# Avoid current spike in buck converter

In image my model to simulate PV array & MPPT with buck converter . The result from this model have two problem:

1. At t=T=1/f occur current spike in diode current and Vpv up above Voc.
2. In battery , charger current in t=0 is 3000A ! May be because internal resistor of battery = 0.004 ohm and voltage =12v --> 12/0.004 = 3000A.

How can avoid this problem in my design ? Any tips can be provided to me to Implementation this design? (Apologies for my language)

• The 3000 A is most likely that your 4700 uF cap has an initial condition of 0 VDC – sstobbe May 30 '17 at 2:05

The issue stems from the relatively large parallel capacitance to the battery. The low impedance of the battery exacerbates the situation.

Here a 12V battery with the internal impedance set as per your statement (0.004R) is placed in parallel with a 4.7mF capacitor with an initial voltage of zero.

Essentially you have a 12V low-impedance source in parallel with a 0V low-impedance capacitor.

How to improve it this

1. Set the initial voltage on the capacitor to 12V. This will mask the issue as you REALLY need to deal with this inrush in practice
2. Add some realistic impedance to the capacitor
3. contemplate some form of soft-charge circuit for this bulk capacitor that can be shorted out via a MOSFET

This phenomenon is called in-rush current. The initial charging of all the caps in your system causes a large current spike when you power it on. You can improve the situation by selecting a buck controller IC with soft-start functionality: https://www.digikey.ca/en/articles/techzone/2012/jun/managing-converter-in-rush-current