Control strategy resilient to unbalanced faults for interlinking converters in hybrid microgrids

Abstract

Hybrid microgrids (HMGs) consist of AC and DC microgrids (MGs) that are connected through bidirectional interlinking converters (ICs). In order to optimally utilize renewable generations and address their intermittency, efficient control strategies are needed for power management of ICs. The performance of available control strategies for HMGs in case of faults may be limited since the converters are usually set to trip in the event of transient stability related problems to protect converters from being damaged. Also, HMGs may face frequency instability problems due to the lower damping capability of converter-based generations compared with classical synchronous generators. In this paper, an enhanced control strategy based on the concept of 3-D droops is proposed for ICs. The proposed method makes HMGs more resilient against faults at the utility side. It also improves stability of HMGs by mitigating quasi-static active and reactive power oscillations that may be generated by renewable intermittent generations. Also, it ensures a proper transient power sharing without deteriorating the transfer capability of ICs when unbalanced faults, as the most prevalent ones, occur in HMGs. In addition, the synchronverter technology with an adaptive virtual inertia is applied to the control strategy of ICs to enhance frequency stability of HMGs in case of occurring faults or volatile renewable generations. The performance of the proposed features is evaluated by their testing on a typical HMG.