Overcurrent-Limiting Control Method for Grid-Forming Inverters Based on Seamless Transition to GFL Mode

초록

With the increasing penetration of renewable energy, the proportion of synchronous generators in power systems has been decreasing, leading to concerns about reduced grid strength. As a result, grid-forming (GFM) inverters that can autonomously establish voltage and frequency have gained significant attention. However, GFM inverters are prone to overcurrent during voltage sags caused by grid faults, and conventional overcurrent limiting methods suffer from drawbacks such as output distortion, angle instability, and control loop saturation. To address these issues, this paper proposes a seamless transition based overcurrent limiting control method that switches from GFM to grid-following (GFL) operation during fault conditions. The proposed method maintains control continuity without transient disturbance and effectively suppresses overcurrent. Experimental verification using a 20 kW three-level T-type inverter demonstrates that the proposed method enhances fault ride-through (FRT) capability and overall system stability. © 2026 IEEJ-IAS.

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