[Paper Review] Grid-Forming Inverter-based Wind Turbine Generators: Comprehensive Review, Comparative Analysis, and Recommendations

Thai-Thanh Nguyen, Tuyen Vu+3 more|arXiv (Cornell University)|Mar 4, 2022

Microgrid Control and Optimization31 citations

TL;DR

The paper reviews grid-forming control approaches for wind turbine generators, presents a comparative analysis of GFM WTGs under various conditions, and offers recommendations for design, protection, and standards.

ABSTRACT

High penetration of wind power with conventional grid following controls for inverter-based wind turbine generators (WTGs) weakens the power grid, challenging the power system stability. Grid-forming (GFM) controls are emerging technologies that can address such stability issues. Numerous methodologies of GFM inverters have been developed in the literature; however, their applications for WTGs have not been thoroughly explored. As WTGs need to incorporate multiple control functions to operate reliably in different operational regions, the GFM control should be appropriately developed for the WTGs. This paper presents a review of GFM controls for WTGs, which covers the latest developments in GFM controls and includes multi-loop and single-loop GFM, virtual synchronous machine-based GFM, and virtual inertia control-based GFM. A comparison study for these GFM-based WTGs regarding normal and abnormal operating conditions together with black-start capability is then performed. The control parameters of these GFM types are properly designed and optimized to enable a fair comparison. In addition, the challenges of applying these GFM controls to wind turbines are discussed, which include the impact of DC-link voltage control strategy and the current saturation algorithm on the GFM control performance, black-start capability, and autonomous operation capability. Finally, recommendations and future developments of GFM-based wind turbines to increase the power system reliability are presented.

Motivation & Objective

• Survey state-of-the-art grid-forming (GFM) controls for wind turbine generators (WTGs) and identify how DC-link voltage regulation affects WTG control.
• Categorize GFM WTGs by DC-link regulation strategy (G-GFM, M-GFM, E-GFM) and by inner control loop (multi-loop vs single-loop).
• Perform a fair comparative analysis of four GFM WTG types against grid-following controls under normal and abnormal conditions, including black-start capability.
• Analyze challenges such as DC-link voltage control, current saturation, fault ride-through, and autonomous operation in GFM WTGs.
• Provide recommendations and future directions for controls, protection, standards, and testing to enhance grid stability and reliability.

Proposed method

• Classify GFM WTGs into three DC-link regulation categories: G-GFM (grid-side regulates DC link), M-GFM (machine-side regulates DC link), E-GFM (external energy storage regulates DC link).
• Within each category, distinguish multi-loop (MGFM) versus single-loop (SGFM) inner control structures.
• Model and design outer inertia-like schemes: VIC for G-GFM and VSM for M-GFM to mimic synchronous-machine behavior.
• Use a 15 MW direct-drive Type-4 WTG as the baseline for comparisons under dynamic wind, power-curtailment, and fault scenarios.
• Optimize virtual synchronous machine (VSM) parameters via gradient-descent-based constrained optimization to balance DC-link voltage stability and active-power response.
• Assess performance under normal and abnormal grid strength (SCR variations) and evaluate black-start/autonomous operation for M-GFM types.

Experimental results

Research questions

• RQ1 How do different GFM control strategies (G-GFM, M-GFM, with MGFM/SGFM variants) perform in WTGs under strong and weak grid conditions?
• RQ2 What is the impact of DC-link voltage regulation strategy on WTG stability, inertia support, and fault response?
• RQ3 Can GFM WTGs provide black-start and autonomous operation without external sources, and under what configurations?
• RQ4 What are the challenges of current-limiting strategies and fault ride-through for GFM WTGs, and how do MGFM vs SGFM compare?
• RQ5 What recommendations arise for controls, protection, standards, modeling, storage integration, and testing to improve grid reliability?

Key findings

• GFL WTGs lose stability under weak grids where GFM WTGs remain operable, with GFL failing to maintain stable operation in some scenarios.
• MGFM types regulate DC-link via grid-side or machine-side controllers, showing fast power response and effective DC-link voltage management, but can experience stability issues during faults.
• SGFM types offer stability under faults but exhibit higher transient currents, requiring overload-mitigation strategies to avoid converter damage.
• M-GFM types, where the machine-side controls DC-link, provide robust post-fault stability and enable autonomous operation when wind power is sufficient, but inertia support depends on VSM parameters.
• Optimal tuning of VSM parameters balances DC-link oscillations and active-power response; parameter sets significantly affect rise time and power tracking.
• Under fault conditions, current-limiting strategies differ: MGFM types can limit fault currents but may struggle to recover post-fault, while SGFM types show higher transient currents but benefit from overload-control schemes.