Decentralized Impedance Specifications for Grid-Tied Converters Connected to an AC Bus

In complex grid scenarios, with many power electronics (PE) converters connected, having specifications for converters can ease the design process. A practical approach is to impose the specifications on the converter's small signal impedance in the frequency domain. This is advantageous since impedance is a physical property that can be measured. This paper focuses on providing decentralized impedance specifications for each converter connected to an ac bus. With decentralized specifications, each converter has its own independent specifications, which are independent of other converters' impedance. This enables competitive multi-vendor environment while guaranteeing system stability. In this paper, several methods of imposing decentralized specifications, which are based on the small gain theorem, passivity theorem, and Gershgorin theorem, are presented. Additionally, strategies to reduce the conservativeness of these specifications are explored, including transforming impedances into a modified sequence domain and combining different methods of imposing specifications together. The methods are compared on several examples, using both analytical models and black-box impedance obtained from simulations.