smooth capacitor to prevent ripple voltage

[Derun93]

Hi everyone,
I have a circuit simulation to balance 1.5Ah battery cells in Simulink. If you know how the circuit works, you know that battery voltages are going to high and low or vice versa which means behaving like ripple voltage so I put 2 capacitors parallel to batteries to smooth voltages but they are not working properly. why? please help me.
L:10mH
Vf diode:0.3V
C:0.1uF
period of the switch: 20ms
Duty cycle:%40

 

[FvM]

I can't imagine that a tiny 100 nF capacitor has noticeable effect when parallel connected to a 1.5 Ah battery. But you can refer to the battery model parameters and calculate impedances exactly.

 

[Derun93]

What is your suggestion for the value of the capacitor,sir? Because I tried lots of times with the difference capacitor values but I have not see any noticeable results.

 

[BradtheRad]

It's not clear how your circuit operates. Are you charging the batteries? And you wish their volt levels to stay balanced?

 

[FvM]

I wonder what's the purpose of the capacitors? Battery cells have already very low impedance. You'll large capacitors > 1 mF to reduce it further.

I never saw similar capacitors in a real battery balancing circuit.

 

[Derun93]

The circuit shuttles energy from higher cells to lower cells via inductor.The aim of the capacitors are to keep small ripple voltage for the battery voltages.

 

[KlausST]

Hi,

The switches on the right side are driven by an exact 50% duty cycle signal.

With the L (and C) it should generate an exact 50% of total voltage.
So if the lower battery voltage is lower than the upper battery voltage, then the resulting current charges ( or supports) the lower battery by drawing current from the upper battery.

..an efficient way to use about 100% of the battery even when the Ah values differ.

With in series connected batteries the weakest battery limits the useful Ah wich can be drawn, but the weakest battery will become over discharged and becomes weaker and weaker.

Both batteries will wear out equally..it results in optimized lifetime.

Klaus

- - - Updated - - -

*********
Added:
About ripple.
The batteries have relatively high impedance for high frequencies, so adding a low ESR capacitor will improve high frequency impedance.

Klaus

 

[FvM]

The switches on the right side are driven by an exact 50% duty cycle signal.

That's not a useful way to operate a battery balancer because it would involve permanent losses. Technical balancers implement a voltage regulator that activates the balancer circuit temporarily either with defined current or charge pulses.

 

[KlausST]

Hi,

That's not a useful way to operate a battery balancer because it would involve permanent losses. Technical balancers implement a voltage regulator that activates the balancer circuit temporarily either with defined current or charge pulses.

In case of "imbalace" this is an effective way to transfer charge from one battery to another.
But you are correct, if the PWM is continously running there will be switching losses, so I assume there will be some balancing controller wich switches the PWM OFF and makes both switches high impedance when the battery voltages are equal.

Klaus

 

[Derun93]

ı agree that there must be a switch control. I think I need a hystesis m file to control it. What are your suggestions?

 

[KlausST]

Hi,

maybe like this:
* activate PWM when center voltage is 3% OFF desireds value.
* deactivate PWM when center voltage is within 0.5% of desired value.
(Values just for example)

Klaus