Charging a battery with pulsed voltage (and thus, pulsed current)

Hello!

I have designed a battery charger model, however I want to control the voltage(using controlled voltage source) by supplying pulses from a PWM, but it seems the current supplied to the battery goes to negative, causing discharge. Is there a way to always ensure that the battery is being charged by positive current only, while I control the voltage source to demonstrate pulse charging?

I would really appreciate if anyone could shed some light on the matter