Every pure sinewave inverter, I knew or heard of (12Vdc or 24Vdc to 220Vac), that uses laminated iron transformer (input: 1 coil, output: 1 coil) drives its transformer with a 4-MOSFET bridge.

Lately, I am designing a pure sinewave inverter but by using 2-MOSFET push-pull driver (lower side only) with a half-wave transformer (input: 2 coils, output: 1 coi).

I used to believe that simplifying a board likely creates some disadvantages.

So, I hope some experienced engineers here could help me know in advance certain expected disadvantages in using the push-pull configuration, in this case, instead of a bridge.

Thank you.
Kerim

What do you mean by 2 mosfet push pull ?
If you mean 2 N MOSFETS in half wave drive, yes, that saves 2 MOSFETS but
* you now need 2 clamp circuits
* worse, is the current flows in half the transformer copper at a time.

It’s the same reason half wave rectifiers ‘waste’ transformer resource, and bridge rectifiers are preferred.

Good remark,
If I understood you well, the price is more copper at low-voltage side in order to get the same resistance of the 1 coil transformer (driven by a bridge).
But let us also recall that the resistance added by a bridge is 2*Ron instead of 1*Ron in case of half wave drive.

Quote from: coromonadalix on March 18, 2024, 01:59:34 am

using any mcu for generating a sinal will not be pure as you need, it will be called pseudo sinusoidal, you’ll need good filtering, if you want to acheive a somewhat good sinus wave out of it

You are right in case the code is not well written. For instance, I had to write my codes, since early 80′s, in assembly language only because I couldn’t get, for free or else, high language compilers as of C for example.

I managed to output the SPWM signals at pins OC1A and OC1B of ATmega8 (using fast PWM of timer 1). The rate is 15,625 Hz. The number of samples per cycle (50 Hz) is 312.
The amazing thing is that the small leakage inductance of the iron power transformer does the filtering with a relatively small high voltage capacitor (around 1 uF). I am not sure how good (speaking THD) the sinewave, I got, is. But it looks on the scope screen it looks a sine wave without ripple.

Naturally, to maintain 220V at the output, the MCU reads the output voltage in every cycle (50 Hz) to adjust the gain of the PWM for the next cycle. This voltage regulation allows a soft start at boot (from 0V to 220V, in 800ms). The MCU has other functions related to safety in case of faults.

Quote from: coromonadalix on March 18, 2024, 01:59:34 am

you could have some equipment compatibility problems
IE i have some laptop chargers who wont refuses to start even with pseudo signal inverters, with pure sinewave they start etc …. some tv’s dont work too (they use ac-dc adapters)

In the last 12 years, I produced and sold about 5 thousand ‘adaptive square wave’ inverters (regulated by varying the duty cycle). Lately, it became clear that every device (made for 50Hz sinewave) whose power supply uses a series capacitor to limit the internal supply current, is damaged, sooner or later, by a square wave inverter. Summer is at the door and electric fans will be used soon. Most of these fans are controlled by electronic boards supplied internally by a series capacitor (no more by a small transformer). So, I decided to also produce low-cost sinewave inverters, at least for these fans.

I admit that with the limited available components around me I can’t do miracles by making such inverters also with high efficiency. Losses in the iron transformer whose available laminated core is also of the lowest possible grade! (Bs=1.05 Tesla, Br=0.7 Tesla and Hc=100 A/m) is much higher than of ferrite’s.

Re: Disadvantages of Using half-wave instead of full-wave in Pure Sinewave Inverter?
« Reply #22 on: March 19, 2024, 03:43:02 am »
Quote from: Zero999 on March 18, 2024, 03:48:17 pm

Why not put the filter before the transformer?

Only half of the power in the PWM waveform is delivered to the load. Half of it is blocked by the filter. There’s no point in the transformer passing the unnecessary harmonics and generating the associated losses. It’s better to filter them out first.

For instance, Zero999 (reply #4) reminded us of the most efficient topology to build a pure sinewave:
“The ones I’ve seen use an isolated DC:DC converter to a get DC of the peak voltage of the mains, followed by a MOSFET H-bridge and filter.”
I guess you know that in this case the DC:DC converter and the output filter have to be made on ferrite cores which I can’t get in quantities.
Should I forget producing pure sine wave inverters just because the new world allows me to use the lowest grade of laminated iron only (besides many other limitations)? On the other side, almost all engineers around the world (I hope) can get, in one way or another, whatever they may need in their designs.

I even chose the half wave drive instead of the full wave one to reduce even more the cost and labor.

Now, returning to your suggestion, how the filter could be done without using a ferrite choke? I hope you get the idea.

Re: Disadvantages of Using half-wave instead of full-wave in Pure Sinewave Inverter?
« Reply #24 on: March 19, 2024, 04:36:20 am »
Quote from: Kim Christensen on March 18, 2024, 03:39:27 pm

Quote from: KerimF on March 18, 2024, 09:44:10 am

I am somehow surprised that most members here didn’t hear yet how pure sine wave inverters can also use a laminated iron power transformer. I heard of such inverters in many other EE forums, since more than a decade ago.

Because there are much better ways of doing it. (I know you can’t do it the standard way due to lack of parts). You’re going to have large eddy current losses in the transformer which will cause it to heat up. This will reduce efficiency and require extra cooling of the transformer and/or require it’s power output to be derated. After Googling about others who have done the same as you’re proposing, they run into exactly this problem. The transformer overheats and requires extra cooling.

I agree with all you said.
About the extra dissipation of the transformer, this may be a problem if the inverter is loaded at its maximum power for a long time. Actually, it is not the case for most local consumers, if not all, who have to preserve their battery charge as long as possible.
Soon after year 2011, we lost the mains network completely. With time, mains electricity has been restored gradually. And now (after 12 years), we get the mains voltage (220V, 50Hz) 6 hours per day at best.

Finally, I make a homemade Full sinusoidal Inverter suing the EGS002 driver. It could easily deliver 500W or more at 220V 230V and 50Hz. Get the PCB files and make your own and also learn how it works.