H-Bridge Inverter: Voltage Drops as I keep Increasing Power

Discussion in 'General Electronics Chat' started by Tariqul Islam, Jul 15, 2015.

  1. Tariqul Islam

    Thread Starter New Member

    Jun 27, 2015
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    I have created an Inverter system with 48V DC in the input.
    The DC Voltage is stepped up using a Full Bridge DC-DC converter to 360V.
    Then, this voltage is fed to a H-Bridge Inverter run by an 8KHz SPWM (generated in Arduino Nano). The desired Output of the inverter is 230V (RMS) AC.
    I'm using a RLC network to filter out the hi frequency components. Additional Loads are attached to parallel RC branch of the filter. Values are L=26mH, C=2.2uF, R=100ohm.

    Currently I'm using 100W light bulbs as loads. When I use as single light bulb the output voltage is around 230V. And when I use two light bulbs the voltage drops to 180V.

    I'm not submitting any schematics as of now. Just want to know your general opinion. What could be the cause of this? What are the mechanism to increase voltage.
     
  2. Alec_t

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    What does the 360VDC drop to when using those bulbs as loads?
     
  3. shortbus

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    More amperage in the input. When you double voltage the current halves. I know that's not what your doing but it's the easy explanation. The voltage drops to keep trying to deliver the current being pulled from the circuit. If you put a 50W bulb as a load the voltage would get higher.

    Could I ask why such a high switching frequency? The old rule of thumb was IIRC, 100 times the output Hz needed, for the carrier frequency.
     
  4. Tariqul Islam

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    Jun 27, 2015
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    It stays constant as far I have seen. I've connected a Multimeter to the output of DC-DC Stage. Sometimes the voltage drops or increases momentarily when I turn on the switches of the loads and then the multimeter reading goes back to 360V DC.


    But the DC-DC voltage does not drop. How can I increase the amperage then?
    I selected the frequency because I read few papers where they used these frequencies: 8KHz, 16KHz, 20KHz etc.

    Sorry for replying late though.
     
  5. tcmtech

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    Nov 4, 2013
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    What is the voltage drop across your RC filter?

    I'm going to sort of agree not not entirely. For a high precision PWM wave form like in an audio signal or specialty drive application yes but in a power inverter type application 10:1 followed by a simple RC filter is typically going to be plenty good.
     
  6. Tariqul Islam

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    Jun 27, 2015
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    This is the filter arrangement.
    [​IMG]
    The voltage I mentioned in the post is the voltage across RC Branch.
    It drops from 230V to 180V as I switch on 2nd light bulb.

    Edit: How do I scale the image down? [img=WidthxHeight] code doesn't seem to work.
     
  7. #12

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    Xl = 2 Pi F L
    Xl = 6.28 x 8000 x 0.026
    Xl = 1307 ohms
     
  8. Tariqul Islam

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    Jun 27, 2015
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    That is the 8KHz component. Doesn't the 50Hz Component has much lower impedance? Like 2*pi*50*0.026 = 8.16 ohm.
     
  9. #12

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    Did I get that wrong? "Additional (unknown) loads are attached to this RLC filter." but not the 8KHz H-bridge load.

    You asked about light bulb loads. Are they attached to the H-bridge or are they the, "additional" loads?

    Where is this RLC filter attached and what is driving it? The H-bridge?

    and so, loading the circuit reduces the output voltage. There must be some impedance in the H-bridge, right?

    How is the 50 Hz coming into this circuit? I have looked 3 times and I can not see where you mentioned 50 Hz.
     
    Last edited: Jul 17, 2015
  10. Alec_t

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    Simulation shows only a small voltage drop across the filter: therefore the voltage drop you are experiencing under load must be due to poor regulation by the inverter.
     
  11. Tariqul Islam

    Thread Starter New Member

    Jun 27, 2015
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    I'm sorry I did not make that clear. The switching/carrier frequency of Sine PWM is 8KHz. And the modulating signal is 50Hz Sine Wave.

    This might be the problem. Can you tell me how can I increase the voltage of the H-Bridge output? Any suggestions?

    However, The output of the Inverter is 50Hz. But not quite sine wave. Looks like heavily tapered Squared wave.
     
  12. tcmtech

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    Nov 4, 2013
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    What is driving the H bridge components?

    Your voltage drop should be fairly easy to find just by looking for where the voltage is changing as the load changes.

    If the DC side is stable and the AC voltage is stable before the filter then the filter is the problem. What is the actual DC resistance of the inductor?
     
  13. Alec_t

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    Can you post the schematic of your inverter?
     
  14. #12

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    How does the 8KHz which is being modulated by a 50Hz frequency turn into 50 Hz before it gets to the filter in post #6?
     
  15. Tariqul Islam

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    Jun 27, 2015
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    IR2112 ICs are driving the H Bridge.
    Inductor DC resistance is around 1.2ohm.

    Sure. http://imgur.com/LLSDvVI ; this is half of the H bridge. other half of h bridge is mirror of this circuit.

    It doesn't, I guess. This filter is supposed to remove the high frequency components.
     
  16. #12

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    This is no way the final choice for components but it might demonstrate a method.
     
  17. shortbus

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