bi-directional dc-dc converter transfer function and controller design

Discussion in 'The Projects Forum' started by nuflia, Feb 8, 2013.

  1. nuflia

    Thread Starter New Member

    Nov 18, 2010
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    I’m doing a hybrid power generation project, a part of my work is a bi-directional dc-dc converter that charges and discharges a battery to keep the dc-bus voltage constant 380-420, the battery is 96vdc, I’ve made the Simulink model that works well, the problem is that my bi-directional dc-dc converter does not keep the voltage stable, i know it is due to the modeling of dc-dc converter that I am not able to design the optimum and best PI controllers( voltage and current controllers)
    I appreciate any idea or recommendation on how to model the bi-directional dc-dc converter to find the suitable TF and then design the current and voltage controllers that will charge / discharge the battery to keep the DC-bus volatge stable
    attached the simulink model of the proposed model
     
    Last edited: Feb 8, 2013
  2. nuflia

    Thread Starter New Member

    Nov 18, 2010
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    hope the Question is not difficult, it's week-end no one sees the forum
     
  3. crutschow

    Expert

    Mar 14, 2008
    13,056
    3,245
    It's not clear how your circuit works. Is there a DC-DC switching converter that converts the 96Vdc battery to the 380-420V bus? You need to show more details of your model.
     
  4. nuflia

    Thread Starter New Member

    Nov 18, 2010
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    Thanks for the reply
    It is said the circuit is bi-directional dc-dc converter (buck-boost)
    it is a part of hybrid power energy, the circuit is used to keep the DC-bus constant by discharging the battery to compensate for voltage variations, and to charge the battery form the dc-bus when the battery has no sufficient voltage
    Hope it is clear now
     
  5. kokkie_d

    Active Member

    Jan 12, 2009
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    Hi Nuflia,

    The transfer functions of dc-dc converters can be found through equivalent circuit modelling / average state space modelling and is very well described in: http://www.amazon.co.uk/Fundamental...3635/ref=sr_1_1?ie=UTF8&qid=1361890009&sr=8-1
    It is a bit of a read, but very well explained.

    From your picture you are trying to use the SimPowerSystems toolbox in matlab.

    I am working on something similar and am trying to work out one the equations in the book. Is there anyone here that has some more knowledge about average state space modelling of the basic buck converter?

    Some of the book chapter can be found here:
    http://ecee.colorado.edu/copec/book/
     
    Last edited: Feb 26, 2013
  6. muralikrishna1234

    New Member

    Mar 4, 2014
    6
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    Hi,

    I also working on Bi -directional Converter .I need to control the charge and discharge of battery using PI controller, Can some one help me on this. I need to buck voltage from 400 to 96V and need to boost from 96V battery to 400 V.
     
  7. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
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    why does the converter need to be bidirectional? why not have a seperate charger and stepup converter? couldnt you make both more efficient that way?
     
  8. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Your circuit will do that just fine.

    Why do the think you need a PI controller?

    Just set the PWM to 96/400 = 24% duty and it will automatically perform bidirectional conversion from 400v->96v or from 96v->400v. (Whichever of the two sources is proportionally higher will feed current to the other source).
     
  9. muralikrishna1234

    New Member

    Mar 4, 2014
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    I need to make a closed loop operation. I need to charge the battery when grid is present and when grid goes off my battery has to supply to the load.So only i need BDC.
     
  10. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    That function should happen automatically.

    Do you understand how a bidirectional DC to DC converter works?
     
  11. muralikrishna1234

    New Member

    Mar 4, 2014
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    Hi RB,
    Thanks for reply

    Ya i have Idea on its working operation.I have been able to discharge from battery to load.Both Charging and discharging is closed loop operation using PI controller.But i am unable to charge my battery from 680 to 192V,and i am using an closed loop PI voltage and current controller to regulate the voltage and current.

    Problem-During Discharge mode , in voltage controller loop Input to the PI controller is stable but output of PI controller is unstable. I have tried changing PI values but i am unable to control it.Can you kindly help regarding this.
     
  12. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    I think you misunderstood me!

    I would get rid of the PI controller and just run the PWM fixed at 24% duty (read my post #8 again).

    Then current flow will be based on whichever voltage is proportionally higher. (96v:400v)

    So if you raise the 400v battery by charging it (with an external PSU), current will flow to the 96v battery and charge it too.

    Or if you raise the voltage of the 96v battery by charging it (with an external PSU) then current will flow from it to the 400v battery.

    I think at this point you need to explain what these two batteries do, and how you are charging them and what is discharging them. Please describe the entire system.
     
  13. Thasneem001

    New Member

    May 12, 2014
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    Hi can you tell me how to find the transfer function of bidirectional dc dc converter. As I am working on a similar project like yours
     
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