Comparative Analysis of the Power Output Capabilities of Grid-Following and Grid-Forming Inverters Considering Static, Dynamic, and Thermal Limitations

This article investigates the maximum transferable power (MTP) of inverter-based resources (IBRs) and provides the output capability curves (OCCs) of grid-tied grid-following inverters (GFLIs) and grid-forming inverters (GFMIs). To this end, in the first part of the article, mathematical equations for GFLI static, thermal, and phase-locked loop (PLL)-induced power transfer limits are derived in terms of the grid short-circuit ratio (SCR) and its X/R ratio. Then, considering other operational limitations, such as the IBR AC- and DC-side voltage limits, the OCC of the GFLI is obtained. Additionally, the impact of the reactive current and the reactive control mode on the OCC is further studied, and accordingly, an auxiliary control loop is proposed to maximize the GFLI MTP. In the second part of the article, a similar approach is employed to derive mathematical equations for GFMI static and thermal limits, and accordingly, the OCC of a GFMI is obtained. The effects of the variation of the voltage set-point of the GFMI on its OCC are then studied, and the superiority of GFMIs compared to GFLIs is shown in terms of the MTP capability. Eventually, several simulation and experimental cases are conducted to validate the obtained equations and OCCs for both grid-following and grid-forming control modes.