the performance of directional elements. Electromagnetic transient (EMT) simulations are given to verify the theoretical analysis.
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| 38. |
- Li, Yufei, et al.
(författare)
-
Machine Learning at the Grid Edge : Data-Driven Impedance Models for Model-Free Inverters
- 2024
-
Ingår i: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 39:8, s. 10465-10481
-
Tidskriftsartikel (refereegranskat)abstract
- It is envisioned that the future electric grid will be underpinned by a vast number of smart inverters linking renewables at the grid edge. These inverters' dynamics are typically characterized as impedances, which are crucial for ensuring grid stability and resiliency. However, the physical implementation of these inverters may vary widely and may be kept confidential. Existing analytical impedance models require a complete and precise understanding of system parameters. They can hardly capture the complete electrical behavior when the inverters are performing complex functions. Online impedance measurements for many inverters across multiple operating points are impractical. To address these issues, we present the InvNet, a machine learning framework capable of characterizing inverter impedance patterns across a wide operation range, even with limited impedance data. Leveraging transfer learning, the InvNet can extrapolate from physics-based models to real-world ones and from one inverter to another with the same control framework but different control parameters with very limited data. This framework demonstrates machine learning as a powerful tool for modeling and analyzing black-box characteristics of grid-tied inverter systems that cannot be accurately described by traditional analytical methods, such as inverters under model-predictive control. Comprehensive evaluations were conducted to verify the effectiveness of the InvNet.
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| 39. |
- Li, Yufei, et al.
(författare)
-
Neural Network Models and Transfer Learning for Impedance Modeling of Grid-Tied Inverters
- 2022
-
Ingår i: 2022 IEEE 13TH INTERNATIONAL SYMPOSIUM ON POWER ELECTRONICS FOR DISTRIBUTED GENERATION SYSTEMS (PEDG). - : Institute of Electrical and Electronics Engineers (IEEE).
-
Konferensbidrag (refereegranskat)abstract
- The future power grid will be supported by a large number of grid-tied inverters whose dynamics are critical for grid stability and power flow control. The operating conditions of these inverters vary across a wide range, leading to different small-signal impedances and different grid-interface behaviors. Analytical impedance models derived at specific operating points can hardly capture nonlinearities and nonidealities of the physical systems. The applicability of electromagnetic transient (EMT) simulations is often limited by the system complexity and the available computational resources. This paper applies neural network and transfer learning to impedance modeling of gridtied inverters. It is shown that a neural network (NN) trained by data automatically acquired from EMT simulations outperforms the one trained by traditional analytical models when unknown information exist in simulations. Pre-training the NN with analytically calculated data can greatly reduce the amount of simulation data needed to achieve good modeling results.
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| 40. |
- Li, Yunwei Ryan, et al.
(författare)
-
Editorial : Special Section on Patent-Related Short Articles
- 2023
-
Ingår i: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 38:6, s. 6748-6749
-
Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 41. |
- Li, Zejie, et al.
(författare)
-
Adaptive Anti-Saturation Control Design of Transformers in Converter-Based Grid Emulators
- 2024
-
Ingår i: IEEE Journal of Emerging and Selected Topics in Power Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 2168-6777 .- 2168-6785. ; 12:3, s. 2809-2819
-
Tidskriftsartikel (refereegranskat)abstract
- Transformer saturation is a common issue in megawatt converter-based grid emulators (GEs) when emulating grid faults. This problem necessitates the use of anti-saturation control (ASC) with GEs. However, conventional ASC methods tend to distort the emulated grid voltage or even interact with the voltage control (VC) of GEs, causing instability in the system. This article, thus, proposes an adaptive ASC method and superimposes its output command to both modulation and VC references, which not only alleviate transformer saturation with the lower output voltage distortion, but mitigate its adverse interaction with the VC of converter-based GEs. Experimental results confirm the effectiveness of the adaptive ASC.
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| 42. |
- Li, Zejie, et al.
(författare)
-
Medium-Voltage Megawatt Power-Electronic-Based Grid Emulators : Testing Capability Requirements and Dynamics Challenges-A Review
- 2024
-
Ingår i: IEEE Journal of Emerging and Selected Topics in Power Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 2168-6777 .- 2168-6785. ; 12:2, s. 1545-1559
-
Tidskriftsartikel (refereegranskat)abstract
- Power-electronic-based grid emulators are emerging as a promising way to test the grid-code compliance of renewable energy resources. Yet, the ever-increasing power and voltage levels of device under test (DUT) pose new requirements and challenges to power-electronic-based grid emulators. This article first gives an overview of testing capability requirements based on the recent grid codes and standards and then discusses the resulted dynamic interactions and solutions for power-electronic-based grid emulators. Perspectives on the open issues and emerging trends of grid emulators are finally shared.
