One could say the primary use of inductors is for filtering. Take for example a buck regulator. We would agree the inductor is an integral part of buck regulation. It acts as a current filter. But we could remove the inductor and still achieve some sort of pwm regulation. The output would have higher ripple and switching noise. We would then state "it also may not be a bad idea to have a small inductor on the output".Filtering inductors in the output are not what I am talking about.
I would like to read this paper, but I cannot seem to download. Do you have this in pdf, or can you tell me how to download? When I snap on it it is too small to read.Here is a legible version of the Hahn paper.
Modified Sine-Wave Inverter Enhanced - Power Electronics
Modified Sine-Wave Inverter Enhanced - Power Read more about modifi, voltage, waveform, distortion, switching and inverter.www.yumpu.com
Sorry, it comes up on both my cell (Droid) and PC (Win).I would like to read this paper, but I cannot seem to download. Do you have this in pdf, or can you tell me how to download? When I snap on it it is too small to read.
On my computer, at the very bottom and right hand side there is a slider button. -_________________+ to zoom in.I would like to read this paper, but I cannot seem to download. Do you have this in pdf, or can you tell me how to download? When I snap on it it is too small to read.
For anyone curious, this tech has been around for a while now (1990s) and is REALLY STOUT. They have great surge/overload capabilities. They are called Multilevel Inverters and are showing prominence in MV grid tie solar applications. They have extremely low switching frequencies <1kHz and require no output filtering unlike their HF counterparts; this is a huge advantage as a large portion of inverter losses are switching losses. It appears in this specific case, the design was a 1:3:9 (ratios of voltage supplies) cascaded half bridge inverter using a NLM (nearest level modulation) scheme. This 1:3:9 ratio is referred to as asymmetrical and allows for much higher efficiency by increasing the number of levels (or steps) in the sine wave per cycle for a given amount of hardware (switching) components. In this case, this should be a 27 level inverter. The inverter would have an output THD (distortion) of around 1-2% (R load). They are very flexible and expandable. In my mind they are the best type of inverter for solar energy applications. I've been thinking of making something much like this. I'm in the coding stages right now, but I want to make mine programmable/customizable.Thought someone DIY minded might be interested.
https://www.hackster.io/news/new-of...ign-reaches-99-5-peak-efficiency-75eb22fad017
True. This definitely isn't practical for most people to make or even use.Well, they're great in MW applications, but for home applications we are talking 3 battery banks floating at dangerous (and changing) voltages so you need separate and floating SCC and PV panels for each bank...
That's not a problem on big installations where anybody who goes in knows all the dangers, but in a home it's not a good idea, at all.
Good luck with this project.For anyone curious, this tech has been around for a while now (1990s) and is REALLY STOUT. They have great surge/overload capabilities. They are called Multilevel Inverters and are showing prominence in MV grid tie solar applications. They have extremely low switching frequencies <1kHz and require no output filtering unlike their HF counterparts; this is a huge advantage as a large portion of inverter losses are switching losses. It appears in this specific case, the design was a 1:3:9 (ratios of voltage supplies) cascaded half bridge inverter using a NLM (nearest level modulation) scheme. This 1:3:9 ratio is referred to as asymmetrical and allows for much higher efficiency by increasing the number of levels (or steps) in the sine wave per cycle for a given amount of hardware (switching) components. In this case, this should be a 27 level inverter. The inverter would have an output THD (distortion) of around 1-2% (R load). They are very flexible and expandable. In my mind they are the best type of inverter for solar energy applications. I've been thinking of making something much like this. I'm in the coding stages right now, but I want to make mine programmable/customizable.
Essentially, yes.If I had to guess, it works like using a cascade air bank for filling scuba tanks? You have to switch on the next voltage above until it almost matches, and then the next one, and so on. Coming down you are just doing the opposite.
Hi, all.Essentially, yes.
Very good points.The reality is that for a domestic inverter the average power level is quite low, huge power peaks are fairly infrequent. But at night there will be almost no load at all.
