Grid-forming high-voltage transformerless energy storage is a critical equipment for supporting the steady-state power balance and transient active support of new power systems. To achieve transient support

a certain overcurrent capability is required. However

the current practice of over-sizing devices leads to increased system costs. This paper leverages the modular topology and control flexibility of high-voltage transformerless energy storage systems to propose a dynamic topology reconfiguration method for enhancing overload capability. Furthermore

an electro-thermal coupling model for the devices is established

and an online junction temperature estimation method is introduced. By implementing closed-loop control of the junction temperature

the thermal stress margin of the power devices is fully exploited

leading to the development of methods for maximizing and regulating the overcurrent capability of grid-forming equipment. Based on the above research

the transient overcurrent capability of the equipment is economically enhanced without oversizing the power devices. Finally

the effectiveness of the proposed design method and control strategy is verified through electromagnetic-thermal co‑simulation. During faults

the equipment can deliver up to 3.65 times the rated transient current

significantly improving the voltage support capability of the grid‑forming converter at the point of common coupling