All new parts gets very cost prohibitive very fast!

The listed IGBT's, big heat sinks, 450 volt capacitors, and transformer are all items that I have found on eBay for around 10 - 15% of the list prices according to your BOM sheet. (most were Buy It Now listed too!)

That will save you a pile of money right there!
Does the transformer have to be a toroid? If not a standard commercial isolation transformer will probably be way cheaper and far easier to find surplus or used.

If you dont mind recycling a box from something else or just getting some sheet metal and making one yourself you can get by cheap on the box too.

How much or how little a person spends is inversely proportional to how resourceful and creative they are.
Little resources or creativity spends big. Big resources and creativity spends little.

Do you have more schematics related to the control system?
And more detailed specs relating to the input voltages and operating conditions?

It may be possible to reverse engineer the inductors from what the system is intended to work with power input wise.

I assume they are working as part of a boost converter of some sorts.
Once the amps, volts and switching frequency are known then its not hard to calculate their values.

__________________
"Issue a general safety warning. Then look the other way and allow stupidity the chance to eliminate itself." -- tcmtech
"Those who can, Will. Those who can't, will achieve positions of power over those who can and then promptly stop them." -- tcmtech
"Your impossibility may just be my day to day routine." -- tcmtech

 

I tried to find off-the-shelf components so that I could duplicate the design in any quantity. Substitutions are allowed as long as the general topology is followed. The semiconductors specified are robust enough to handle any power up to 10kW. The magnetics will ultimately determine how much power can be produced. The largest transformer I could find is 1500 watts. I suppose that one could find standard isolation transformers that can handle more power. The best thing, of course, is to get rid of the transformer altogether and rely on the distribution transformer. However, from what I have read, a transformer in the inverter is required in North America but not in Europe. I am not sure this information is correct.

I have a general idea for the signal conditioning electronics but have not inputted the design into CAD. The microcontroller stuff is standard and can take many different forms.

The input voltage is 150 to 250 volts. I read somewhere that the practical limit for a boost converter is around 5 times the input voltage. Splitting the power path into 2 reduces the current requirements for each of the inductors and improves the ripple in the output.

 

@TCM
I started a new thread named "Multi KW Grid-Tie Inverter Build", hopefully we can learn how to do something this powerful and not blow ourselves up!!

In response to your question about 850VAC... You're into wind power right? Well, as you know the wind turbines can easily reach over 600 volts. If you look at ginlong's web site their 5KW generator can reach like 800-850 volts at 260 RPM! (open-voltage). Of course they're $3K. This WAS what i was desiging my system around (until i found out they were $3k!). I've since decided to go to ~3KW but the voltages are still mostly the same. My mains are 120/240 60Hz NA. I'm not 100% sure if Ginlong's generators are 3-phase or not, but i would think so. I do have one question about 3-phase. If we had a generator that was 3-phase, could we just use a 3-phase-to-240VAC converter to put voltage into our mains? Most of the wind turbines i've seen are 3-phase and i was just wondering if we could bypass the 3-phase - rectifier - inverter system with just the 3-phase converter, since you can buy them off the shelf. Also, i have a transformer out of a 1440 VA UPS, would that transformer be good enough for a modest inverter? It weighs about 10 lbs, but i can't find the specs anywhere. Anyways, i'm super interested in learning about the bigger inverter!! Thanks so much!!

 

I am not exactly sure about the needing an actual transformer on an American system or not.
I cant find anything in specific related to needing full isolation from the actual power source if the power source itself is not actually electrically connected to the earth ground or if it has full electrical shielding to prevent human contact with any live circuits or wiring in the NEC code book though.

I would think your set up could work with a direct line connection but the main transformer would be replaced with a set of inductors and PF capacitors to help clean up the wave form going back onto the line.

I dont see any reason why a standard isolation or step up or down transformer would not work. I use them on all of my experimental GTI's and have never found a reason not to use them. Their cheap and easy to find. Toroids do have a typically smaller size per VA and slightly better efficiency but I dont think the overall gain can justify the added cost.
I personally use isolation transformers because of the voltage differences on my systems and just to keep the power sources isolated from the main line.
My present wind generator uses a negative earth ground for added static protection.
Fiber glass blades can generate static under some conditions I have been told.

