Small power inverter agent

In this paper, the explicit state-space model for a multi-inverter system including grid-following inverter-based generators (IBGs) and grid-forming IBGs is developed by the two-level component connection method (CCM), which modularized inverter control blocks at the primary level and IBGs at the secondary level.

Based on the comprehensive model representing full order of system dynamics, eigenvalues of the overall system are thoroughly analyzed, otential adverse impacts of not only grid-following inverters, but also grid forming inverters on the system small- ility, with the underlying principle of oscillations also understood.

Operating condition of inverters in a grid is often not taken into account in impedance model-ing. For example, in, a type-3 wind turbine's impedance model is derived and measured without considering power control nor operating condition.

However, the critical point and stability margin for grid-forming inverters have not been clearly defined. Additionally, most of the converter-driven power system stability analyses are based on single machine infinite bus (SMIB) scenario, where the system is equivalent to a voltage source with impedances behind.

High penetration of inverters introduced many new dynamic phenomena in power grids. First severe wind farm subsynchronous resonances (SSR) due to wind farm interactions with RLC circuits occurred in Texas in 2009 . Similar phenomena were observed in North China in the years followed. In 2017, three more events were observed in Texas .

A major challenge in dynamic modeling and analysis is that unlike synchronous generators, whose analytical models are well studied and known to system planners, inverter models are proprietary information with black box models provided to utilities.