# how to keep input power constant for bi-directional buck-boost converter using cosine pwm?

#### kittoo

Joined Jul 11, 2016
27
hello sir/mdm,

I am designing a bi-directional buck-boost converter for battery charger,to keep the power factor unity. I need a constant input power (i.e, if current is minimum the voltage will max & vice versa) . you can see in fig2 the current is max when voltage is max,how to keep input power constant for bi-directional buck-boost converter using cosine pwm?

#### tcmtech

Joined Nov 4, 2013
2,867
Okay? why do you think you need to keep the PF at unity while charging a battery?

Is this a commercial application where the battery holds hundreds to thousands of kilowatts?

#### crutschow

Joined Mar 14, 2008
25,656
You don't regulate input power.
The circuit takes whatever power it needs to operate and supply current to the load.

#### kittoo

Joined Jul 11, 2016
27
Okay? why do you think you need to keep the PF at unity while charging a battery?

Is this a commercial application where the battery holds hundreds to thousands of kilowatts?
if PF is unity then the efficiency of the circuit is good.
no,it is not a commercial application

#### crutschow

Joined Mar 14, 2008
25,656
The efficiency of the converter circuit has little to do with the power factor.
All a poor power factor does is increase the losses some in the main's power line.

#### tcmtech

Joined Nov 4, 2013
2,867
if PF is unity then the efficiency of the circuit is good.
No it's not. Power Factor of a circuit has very little effect on overall system efficiency. Typically fractions of a percent at best in an application like yours.

Especially so when compared to the unavoidable losses that are present in charging a battery which are measured in multiple 10's of percents.

#### kittoo

Joined Jul 11, 2016
27
No it's not. Power Factor of a circuit has very little effect on overall system efficiency. Typically fractions of a percent at best in an application like yours.

Especially so when compared to the unavoidable losses that are present in charging a battery which are measured in multiple 10's of percents.
I am building this charging circuit for 72v ,10amps battery ,
when i simulate this circuit in matlab, the 2nd harmonics content is very high in source current.
is there any method to eliminate 2nd harmonics ?

#### Papabravo

Joined Feb 24, 2006
14,679
The harmonic content arises from the use of waveforms with sharp edges and corners. There is presumably a reason for doing this; but where do you want to eliminate this harmonic content? I suggest you try a different method.