Inner Grid-Forming Control Loops – Considerations for Physically Meaningful Controls

Abstract:
This paper uses a physics-based approach to analyze inner grid-forming control schemes that can be implemented to generate the modulation signals for the converter. Firstly, it highlights the advantages and disadvantages of a control scheme with and without an underlying current controller. Based on that, four inner grid-forming control schemes are analyzed regarding their block diagram structure, control plants, response time, current limiting capabilities, and behavior during asymmetrical faults. Critical assumptions and considerations are highlighted from a physically meaningful perspective for the design of the controls.