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| 43. |
- Li, Zejie, et al.
(författare)
-
Power-Hardware Design and Topologies of Converter-Based Grid Emulators for Wind Turbines
- 2023
-
Ingår i: IEEE Journal of Emerging and Selected Topics in Power Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 2168-6777 .- 2168-6785. ; 11:5, s. 5001-5017
-
Tidskriftsartikel (refereegranskat)abstract
- Power-electronic-based grid emulators (GEs) emerge as a favorable method for testing grid-code compliances of wind turbines (WTs), thanks to their full controllability and improved efficiency. To accommodate the increasing power and voltage levels of WTs, scalability becomes a critical requirement for the topologies of converter-based GEs. This article identifies first the power rating of future GEs based on the system architecture and the evolution of WTs, followed by evaluating converter topologies of GEs for high scalability. Design considerations of power semiconductor devices, step-up transformers, dc chopper, and dc capacitors are also discussed for existing and prospective GEs.
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| 44. |
- Liao, Yicheng, et al.
(författare)
-
Controller design-oriented analysis of grid-forming converters for stability robustness enhancement
- 2021
-
Ingår i: Chinese Journal of Electrical Engineering. - : Institute of Electrical and Electronics Engineers (IEEE). - 2096-1529. ; 7:4, s. 37-48
-
Tidskriftsartikel (refereegranskat)abstract
- Grid-forming converters can suffer from control interaction problems in grid connections that can result in small-signal instability. Their inner-loop voltage controller tends to interact with the outer-loop power controller, rendering the controller design more difficult. To conduct a design-oriented analysis, a control-loop decomposition approach for grid-forming converters is proposed. Combined with impedance-based stability analysis, the control-loop decomposition approach can reveal how different control loops affect the converter-grid interaction. This results in a robust controller design enabling grid-forming converters to operate within a wider range of grid short-circuit ratios. Finally, simulation and experimental results, which validate the approach, are presented.
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| 45. |
- Liao, Yicheng, et al.
(författare)
-
Neural Network Design for Impedance Modeling of Power Electronic Systems Based on Latent Features
- 2024
-
Ingår i: IEEE Transactions on Neural Networks and Learning Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-237X .- 2162-2388. ; 35:5, s. 5968-5980
-
Tidskriftsartikel (refereegranskat)abstract
- Data-driven approaches are promising to address the modeling issues of modern power electronics-based power systems, due to the black-box feature. Frequency-domain analysis has been applied to address the emerging small-signal oscillation issues caused by converter control interactions. However, the frequency-domain model of a power electronic system is linearized around a specific operating condition. It thus requires measurement or identification of frequency-domain models repeatedly at many operating points (OPs) due to the wide operation range of the power systems, which brings significant computation and data burden. This article addresses this challenge by developing a deep learning approach using multilayer feedforward neural networks (FNNs) to train the frequency-domain impedance model of power electronic systems that is continuous of OP. Distinguished from the prior neural network designs relying on trial-and-error and sufficient data size, this article proposes to design the FNN based on latent features of power electronic systems, i.e., the number of system poles and zeros. To further investigate the impacts of data quantity and quality, learning procedures from a small dataset are developed, and K-medoids clustering based on dynamic time warping is used to reveal insights into multivariable sensitivity, which helps improve the data quality. The proposed approaches for the FNN design and learning have been proven simple, effective, and optimal based on case studies on a power electronic converter, and future prospects in its industrial applications are also discussed.
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| 46. |
- Liao, Yicheng, et al.
(författare)
-
Small-Signal Modeling of AC Power Electronic Systems : Critical Review and Unified Modeling
- 2021
-
Ingår i: IEEE OPEN JOURNAL OF POWER ELECTRONICS. - : Institute of Electrical and Electronics Engineers (IEEE). - 2644-1314. ; 2, s. 424-439
-
Forskningsöversikt (refereegranskat)abstract
- The harmonic state-space (HSS), the dynamic phasor (DP), and the generalized dq (GDQ) modeling are three widely used methods for small-signal analysis of ac power electronic systems. By reviewing their principles and deriving their mathematical relationships, this paper proposes a unified framework for all the three approaches. The unified modeling reveals that the linearization and transformation can be exchanged flexibly in the modeling process, and the initial phase takes a role in transforming the GDQ model into the HSS or DP model. Case studies on a three-phase voltage-source converter in unbalanced power grids are provided for validation. The relationships of three modeling methods are verified by mathematical proofs and time-domain simulations. The unified frequency-domain model is further validated through the frequency scan in experiments. Insights of the unified modeling framework and recommendations from engineering perspectives are finally discussed.
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| 47. |
- Liao, Yicheng, et al.
