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

Discussion in 'Power Electronics' started by kittoo, Aug 22, 2016.

  1. kittoo

    Thread Starter New Member

    Jul 11, 2016
    25
    1
    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?






    Screen Shot 2016-08-22 at 14.55.17.png Screen Shot 2016-08-22 at 14.55.17.png Screen Shot 2016-08-22 at 14.56.42.png Screen Shot 2016-08-22 at 14.56.42.png
     
  2. tcmtech

    Well-Known Member

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

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

    Expert

    Mar 14, 2008
    13,028
    3,238
    You don't regulate input power.
    The circuit takes whatever power it needs to operate and supply current to the load.
     
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  4. kittoo

    Thread Starter New Member

    Jul 11, 2016
    25
    1
    if PF is unity then the efficiency of the circuit is good.
    no,it is not a commercial application
     
  5. crutschow

    Expert

    Mar 14, 2008
    13,028
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    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.
     
  6. tcmtech

    Well-Known Member

    Nov 4, 2013
    2,039
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    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.
     
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  7. kittoo

    Thread Starter New Member

    Jul 11, 2016
    25
    1
    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 ?
     
  8. Papabravo

    Expert

    Feb 24, 2006
    10,150
    1,792
    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.
     
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