Stability Analysis and Transient Feedback Compensation with Virtual Impedance-Based Method for Parallel-Connected Synchronverters

It is a promising solution to connect distributed generators (DGs) units to the grid via synchronverter. However, the differences between the parallel system composed of two synchronverters will affect the transient stability of the system, the fixed parameters cannot be applied to both steady state and dynamic state, which could threaten the stable operation of the system. Variable parameters using frequency or rate of change of frequency (ROCOF) are affected by grid voltage unbalance and harmonics. Thus, an adaptive variable virtual impedance control strategy is proposed in this paper. First, a small-signal stability analysis for parallel-connected synchronverters in a Micro-Grid is analyzed. The control method using feedback compensation of variable virtual impedance is proposed, which can reduce the power distribution difference between the parallel-connected VSG-based inverters in the transient state and keep the output voltage stable without any additional communication lines.