No load idling current, and low load efficiency are far more important than full load efficiency.
With regard to the direct switched battery bank idea, its been done many times before, and its a pretty rough stepped waveform.
There are two inherent problems, the first one is charging the individual battery banks while its being switched around "live" in the inverter.
That requires multiple battery chargers, multiple banks of solar panels, and multiple MPPT controllers, all fully electrically isolated !
It all becomes vastly complex and impractical.
The second problem is the individual battery banks will not see identical loading. Some will be on for longer periods than others, and the current varies depending where each battery bank is being switched on and off in the sine wave. You need a random sequencing to ensure equal discharge of each battery bank over time. Not difficult, but it needs to be done.
The whole thing sounds conceptually simple, but its not when you look into it a bit more deeply.
If you want pure sine waves PWM is still the best approach at relatively low power and low voltage. A transformer PWM inverter will be more robust than a high voltage dc/dc PWM inverter, because peak power will always be limited by the dc/dc converter stage.
If you build a 1Kw dc to dc converter you cannot suddenly get it to deliver a 3Kw surge. But a 60Hz transformer can do that, without blowing up, provided you have enough parallel mosfets to drive the transformer.
The main limitation with PWM is that it does not scale up very well. Its fairly easy up to about 4Kw or 5Kw, but above that it gets really difficult to get large numbers of mosfets in parallel to switch together and load share. Its been done, but its not the sort of project a novice is likely to get going first attempt. However PWM is still the best choice up to around 5Kw.
Above that, the Warpverter has a great many advantages. It uses four square wave inverters driving four transformers. The secondaries are all connected in series so the voltages add. The secondary voltages go up in a 1 : 3 : 9 : 27 sequence. By switching the inverters on and off in the correct sequence, you can generate 40 voltage steps up, zero, and forty steps down. Its direct digital to analog conversion on steroids.
With 81 steps peak to peak, the measured harmonic distortion is typically 0.85% without any filtering. Third harmonic is the largest and its down to -40 db. General industry practice is that anything less than 2% THD is considered a pure sine wave. Around here the grid is more like 5% THD.
Anyhow, the big advantage is that all this square wave switching goes on at a relatively low switching frequency, and that is far less critical of layout. It also reduces switching losses and is theoretically more efficient. In practice the efficiency is pretty much identical to a good PWM inverter, about 92% to 94% at flat out full power. Zero load idling power is about the same too. A 5Kw Warpverter will have an idling power of around 20 to 30 watts, depending mostly on transformer design.
The biggest advantage of the Warpverter is it can very easily be scaled up in power. If you wanted 10Kw, 20Kw, 50Kw, it would be possible if you could get the transformers wound. With IGBTs, single devices rated to hundreds of amps are available, and they are far more rugged than mosfets and can withstand high fault currents, so can be protected with a circuit breaker.
But the really big IGBT power blocks are very slow, and unsuitable for high frequency PWM. But they will switch 60Hz just fine and withstand massive abuse.
The big down side with the Warpverter is the requirement for four transformers and four switching bridges. Its a lot of parts (and dollars) so its not worth doing for low power. But for 5Kw and above, its a lot easier to build and get going. There are now about fifteen warpverters in the 5Kw to 7.5Kw range now running successfully in various countries around the world, mostly in Australia, and several more being constructed including a three phase version.
So up to 5Kw your best bet is still a PWM transformer inverter, and that would probably suit most people.
Above that power, the Warpverter is well worth consideration.
The Warpverter has no commercial value, its just far too expensive to build, and just not cost competitive. But for home brewing, if you are prepared to wind your own transformers out of recycled junk, its a lot of work, but you can do it a lot cheaper than a manufacturer can, a manufacturer has to use all new copper and steel, you do not.
