Disadvantages of Using half-wave instead of full-wave in Pure Sinewave Inverter? - Page 1
Forum section: electronics / projects

author: KerimF
author_rank: Frequent Contributor
timestamp: March 17, 2024, 03:46:18 pm
content: 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

author: PCB.Wiz
author_rank: Super Contributor
timestamp: March 17, 2024, 06:14:45 pm
content: 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.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 17, 2024, 06:43:53 pm
content: and you think you can re-invent the wheel ?the push pull is the best, if you dont use that, it work in a flyback fashion, if the push pull is well made you have zero cross over defectsyour single side mosfets seems more like an class A amplifier, it will heat more for nothingand pls give some schematics to show your idea

author: Ian.M
author_rank: Super Contributor
timestamp: March 17, 2024, 06:50:45 pm
content: Also, the end of the primary not currently driven must swing above the supply rail so you need MOSFETs with double the Vds rating.

author: Zero999
author_rank: Super Contributor
timestamp: March 17, 2024, 07:15:02 pm
content: I've not seen any which use a large laminated iron transformer. 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.

author: KerimF
author_rank: Frequent Contributor
timestamp: March 17, 2024, 08:59:44 pm
content: Quote from: PCB.Wiz on March 17, 2024, 06:14:45 pmGood 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.

author: KerimF
author_rank: Frequent Contributor
timestamp: March 17, 2024, 09:14:09 pm
content: Quote from: coromonadalix on March 17, 2024, 06:43:53 pmThe driver is simple. The MCU (actually an ATmega8) generates two anti-phase SPWM (sinewave PWM) at relatively high frequency (actually 15,625Hz).The N-MOSFET driver is a conventional one that uses 3 BJT transistors. The dead time between the two drivers is 1us.

author: KerimF
author_rank: Frequent Contributor
timestamp: March 17, 2024, 09:19:28 pm
content: Quote from: Ian.M on March 17, 2024, 06:50:45 pmAnother good remark.Fortunately, the new power MOSFETs have ratings (Vds and Id) suitable for power inverters if supplied by 12Vdc or 24Vdc.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 17, 2024, 09:32:36 pm
content: why dont you use already know smps parts, pwm ic's etc ...

author: KerimF
author_rank: Frequent Contributor
timestamp: March 17, 2024, 09:35:09 pm
content: Quote from: Zero999 on March 17, 2024, 07:15:02 pmYou don't surprise me because you refer to the most efficient topology which could be used for a pure sine wave inverter.In where I live, I can't design and produce a product which needs ferrite transformers because I can't get the types I may need in quantities.So, I had to use the available laminated iron cores if I like to add such inverters to my collection.I used to believe that having/doing something (not very good) is much better than having/doing nothingFor instance, the small leakage inductance of an iron transformer does the filtering if a relatively small capacitor (about 1uF, high AC voltage) is added at its output.

author: KerimF
author_rank: Frequent Contributor
timestamp: March 17, 2024, 09:53:34 pm
content: Quote from: coromonadalix on March 17, 2024, 09:32:36 pmThe answer is simple. They are not available, or their prices are relatively high, in my local market. (Unfortunately, after year 2011, ordering electronic components from abroad by ordinary people like me became out of question... my golden years are things of the past after the world... saved the people among whom I was born and live).On the other side, the price of the available ATmega8 is not high (perhaps because it is old and replaced by new ones). Also, the price of BJTs is good.And to gain my daily bread, my designed products have to compete similar ones that are imported from abroad (lately by the privileged rich families only) or made locally.

author: PCB.Wiz
author_rank: Super Contributor
timestamp: March 17, 2024, 10:34:35 pm
content: Quote from: KerimF on March 17, 2024, 08:59:44 pmBasically, yes. Each winding has the same peak current as a bridge, but half the time.So you have wasted space in the transformer andcan get less loss, by using a larger copper gauge, single winding in the same physical space.Quote from: KerimF on March 17, 2024, 08:59:44 pmIn 2024 that's immaterial, the days when low milliohms FET were hard to come by, are long gone.

author: KerimF
author_rank: Frequent Contributor
timestamp: March 17, 2024, 10:51:12 pm
content: Quote from: PCB.Wiz on March 17, 2024, 10:34:35 pmKnowing that the primary resistance (in a power inverter) is around a few mR, the low values of Ron (also around a few mR) are not negligible even if every set is formed by 4 N-MOSFET in parallel.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 18, 2024, 01:59:34 am
content: and you do know, i hopeusing 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 ityou could have some equipment compatibility problemsIE 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)while i salute your idea, you may face other challenges you dont even knowi can understand some material could not be available ... etc ... but its not a reason to play with safety, protection etc ..

