Transient Characteristics and Accommodative Current Limiting Strategy for Bidirectional Interlinking Converters in Hybrid AC/DC Microgrids

Abstract

Bidirectional interlinking converter (BIC) is the core equipment in a hybrid AC/DC microgrid connected between AC and DC sub-grids. However, the variety of control modes and flexible bidirectional power flow complicate the influence of AC faults on BIC itself and on DC sub-grid, which potentially threaten both converter safety and system reliability. This study first investigates AC fault influence on the BIC and DC bus voltage under different BIC control modes and different pre-fault operation states, by developing a mathematical model and equivalent sequence network. Second, based on the analysis results, a general accommodative current limiting strategy is proposed for BIC without limitations to specific mode or operation condition. Current amplitude is predicted and constrained according to the critical requirements to protect the BIC and relieving the AC fault influence on the DC bus voltage. Compared with conventional methods, potential current limit failure and distortions under asymmetric faults can also be avoided. Finally, experiments verify feasibility of the proposed method.

Keywords

• Bidirectional interlinking converter
• current limiting
• fault characteristic
• hybrid AC/DC microgrid
• variation/oscillation of DC bus voltage