Static inverter design

[AshwinNambiar]

How do i design an inverter where the input voltage (dc)= 28 volts and at the output obtained is a 115volts and 28volts output,with a frequency of 400 hertz.
How do i develop a design?What kind of inverter should i use ?I'm unable to come up with a circuit design for the same.How do i design a circuit for the above mentioned specification?

 

[AshwinNambiar]

Say ,i choose a 3 phase inverter ,28 volts DC is the input.I need a sine wave at the output of voltages 28v ac and 115 volts ac both @400Hertz.Now if i go by the normal working of a 3 phase inverter with the 180 degree mode ,i obtain a sqaure wave output of 28 volts ac,correct???How do i go about with designing this?
Please help

 

[Harald Kapp]

Do you need a 3-phase output or a single phase output?
Do you require a sine waveform of will a non-sinusoidal waveform suffice?
Does the 28V output need to be insulated from the 28V DC input?
What power do you require for each voltage?

A basic design can be as simple as:

• 400Hz sine generator operated from 28V
• Amplifier operated from 28V to drive the 28V power output from the 400Ht input
• Transformer to step up the 28V sine from the power output to 115V

Operating the device with sine waves will create lots of waste power. Using square waves or a PWM schem (both of which may need additional filterinmg on the power side to remove higher frequency residues) may greatly reduce waste power.

 

[AshwinNambiar]

I need a 3 phase output. So with a 28 volts DC ,using a 3 phase inverter ,with it working in the 180 degree mode,will i be able to obtain a 28 volts AC?yes,if not sinusoidal,a quasi sine wave will also serve the purpose.
Now say,i have this 3 phase inverter ,if at all a 28 volts ac is obtained at the output load,how do i connect the step up trasformer??i find it a little confusing

 

[ramussons]

I need a 3 phase output. So with a 28 volts DC ,using a 3 phase inverter ,with it working in the 180 degree mode,will i be able to obtain a 28 volts AC?yes,if not sinusoidal,a quasi sine wave will also serve the purpose.
Now say,i have this 3 phase inverter ,if at all a 28 volts ac is obtained at the output load,how do i connect the step up trasformer??i find it a little confusing

Could you please explain the Red part?

Why generate 28 VAC and then step it up to 115 V? If you need 115 VAC and 28 VAC, both 3 Phase, the Invertor Transformer will have to be wound that way.

 

[AshwinNambiar]

By 180 degree mode ,i meant ,switching on and off of the switches w.r.t logic states 1 and 0. I'm not sure,but the output voltage levels obtained by this can give a current that is more sinusoidal,correct?because the more pulsating it is ,the better sinusoidal current waveform obtained??
"The inverter transformer will have to be wound that way" ??how to i introspect on that design??
1st.HOW DO I OBTAIN A 28VOLTS AC from 28 volts dc @400Hertz
2nd.HOW DO I ALSO OBTAIN a 115volts AC for "THE SAME " 28 VOLTS DC @ 400 HERTZ?
ok,say step up transformer?How do i design an inverter with a step up transformer?
Will the circuit attached below serve the purpose??I need to design a "static" inverter ,frequency "400HERTZ"

 

[Harald Kapp]

A 3-phase system has 120° phase shift between the phases, not 180° - or do I misinterpret your statement?

1st: Use any oscillator circuit set to 400Hz - or an oscillator that runs directly off 28V. Use three coupled oscillators or one oscillator+ phase-shift circuits (+120° and -120°) to obtain three phases. Use three amplifiers to genertae the power output for the three phases.
2nd: Use a transformer with a winding ratio of 28/115, one transfoerm per phase.

 

[duke37]

The CMOS cookbook p334 by Don Lancaster shows a simple way of generating three 3 phase singals. It uses a 4018B and needs an input of six times the output frequency (2400Hz).