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 18, 2024, 04:39:02 am
content: Quote from: KerimF on March 17, 2024, 03:46:18 pmQuote from: KerimF on March 17, 2024, 09:14:09 pmAre you attempting to drive a standard laminated iron power transformer at 15Khz instead of 50Hz or 60Hz?How much power (Watts @ 220Vac) will this inverter be outputting?

author: KerimF
author_rank: Frequent Contributor
timestamp: March 18, 2024, 08:52:37 am
content: Quote from: coromonadalix on March 18, 2024, 01:59:34 amYou 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 amIn 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.Quote from: coromonadalix on March 18, 2024, 01:59:34 amIn the initial tests, it became clear that the transformer acts as a current source when overloaded. In this case, the output cannot reach the sine flat top and starts to look like a triangular wave instead. Fortunately this wave doesn't damage the series capacitor supplies, as the fast edges of a square wave do.

author: KerimF
author_rank: Frequent Contributor
timestamp: March 18, 2024, 09:44:10 am
content: Quote from: Kim Christensen on March 18, 2024, 04:39:02 amI 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.Unfortunately, I also didn't believe first that this can be done, mainly without external filtering. But since my private business has slowed down lately, I had to re-think carefully about it. And I realized that the small leakage inductance of the iron transformer is good enough to acts as LPF for the sinewave PWM high frequency (modulated to produce 50Hz sinewave if filtered) by adding a small high voltage capacitor.Quote from: Kim Christensen on March 18, 2024, 04:39:02 amThe planned powers are 500W and 1000W on 12Vdc, 1000W and 2000W on 24Vdc.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 18, 2024, 10:04:57 am
content: well you do sound like a specialist with your written text tone who frankly did not need to come here i think .......

author: KerimF
author_rank: Frequent Contributor
timestamp: March 18, 2024, 10:59:25 am
content: Quote from: coromonadalix on March 18, 2024, 10:04:57 amGood remark.But I never believed that I could reach perfection in knowledge (unless it is about the spiritual realm) no matter how long I may live.So, in the material world, I see myself always in the learning stage. After all, I am not that smart. It took me about 10 years to believe that a conventional iron power transformer can be used practically in a pure sinewave inverter (though with lower efficiency).By the way, if I didn't come asking for possible new knowledge, I may have missed, and I simply presented what I did lately, I would look also as a bad guyThis happened to me when I started a thread (in the RF forum) about my simple reliable topology to demodulate DSB-SC signal which combines the two known ones, Costas Loop and Squaring Loop. It has no I-Q signals (as in Costas Loop) and has no selective filter at 2*fc (as in the Squaring Loop). Lately I called it 'Harmonic Loop' since its PLL locks to the second harmonic of the suppressed carrier frequency. I did it as an MS thesis at the American University of Beirut (AUB) in spring 1979. But I didn't submit it (as a document) because I had to return home early for financial reasons. But I took advantage of it in my short-range RF links (between home and workplace, 3 Km) for many years in the 80’s.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 18, 2024, 03:39:27 pm
content: Quote from: KerimF on March 18, 2024, 09:44:10 amBecause 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.

author: Zero999
author_rank: Super Contributor
timestamp: March 18, 2024, 03:48:17 pm
content: 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.

author: Xena E
author_rank: Frequent Contributor
timestamp: March 18, 2024, 04:41:42 pm
content: Quote from: KerimF on March 18, 2024, 08:52:37 amInteresting.(To be pedantic the number of samples per second is 312.5 BTW).This post really jumps out at one who designs this sort of thing for a living.Now if I were to use standard power line frequency iron, which even if it were a low frequency design, I wouldn'tI'd say that you could perhaps expect the most efficient frequency to transfer power at would be in the range of 500Hz to 2kHz.Any fancy synthesis of a 50Hz wave form would need to be filtered before hitting the primary of your power transformer.Also has anyone noted that 15,625Hz is the horizontal scan frequency of the 625 line analog television standard?Very Faringdon-esque O/PStill, I'll continue watching, I may learn something from the other honorable posters.Regards Xena.

author: KerimF
author_rank: Frequent Contributor
timestamp: March 19, 2024, 03:43:02 am
content: Quote from: Zero999 on March 18, 2024, 03:48:17 pmFor 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.

author: KerimF
author_rank: Frequent Contributor
timestamp: March 19, 2024, 04:16:43 am
content: Quote from: Xena E on March 18, 2024, 04:41:42 pmYour calculation is right. But, on my side, the calculation is:64 us (15,625 Hz) * 312 = 19968 us, that is 50.08 HzQuote from: KerimF on March 18, 2024, 08:52:37 amThe main reason of generating a pure sign wave 'at any efficiency' is that, where I live, consumers are more concerned for the price and reliability (a product that doesn't need to be repaired one a while). And as long the efficiency is not too bad, they don't complain.Quote from: KerimF on March 18, 2024, 08:52:37 amI think I have to repeat what I replied to some others.If I can get ferrite cores suitable for my designs, I simply build my new inverters as the one which Zero999 (reply #4) was referring to.Quote from: KerimF on March 18, 2024, 08:52:37 amIt is just a mere coincidence. The MCU crystal is 8 Mhz. The timer 1 prescaler is 1 (its clock = 0.125 us). The PWM register is 9 bit (512). Therefore, the PWM period is 64us (512*0.125) and its frequency is 15,625 Hz.

author: KerimF
author_rank: Frequent Contributor
timestamp: March 19, 2024, 04:36:20 am
content: Quote from: Kim Christensen on March 18, 2024, 03:39:27 pmI 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.

author: Zero999
author_rank: Super Contributor
timestamp: March 19, 2024, 08:25:46 am
content: Quote from: KerimF on March 19, 2024, 03:43:02 amBy using a lower frequency.Putting the filter before the transformer will not change how the filtering is done. The only difference is, the transformer doesn't have to pass the high frequency components of the signal, which will dramatically reduce the losses.

