As far as I know, the control structures of grid-forming converters can be classified into 2 categories: one is single-loop without current control loop; the other includes a voltage loop and an inner current loop. What's the advantages and disadvantages between them two? Which one is more promising?
Zhaoshun Deng ,
The greater advantage of the second strategy (outer voltage loop with an inner current loop) is that it makes it possible to limit the output current in case of some disturbance in the grid (either fault or overload).
Besides that, this approach also allows damping resonances of the output LC filter. The following articles discuss these questions (maybe you could find some references that address deeply this topic in their bibliography list):
Article Transient Stability of Voltage-Source Converters With Grid-F...
Article Modeling, Analysis and Testing of Autonomous Operation of an...
I would definitely prefer the 2nd strategy because of its control over limiting the current. This also insures that that the bus voltage under autonomous mode is regulated at 120 Vrms.
There are several advantages of using double loop control，take a Boost converter as a example:
1. Open loop Boost system is a non minimum phase system，and it has one or more unstable zero points. If the single loop voltage loop control is used, the system will be unstable. If dual loop control is used, there will be no zero point. This reason also suits for any other non minimum systems. (Buck converter is not a non minimum system, so any of single loop and dual loop control is OK)
2. Sometimes, we need to limit the work current of the converter to ensure the safety of the controlled system. So, dual loop control can help us to reach this goal.
3. When it is used in a micro grid power system, dual loop control structure can also help to realize changing the work mode between CC mode (conatant current) and CV mode (constant voltage), which is needed for energy management.
Therefore, dual loop control stracture (voltage outer loop and current inner loop) is more promising.
I hope my answer can really help you.
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