Reduced-Order Model of Distributed Generators with Internal Loops and Virtual Impedance
Challenge and objective
Reduced-order converter models are useful in microgrid applications for being less computationally expensive and simpler to analyse.
Models already used, only include basic control loops (ignores virtual impedance and internal control loops).
The frequency range validity of these models has neither been thoroughly studied.
Work performed
A low-order model of a droop-controlled converter that includes internal control loops and virtual impedances is derived.
The validity of the assumptions used to reduce the model is analysed and a criterion for deciding the frequency range in which the model can be used is proposed.
Significant results
The model shows that the DG internal control loops tends to reduce the stability margins.
It is also shown that including quasi-stationary virtual impedances increases the stability margins.
While the transient part of the virtual impedance, reduces the stability margins.
Impact for distribution system innovation
The inclusion of critical control designs will preserve a simple model but improve the accuracy.
