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?

 

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?

 

You don't regulate input power.
The circuit takes whatever power it needs to operate and supply current to the load.

 

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

 

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.

 

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.

 

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 ?

 

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.