A Nearly Decoupled Admittance Model for Grid-Tied VSCs Under Variable Operating Conditions

Impedance/admittance models (IM/AMs) have been effectively utilized for the stability analysis of converter participated emerging oscillation issues. The IM/AMs are either derived from existing theoretical knowledge or measured by experimental approaches. However, it is quite challenging to get the IM/AMs of black/gray-box devices [such as converter based wind turbine generators (WTGs)] over a wide range of operating conditions. This article proposes a method to identify the AM of voltage-sourced converters by exploiting the relationship between measured AMs and the bus voltage and line current at the point of common coupling. First, an AM is analytically derived, which is almost decoupled with the operating points, and is named as nearly decoupled AM (NDAM). Then, a measurement-based method is further proposed to identify the NDAM. Furthermore, time-domain simulations are used to verify the accuracy of the method. Finally, control-hardware-in-the-loop tests are carried out to demonstrate the effectiveness of the developed method to identify the AM of a direct-drive WTG under variable operating conditions.