General Method to Foresee the Behavior of Virtual Synchronous Machines working with Distorted and Unbalanced Voltage Conditions

To make photovoltaic and wind power plants able to provide grid services (i.e., inertial behavior, grid support and harmonic compensation), several control algorithms have been proposed in the literature during the last years. The most promising ones make the power electronic converters behave as conventional alternators, using the concept of Virtual Synchronous Machine (VSM). Several VSM models are available in the literature, some of which can improve the voltage quality at the point of connection with the grid behaving as harmonic and unbalance sinks under non–ideal grid voltage conditions. However, the literature lacks a general method to foresee the behavior of a generic VSM configuration in such conditions along with a well–established definition of the needed features to make VSMs able to work as harmonic or unbalance sinks. Therefore, this paper proposes a simple and general method to foresee the behavior of different VSM configurations under non–ideal grid voltage conditions before any experimental verification. The proposed method accurately foresees the VSMs behavior, as experimentally demonstrated on five VSM models available in the literature, working with fifth harmonic and inverse sequence voltage distortions. Moreover, the method identifies which VSM configuration can feature a beneficial harmonic and unbalance compensation.