Now, returning to your suggestion, how the filter could be done without using a ferrite choke? I hope you get the idea.
Now, returning to your suggestion, how the filter could be done without using a ferrite choke? I hope you get the idea.By 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.
Now, returning to your suggestion, how the filter could be done without using a ferrite choke? I hope you get the idea.By 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.
Thank 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.
so far
Lots of talk, nothing on paper .....
• 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.
• 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.
• 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'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.
This may be of interest to you since they briefly discuss using a low frequency transformer:
https://www.ti.com/lit/an/sprabw0d/sprabw0d.pdf
Some key points from the article:Quote• 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.
• 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.
• 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'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.
ahhhhhhhhhhh still talk talk talk, nothing more pfffff ill leave this thread
After 2 pages of threads, nothing good will be added, it's time to leave
nothing practical, purely theorical etc ... like XenaE wrote
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.
I 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).
It'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.
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 am somehow surprised that most members here didn't hear yet how pure sine wave inverters can also use a laminated iron power transformer.Here 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
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).
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.
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
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.
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.
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.Back 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.