author: KerimF
author_rank: Frequent Contributor
timestamp: March 19, 2024, 02:31:14 pm
content: Quote from: Zero999 on March 19, 2024, 08:25:46 amThank you for your feedback.Just to be sure I understand to what you are referring as 'transformer's losses', a 500W transformer under test, for example, draws about 1 A DC from the 12V acid battery when in standby (no load). Do you refer to this kind of loss?As you know, the extra losses in a loaded transformer are in the wirings (copper), not in the core. At high frequencies, the fundamental 15625 Hz and its harmonics, the resistance of wires increases due to the skin effect.On the one hand, this increase helps the leakage inductance in filtering at the transformer's output that has a capacitor of a relatively small value.On the other hand, this also increases the dissipation of the copper.Unfortunately, since we get lately a couple of hours of electricity only in daylight and the same at night, it is not easy for me to do various tests and measurements anytime I like (I am fortunate for ordering a fluke 200MHz digital scope before year 2011 because this the only tool I have now).And on my sole desk of work, I have to also test and adjust the various assembled boards of what we produce already.Also, my acid battery (made locally, supposed to be 100 AH) is somehow old (its internal resistance is around 50mR). And the length of the thick wires (10 mm2) from the battery to the desk had to be around 3m (6m all). This relatively long distance is not a problem at low frequencies and loads. But to supply currents pulsed at 16 Khz, they act as thin wires instead (besides adding an inductive reactance).My real problem is that, lately, I am almost broken while I have to design new products good enough to compete similar ones in the local market. Yes, there are already pure sine wave inverters in the local market that uses iron transformers which are imported from India, China or made locally. But all of them use transformers, having 1 primary coil, instead of two coils in mine. So, I suppose that their efficiency will be comparable to mine since they also use a SPWM high frequency which is filtered solely by the power transformer to also produce a clean sinewave at 50 Hz.

author: Zero999
author_rank: Super Contributor
timestamp: March 19, 2024, 03:03:54 pm
content: Quote from: KerimF on March 19, 2024, 02:31:14 pmThere are other losses at higher frequencies, than the skin effect.Losses due to eddy currents and hysteresis also increase, which will also increase the standby power consumption.I'm not sure if you understood my point about harmonic power. A bi-polar 325V PWM waveform has an RMS voltage of 325V, whilst the demodulated 230V 50Hz waveform only has an RMS voltage of 230V. Putting this excess voltage though the transformer results in additional losses.Ferrite cores are used at higher frequencies because they have lower hysteresis and eddy losses, but they also aren't as magnetic so it's impractical to use them for large, mains frequency transformers and chokes.

author: coromonadalix
author_rank: Super Contributor
timestamp: March 19, 2024, 03:06:12 pm
content: so farLots of talk, nothing on paper .....

author: KerimF
author_rank: Frequent Contributor
timestamp: March 19, 2024, 03:15:14 pm
content: Quote from: coromonadalix on March 19, 2024, 03:06:12 pmIsn't it also the trend in the great speeches around the world?

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 19, 2024, 03:57:14 pm
content: This may be of interest to you since they briefly discuss using a low frequency transformer:https://www.ti.com/lit/an/sprabw0d/sprabw0d.pdfSome key points from the article:Quote

author: KerimF
author_rank: Frequent Contributor
timestamp: March 19, 2024, 04:07:23 pm
content: Quote from: Zero999 on March 19, 2024, 03:03:54 pmI hope you agree with me that, in standby mode (no load), the core losses predominate. So, if the current, supplied by the 12 V battery in this mode, is 1 A DC, we can deduce that the power, lost by the core, is 12 W.I am afraid that the core loss doesn't increase when the transformer is loaded. Only the coils losses increase.So, while in square wave inverters most of the wire section is used by the current (the skin effect works at the waveform edges only, 2 times in a cycle), in the sine wave inverters the effective section is smaller. This leads us to use thicker wires in order to reduce the extra power dissipation due to the skin effect.I can't give more detail till I will have the chance to make more measurements related to powers.I just know now that the standby power is not too high (though it can be lowered when necessary) and the output voltage is a sinewave, clean from ripple (after adding a relatively small bi-polar capacitance). For instance, without the small output capacitor, very high pulses could be seen on the scope (this time, I protected my 1000V/10MegaOhm probe with a 100K resistor in series because a few years ago I damaged one during a similar experiment).

author: KerimF
author_rank: Frequent Contributor
timestamp: March 19, 2024, 04:36:04 pm
content: Quote from: Kim Christensen on March 19, 2024, 03:57:14 pmThank you for providing the key points because I have no more the privilege to access any site related to Texas Instruments (though they were kind to send me many of their data and application books in the 70's).Let us see each point:"For a given input voltage, the voltage stress on the transistors is double in case of the push-pull topology than Half Bridge and Full Bridge configuration."This is not a problem now because...The typical 55V DS voltage is good for 12V battery.The typical 100V DS voltage is good for 24V battery."The center tapped primary in the case of the push-pull converter limits the operation for a higher VA rating for the same core size when compared to the Half Bridge and Full Bridge converter."This is true. In fact, this is the key price of using the simple low-cost topology of push-pull. A bigger transformer is needed for the same VA."To prevent flux walking in the DC-DC stage, the current in both the halves need to be sensed and the duty cycle needs to be corrected accordingly."I solved this by writing a well precise code (in assembly, as I used to do for 4 decades). And I had the chance to build two discrete MOSFET drivers (3 BJTs each) which work together in harmony very well (1us dead time) while they are driven by the two MCU pins (two anti-phase PWM).

