Voltage and Current Control or Voltage Control only for a Converter within a DC Microgrid System

[dzt]

Hi,

I am researching information to understand better DC microgrids, and at the moment I am reading on different control techniques to control different converters (Buck, Boost, Buck-Boost etc) within the DC microgrid. One method to control a converter within the dc microgrid is Droop control operating over inner loops of voltage and current control. Droop control is used to provide load sharing between the converters connected to the common dc microgrid bus, by varying the reference voltage of the voltage controller. The control system is shown in the figure below.

I am finding a problem to understand why precisely is the current control needed. Would not inner voltage control alone and outer Droop control suffice to control the converter?

There is a lot of literature on Droop control on the internet but I did not manage to find a direct explanation on the current controller. Any help would be appreciated.

 

[Comcokid]

The selection of current mode control or voltage mode control is a basic issue of switch-mode power supply design and not specific to the end power supply use, or DC microgrids in your case.

Voltage mode control is an older technique for control of the feedback loop. In voltage mode control the ESR of the output filter capacitor appears in the equations of the feedback loop. Because of an extra pole in the equations type III compensation is usually required. Otherwise extremely cold temperatures, or aging of the capacitors may change the ESR enough to cause power supply response problems or feedback loop stability issues. Voltage mode is a little easier to design as the primary side current does not have to be sensed.

Current mode control methods were developed later. The current through the switching power devices can be sensed and limited to a safe value on a pulse-by-pulse basis making it desirable for high performance or high reliability power supplies. The ESR of the capacitor on the output is not an issue, and Type II compensation is usually sufficient for stability.

What I've indicated above are just generalities of what can be a very complex topic if explored in depth.

 

[dzt]

Thanks for your help, Comcokid.