Harmonic virtual impedance design for a synchronverter-based battery interface converter

The role of inertia emulation and voltage control is fundamental to support the integration of distributed generation in weak power grids and Virtual Synchronous Machines (VSMs) represent an attractive solution to assume both of these roles. However, VSMs act as voltage sources and this makes it difficult to address power quality issues. Virtual impedances are commonly applied in the literature to address voltage and quality problems, but this control strategy has been seldom studied for synchronverters. This paper presents a detailed discrete-time design procedure of harmonic virtual impedances for a battery interface converter that emulates a synchronous generator. It will be shown that the proposed virtual impedance provides configurable output impedance in the case of a weak grid while stability margins are maximized. All the control system improvements were tested experimentally by using two 15 kVA synchronverters connected to a configurable weak grid.