author: Xena E
author_rank: Frequent Contributor
timestamp: March 19, 2024, 08:22:35 pm
content: @ KerimFI'm a little lost now, what I'd like to know is if this power transformer design you are considering is one that is readily available, or if you have built a prototype from materials that you have available?If you are trying to use a ready made power transformer 'in reverse' then you are likely to find that copper losses are greater than if a bespoke unit is designed.Core losses, as in magnetising current at no load can be largely tuned out, so their impact is largely null, though a starting point of only 12 Watts core loss in a 500W (?) Iron component is quite incredible.The form and order of the windings are also important so as to provide best coupling. You use the term leakage inductance as if it is a good thing, but in this type of project particularly it will have a negative impact on the regulation not to mention efficiency.You say that efficiency is of no concern provided that it's not 'too' bad, a sine wave inverter based on iron cored inductors working at 50Hz may not exceed a maximum of 60-70% in reality, possibly somewhat less. The suggestion you made of supplying a load of 1kW will create a great deal of heat...In the conjunction that you synthesised a 50 Hz sine wave from a much higher frequency it would have to be filtered with suitable low loss core materials, and high frequency techniques, not heavy iron.What I'm also unable to understand is that an inverter that is ready made can be imported into your country for sale but not the components to make a comparable product. Cost cannot be a consideration as the value of the laminations for a transformer core, and the cost of the extra copper required to create a component of high enough inductance for low frequency working, would be far in excess of the cost of suitable ferrite parts. This is the major reason these topologies have dominated.Please let us help you by including in your next post the details of the proposed project, it's circuit diagram, and the design of any bespoke components.Best regards,Xena.

author: KerimF
author_rank: Frequent Contributor
timestamp: March 20, 2024, 08:10:00 am
content: Quote from: Xena E on March 19, 2024, 08:22:35 pmYes, I built a prototype using the same iron laminations which I use for the square wave inverters.Quote from: Xena E on March 19, 2024, 08:22:35 pmI design everything in a new product (hardware and software) which is made for sale or for my personal need. But I also avoid re-inventing the wheels, mainly if the needed device is cost-effective, like the ready-made SMPS units (but, if necessary, I extend their voltage rating up to 400Vrms by adding an external circuit).Quote from: Xena E on March 19, 2024, 08:22:35 pmMe too, I wasn't expecting this. But this is what I got.Quote from: Xena E on March 19, 2024, 08:22:35 pmToday, I tested a well-coupled transformer made for 1000W/12V square wave inverter. Even its tiny leakage inductance was enough to filter the 16Khz PWM with 1uF at the transformer output.Let us calculate approximately the minimum value of such inductance (Lmin) to do the job.In an LC low pass filter, if w*L > 20/(w*C), the attenuation (Vout/Vin) is less than 0.13%.Lmin > 20/(w^2*C)wherew = 2*pi*F = 2*pi*15625 ~= 98175 rad/sw^2 ~= 9,638 rad/usThereforeLmin > 20/(w^2*C)Lmin > 20/(9,638*1uF)Lmin > 2mHThe leakage inductance seen at the secondary (L_lk, at the high voltage side) could be approximated (assuming Ls_lk ~= Lp_lk*N^2):L_lk = 2 * Ls*(1-K^2)Ls = Ls_lk/(1-K^2)/2whereK is the coupling coefficientLs is the secondary inductance measured while the primary is open,If K=0.9999 we get:Ls = 0.002/(1-0.9999^2)/2 ~= 5 HThe value 5H is comparable to actual transformer's inductance, seen at its high voltage side.Quote from: Xena E on March 19, 2024, 08:22:35 pmYou may be right.But, on the one hand, this depends on how much copper will be used.On the second hand, producing 1000 W or 2000 W inverters doesn't mean that the user will discharge his battery by a permanent 1000W or 2000W load. Actually, the user's average load will be around 350W/700W in this case. The 1000 W or the 2000 W inverter is made to supply the inrush current of certain appliances (like a refrigerator and a water pump).Quote from: Xena E on March 19, 2024, 08:22:35 pmIf it happens that the same transformer does the two required tasks, increasing the voltage and filtering the 50Hz carrier, why do we need looking for something else?Quote from: Xena E on March 19, 2024, 08:22:35 pmYou are right to be confused from where you live.After year 2011, the local high class only are allowed legitimately to import products from abroad (and behind the scenes, those who are related to, you know, also don't have to pay the taxes which are imposed on the ordinary citizens in case they are allowed to trade).On the other side, the prices of the imported raw materials (from the small electronic elements to copper and iron) became relatively very high lately due to political sanctions which have been increased exponentially since year 1980.In brief, after the world saved the people among whom I was born and live, there is no more a local medium class, only high and low classes only (after all, this is the case of all peoples saved by the world since year 2011).Quote from: Xena E on March 19, 2024, 08:22:35 pmNow, most of my work on this project is on draft papers (I mean not finalized). When I will draw its complete circuit/schematic on Kicad (a very old version, since I have also no privilege to download the newer releases) I will upload its Kicad files and its image for those who can't open them.Kerim

