Exploring the range of impedance conditioning by virtual inductance for grid connected voltage source converters

Conditioning of network impedance by insertion of a virtual inductance as an inherent feature of the converter control system has the potential to extend the range of stable operation of the overall system. This paper presents a scenario in which such potential is explored and its range of application is identified. It shows first that implementation of a virtual inductance is naturally suited for combination with Virtual Flux-based control systems, and that it can be extended to the more general case of a virtual reactance. The paper then presents the structure of a control system for operation under unbalanced conditions, where the virtual inductance directly influences the current reference calculation. Compared with the standard approach of unity power factor control of grid integrated converters, the suggested technique allows for improving the stability range of converters operating in high-impedance grids, and for remote point control of reactive power or power factor.