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Pure sin wave inverter

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which of the circuit diagram you used, it think you need to connet your feed back for proper work of the inverter.
 

hi tahmid
At the transformer output i have used a bridge rectifier using ultrafast HER503 diodes and 400V 47uFD capacitor, when i measure the output voltage with NO LOAD the voltage is around 560volts, but when I connect 100watt bulb ,the output dc voltage goes to 227volts. and when i connect 2 bulbs of 100watt each then output voltage goes to 130volts. till now i havn't used any feedback ,so i want to know where is the problem? is there a problem in my transformer ? my turn ratio is around 35,, and ETD44 core can handle around 450 watts but in my case it cannot handle 200watts,, so please tell me where is the problem??
 

tahmid , i have also read about SPWM, one thing that i want to know is ..What level spwm can we generate using PIC, i.e. (2nd level, 3rd level etc)??
 

--BawA-- said:
tahmid , i have also read about SPWM, one thing that i want to know is ..What level spwm can we generate using PIC, i.e. (2nd level, 3rd level etc)??
Click to expand...

i dont understand. what you mean by 2nd and 3rd level SPWM.

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--BawA-- said:
tahmid , i have also read about SPWM, one thing that i want to know is ..What level spwm can we generate using PIC, i.e. (2nd level, 3rd level etc)??
Click to expand...

i dont understand. what you mean by 2nd and 3rd level SPWM.
 

hi kabeer
as we know tha simplest way of producing the PWM signal is through comparison of a low-power reference sine wave with a triangle wave . Using these two signals as input to a comparator, the output will be a 2-level PWM signal . This PWM signal can then be used to control switches connected to a high-voltage bus, which will replicate this signal at the appropriate voltage. Put through an LC filter, this PWM signal will clean up into a close approximation of a sine wave . this technique produces a much cleaner source of AC power than either the square or modified sine waves,

In order to create a signal which is closer to a true sine wave, a 3 level PWM signal can be generated with high, low, and zero voltage levels. For the resulting 3-level PWM signal to correspond to a sine wave, the signal comparison stage must also be 3-level . A triangle wave is used as it is in the 2-level PWM comparison, but it half the amplitude and summed with a square wave to compare one half of the sine reference signal at a time. The resulting PWM signal is used to control one half of an H-bridge , which controls how long the bus voltage is allowed through to the load. The other half of the H-bridge controls the polarity of the voltage across the load, and is controlled by a simple square wave of the same frequency and in phase with the sine signal. Generally, this square wave can simply be created in a stage of the sine wave generation circuit. The resulting 3-level high-voltage PWM signal can be filtered into a very close approximation of the desired sine wave using LC low pass filter.
 

--BawA-- said:
thanx tahmid
that fault is resolved now,,there was a problem in my wire that connects the battery to the circuit.wire was too thin to drive the 10 amp current ,, as i replaced the wire with a thick one ,,100 watt bulb glowed ,,, :)
but there is still a small problem- At the transformer output i have used a bridge rectifier using ultrafast HER503 diodes and 400V 47uFD capacitor, when i measure the output voltage with NO LOAD the voltage is around 560volts, but when I connect 100watt bulb ,the output dc voltage goes to 227volts. and when i connect 2 bulbs of 100watt each then output voltage goes to 130volts. till now i havn't used any feedback ,so i want to know where is the problem? is there a problem in my transformer ? my turn ratio is around 35,, and ETD44 core can handle around 450 watts but in my case it cannot handle 200watts,, so please tell me where is the problem??
Click to expand...

You will need to use feedback to maintain constant output voltage. However, even without feedback, with 200W load, the voltage shouldn't drop that low. It's possible that the battery voltage drops too low when using the 200W load. What is the current rating of the battery? Measure the battery voltage when using the 200W load.
 

Hi tahmid
I have used an iverter battery ..I.e. 12v 150ah
Battery voltage is not droping...
Is there any problem in my transformer..I hve wound the primary winding by twisting 12wire strands of 25 gauge..together...I m confused whether I should twist all the wires or just keep the wires parallel as it is....please suggest me...

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Also tell m can we generate 3 level pwm using pic??
 

--BawA-- said:
Hi tahmid
I have used an iverter battery ..I.e. 12v 150ah
Battery voltage is not droping...
Is there any problem in my transformer..I hve wound the primary winding by twisting 12wire strands of 25 gauge..together...I m confused whether I should twist all the wires or just keep the wires parallel as it is....please suggest me...
Click to expand...

What are you using as your PWM controller? How are you driving the MOSFETs? There may be a problem with MOSFET drive causing the problem. You can keep the wires parallel as is or twist them. Parallel takes up less space. But if you don't twist, you might not be able to wind the wires properly. I think you should twist them and don't give such force that the insulating coating on the wire is disturbed.

I've done both with no problems. But for more than two wires, I twist the wires.

Hope this helps.
Tahmid.
 
i am using sg3525 for as a pwm controller,,,
tahmid ,
1) i want to make a three level pwm inverter,,so can we generate 3 level pwm using PIC ??
2) from which stage should i take the feedback,,i.e from 311vdc bus or 220v ac sin wave bus ??

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one more question ,, is it normal that my transformer no load voltage goes upto 560,,, as i connect the bulb ,it comes on 230v ,,, m not getting 311v??
 

tahmid please reply m waitng
n one more help plzz,,how to calculate the vale of resistance that wil be needed between gate to source and b/w sg3525 to gate of mosfet..??
 

what type of mosfet do you used, your input voltage and capacity?
 

mosfet is irfz44n
input voltage is 12.5
capacity is 450watts
 

ok you can used 47ohms resistor from your buffer to gate and 4.7k from gate to ground that what i used for my 650watts inverter.
 

thank you kabeer
but i have used 10 ohm resistor for each gate , and i hve used 2k resistor from gate to source in each n every mosfets in the bank,,,can u please tell me how hve u selected these values? which formula have u used for calculating these values,, and also tell me what will be the change in the output if i change these resistance values??
 

The gate series resistor does depend on your used frequency. For your application, I would say that 4.7Ω to 10Ω should be okay. Don't go for too high or low.

The gate-to-source resistor could be between 1kΩ and 10kΩ. So, your selection of resistors is okay, assuming that 2kΩ is the total combined resistance from gate-to-source of the combined paralleled MOSFET setup.

Hope this helps.
Tahmid.
 
Last edited:
Thanx tahmid...
If I am using three mosfets at each side..then first of all I should connect then in parallel and then add a 2k resistor between gate n source and 10ohm at the gate...or I should connect 2k resistor from gate to source and 10ohm resistor to the gate to each of three mosfet and then combine the drain....which is the better way???
 

The 2nd option is better. Connect the 2k resistor from gate to source of each MOSFET. Also connect a 10R resistor in series with each gate. Then, combine the drains and combine the sources. Don't directly combine the gates, but combine them through the 10R resistors, so that each MOSFET has a 10R resistor in series with each gate.

I would suggest you slightly increase the gate-to-source resistance of each MOSFET from 2k to 4.7k. You should also use a proper gate driver circuit employing a totem-pole driver using NPN-PNP combination or a dedicated driver such as TC427.

Hope this helps.
Tahmid.
 
thanx again tahmid,,
what is totem pole ?
i have used sg3525 as a driver circuit and i hve connected mosfet through sg3525 with a resistance between pin 14 and gate ...pin 11 and gate ... so what is the dedicated driver? is there any need to modify my circuit? and is there any way to protect the mosfet if there is fault in driver circuit??
 

tahmid i tried alot to get TC427 but i was unable to find , can u tell me anyother famous low side high speed, mosfet driver ic,?
 

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