Could some electronics guru please clarify this a bit ? A pure sine wave inverter needs to have an oscillator to produce the sine waves. So what type of oscillator is used typically -- Z-source inverter, or a some other type ? Any hints, suggestions would be very helpful.
Producing sine waves comes in a multitudes of ways..
The most basic way to do it is, the frequency is fixed is to create a triangle wave and then pump that into an integrator or (RC) network where it gets rolled over and then looks like a sine wave.
From there you can drive other circuits for the amplification of that signal. As for an inverter, you could use a class B type circuit with bipolar power transistors in that section how ever, I must warn you that to get high power transfer to the secondary of the transformer you'll need to use some hefty transistors. The other way would be to use power MosFets and PWM (pulse width modulate) along the sine curve via the sine wave signal you now would have. The Pulse Width can be metered via your sine wave reference and the base frequency can be fixed.
Essentially, the Pulse width duty cycle will be low at the base and high at the peaks to give you the sine wave power drive to the primary side of the transformer.. At the output side, things will look rather clean because the transformer isn't going to pass much of that switching noise to that side. This means a transformer for 50/60hz.
Have a good day.
Jamie
It's usually a (cheap) micro controller or special PWM chip. That has either a math function or look-up table in there from which it derives the proper pulse widths to follow a sine wave.
-- Regards, Joerg http://www.analogconsultants.com/
The Baxandall Class-D oscillator produces a tolerably clean sine wave
- typically with a few percent of third harmonic content.
Jim Williams wrote quite a bit on this circuit (which he didn't describe as a Baxanadall class-D oscillator, presumably because Baxandall's paper was published in an obscure English journal and doesn't seem to have made any impact in the US) in Linear Technology's application notes AN45, AN49, AN51, AN55, AN61, and AN65.
I've got a couple of pages about it on my web-site
Baxandalls 1959 paper is fairly comprehensive
In 1986 I devised a variant that is less efficient - 50% rather than
95% - but has much lower harmonic content and better amplitude stability. I hope to publish it eventually, so it isn't detailed on the web-site. E-mail me - at snipped-for-privacy@ieee.org - if you do need something with a low harmonic content.-- Bill Sloman, Nijmegen
...and it's not all that "pure", except as compared to the so-called "modified sine wave" (marketing-speak for a square wave.) When I was seriously shopping offgrid stuff (which got so expensive to do right and up to code that the grid won after all) the better ones were doing 232 steps IIRC for a 240V RMS sine wave.
-- Cats, coffee, chocolate...vices to live by Please don't feed the trolls. Killfile and ignore them so they will go away.
Inverters usually generate a digital PWM signal (Like Don Lancaster's Magic Sine Wave idea) and apply that to hard switching transistors, and only lowpass filter at the very end.
The oscillator is then any digital oscillator, maybe a crystal, that is processed by digital logic to make the complex PWM waveform.
Older inverters would sometimes generate a real analog sine wave and use an analog comparator/PWM sort of loop thing to drive the switching transistors, kind of a delta-sigma ADC. Some may still do that.
What's a Z-source inverter?
John
A quite simple micro controller should be able to handle the NCO (Numerically Controlled Oscillator) principle. Practically any crystal frequency will do (so select the cheapest crystal) and still get quite accurate (within a few ppm) 50 or 60 Hz frequency. Then a 256 or 1024 element sine look-up table is needed followed by a DAC.
Then only a voltage amplifier stage and a few current amplifier class B stages with a lot of heat sinks and heavy 50/60 Hz transformers are needed :-).
Most small uCs do not have real DAC outputs but rather some PWM outputs, so why not use it to drive some switching transistors, filter the result and feed it to 50/60Hz transformers.
Alternatively, use some simple square wave inverters to generate
+/-350 V DC bus voltage and then a half bridge PWM switching to generate 230/400 AC sine wave and get rid of the heavy 50 Hz transformer.
A "modified sine wave " inverter is not a square wave.
It is a gapped square wave.
The advantage of the gap is that the amplitude of can be set to provide the correct peak to peak value which is important for electronics and the gap (duty cycle) can be set for the correct RMS value which is important for lights and heaters etc.
A correctly adjusted modified sine (gapped square wave) inverter is simple and effective.
Mark
Only the deluxe editions have lowpass filters. Well, some of them.
A Japanese sports car :-))
-- Regards, Joerg http://www.analogconsultants.com/
flipped on its back?
Actually, I looked it up. It's kinda like the thing I "invented" here a while back, namely switching an voltage+inductor through an h-bridge into a capacitor. I was trying to make a triangle. The thread is around here somewhere...
John
__ It's easy to show that a "modified sine wave" _| |_ _ has zero | __| third harmonic content if the transitions are set to fall at 30,
150,210 and and 330 degrees.The fifth and seventh harmonic content is appreciably less that of a square wave.
Don Lancaster's "magic sine-waves"
take the idea further. Every time I've tred to use them they've turned out to be impracticable for one reason or another, but the idea is undeniably cute.
-- Bill Sloman, Nijmegen
It doesn't cost that much more to get true sine these days. I wouldn't put anything expensive on a modified sine inverter.
"Bill Slowman Creeps"
" It's easy to show that a "modified sine wave" has zero third harmonic content if the transitions are set to fall at 30,
150, 210 and and 330 degrees. "** That means the conduction angle is 120 degrees in each half cycle or 66% duty cycle.
Makes the rms value 0.66 * 0.5 or 81.6% of the peak value.
The peak should be close to 330 volts in a 230 volt country, so the rms value is 269 volts.
Tad high for incandescent lamps.
Pop, pop....
... Phil
6%
It doesn't take much low pass filtering to make it more respectable.
-- Bill Sloman, Nijmegen
<
-- Many thanks, Don Lancaster voice phone: (928)428-4073 Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552 rss: http://www.tinaja.com/whtnu.xml email: don@tinaja.com Please visit my GURU's LAIR web site at http://www.tinaja.com
6%
Phil, sorry I'm not following you...
wouldn't the ideal DF for the correct peak to RMS ratio be 70.7%?
230 * 1.414 =3D 325 peak so we set the peak to 325 Vand of course at 70.7% that brings it back to 230 RMS.
and 60.6% which minimizes the harmonic would result in an RMS value that was a bit low? 325 * 66.6% =3D 217 VRMS?
no?
Mark
"Mark" "Phil Allison" "Bill Slowman Creeps"
Phil, sorry I'm not following you...
wouldn't the ideal DF for the correct peak to RMS ratio be 70.7%?
** Nope.The rms value is the sq rt of the duty cycle.
Consider a 1 amp current in a resistive load that is switched on for 50% of the time.
The heating effect is 50% and so the rms current must be 0.7071 amps.
Cos the square of 0.7071 is 0.5.
The ideal duty cycle for 230 volts rms equivalence is 50%.
... Phil
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