Impedance Circuit Model of Grid-Forming Inverter: Visualizing Control Algorithms as Circuit Elements

The impedance model is widely used for analyzing power converters. However, the output impedance is an external representation of a converter system, i.e., it compresses the entire dynamics into a single transfer function with internal details of the interaction between states hidden. As a result, t...

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Bibliographic Details
Published in:IEEE transactions on power electronics 2021-03, Vol.36 (3), p.3377-3395
Main Authors: Li, Yitong, Gu, Yunjie, Zhu, Yue, Junyent-Ferre, Adria, Xiang, Xin, Green, Timothy C.
Format: Article
Language:English
Subjects:
Algorithms
Analytical models
Circuits
Control algorithms
Decoupling
Feedforward control
Grid-forming inverter
Impedance
impedance circuit model
Integrated circuit modeling
Inverters
Mathematical models
Modelling
output impedance shaping
Parameters
Power converters
power system stability
Step response
Transfer functions
virtual impedance
Visualization
Voltage control
Voltage controllers
voltage source inverter (VSI)
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Summary:The impedance model is widely used for analyzing power converters. However, the output impedance is an external representation of a converter system, i.e., it compresses the entire dynamics into a single transfer function with internal details of the interaction between states hidden. As a result, there are no programmatic routines to link each control parameter to the system dynamic modes and to show the interactions among them, which makes the designers rely on their experience and heuristic to interpret the impedance model and its implications. To overcome these obstacles, this article proposes a new modeling tool named as impedance circuit model , visualizing the closed-loop power converter as an impedance circuit with discrete circuit elements rather than an all-in-one impedance transfer function. It can reveal the virtual impedance essence of all control parameters at different impedance locations and/or within different frequency bandwidths, and show their interactions and coupling effects. A grid-forming voltage source inverter is investigated as an example, with considering its voltage controller, current controller, control delay, voltage/current dq-frame cross-decoupling terms, output-voltage/current feedforward control, droop controllers, and three typical virtual impedances. The proposed modeling tool is validated by frequency-domain spectrum measurement and time-domain step response in simulations and experiments.
ISSN:0885-8993
1941-0107
DOI:10.1109/TPEL.2020.3015158