(författare)
-
Stability and Sensitivity Analysis of Multi-Vendor, Multi-Terminal HVDC Systems
- 2023
-
Ingår i: IEEE OPEN JOURNAL OF POWER ELECTRONICS. - : Institute of Electrical and Electronics Engineers (IEEE). - 2644-1314. ; 4, s. 52-66
-
Tidskriftsartikel (refereegranskat)abstract
- Multi-terminal HVDC projects are increasingly developed in recent years to enhance the flexibility of energy transmission. Differing from the point-to-point HVDC systems, it is more challenging to design the multi-terminal HVDC system and ensure stable interoperability among converter systems, especially when the converters are manufactured from different vendors. Although impedance-based stability analysis allows for analyzing such systems based on black-box models, it is still difficult to utilize those black-box models to identify the root cause of potential instability. To tackle this challenge, this paper proposes a multi-level sensitivity analysis approach using frequency-domain sensitivity functions based on the impedance-based stability criterion. The proposed method differs from the classical sensitivity analysis based on state-space or transfer-function models, as it is purely based on black-box impedance models. Case studies on a four-terminal HVDC system are carried out for stability and sensitivity analysis based on the impedance measurement in PSCAD, through which the most sensitive HVDC station can be identified. The proposed theory and the analyzed results are finally validated by electromagnetic transient simulations.
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| 48. |
- Liao, Yicheng, et al.
(författare)
-
Vector-Norm Based Truncation of Harmonic Transfer Functions in Black-Box Electronic Power Systems
- 2022
-
Ingår i: IEEE OPEN JOURNAL OF THE INDUSTRIAL ELECTRONICS SOCIETY. - : Institute of Electrical and Electronics Engineers (IEEE). - 2644-1284. ; 3, s. 163-173
-
Tidskriftsartikel (refereegranskat)abstract
- Power systems equipped with power electronic converters can be modeled by harmonic transfer functions (HTFs) in a black-box manner for dynamic analysis. This paper studies the truncation of HTFs. It is proposed to define the gain function of an HTF as the norm of its central-column vector. Then, the error bound of the gain function in relation to the truncation order is explicitly derived, which can be used as an indicator for the HTF truncation. Compared with existing solutions, the proposed method is practical in truncating black-box systems with unknown internal parameters, since the truncation error bound can be estimated by the central-column elements of the HTF, which can be easily measured through frequency scan. The truncation approach is finally verified on a three-phase electronic power system by electromagnetic transient simulations.
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| 49. |
- Luo, Cheng, et al.
(författare)
-
A Flexible Saturation Limiter for DC-Link Voltage Control of Grid-Forming Inverters With Enhanced Transient Stability
- 2023
-
Ingår i: IEEE transactions on energy conversion. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8969 .- 1558-0059. ; 38:4, s. 2514-2524
-
Tidskriftsartikel (refereegranskat)abstract
- This article analyzes the influence of the saturation limiter used with dc-link voltage control (DVC) on the transient stability of grid-forming (GFM) inverters and proposes a flexible saturation limiter to alleviate its adverse impact. First, it is found that the conventional saturation limiter (CSL) can enhance transient stability. Yet, it would boost the dc-link voltage or even trigger overvoltage protection, especially when the threshold value of CSL is small. To tackle the adverse impact of CSL on dc-link voltage, a flexible saturation limiter is proposed, which only begins to limit the active power reference when the derivative of dc-link voltage turns from positive to negative (the dc-link voltage reaches its peak value at this instant). Finally, experimental tests confirm the effectiveness of the scheme.
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| 50. |
- Luo, Cheng, et al.
(författare)
-
Adaptive-Output-Voltage-Regulation-Based Solution for the DC-Link Undervoltage of Grid- Forming Inverters
- 2023
-
Ingår i: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 38:10, s. 12559-12569
-
Tidskriftsartikel (refereegranskat)abstract
- This article proposes an adaptive-output-voltage-regulation (AOVR)-based solution to alleviate the dc-link undervoltage for grid-forming (GFM) inverters. First, it is shown that large disturbances may cause the dc-link undervoltage for GFM inverters threatening the safe operation of the system. To tackle this issue, an AOVR-based control strategy is proposed, whose main idea is to reduce the output voltage of the GFM inverter and also speed up the dynamic process of the power angle by intentionally enlarging the frequency deviation of the active power control loop. By doing so, the dc-link output energy will reduce to avoid possible undervoltage. The parameter design of the proposed method is based on the overmodulation constraints, and an auxiliary module is configured for the low-voltage-ride-through (LVRT) requirements. The applicability of the proposed solution is checked when considering the current limitation. The pros of the proposed solution are also depicted when compared with state-of-art solutions. The effectiveness of the proposed control strategy is finally confirmed by the experimental tests.
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