In my understanding, primary control is usually designed to cope with perturbations in the demand/supply of one or several terminals in a DC grid. In voltage droop control direct current references are properly adjusted in order to guarantee sovability of the power balance and the verification of two additional properties: current (or power) sharing and small DC voltage deviations from their nominal value. It is also known that such objectives cannot be achieved simultaneously using decentralized voltage droop control.
However, and independently from the resulting voltage deviations, I'm questioning if it is at least possible to guarantee appropriate current sharing using only decentralized voltage droop control, i.e. without the need of a secondary controller that determines the droop gains. In fact, as far as I know, a centralized secondary controller, based on power flow equations, is typically adopted to ensure current sharing.
Hi Zonetti,
You may refer to our recent work on DC-microgrid for power sharing and voltage regulation. Instead of using conventional droop-control, we have a similar droop-like parameter for the inner-current control, and we augment another controller, which is optimized for the chosen value of droop-like parameter. This design achieves excellent power-sharing, while ensuring that the voltage output is regulated near the desired set-point. This is all done in a perfectly decentralized setting.
http://baranwa2.web.engr.illinois.edu/docs/dcdc.pdf
Regards,
Mayank
Hi Zonetti
I think you should use virtual impedances to engance current sharing. Another option is to use adaptice droop control gains
Best regards
Mohammad Hadi
Yes, you have to consider two parameters voltage drop and length, for prescribe current sharing, though resistance changes with ageing(oxide formation in presence of moisture and heat)) should be considered.....
Hi Zonetti,
As I understand it, simultaneous, accurate Voltage-Current sharing is feasible only for symmetric (electrically) microgrids. In other (unsymmetrical) grids, the voltage differences are vital for precise current sharing among generation units. On the other hand, V-I droop mechanism is a local controller without any global information (neither measurement nor model parameters). Therefore, to tackle this problems one should i) mimic the structure of symmetric microgrids (e.g., by including virtual impedance loops etc.), and ii) compensate for voltage deviations, in order to achieve a formation around the desired voltage.
To the best of my knowledge, generally,the proposed controllers (primary and secondary) so far, can be categorized in two groups; 1) measurement-based methods (e.g., centralized controllers, consensus-based controllers, and averaging-based controllers), and 2) model parameter-based methods (e.g., estimation-based methods, optimization-based (optimizing droop coefficients or virtual impedance) methods.
I suggest that you think about a combination of these two methods; i.e., a model based decentralized method with the ability to learn and update itself when needed (e.g., after model changes like load variations, PnP functions, and so on).
Hope you find this note effective.
With my kindest regards,
Babak
- Badges
- Science topic
- Similar topics
- Biological Science
- Bioecology
- Systems Ecology
- Landscape Ecology
- Connectivity