author: coromonadalix
author_rank: Super Contributor
timestamp: March 20, 2024, 09:14:45 am
content: ahhhhhhhhhhh still talk talk talk, nothing more pfffff ill leave this threadAfter 2 pages of threads, nothing good will be added, it's time to leavenothing practical, purely theorical etc ... like XenaE wrote

author: KerimF
author_rank: Frequent Contributor
timestamp: March 20, 2024, 01:19:49 pm
content: Quote from: coromonadalix on March 20, 2024, 09:14:45 amSorry that you didn’t find around here the answers to the questions in your mind.On my side, I asked, and I had the chance to hear many interesting answers and hints.After all, not in vain, it was said 'Ask, and it shall be given you'.But, in real life, 'asking' is much harder for most people to do than 'giving'. I even met and knew some people who find very hard for them to ask and to give as well. But there are also some others who don’t mind asking whenever in real need and are pleased to answer/give whenever they are asked and they have the means to do it.

author: Zero999
author_rank: Super Contributor
timestamp: March 20, 2024, 08:48:08 pm
content: Quote from: KerimF on March 19, 2024, 04:07:23 pmIt's true core losses don't increase when loaded. As you've said, the copper losses will be higher and much higher, given the high frequency content. It's still a silly idea to pass the high frequency content though the transformer. You need to use a much lower frequency. Note how motor inverters use much lower frequencies than this.I don't see the problem with getting hold of ferrite cores. You must be able to get hold of some old computer power supplies. I wouldn't worry about reusing ferrite cores, just don't do the same with capacitors.

author: KerimF
author_rank: Frequent Contributor
timestamp: March 20, 2024, 11:02:08 pm
content: Quote from: Zero999 on March 20, 2024, 08:48:08 pmI guess you agree with me that this extra heat will exist no matter if the transformer is driven by an H-bridge or push-pull.So, I wonder how this type of inverters (using H-bridge) were sold locally since many years without hearing any complain about it (from users in the least).But I still need to do my own studies and tests to have numerical results of the various dissipated powers (even approximately, since I don't have advanced tools and I have one hour daily to work on this, due to lack of electricity). And since all powers, useful and losses, are proportional to the transformer power, my next tests will be on a transformer of 100W only. I will let you know what I will get; for example, the plot of efficiency versus output power.Quote from: Zero999 on March 20, 2024, 08:48:08 pmYes, I have a few ones. But their number is good for hobby projects, not for production.Lately, I had the idea to try asking a local retailer (there were tens of retailers before year 2011, now there are just a few ones only) if it is possible for him to order for me a certain quantity of cores/bobbins with a reasonable price. Perhaps this will work.Meanwhile it is better that I keep working on the project I started with.

author: KerimF
author_rank: Frequent Contributor
timestamp: March 21, 2024, 08:27:37 am
content: So far. we (or I in the least) know from experiment that when the iron transformer is open (no load) a small capacitor (as 1uF) at its output shorts the PWM high frequencies (16Khz) while leaving the average of its pulses (50Hz).In other words, we have here a low pass filter. The problem is that we can think of 3 forms of LPF. They are RC, LC and RLC filters. We have:L_lk = the total leakage inductance seen at the secondary side.R_wire = the total effective resistance seen at the secondary side.Although R_wire is usually small at 50Hz (R_lo), it could become high at 16 Khz (R_hi) at which the effective depth of the wire is around 0.5mm (for copper).The impedance of 1 uF at 16 Khz is:Zc = 1/wC ~= 10 OhmsAnd we found earlier that we need only 2mH (Z_lk = 20*Zc = 2000 Ohms) as a leakage inductance to get a clean since wave with 1uF.The question is now:Is the value of R_hi comparable to reactance Z_lk? Or it is much lower or higher than Z_lk?In case L_lk is the dominant element in this LPF, it is better to use many thin wires of copper (D=0.5 mm for example) in parallel for the coil's windings. This will decrease both the voltage drop and the coils dissipation when the transformer is loaded. But there is here a trade-off because by using enameled thin wires instead of thicker ones the effective area of the core window will also decrease.To be continued... if you don't mind.

author: The Electrician
author_rank: Frequent Contributor
timestamp: May 08, 2024, 05:15:00 pm
content: Quote from: KerimF on March 18, 2024, 09:44:10 amHere is just one example of such an inverter. The smallest one has a 2000W rating with typical efficiency of 90% and idle power (which is mostly core loss) of 20W and typical 2% distortion.https://outbackpower.com/downloads/documents/inverter_chargers/m_series/m_series_mobile_marine_specsheet.pdf

author: Xena E
author_rank: Frequent Contributor
timestamp: May 08, 2024, 10:42:00 pm
content: Quote from: The Electrician on May 08, 2024, 05:15:00 pmThank you for posting the link.However, could you highlight where on those two pages the manufacturer states that a laminated iron cored transformer is used for the output device, and that it is fed from an HF PWM source to emulate a sinewave?Regards,Xena.

