Power electronics

[hinagohar1302]

I am implementing this circuit of switched capacitor boost converter having problem.How I can vary duty cycle in this circuit plus Vbe of both transistor have also be varied but there is no option in components values plz help.especially duty cycle.

[johnsold]

This sounds very much like a problem someone else posted a few weeks ago.  I have cannot find that post now for comparison.

The circuit you have appears to be the same circuit. The comments about varying duty cycle and Vbe also were used in that earlier post.

As I recall the circuit was derived from a published paper (which should have never made it past the reviewers in my opinion).

1. You typically do not vary the duty cycle of a sine wave.

2. You typically do not attempt to control a transistor by varying its Vbe. If you intend to implement this circuit, you should be able to explain why this is not a good practice.

3. The rectifier/capacitor part of this circuit looks very much like a standard voltage doubler circuit. It tends to track peak voltages, so duty cycle variations probably will have little effect.

4. If you decide to try to do 1 and 2 anyway, you need a much different circuit than V2 and T1.

Lynn

[hinagohar1302]

Yeh previously I posted that post and again asked because not getting resonable reply. Duty cycle variation has been implemented in that paper but donot know how.I changed sinusoidal source to pulse but even then no changes in output.Let say there is a need of duty cycle variation for PV application

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@johnsold wrote:

This sounds very much like a problem someone else posted a few weeks ago.  I have cannot find that post now for comparison.

The circuit you have appears to be the same circuit. The comments about varying duty cycle and Vbe also were used in that earlier post.

As I recall the circuit was derived from a published paper (which should have never made it past the reviewers in my opinion).

1. You typically do not vary the duty cycle of a sine wave.

2. You typically do not attempt to control a transistor by varying its Vbe. If you intend to implement this circuit, you should be able to explain why this is not a good practice.

3. The rectifier/capacitor part of this circuit looks very much like a standard voltage doubler circuit. It tends to track peak voltages, so duty cycle variations probably will have little effect.

4. If you decide to try to do 1 and 2 anyway, you need a much different circuit than V2 and T1.

Lynn

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then what modification should introduce in that respective circuit.kindly help

[hinagohar1302]

Yeh previously I posted that post and again asked because not getting resonable reply. Duty cycle variation has been implemented in that paper but donot know how.I changed sinusoidal source to pulse but even then no changes in output.Let say there is a need of duty cycle variation for PV application then what modification should be there in that particular topology.

[johnsold · Accepted solution]

As I pointed out that topology does not seem appropriate for duty cycle variation as a means of control. The capacitors charge almost instantly to the value of the DC source when the transistors or diodes conduct.  This is not a topology which is typiclaly used for voltage regulation, only for voltage mutiplication. If the input source voltage or the load current vary, the output voltage will also change.

Consider how an inductor-based switching regulator uses duty cycle changes for regulation: The current in the inductor changes throughout the time interval during which the switch conducts - it never reaches a stedy state condition. So the amount of current, and thus the stored energy, is related to the ON time of the switch.

The analogous configuration for a capacitor based circuit would switch a current and allow the voltage on the capacitor to change with time.  The practical problem you will have with this approach is that curretn sources are either active linear circuits with low efficiency or are inductors.

Lynn

[hinagohar1302]

Ok how I can observe current waveform on oscilloscope in multisim.I attached current probe on load side but on oscilloscope it is showing  voltage on respective channel.If I want to observe efficiency of this circuit and load power then how I can get these waveforms.

[hinagohar1302]

Though using transient analysis I can observe cuurent and even some expressions.But I need steady state response not transient like we get using oscilloscope.

[johnsold]

You may want to start a new thread. 1. Once a thread has been marked as Solved, many people pay little attention to it.

2. Your question is really unrelated to the topic.

I do not use Multisim, so I cannot answer your question.

Lynn

[hinagohar1302]

Yeh I accepted this as solution.But there is one more question in my mind .

What modification should bring in this topology so it will act like conventional boost converter without inductor.There are numerous research articles on switched capacitor boost converter using different topologies on 
IEEE and other journel papers which are not using inductors..

[johnsold]

I have not looked at those articles and have not designed or built a switched capacitor boost converter.  My suggestion is that you read the abstracts of those articles, pick out two or three which seem relevant and read the eniter articles carefully. Select a topology which seems best suited to your application. Then modifiy the design to meet your needs.

Lynn