Grid Forming Inverters: A Review of the State of the Art of Key Elements for Microgrid Operation

Anttila, Sara; Döhler, Jéssica S.; Oliviera, Janaína G.; Boström, Cecilia

doi:10.3390/en15155517

Cited by 48 publications

(16 citation statements)

References 196 publications

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“…The decentralized control design is very important for the GFM inverter's performance. Various control approaches for GFM inverters are examined and compared with the GFM characteristics exhibited by synchronous machines in [13]. A hybrid grid-forming/following controller was proposed in [14].…”

Section: Related Workmentioning

confidence: 99%

Design, Modeling, and Validation of Grid-Forming Inverters for Frequency Synchronization and Restoration

Bennia,

Elbouchikhi,

Harrag

et al. 2023

Energies

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This paper focuses on the modeling, analysis, and design of grid-forming (GFM) inverter-based microgrids (MGs). It starts with the development of a mathematical model for three-phase voltage source inverters (VSI). The voltage and current controllers consist of two feedback loops: an outer feedback loop of the capacitance-voltage and an inner feedback loop of the output inductance current. The outer voltage loop is employed to enhance the controller’s response time. The inner current loop is used to provide active damping for the resonance created by the LCL filter. A two-layer control scheme is adopted for the GFM inverter control. The primary decentralized control uses droop control and virtual impedance loops to share active and reactive power. Simultaneously, the centralized secondary control addresses frequency and amplitude deviations induced by the droop control. Additionally, a synchronization loop is proposed for seamless reconnection of GFM inverters to the MG and to connect the GFM-controlled MG to the main grid. It has the advantage that the inverter operates in GFM mode even after the synchronization has occurred. The simulation results have shown that the voltage controller ensures a 0.005 s settling time and maintains the steady-state error at its minimum value of 0.1 V. Similarly, the current controller ensures a 0.006 s settling time with a 10−5 steady-state error. The system with the designed controller has a low total harmonic distortion (THD) of 1.46% and improved power quality of the output voltage. Furthermore, a quick restoration time is observed during load steps and tripping events, with a restoration time of 1 s with 10−10 steady-state error. Synchronization is achieved within 0.8 s for the incoming inverters and requires 3 s to synchronize the MG with the main grid, maintaining a steady-state error of 10−9.

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Section: Related Workmentioning

confidence: 99%

Design, Modeling, and Validation of Grid-Forming Inverters for Frequency Synchronization and Restoration

Bennia,

Elbouchikhi,

Harrag

et al. 2023

Energies

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“…Liansong Xiong, Xi'an Jiaotong University, China REVIEWED BY which can enhance the synchronization stability of grid-connected RESs in a weak grid (Anttila, et al, 2022).…”

Section: Open Access Edited Bymentioning

confidence: 99%

Stability analysis of different control modes of grid-connected converters under different grid conditions

Xu,

Qin,

et al. 2023

Front. Energy Res.

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With the sustained popularity of renewable energy generation, high penetration of variable energies, e.g., wind and solar, is reshaping the form of power systems and weakening the strength of the grid. The stability mechanism of the grid-connected converter in a weak power network, however, has yet to be evaluated. This paper establishes impedance and transient models for Grid-Following (GFL) as well as Grid-Forming (GFM) converters through the impedance analysis method and equal area criterion analysis method. The stability of these two control methods is then comprehensively studied under small and large interference with different grid conditions. The analytical results show that the GFM control is more stable against small disturbances in a weak network. In contrast, it is prone to a significant disturbance stability problem in the strong grid due to the large grid impedance. The GFL control is more suitable for a vigorous power grid, whereas introducing oscillation in a weak power grid due to its negative damping. Simulation experiments have verified the accuracy of the analytical results.

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“…Although the concept of GFMIs originally emerged for islanded microgrids, the control of these inverters can be configured to operate in either islanded or grid-connected mode. In islanded microgrids dominated by IBRs, one or more inverters must operate as voltage sources to establish and energize the local power grid [6], [7]. However, the increasing penetration of IBRs has made it necessary for GFMIs to emulate synchronous generator characteristics even in grid-tied mode, as the system's inertia reduces and frequency stability becomes a major concern [8].…”

Section: Introductionmentioning

confidence: 99%

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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Grid Forming Inverters: A Review of the State of the Art of Key Elements for Microgrid Operation

Cited by 48 publications

References 196 publications

Design, Modeling, and Validation of Grid-Forming Inverters for Frequency Synchronization and Restoration

Design, Modeling, and Validation of Grid-Forming Inverters for Frequency Synchronization and Restoration

Stability analysis of different control modes of grid-connected converters under different grid conditions

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

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