author: johansen
author_rank: Super Contributor
timestamp: May 08, 2024, 11:11:15 pm
content: Quote from: KerimF on March 21, 2024, 08:27:37 amWarpspeed, oz inverter, and a couple others have built very low idle loss, 5 to 15kva inverters. You should read their papers.You need an inductor between the h bridge and the transformer to reduce the capacitance of the transformer to reduce the hf switching losses.The leakage inductance of the transformer in series with the inductor also have two different resonant frequencies with the parasitic capacitance of the transformer and the output capacitor. This can cause some unexpected problems if you just throw parts together and see what they do.

author: mag_therm
author_rank: Frequent Contributor
timestamp: May 08, 2024, 11:58:35 pm
content: Comment without seeing Kerim's original circuit:The 50 Hz transformer will be acting at 16 kHz like the inductor in a boost converter, and the antiparallel diodes in the Mosfets could be conducting during part of the 50 Hz cycle the cycle.There will be 100's of volt of 16kHz on the primary, and as Kerim said, acceptably low ripple out with a small capacitor.The flux density swing due to the 16 kHz will be ~ 50/16000 of the 50 Hz swing ( If 50 Hz is 1.2T, 16 kHz would be 3.75 milliTesla for the same RMS Voltage) , so core losses will be dominantly from the 50Hz, as measured values indicate.The 16kHz component of AC in the transformer primary windings could be measured with a Rogowski, possibly causing neglible heating by skin effect.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 09, 2024, 04:30:32 am
content: Quote from: mag_therm on May 08, 2024, 11:58:35 pmMhmm, there's a historical lesson for young players in here!Back in the day, we used vacuum tubes for everything, including amplifying audio. For various reasons, speakers have always been in the low-impedance range (8 or 16 back then, 4 and 2 nowadays, the latter mainly for automotive for obvious(?) reasons), while vacuum tube power amplifiers have load impedances of some kohms: this necessitates a matching transformer.A typical tube amp, you can run at full rated power, day in day out, at any frequency in the passband, without anything overheating. That is, equal voltage at 20Hz or 20kHz will be applied to the output transformer. Losses generally decrease with frequency, because Bpk decreases faster than f^alpha rises, though it does depend on the exact Steinmetz parameters the core material possesses.Well, "typical" might be pushing it, amps of course spanned the gamut of quality and specsmanship (or lack thereof) as much as anything ever has; but suppose a platonic ideal of something rated for the usual range and all that, and at least cromulently designed, okay?We can model core loss with the modified Steinmetz formula: \$p = B^\alpha F^\beta\$, with typically \$\alpha\$ around 2 and \$\beta\$ around 1. An "ideal" lossy material (as in having eddy currents) has exactly these parameters, corresponding to a constant resistance "shorted turn".Real materials don't have constant eddy currents, but skin effect instead, the impedance of which generally increases as \$\sqrt{F}\$ -- a diffusion process. This might put \$\beta\$ near 0.5 or 1.5, or something inbetween when considering a wide curve-fitting range. Real materials are also nonlinear, hence the \$\alpha\$ differing.In any case, the lesson is, because B decreases so fast with F (at constant V), and the exponents tend to be what they are, losses tend not to go up with frequency, and indeed can go down.Putting it another way: we might run such an inductor at high frequency, but we need basically the whole thing we would need at a lower frequency, to meet similar core loss requirements. And such a big core necessitates just as much wire, so we have no win by running at high frequency. We prefer a lower Fsw simply because it has lower switching loss (and those losses can be fairly high such as due to leakage inductance, also inevitable from the copper requirement), since we can't take much size out of the magnetics -- or we at least need different materials (thinner than mains-frequency iron, or other alloys) to do so.Another point of historical reference: it was some DEC minicomputers, desktop PDPs I believe, had a rudimentary switching power supply -- the design was quite basic in terms of switching behavior, but it saved just enough efficiency to be worthwhile compared to a pure linear design -- which used a laminated-iron choke for bucking. I don't remember the particular ratings or values though. Probably something like 5V 10A, and Idunno, a couple mH? Might also be using finer laminations to help reduce size. Probably a lot of other products too, but this vintage computing reference happens to come to mind.I'm assuming materials other than mains-frequency electrical steel are strictly unavailable, so there's not much to gain by raising Fsw. In this application, it mainly pushes carrier + sidebands well enough above signal frequency that it's easily filtered (as said, with leakage and a capacitor, and hopefully/preferably an R+C to dampen that in turn).I am a bit curious (if not to the point of incredulity as others apparently have been) what really is available, or with what difficulty. If trade with India is available, but India makes (or imports themselves) ferrites, is that not a thing? Perhaps there are restrictions on materials, even as seemingly basic as ferrite, or equipment containing it. I guess it would be interesting tomake somefrom materials; all that's needed is Zn, Mn and Fe oxides of sufficient purity, a press, and an electric kiln. (Preferably they would be, well, the whole process: sintered, ball milled, pressed in molds with binder, and not to mention ground, tested, and process optimized to mimic common materials like N97 and etc. Perhaps processes this elaborate aren't feasible in the country for various reasons.)Whatever the case, most such issues are largely out of ones' control, and the engineer must make do with whatever is available. I might not know the particulars, but it's a very unstable region, generally, an unfortunate state of things for many (often not good) reasons, particularly by several large actors.Tim

