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.
Single-line diagram for experimental setup
Single-line diagram for experimental setup

Oddbjørn Gjerde

WP2 Lead
+47 99 730 027
Oddbjørn Gjerde
WP2 Lead


Reference in CINELDI