Fig. 1. Grid-interface converter that behaves as a synchronous machine
With the recent revision of the IEEE 1547 standard so that it now, for the first time, allows distributed generation to regulate voltage at the point of common coupling, a number of research groups have started exploring unconventional ways to control grid-interface converters. This kind of change requires new concepts for the advanced control of all energy flows in order to improve system stability, energy availability, and efficiency. Consequently, high adoption of renewable energy sources will greatly depend on engineers' capability to understand, model, and dynamically control power sharing and subsystem interactions. This paper presents an informed method of controlling power converters as synchronous machines of any type in the d-q coordinate system by formally establishing electromechanical-electrical duality, which requires an understanding of which parameters of power converters relate to which parameters of isotropic or anisotropic synchronous machines.
The paper describes a generic d-q model of the grid-interface converter that behaves as a synchronous machine of any type, and shows how to control power converters in the d-q frame in order to emulate both isotropic and anisotropic machines with more than one damper winding. It also shows that d-q transformation (and converter synchronization) can be done by using an internal angle obtained by integrating dc-link voltage, and how to realize the concept of virtual inertia. The model developed can be used for the system-level simulations to address grid system stability and performance improvement.
Fig. 2. Power converter-based d-q average model of the synchronous machine, and an average d-q average model of the power converter