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control technique for dc-dc converter

I simulated successfully this Switched Capacitor DC-DC converter which step up input voltage..Now main task is to  maintain output at fixed 14V irrespective of input.I am trying to implement this through PWM which will provide variable duty cycle to switches.Ouput of converter be compared to fixed reference of 14V then comparator will estimate error signal..that error signal will be compare to sawtooth which generates switching signal for switches,I tried this but it is not working.plz guide where is error..2nd I am directly giving output of converter to comparator is this correct way..as shown in below fiqure output of converter which is Vo actual while Vo desired is fixed 14V for my case ..it will estimate Ve which will be compared to sawtooth to generate particular pulse width..This sawtooth magnitude and frequency would be how much for this case..any formula or lgic for this setting,,

 

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Message 1 of 16
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Hi there,

 

Your circuit looks OK, but could you please send me your original multisim file. I will help you check and test it.

 

Regards,

 

Chen_T
National Instruments
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Message 2 of 16
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Make sure that the 14 V input signals are within the specified common mode input range for the devices and power supply voltages you are using.  For example some op amps or comparators with 15 V power supplies will not work properly with input voltages above 13 to 13.5 V.

 

Lynn

Message 3 of 16
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This is actual simulation file in Multisim.Input supply will be from 8 to 14V while output should be fixed at 14V through PWM control technique.This circuit is step up converter which  is inductor less.On output 14V is required as this circuit will charge 12V battery at fixed voltage.

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Message 4 of 16
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Hi there,

 

You need to add an inductor between the 10V V1 and the Diode D3 shown as below.

Capture3.PNG

 

When the converter is in on state, the energy transfers from the input source, which is V1, to the inductor L1. Now if the converter is then turned off, the magnitude of energy stored in the inductor is forced to your battery E (12V).

 

A typical buck converter is shown as follows. 

Capture2.PNG

 

Hope it helps.

 

Regards,

 

Chen_T
National Instruments
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Message 5 of 16
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If u kindly introduce necessary changes in my multisim file which was with previous email.Novality of this circuit is that it is inductor less boost up converter as I am doing it for research work so cannot use inductor as you proposed.Second my main concern is how to maintain constant 14V at output.Load in my case is battery which will be charged through this circuit and battery internal resistance is normally 5 mohm or less so then how I can form resistor divider circuit at output.

Please guide how to stablize this circuit at 14V using PWM technique or modify multisim file.

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Message 6 of 16
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Do you understand how a boost converter works? It stores energy in some device (typically an inductor) during one phase of the operation and recovers that energy at a higher voltage in another phase.

 

A boost converter MUST have an energy storage device which can operate on a cycle by cycle basis. What is the energy storage mechanism in your novel circuit?

 

What does the nature of the load have to do with the voltage sensing for the feedback?

 

People on this Forum are here to help you understand how to use the NI products but not to do your work for you. The design of the circuit is your responsibility. 

 

Lynn

Message 7 of 16
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Yes capacitor here works as energy storing element.In my first post I attached multisim file in which DC-DC control technique through PWM is done.Load for this circuit is 12V battery which will be charged through this charger.PWM main purpose is to vary duty cycle of both switches T1 and T2 in order to maintain 14V constant at output while input varies from 8 to 14V.But my circuit is not given correct output that'swhy I asked where is error in multisim file. 

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Message 8 of 16
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I do not have Multisim. Can you post an image of the schematic diagram?

 

Lynn

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Message 9 of 16
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Here is the original one without the inductor:

1.PNG

Chen_T
National Instruments
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Message 10 of 16
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