author: Le_Bassiste
author_rank: Frequent Contributor
timestamp: May 09, 2024, 10:42:07 am
content: Quote from: KerimF on March 17, 2024, 03:46:18 pmfrom your wording, i read that you are planning to do a center-tapped push-pull design with some kind (PWM?, trapezoid?, modified squarewave?,...?) modulation. to the best of my knowledge, such center-tapped designs are used (in comparison to full bridge designs) to save cost on "expensive" power transistors and associated drive circuitry.Although these designs can fare pretty well in DC/DC converters, they do not live up to expectations in sinewave inverters with transformers that are designed for mains frequencies. some real-life reasons why i prefer a full-bridge design:1) sinewave inverters must be able to handle apparent power.2) the energy from braking a motor that "overturns" the inverter's output frequency can be fed back into the battery.3) output-side over-voltage events get clamped by the full-bridge's internal diodes and the battery.4) full bridge designs are pretty forgiving in overload conditions such as starting vacuums or compressors, switching on cold incandescent bulbs, and, seriously, most important of all, blowing mains fuses without going down. that is not to say that center-tapped designs can't do that, but they would require some serious effort in terms of overvoltage protection of the power transistors, while a full bridge can directly use the battery as "clamping device".

author: mag_therm
author_rank: Frequent Contributor
timestamp: May 09, 2024, 02:34:46 pm
content: Hi T3,Yes, Steinmetz gave a useful function still used today with some minor improvements to the exponent term.Years ago I was using QuickField (and still occasionally do in the hobby), and I suggested to the developers that Steinmetz should be added to the nonlinear magnetic data property entry.That was because I had to include Steinmetz contribution loss via the API which was cumbersome amd slowed the solver.That has been done and now there is a separate pane in the QF AC Magnetic Solver for Steinmetz, Eddy, plus a Trim loss.In 1980's I assisted Indian engineers with high frequency transformer and inductor designs using local materials.At that time India was producing high freq (thin) GOSS, and local ferrites were available. I just looked and amorphous steels are now being locally produced.And amorphous will take over from GOSS.I agree with Le_Bassiste that push pull is largely obsolete. I think it would have applications today in low power electronics up to 30 kW or so.The disadvantage of Vds doubling is partly overcome by Silicon carbide with Vds up around 2000V while seemingly holding the high frequency attributes.For example I am using Genesic SiC mosfets rated 1700V, at 14 MHz 200 V in a linear power amplifier.The push pull inverter can handle varying power factor if suitable antiparallel diodes are used. The following circuit is of a push pull 30 kHz phase controlled inverter model which I built and tested using SiC bjt and fred diodes. The diodes conduct as needed, with varying load Cos_phi, recharging back to the DC capacitor. Note the high voltage snubber (top left) which returns some energy to the DC capacitor too.I use this style snubber in Solar/Batt DC converters here, and it helps to keep the push pull topology viable.https://app.box.com/s/3k975qy99yox2xqtk58evxu5nb0mw85lhttps://app.box.com/s/5255lm6fu95y72xrhevcm8fl1b6j7375I would be interested to spin off this qucs model to Kerim's idea, but that is sizeable job and I am too busy with ham radio now.

author: KerimF
author_rank: Frequent Contributor
timestamp: May 09, 2024, 03:09:58 pm
content: Quote from: johansen on May 08, 2024, 11:11:15 pmFortunately, when I threw parts (hardware and software) together, I saw a pure sinewave (220V, 50Hz) on my scope's screen.

author: schmitt trigger
author_rank: Super Contributor
timestamp: May 09, 2024, 03:23:58 pm
content: Quote from: Zero999 on March 17, 2024, 07:15:02 pmBack in the 1980s, push-pull driven steel laminated inverter transformers were actually common. But technology has superseded them. However, the TS lives in a country where this technology is not available. Or prohibitively expensive.

author: Xena E
author_rank: Frequent Contributor
timestamp: May 09, 2024, 05:38:43 pm
content: Quote from: schmitt trigger on May 09, 2024, 03:23:58 pmCurious minds want to know how it is possible to drive a iron cored line frequency transformer with a PWM 15,625Hz square wave directly into the windings, and it does it with high efficiency and producing an averaged pure sine wave at nominal line frequency over its full range of loads, as an output.Perhaps not having read the original assertions, all those who say this is a thing have given caveats on the original.We've not yet seen the honorable members ingenious circuits schematic yet, or detailed specifications of the transformer.Regards.

author: The Electrician
author_rank: Frequent Contributor
timestamp: May 09, 2024, 06:22:19 pm
content: Quote from: Xena E on May 08, 2024, 10:42:00 pmThe manufacturer doesn't discuss inner workings on those two pages or anywhere else, but you can get an idea of what's inside from images in the service manual:https://outbackpower.com/downloads/documents/inverter_chargers/fx_vfx_series/fx_fxr_service_manual.pdf

