Online Grid Impedance Estimation-Based Adaptive Control of Virtual Synchronous Generators Considering Strong and Weak Grid Conditions

Mohammed, Nabil; Ravanji, Mohammad Hasan; Zhou, Weihua; Bahrani, Behrooz

doi:10.1109/tste.2022.3223976

Cited by 36 publications

(11 citation statements)

References 36 publications

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“…The problem associated with the conventional PLL is eliminated by replacing it. Now, the inverter can use self-synchronization mechanisms embedded into the UDC [32,44,56]; as a result, the inverter can mimic [57] a synchronous generator. Furthermore, another problem related to inverters that act as a current source is that the high penetration of GFL inverters can cause instability in the system.…”

Section: Proposed Gfm Inverter Controlmentioning

confidence: 99%

Analysis of Grid-Forming Inverter Controls for Grid-Connected and Islanded Microgrid Integration

Ward,

Subburaj,

Demir

et al. 2024

Sustainability

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Autonomous grid-forming (GFM) inverter testbeds with scalable platforms have attracted interest recently. In this study, a self-synchronized universal droop controller (SUDC) was adopted, tested, and scaled in a small network and a test feeder using a real-time simulation tool to operate microgrids without synchronous generators. We presented a novel GFM inverter control adoption to better understand the dynamic behavior of the inverters and their scalability, which can impact the distribution system (DS). This paper provides a steady-state and transient analysis of the GFM power inverter controller via simulation to better understand voltage and frequency stabilization and ensure that the critical electric loads are not affected during a prolonged power outage. The controllers of the GFM inverter are simulated in HYPERSIM to examine voltage and frequency fluctuations. This analysis includes assessing the black start capability for photovoltaic microgrids, both grid-connected and islanded, during transient fault conditions. The high photovoltaic PV penetration levels open exciting opportunities and challenges for the DS. The GFM inverter control demonstrated appropriate response times for synchronization, connection, and disconnection to the grid. The DS has become more resilient and independent of fossil fuels by increasing the penetration of inverter-based distributed energy resources (DERs).

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Section: Proposed Gfm Inverter Controlmentioning

confidence: 99%

Analysis of Grid-Forming Inverter Controls for Grid-Connected and Islanded Microgrid Integration

Ward,

Subburaj,

Demir

et al. 2024

Sustainability

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“…2(d) illustrates the block diagram of the primary loop of a GFMI equipped with the primary AVSG. This control strategy, as proposed in [29], aims to enhance the performance of the VSG, particularly in strong grids characterized by poor dynamic performance, including high overshoot and long settling time oscillations.…”

Section: ) Avsg-based Gfmismentioning

confidence: 99%

“…For more detailed explanation on the adaptive tuning procedure of the AVSG parameters, please refer to [29].…”

Section: ) Avsg-based Gfmismentioning

confidence: 99%

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Grid-Forming Inverters: A Comparative Study of Different Control Strategies in Frequency and Time Domains

Mohammed,

Udawatte,

Zhou

et al. 2024

IEEE Open J. Ind. Electron. Soc.

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Grid-forming inverters (GFMIs) are anticipated to play a leading role in future power systems. In contrast to their counterpart grid-following inverters, which employ phase-locked loops for synchronization with the grid voltage and rely on stable grid connections, GFMIs primarily employ the power-based synchronization concept to form the voltage. Hence, they can not only stably operate in regions of the grid characterized by low strength but also provide critical ancillary services to power systems, including voltage, frequency and inertia support. Several control strategies have been employed for GFMIs, making it crucial to comprehend their stability characteristics for the analysis of small-signal stability and low-frequency oscillations. This article examines the performance of GFMIs when equipped with four different control strategies, namely: droopbased GFMI, virtual synchronous generator (VSG)-based GFMI, compensated generalized VSG (CGVSG)based GFMI, and adaptive VSG (AVSG)-based GFMI. The comparative analysis assesses the performance and robustness of these four control strategies across various operational scenarios in frequency and time domains. Initially, the impedance-based stability analysis method is employed to evaluate these control strategies across different case studies in terms of grid strengths, grid impedance ratios, the dynamics with/without virtual impedance and inner voltage and current loops, and variations in the inverter's operating points. Subsequently, time domain verification using the electromagnetic transient models are conducted for these case studies as well as to assess the power tracking capability of these control strategies in response to changes in power references. Finally, the robustness of these four controllers is explored against external grid disturbances, including grid frequency deviations, phase jumps, and voltage sags, considering varying levels of disturbance magnitudes in both weak and strong grid connections. In conclusion, the evaluation of these control techniques in various operational scenarios reveals their strengths and weaknesses, offering valuable guidance for the selection of the most appropriate control technique to suit desired practical applications.

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“…The SCR is represented as the quotient of the short-circuit capacity at the PCC and the rated capacity of the inverter connected to the grid, S g /S n . Typically, the strength of the power grid is evaluated as strong when SCR > 3, weak for 2 ≤SCR≤ 3, and very weak for SCR < 2 [30].…”

Section: Conventional Psgflimentioning

confidence: 99%

Double-Synchronous-Reference-Frame-Based Power-Synchronized PLL-Less Grid-Following Inverters for Unbalanced Grid Faults

Mohammed

Zhou

Bahrani

2023

IEEE Open J. Power Electron.

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This article proposes a double-synchronous-reference-frame-based power-synchronized gridfollowing inverter (DS-PSGFLI). In contrast to existing types of phase-locked-loop (PLL)-based gridfollowing inverters (GFLIs) and PLL-less power-synchronized GFLIs (PSGFLIs), the suggested PLL-less DS-PSGFLI operates seamlessly during unbalanced grid faults in both strong and weak grid connections, while maintaining stability and avoiding oscillations. Furthermore, unlike previous control strategies for PSGFLIs that regulate terminal output power, the proposed method regulates the power at the point of common coupling (PCC). This approach aligns with common PCC control strategies in GFLIs and grid-forming inverters, thereby avoiding the impacts of voltage drop across the inverter output filter and high voltage harmonics at the inverter terminal. In the proposed DS-PSGFLI, the positive and negative sequences of the PCC voltage and current measurements are first extracted. Then, an outer power controller is employed to regulate the positive active and reactive power at the PCC to the desired references. The outer power controller generates both the positive internal angle required for grid synchronization and the positive current reference for the inner current of the positive sequence loop. When unbalanced grid faults occur, the negative sequence loop adjusts its output signals to mitigate the resulting oscillations at twice the fundamental frequency. The effectiveness of the proposed control strategy is validated through simulations and experimental tests, demonstrating its reliable performance across a wide range of test scenarios.INDEX TERMS Phase locked loops, positive and negative sequence control, power-synchronized control, PLL-less inverters, short-circuit-ratio, stability, unbalanced grid voltage, weak grid.

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Online Grid Impedance Estimation-Based Adaptive Control of Virtual Synchronous Generators Considering Strong and Weak Grid Conditions

Cited by 36 publications

References 36 publications

Analysis of Grid-Forming Inverter Controls for Grid-Connected and Islanded Microgrid Integration

Analysis of Grid-Forming Inverter Controls for Grid-Connected and Islanded Microgrid Integration

Grid-Forming Inverters: A Comparative Study of Different Control Strategies in Frequency and Time Domains

Double-Synchronous-Reference-Frame-Based Power-Synchronized PLL-Less Grid-Following Inverters for Unbalanced Grid Faults

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