Extension and Tuning of Virtual Synchronous Machine to Avoid Oscillatory Instability in Isolated Power Networks

The risk of oscillatory instability introduced by virtual synchronous machines (VSM) control in isolated power networks is investigated. The considered control is a common scheme widely studied in literature, in several configurations and for different case studies. The impact of the VSM control on the system stability is examined for the existing power network of a Mediterranean island. The VSM control is implemented within the power converters interfacing the energy storage systems (ESS) installed in the network. Simulations and analysis show the occurrence of oscillatory instability in the system, with the ESS-VSM and the synchronous machines of the network progressively swinging against each other. The reasons of the instability are identified as the lack of damping in the system and the adverse interaction between the VSM converter control and the synchronous machine dynamics. The possibility of extending the VSM control with a corrective action for the stabilization of the system is analyzed and discussed. A proper tuning procedure of the extended control is also provided.