Grid-Forming Control and Experimental Validation for High Voltage Transformerless Battery Energy Storage System

Abstract

Advantages of single-device large capacity of combining with grid forming (GFM) control effectively help high voltage transformerless battery energy storage system (BESS) to support grid frequency and voltage stability. However, the transient stability characteristics of the converter under current-limiting mode during a fault and its capability to provide effective support to the grid are the major differences from conventional synchronous machines. Therefore, this article first investigates transient synchronization stability problems at occurrence of high-voltage and low-voltage fault-ride-through by theoretically deduced virtual power angle curves considering current limitation mode. Then, the strategies of enhancing transient synchronization stability in face of grid voltage sag and rise are proposed and verified by simulation results. Thereafter, an adaptive gain coefficient is proposed to be embedded into power feedback loop to improve the capability of fast low voltage supporting during fault occurrence. More importantly, a practical 35 kV/10 MW/5 MWh Lithium BESS engineering project validates the GFM control in steady charging/discharging operation and its voltage fault ride through support ability.