The three transfomers will probably use an iron core but this will be much smaller than for a transformer for 50Hz. The transfomer should be bifilar wound and driven with a pair of FETs, possibly with a delay of switch on of one fet after the other is turned off to eliminate 'shoot through'. There may be a dedicated chip to do this.

 

[AshwinNambiar]

A 3-phase system has 120° phase shift between the phases, not 180° - or do I misinterpret your statement?

1st: Use any oscillator circuit set to 400Hz - or an oscillator that runs directly off 28V. Use three coupled oscillators or one oscillator+ phase-shift circuits (+120° and -120°) to obtain three phases. Use three amplifiers to genertae the power output for the three phases.
2nd: Use a transformer with a winding ratio of 28/115, one transfoerm per phase.

I wasn't clear in my explanation.By 180degree i meant ,the conduction mode.There is this 180 and 120 degree conduction mode for inverters.WILL THE MODE OF CONDUCTION HAVE ANY EFFECT IN THE OUTPUT VOLTAGE OBTAINED?this might seem lame,but somehow tend to believe that the mode of conduction can have variance in output voltage.

 

[Harald Kapp]

WILL THE MODE OF CONDUCTION HAVE ANY EFFECT IN THE OUTPUT VOLTAGE OBTAINED

Frankly I don't know.

 

[ramussons]

The 120 degree conduction is for a Quasi Sinewave invertor. Yes, it will have an effect on the output.

Use the RMS values for Turns Ratio of the transformer. But you will need to filter out the Harmonics and the filters will be quite hefty since the switching frequency is 50 Hz.

It's better to go for PWM invertors since the Filters can be much smaller due to higher switching frequency.

 

[AnalogKid]

Five postings and you still have not told us the power levels, the output currents for each of the two outputs. For 1 or 2 watts this is a pretty easy project. For 10,000 watts it is going to be nearly impossible for you. AC output power supplies are not simple devices to discuss even when we have the information we need. Turn off your caps lock key and please tell us the output currents, the output powers in both watts and VA, and the nature of the loads (lights, motors, computers, etc.). Are you looking for a solid-state design or a motor-generator set?

Better information = better answers.

ak

 

[AshwinNambiar]

Five postings and you still have not told us the power levels, the output currents for each of the two outputs. For 1 or 2 watts this is a pretty easy project. For 10,000 watts it is going to be nearly impossible for you. AC output power supplies are not simple devices to discuss even when we have the information we need. Turn off your caps lock key and please tell us the output currents, the output powers in both watts and VA, and the nature of the loads (lights, motors, computers, etc.). Are you looking for a solid-state design or a motor-generator set?

Better information = better answers.

ak

Well ,the power for 1kva i.e 1000 W .Output currents can be of 8.5A to12 A.I'm specific to 28 voltsDC being converted to 28Volts and 115volts ac,both at frequency 400Hertz

 

[AshwinNambiar]

The 120 degree conduction is for a Quasi Sinewave invertor. Yes, it will have an effect on the output.

Use the RMS values for Turns Ratio of the transformer. But you will need to filter out the Harmonics and the filters will be quite hefty since the switching frequency is 50 Hz.

It's better to go for PWM invertors since the Filters can be much smaller due to higher switching frequency.

"Use the RMS values for Turns Ratio of the transformer. But you will need to filter out the Harmonics and the filters will be quite hefty since the switching frequency is 50 Hz".
Could you please get a little elaborate on this?And to be noted is the design is for 400 Hertz frequency.So 400 Hertz frequency will result in a considerably less weight filters.What specific kind of PWM inverter would you suggest?

 

[ramussons]

This is wrt to the 120 degree conduction angle .....

The rms factor of this wave will be (120/180)^0.5 = 0.8 app and this means that the number of windings in the output side of the transformer will need to be 1.25 times the voltage ratio.

You will need to use filters at the output to eliminate harmonics.

A PWM invertor can synthesize a Sine Wave more efficiently and the filter will be much smaller due to high switching frequencies.

Google for PWM invertors. There's a whole lot of information there.