DC-Connected Battery

Hi SAM's Teem, 

I am designing a DC-Coupled system for commercial application and the MPPT charger controllers and inverters I am going to used are "Conext MPPT 80 600" and "Conext XW+ 5548".

The model/diagram  to simulate a PV plus a DC-Connected battery in SAM (DC-connected Solar Plus Storage Modeling and Analysis forBehind-The-Meter Systems in the System Advisor Model) assumed that the battery bank has its own DC/DC (w/BMS) and then it shares a single point with the DC/DC (w/MPPT) and the DC/AC inverter. Here is very clear that the DC/DC (w/BMS) has to increase the voltage to couple with the DC/DC (w/MPPT) to inject current and decrease the voltage to charge the battery. My question then is, how to extrapolate this concept when having a MPPT charge controller coupled with a battery bank and an inverter? May I create/model a Grid-Tie inverter like a "black box" by using the "Inverter Datasheet" that include a MPPT charger in series with inverter inside the box taking into account the losses and all other parameter that apply? See the concept I have in the file attached to accomplish this and let me know what do you think. 

I am power electronic engineer so don't hesitate in using technical words to clarify this issue . 

Best,
Carlos                

   

Hi Carlos,

SAM only considers the inverter input voltage to determine when the input voltage falls outside of the MPPT minimum or maximum voltage ratings to calculate voltage clipping losses. It assumes a battery management system (BMS) is present, but does not explicitly model its functions.

If you want to set the MPPT voltage ratings for the voltage clipping model, then yes, you could use the "Inverter Datasheet" option to  create an inverter where you can set the values of those parameters.

Best regards,
Paul.

Hi Paul, Thanks for your help on this!

I finished the SAM's paper about the DC-connected battery and understand more now your point about the BMS, it is just a model like you said. 

On the other hand, probably I was not clear enough about my final purpose on the DC-connected battery. As I specified in my previous message my real interest is to install a DC-Coupled battery based system and I think we can compare it with a PV plus a DC-connected battery. The system will have MPPT battery chargers (Conext MPPT 80 600) connected to the battery bank and the inverters (Conext XW+ 5548). The question then is, how to model this configuration in SAM? From my view point, we can model this by integrating or connecting the MPPT chargers and the inverters together, as shown in the picture, and form a single Grid-Tie inverter and then we ca add a DC-connected battery to complete the system. Let me know if you are agree with option (or suggest something different) and if I am able to integrate the chargers and inverters by using the "inverter datasheet" model to accomplish this. 

Best,
Carlos        

Hi Carlos,

I think your approach should work.

For DC-connected batteries, SAM assumes that the battery and PV array are connected to the same inverter(s). It does not model a separate maximum power point tracker (MPPT), so the MPPT function is effectively part of the inverter. For PV+battery systems, the inverter power limiting and MPPT voltage clipping functions are performed on the combined output of the PV array and battery.

Best regards,
Paul.