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| 2. |
- Chen, Feifan, et al.
(author)
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Enhanced Q-Axis Voltage-Integral Damping Control for Fast PLL-Synchronized Inverters in Weak Grids
- 2024
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In: IEEE transactions on power electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0885-8993 .- 1941-0107. ; 39:1, s. 424-435
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Journal article (peer-reviewed)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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| 4. |
- Dimitropoulos, Dimitrios, et al.
(author)
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Impact of Synchronous Condensers' Ratings on Mitigating Subsynchronous Oscillations in Wind Farms
- 2024
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In: Energies. - : MDPI AG. - 1996-1073. ; 17:7
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Journal article (peer-reviewed)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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| 5. |
- Dimitropoulos, Dimitrios, et al.
(author)
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Stability Analysis in Multi-VSC (Voltage Source Converter) Systems of Wind Turbines
- 2024
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In: Applied Sciences. - : MDPI AG. - 2076-3417. ; 14:8
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Journal article (peer-reviewed)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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| 6. |
- Li, Zejie, et al.
(author)
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Medium-Voltage Megawatt Power-Electronic-Based Grid Emulators : Testing Capability Requirements and Dynamics Challenges-A Review
- 2024
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In: 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
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Journal article (peer-reviewed)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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| 7. |
- Liao, Yicheng, et al.
(author)
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Neural Network Design for Impedance Modeling of Power Electronic Systems Based on Latent Features
- 2024
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In: IEEE Transactions on Neural Networks and Learning Systems. - : Institute of Electrical and Electronics Engineers (IEEE). - 2162-237X .- 2162-2388. ; 35:5, s. 5968-5980
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Journal article (peer-reviewed)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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| 8. |
- Luo, Cheng, et al.
(author)
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Design-Oriented Analysis of DC-Link Voltage Control for Transient Stability of Grid-Forming Inverters
- 2024
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In: IEEE Transactions on Industrial Electronics. - : Institute of Electrical and Electronics Engineers (IEEE). - 0278-0046 .- 1557-9948. ; 71:4, s. 3698-3707
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Journal article (peer-reviewed)abstract
- This article analyzes the parametric effect of the dc-link voltage controller (DVC) on the transient stability of grid-forming (GFM) inverters. It is found that the decrease of the proportional gain of DVC may lead to the loss of synchronism (LOS) even if the system is locally stable at the new equilibrium point (EP) after disturbance. Its physical insight is attributed to the unstable limit cycle (ULC) in the phase space according to the bifurcation theory. The GFM inverters whose operating point locates outside of ULC will lose synchronism with the grid. The decrease of the proportional gain of DVC will diminish the ULC, resulting in fewer operating points converging to the new EP and a higher risk of LOS. This bifurcation-based analysis provides a novel perspective for investigating the mechanism of parametric effect for the high-order nonlinear system, which is the article's main contribution. The parametric effect of the integral gain of DVC is also analyzed. A holistic parametric space partition for designing DVC is then drawn from the analysis, and a parametric configuration guideline is provided. The theoretical findings are validated by experimental tests.
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| 9. |
- Wu, Yang, et al.
(author)
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Impedance Profile Prediction for Grid-Connected VSCs based on Feature Extraction
- 2024
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In: 2024 IEEE Applied Power Electronics Conference and Exposition, APEC 2024. - : Institute of Electrical and Electronics Engineers (IEEE). ; , s. 1627-1632
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Conference paper (peer-reviewed)abstract
- Impedance-based stability analysis has been widely adopted for voltage source converters (VSCs). Considering unknown controller parameters, impedance measurement based on frequency scan is always required for stability evaluation, which endures complicated implementation and can only be conducted under small amount of stable operating conditions. To solve this problem, a novel impedance profile prediction method for grid-connected VSCs has been proposed. A combined structure of stacked autoencoder (AE) and principal component analysis (PCA) is firstly proposed to extract VSC admittance feature under stable operating points, and a comprehensive VSC admittance set can be further predicted through searching on an enlarged feature space with unstable scenarios included. The stability can then be evaluated on the predicted VSC admittances with a stability boundary derived. Simulations and experiments prove the effectiveness of the proposed method.
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| 10. |
- Zhao, Fangzhou, et al.
(author)
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Closed-Form Solutions for Grid-Forming Converters : A Design-Oriented Study
- 2024
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In: IEEE OPEN JOURNAL OF POWER ELECTRONICS. - : Institute of Electrical and Electronics Engineers (IEEE). - 2644-1314. ; 5, s. 186-200
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Journal article (peer-reviewed)abstract
- This paper derives closed-form solutions for grid-forming converters with power synchronization control (PSC) by subtly simplifying and factorizing the complex closed-loop models. The solutions can offer clear analytical insights into control-loop interactions, enabling guidelines for robust controller design. It is proved that 1) the proportional gains of PSC and alternating voltage control (AVC) can introduce negative resistance, which aggravates synchronous resonance (SR) of power control, 2) the integral gain of AVC is the cause of sub-synchronous resonance (SSR) in stiff-grid interconnections, albeit the proportional gain of AVC can help dampen the SSR, and 3) surprisingly, the current controller that dampens SR actually exacerbates SSR. Controller design guidelines are given based on analytical insights. The findings are verified by simulations and experimental results.
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