# Inductor and Capacitor for Bidirectional DC-DC Converter with Battery

I have to design a bidirectional converter to regulate a DC bus at 250 V with a battery bank at 144 V. My question is how to do it optimally, because I do not know the maximum ripple allowed in the current of the inductor to not damage the battery, I also do not know what would be the ideal switching frequency for this type of application. Anyone with experience in the field could give me some tips?

First of all I already have the closed loop control for the converter. My problem is not the operation, I can control the voltage, but I have doubts if it is correct to subject the battery to high current frequency variations as is happening. Below I show how I designed the parameters of the converter, as I did just for the boost, since according to the principle of power conservation the components must be the same for bust, changing only the switching of the IGBTs. I'm not sure if this is true, I do not know if it's what happens in real life for the application I'm doing, I need a lot of tips and references for it, not is the type of information found in papers or books.

## Parameters

Rated Power = 10kW
Rated Voltage = 250 V
Vbattery = 144 V

Fsw = 25kHz

Ripple Voltage in capacitor = 0.1%
Ripple Current in Inductor (That's my doubt) = 20%

ΔiL = 13.8889

Lmin = 1.7584e-05

L (considering the ΔiL) = 1.7584e-04

C = 0.0027

These are the values calculated on the basis of the specifications that I have dubiously determined.

## Objetive

The purpose of applying this converter together with batteries is to regulate the voltage in a DC bus that varies in a random manner.

I have some power electronics books, but most of them are very straightforward with respect to calculations and provide little theoretical information about converter designs. I would like someone's opinion on the converter specifications for this type of application, and if possible some bibliographical references.

## Circuit and Results

The plots below show the CURRENT (TOP) and VOLTAGE(DONW) in differents scales

• Result with a zoom out

• Result with zoom

• More closely

So I posted all my project and the results in different scales, can someone please help me ?

• well, that initial current spike seems rather worrying, if nothing else. – Hearth May 9 '18 at 18:21
• I have answered ignoring the plots as they are not labeled. Please add all the necessary info. – Vladimir Cravero May 9 '18 at 21:06
• Plots show the CURRENT (TOP) and VOLTAGE(DONW) in differents scales – SrnLord May 10 '18 at 18:23

I do not expect the ripple current in the inductor to affect the peak battery current. You will need to put a lot of caps near the input of your converter, so that they can provide the AC peaks while the battery will only see the DC. This also helps a bit for load transients.

The switching frequency entirely depends on the coil size, saturation current, output current, duty limits, vin, vout. But you have it the other way around: usually the switching frequency is given, as vin, vout, current requirements and duty limits, and then you select the coil.

• Could you plese be more specific about the "lot of caps" in the input of converter ? You mean a capacitor bank (capacitors in parallel?) – SrnLord May 10 '18 at 11:06
• I do not necessarily mean a capacitor bank. It is difficult being more precise without knowing the PDN of the input supply... My point is that you do not need to worry of the AC current in the battery if you put a cap in the input of the converter. – Vladimir Cravero May 10 '18 at 11:40
• What do you think about this comment in other post, and the relation with my question electronics.stackexchange.com/a/333495/186980 – SrnLord May 12 '18 at 12:40