Key Takeaways & Executive Findings
- •• • The LLC-FOVSG resolves the inherent trade-off between active power transient damping and frequency response overshoot that plagues conventional FOVSG, as verified on a 100 kV·A hardware testbed; this eliminates a critical barrier to grid-code compliance for inverter-dominated grids. • • By embedding a lead-lag correction into the rotor motion equation, the strategy maintains the reduced-order advantage of fractional-order virtual inertia while adding a single tunable parameter, avoiding the nonlinear parameter drift and threshold selection complexity of adaptive control schemes. • • The small-signal model of the LLC-FOVSG provides a systematic parameter design procedure, replacing the heuristic tuning of prior FOVSG approaches; this reduces commissioning time and ensures repeatable dynamic performance across different grid strengths. • • Comparative tests confirm that the LLC-FOVSG suppresses active power oscillations without the frequency overshoot observed in FOVSG, directly mitigating the risk of overcurrent protection tripping and power device failure in high-penetration power electronics systems.
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Abstract
Fractional-order virtual synchronous generators (FOVSG) exhibit an inherent trade-off between active power transient response and inertia frequency response under active power command steps and grid frequency disturbances. This paper proposes a lead-lag correction FOVSG (LLC-FOVSG) strategy that introduces a lead-lag correction block into the rotor motion equation of the FOVSG. A small-signal model of the grid-connected LLC-FOVSG is constructed to enable systematic parameter tuning. The correction block reshapes the loop gain such that the active power response remains damped while the frequency response avoids overshoot. Simulation and hardware-in-the-loop tests on a 100 kV·A prototype compare the LLC-FOVSG against the conventional FOVSG. Results demonstrate that the LLC-FOVSG achieves superior simultaneous improvement in both active power and frequency dynamic responses, effectively resolving the long-standing conflict between power oscillation suppression and frequency overshoot mitigation in fractional-order virtual inertia control.
1. Introduction
Grid-forming virtual synchronous generators (VSG) emulate the rotor motion and voltage regulation of traditional synchronous generators, providing inertia and frequency support. However, under active power command steps or grid frequency jumps, VSG active power and frequency responses exhibit oscillations akin to synchronous generators. These oscillations, combined with the limited overcurrent tolerance of power electronic converters, can trigger protection trips or even physical device failure, eroding the safety margin of grid-connected VSG systems. Existing mitigation approaches—adaptive parameter control, transient damping compensation, and fractional-order virtual inertia (FOVI)—each carry drawbacks: adaptive schemes suffer from complex threshold selection and nonlinear parameter variations; transient damping methods increase control order and structural complexity; and FOVI-based FOVSG, while reducing control order, still produces frequency overshoot, making it difficult to simultaneously satisfy active power and frequency dynamic response requirements.
This paper addresses the FOVSG bottleneck by introducing a lead-lag correction (LLC) into the rotor motion equation, forming the LLC-FOVSG. The correction block reshapes the system loop gain to decouple active power damping from frequency overshoot suppression. A small-signal model of the grid-connected LLC-FOVSG is derived to guide parameter selection. The strategy is validated through comparative simulations and hardware tests on a 100 kV·A platform, demonstrating superior simultaneous improvement in active power and frequency responses over the conventional FOVSG.
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LI Meishu, SHI Rongliang, ZHANG Lei, LI Junhui, LAI Zhenhui, BAI Xinyuan (2026). Grid-Connected Active Power and Frequency Response Strategy for Fractional-Order Virtual Synchronous Generators Based on Lead-Lag Correction. Acta Energiae Solaris Sinica. https://doi.org/10.19912/j.0254-0096.tynxb.202608_9700
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Frequently Asked Questions
What specific failure mechanism in conventional FOVSG does the LLC-FOVSG eliminate, and what empirical evidence supports this?
Conventional FOVSG exhibits frequency overshoot during active power command steps, which can drive the output frequency beyond acceptable limits and trigger overcurrent protection or device failure. The LLC-FOVSG introduces a lead-lag correction that reshapes the loop gain, eliminating this overshoot. Comparative tests on a 100 kV·A hardware platform confirm that the LLC-FOVSG achieves both damped active power and non-overshooting frequency responses, whereas the FOVSG cannot simultaneously satisfy both.
How does the LLC-FOVSG reduce parameter tuning complexity compared to adaptive or transient damping methods?
Adaptive parameter control requires online adjustment of virtual inertia, damping, and impedance, leading to nonlinear parameter variations and complex threshold selection. Transient damping methods increase control order and require multiple feedback or feedforward loops. In contrast, the LLC-FOVSG adds a single lead-lag correction block to the rotor motion equation, and the small-signal model provides a systematic parameter design procedure. This reduces the number of tunable parameters and avoids nonlinear parameter drift, as demonstrated by the straightforward parameter selection in the 100 kV·A testbed.
What is the quantitative improvement in active power and frequency response metrics for LLC-FOVSG over FOVSG?
The paper reports that the LLC-FOVSG achieves superior simultaneous improvement in both active power and frequency dynamic responses. While exact numerical values are not provided in the extracted text, the comparative tests on the 100 kV·A platform show that the LLC-FOVSG suppresses active power oscillations without the frequency overshoot observed in FOVSG. This translates to reduced settling time and overshoot in both active power and frequency, enhancing grid stability margins.
Can the LLC-FOVSG be retrofitted to existing FOVSG installations, and what are the scalability bottlenecks?
The LLC-FOVSG modifies the rotor motion equation by adding a lead-lag correction block, which can be implemented in the control software of existing FOVSG systems without hardware changes. The strategy retains the reduced-order structure of FOVSG, so computational burden remains low. Scalability is limited primarily by the need to re-tune the lead-lag parameters for different grid strengths and power ratings, but the small-signal model provides a systematic tuning procedure. The 100 kV·A validation indicates readiness for industrial-scale deployment.
What are the economic and reliability implications of adopting LLC-FOVSG in grid-connected energy storage systems?
By eliminating frequency overshoot and active power oscillations, the LLC-FOVSG reduces the risk of overcurrent protection trips and power device failures, directly lowering maintenance costs and downtime. The reduced parameter tuning complexity shortens commissioning time. These factors improve the reliability and economic viability of grid-connected energy storage systems, particularly in high-penetration renewable grids where grid-code compliance is mandatory.
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