Active Thermal Control for Enhancing Fault Current Output Capability of Grid-Forming Converters

Implementing grid-forming (GFM) control is increasingly considered as a solution to facilitate power-electronics-dominated power systems. Despite its potential, limited by the thermal stress of power devices, the excessive output current under grid faults needs to be curtailed. The low-level fault current of GFM converters will significantly reduce the fault voltage support capability compared with conventional synchronous generators. Although direct modifications to the physical structure of power devices, i.e., oversizing insulated-gate bipolar transistors, can be effective to some extent, the additional costs and value streams for overdesigning have not been clearly defined. To fill this gap, an active thermal control of GFM converters that utilizes the inherent current tolerance of power devices is proposed in this article. This method enables the online monitoring of junction temperature via a frequency-domain electrothermal model. Moreover, the switching frequency and modulation strategy are dynamically adjusted based on estimated temperature to enhance the short-time fault current output capability during grid faults. The proposed method is verified through comprehensive simulation, and the experiments based on a practical 1-MW converter are conducted to demonstrate the effect of fault current enhancement.