Pre-Synchronization Control Strategy for Grid Connection of Synchronverter Cluster

Abstract

It is found that large inrush currents and power oscillations occur when a synchronverter cluster is connected to the utility grid. In this paper, we propose a pre-synchronization control strategy to minimize the inrush current and suppress the power oscillation in the grid-tied synchronverters. The phase of synchronverter is utilized as the reference in the grid voltage transformation to track the voltage error. Then, synchronization will be implemented automatically with compensations obtained by PI controller in the controllers. Subsequently, to suppress the power oscillations during the connection process (here includes the pre-synchronization process and several transient periods after grid connection), the virtual inertia are adapted according to the equivalent output impedances. Additionally, the control architectures are also developed to optimize major control parameters and thus enhance the system stability. Experimental results show that the proposed control strategy guarantees the stable operation of local loads with significantly reduced inrush current and power oscillations.