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 09, 2024, 06:23:29 pm
content: Quote from: Xena E on May 09, 2024, 05:38:43 pmPerhaps curious minds can set up an experiment and demonstrate it themselves.Reporting back with real calculations and waveforms would provide valuable grounding to the discussion in this thread.Tim

author: Kim Christensen
author_rank: Super Contributor
timestamp: May 09, 2024, 06:29:40 pm
content: Quote from: The Electrician on May 09, 2024, 06:22:19 pmSee attached and ignore spelling:

author: mag_therm
author_rank: Frequent Contributor
timestamp: May 09, 2024, 08:06:08 pm
content: Quote from: Xena E on May 09, 2024, 05:38:43 pmTo the contrary, I have confidence that the pwm into conventional iron cored 50 Hz transformer is working well enough.I thought back today to what I was doing 50+years ago as junior engineer developing transistor inverters.In those days we could only do base frequency (2 pulses per cycle) as opposed to 320 pulses in present discussion.The Ott filter was costly, moreover while it was good for Scr inverters capacitive input Z was no good for BJT.The solution I worked on was to connect a LC parallel tank directly to secondary of the push pull transformer.The tank had a 400V AC oil filled capacitor. Tank Q was about 5 for fuse clearing.The switching edges on the secondary were directly applied to the capacitor.I recall the secret sauce was to wind the inverter transformer (EI) with sufficient extra leakage L. to eliminate the AC filter input choke.~ 4 dog bones provided the extra leakage from standard ~ 0.05pu to I suppose 0.12 pu.I remember the collector voltage waveform, which was a replica of the tank voltage, a pure sine.The transistor commutation rectangular pulses was superimposed. and they would get fatter and thinner doing volt regulation,and inherently move back and forward relative to the tank voltage with load power factor changes.However the secondary voltage was almost pure sine ( We used old HP distortion analysers)Given that project, and the diminishing 16kHz flux swing that I mentioned in #43,I am quite confident that an ordinary 50 Hz transformer will work with 16 kHz with today's Mosfets and their ap diodes.

author: KerimF
author_rank: Frequent Contributor
timestamp: May 09, 2024, 10:22:33 pm
content: I built what it was supposed to be a 500W pure sinewave inverter. It seemed to work fine (as it should be) for no load and light load.But by increasing the load gradually (up to 200W), the MOSFETs (2 x 4 STP75NF75) started to be really hot.This didn't surprise me because I used to miss always one or more points in every new designAs you know, the main dissipation of a switched MOSFET occurs at the rising and falling edges.In conventional square wave 50Hz (I use producing), even driving 4 MOSFET gates with 10 mA only used to work!So, I had the impression (which I know now it is wrong) that 300mA will also do the job (in case of 16KHz). For instance, I was able to build the +/- 300mA driver by using 3 BJTs (2*BC337 + 1*BC327). I did it this way to minimize the cost.So, I think now that I have to find an available 'low side' driver IC instead (rated 3A output, in the least).I will likely find costly driver ICs for H-bridge instead (but it is better than doing nothing).Meanwhile, I will try tomorrow to drive 1 MOSFET only (instead of 4) with 300mA. I expect the dissipation will be lowered (also the output attenuation). After all, switching a MOSFET at a rate of 16KHz with +/-75mA only, the rise and fall times will be relatively very long, and there was 4 MOSFETs. And the situation becomes even worse when they start to be hot because this increases their Rds. And this, in turn, increases their temperature (positive feedback?)

author: johansen
author_rank: Super Contributor
timestamp: May 09, 2024, 10:42:40 pm
content: Quote from: KerimF on May 09, 2024, 10:22:33 pmyou should be able to get a lot more than 300ma from those transistors, but if not, find something better. no need to spend money on a 3 amp capable gate driver, which is almost certainly going to be surface mount...

author: Xena E
author_rank: Frequent Contributor
timestamp: May 10, 2024, 01:56:08 am
content: Quote from: T3sl4co1l on May 09, 2024, 06:23:29 pmIf by that Tim, you mean the original poster providing circuit diagrams and details of his build that he was asking for 'help' with, which I have only a very vague impression of, and that impression of what was built would not work to the claimed efficiency then yes, he should.No one can form any opinion about this "project" without the details of what was done.Extraordinary claims require extraordinary proof, there's been no proof and the story keeps changing.I'll wait for Kerim F to post those details, and prepare to have my socks blown off. In the mean time stick to working with the idea that DC link bridge output inverters, are as good as things can get.Regards.X

author: Doctorandus_P
author_rank: Super Contributor
timestamp: May 10, 2024, 07:51:32 am
content: For commercial products, using two primary coils in the transformer is a big issue. Copper is more expensive and bulkier then FET's, so it both increases size, weight and cost.For a one-off or small series, this is not so much of an issue, while using simpler electronics and parts availability are more important. Especially when you live in a part of the world where electronic parts are hard to come by.

author: KerimF
author_rank: Frequent Contributor
timestamp: May 10, 2024, 10:15:53 am
content: Quote from: Doctorandus_P on May 10, 2024, 07:51:32 amVery true.Quote from: Doctorandus_P on May 10, 2024, 07:51:32 amIt happened that this is the situation on my side in these days. (Before March 2011, it was somehow easy to order anything from China, like power ferrite cores for efficient pure sinewave inverters, for example. And during those past golden years, I used to send just the schematics of my various designed controllers, drawn on Kicad for example. Then, the Chinese engineers drew their appropriate PCBs, by using their advanced tools, assembled the components on them and tested the finished boards before exporting them to me).

author: SeanB
author_rank: Super Contributor
timestamp: May 10, 2024, 01:09:17 pm
content: Easiest way to lower cost is to use CCA wire, which should be very easy to get, as it is a lot cheaper than copper, though working with it needs crimped connections all through, or some rather aggressive flux to clean it for soldering. Yes not copper, but if all Chinese products and motors now are made with it.......