.... I want to qualify my statement on the carrier rates of Igbts. They are running super-audio ranges these days and are so much better than the last time I used them doing industrial inverters. Last commercial inverters I did was 20 years ago at ABB. I'm involved with specifying some 1MW inverters and Eaton is doing a nice job with PWW down in Raleigh,NC. So to limit PWM to 5kW is a little bit of an injustice.The reality is that for a domestic inverter the average power level is quite low, huge power peaks are fairly infrequent. But at night there will be almost no load at all.
No load idling current, and low load efficiency are far more important than full load efficiency.
With regard to the direct switched battery bank idea, its been done many times before, and its a pretty rough stepped waveform.
There are two inherent problems, the first one is charging the individual battery banks while its being switched around "live" in the inverter.
That requires multiple battery chargers, multiple banks of solar panels, and multiple MPPT controllers, all fully electrically isolated !
It all becomes vastly complex and impractical.
The second problem is the individual battery banks will not see identical loading. Some will be on for longer periods than others, and the current varies depending where each battery bank is being switched on and off in the sine wave. You need a random sequencing to ensure equal discharge of each battery bank over time. Not difficult, but it needs to be done.
The whole thing sounds conceptually simple, but its not when you look into it a bit more deeply.
If you want pure sine waves PWM is still the best approach at relatively low power and low voltage. A transformer PWM inverter will be more robust than a high voltage dc/dc PWM inverter, because peak power will always be limited by the dc/dc converter stage.
If you build a 1Kw dc to dc converter you cannot suddenly get it to deliver a 3Kw surge. But a 60Hz transformer can do that, without blowing up, provided you have enough parallel mosfets to drive the transformer.
The main limitation with PWM is that it does not scale up very well. Its fairly easy up to about 4Kw or 5Kw, but above that it gets really difficult to get large numbers of mosfets in parallel to switch together and load share. Its been done, but its not the sort of project a novice is likely to get going first attempt. However PWM is still the best choice up to around 5Kw.
Above that, the Warpverter has a great many advantages. It uses four square wave inverters driving four transformers. The secondaries are all connected in series so the voltages add. The secondary voltages go up in a 1 : 3 : 9 : 27 sequence. By switching the inverters on and off in the correct sequence, you can generate 40 voltage steps up, zero, and forty steps down. Its direct digital to analog conversion on steroids.
With 81 steps peak to peak, the measured harmonic distortion is typically 0.85% without any filtering. Third harmonic is the largest and its down to -40 db. General industry practice is that anything less than 2% THD is considered a pure sine wave. Around here the grid is more like 5% THD.
Anyhow, the big advantage is that all this square wave switching goes on at a relatively low switching frequency, and that is far less critical of layout. It also reduces switching losses and is theoretically more efficient. In practice the efficiency is pretty much identical to a good PWM inverter, about 92% to 94% at flat out full power. Zero load idling power is about the same too. A 5Kw Warpverter will have an idling power of around 20 to 30 watts, depending mostly on transformer design.
The biggest advantage of the Warpverter is it can very easily be scaled up in power. If you wanted 10Kw, 20Kw, 50Kw, it would be possible if you could get the transformers wound. With IGBTs, single devices rated to hundreds of amps are available, and they are far more rugged than mosfets and can withstand high fault currents, so can be protected with a circuit breaker.
But the really big IGBT power blocks are very slow, and unsuitable for high frequency PWM. But they will switch 60Hz just fine and withstand massive abuse.
The big down side with the Warpverter is the requirement for four transformers and four switching bridges. Its a lot of parts (and dollars) so its not worth doing for low power. But for 5Kw and above, its a lot easier to build and get going. There are now about fifteen warpverters in the 5Kw to 7.5Kw range now running successfully in various countries around the world, mostly in Australia, and several more being constructed including a three phase version.
So up to 5Kw your best bet is still a PWM transformer inverter, and that would probably suit most people.
Above that power, the Warpverter is well worth consideration.
The Warpverter has no commercial value, its just far too expensive to build, and just not cost competitive. But for home brewing, if you are prepared to wind your own transformers out of recycled junk, its a lot of work, but you can do it a lot cheaper than a manufacturer can, a manufacturer has to use all new copper and steel, you do not.