Impact of Voltage-Loop Feedforward Terms on the Stability of Grid-Forming Inverters and Remedial Actions

Ravanji, Mohammad Hasan; Rathnayake, Dayan B.; Mansour, Milad Zarif; Bahrani, Behrooz

doi:10.1109/tec.2023.3246566

Cited by 8 publications

(3 citation statements)

References 46 publications

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“…It is worth emphasizing that proper tuning of the voltage control loop including its feed-forward coefficient [45] is also deemed important for the reliability of the GFMI under various operating conditions.…”

Section: A Current Control Loopmentioning

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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Section: A Current Control Loopmentioning

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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“…In conventional vector current control loops, feedforward terms are used to eliminate V d and V q terms in the equations based on the system model. These feedforward terms are employed to improve damping [36]. However, for ePSGFLI, the use of terminal voltage in the system equation removes the need for feedforward terms.…”

Section: E Effects Of the Pcc Voltage Feedforwardmentioning

confidence: 99%

Enhanced Frequency Control for Power-Synchronized PLL-Less Grid-Following Inverters

Mohammed

Ravanji

Zhou

et al. 2023

IEEE Open J. Ind. Electron. Soc.

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This article presents an enhanced power-synchronized grid-following inverter (ePSGFLI) for reliable and stable integration of renewable energy resources into the grid. By eliminating the use of a phase-locked loop (PLL) in the control loop, the ePSGFLI resolves instability issues commonly associated with conventional PLL-based grid-following inverters (GFLIs). Furthermore, in contrast to existing PLL-less strategies like linear parameter-varying control of power-synchronized GFLI (LPV-PSGFLI), which suffer from steady-state errors and instability during grid frequency deviations, the proposed ePSGFLI ensures stable performance without steady-state errors, regardless of the strength of the grid. To achieve robust and accurate tracking of grid frequency, even under significant deviations, while effectively decoupling the active and reactive power loops, the ePSGFLI employs a loop-shaping design procedure for real-time auto-tuning of the multivariable second-order 2-by-2 outer power controller. The effectiveness of the proposed ePSGFLI is validated via simulations in MATLAB/Simulink and experimental testing under both strong and weak grid connections. The results demonstrate its superior performance compared to existing PLL-based and PLL-less control strategies in terms of stable operation and accurate tracking of power and grid frequency.INDEX TERMS Adaptive control, phase-locked loop (PLL), PLL-less inverters, power-synchronized control, stability, weak grid.NABIL MOHAMMED (Member, IEEE) received the bachelor's degree (Hons.

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“…shortcircuit power and R/X ratio [8]. In addition, the voltage control loop may become unstable because of the feedforward terms of the current controller [18]. This drawback can be overcome using an ICL based just on a current controller.…”

Section: Introductionmentioning

confidence: 99%

Active Harmonic Filtering With Selective Overcurrent Limitation for Grid-Forming VSCs: Stability Analysis and Experimental Validation

Matas-Díaz,

Barragán-Villarejo,

Maza-Ortega

et al. 2024

IEEE Trans. on Ind. Applicat.

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The high penetration of renewable energy sources (RES) interfaced with power electronics together with new nonlinear loads pose new challenges in the grid operation. In fact, power systems with reduced inertia and high harmonic distortion will be common in a near future. Recently, the grid-forming operation of voltage source converters (VSCs) has emerged to address these challenges, mimicking the contribution of synchronous generators to the system inertia. In addition, these grid-connected VSCs can be used at the same time for reducing the harmonic distortion by applying active filtering techniques. However, these harmonic compensation algorithms can generate VSC overloading. This paper proposes a method for dynamically adjusting the individual virtual impedance of the filtered harmonics to prevent the power converter overcurrent. For this purpose, the value of each harmonic virtual impedance is modified according to a priority which can be set by the final user according to the established power quality standard. The paper includes a theoretical stability analysis of the controller and experimental results to validate the proposed algorithm.

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Impact of Voltage-Loop Feedforward Terms on the Stability of Grid-Forming Inverters and Remedial Actions

Cited by 8 publications

References 46 publications

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

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

Enhanced Frequency Control for Power-Synchronized PLL-Less Grid-Following Inverters

Active Harmonic Filtering With Selective Overcurrent Limitation for Grid-Forming VSCs: Stability Analysis and Experimental Validation

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