__________________
"Issue a general safety warning. Then look the other way and allow stupidity the chance to eliminate itself." -- tcmtech
"Those who can, Will. Those who can't, will achieve positions of power over those who can and then promptly stop them." -- tcmtech
"Your impossibility may just be my day to day routine." -- tcmtech

 

If it turned out that isolation between the DC and AC was required, it makes a lot of sense to do it at the boost converter (high frequency) rather than at the line attachment (lots more iron and copper).

Of course that would make the final stage a lot harder to troubleshoot, since they would always be hot with respect to your test equipment.

__________________
de KI6RWX

 

Here is what I have so far on the Signal Conditioning circuits.

Attached Files

Post3.zip (197.3 KB, 318 views)

 

I see on the switching device drivers your using the PowerEx M57161L-01 devices.
I am just curious as to if thats due to a particular system requirement or not.

I have used the International Rectifier IRF2110 half bridge gate drive IC's for some time now with no problems. They are logic level input compatible and are very cheap yet very durable. Plus with 500 volt isolation on the high side they work well with all most every common voltage.

I'm Just thinking about production cost savings!

So far it looks like a good solid concept! It will likely beat my best units for overall efficiency too!

__________________
"Issue a general safety warning. Then look the other way and allow stupidity the chance to eliminate itself." -- tcmtech
"Those who can, Will. Those who can't, will achieve positions of power over those who can and then promptly stop them." -- tcmtech
"Your impossibility may just be my day to day routine." -- tcmtech

 

There are no particular system requirements. It's just another way of doing things. I got the idea from the PowerEx web site. They make pre-assembled driver boards with isolated +15V and -5V supplies. Then they mount them right onto the IGBT module. I am wondering if that is to minimize any wire inductance from driver to IGBT gate.

What I like about the PowerEx driver is that the components are mounted on a hybrid module. I don't have to mess around with a bunch of components. There are 6 drivers involved. That would be a lot of components to assemble individually onto the board.

Like I said, there are many different ways to achieve the same thing. I started off with probably the most expensive way and will, over time, try and cost reduce the design. I'll check out the circuit you suggested.

 

Here is Rev. B of the Signal Conditioning circuits. Keep in mind that I haven't checked the design and probably will need to tweak a few components.

One interesting thought came to me when working on the Current Transformer Rectifier circuit. Taking the peak value of the AC current won't tell me the direction that the power is flowing. What if my PWM is producing less voltage than the mains. Won't the current flow from the grid to the inverter? My current measurement circuit will still read positive. Is there some directional circuit that can be used to ensure power is flowing from the inverter to the grid?

Every time I post something on this thread, the chatter seems to stop. Please give me some feedback. Is this stuff usefull?

Attached Files

Post4.zip (376.4 KB, 252 views)

 

Hehehe...
I think the chatter stops because your at the front of the knowledge train. When you look for guidance to follow and everyone else is silent it just may be because your at the font of the line!
The lead engine on the train gets the best view but also has to hope like hell that the track he is on is clear. If not, everyone behind him that is blindly following will do their best to run his ass over when he does make a mistake! The leaders don't have any one to follow!
Kinda sucks when it becomes clear that you might just be looked at as the new leader. Wait until the nutters go after you for trivial and non relevant stuff! You will appreciate the silence then!

I will take a look when I can but now that the weather is better I have to work much much more. When I jumped in on this thread it was during my slow season and I had days of time to waste and just needed a way to keep myself occupied and still fell some what useful.

Now I am limited on the time I have for doing on line stuff.
I will think about what you posted and try to get back when I can.

But yea it would be nice if more were here to share ideas and what not!
But so far you have my full support and I do have a question or two as well!

__________________
"Issue a general safety warning. Then look the other way and allow stupidity the chance to eliminate itself." -- tcmtech
"Those who can, Will. Those who can't, will achieve positions of power over those who can and then promptly stop them." -- tcmtech
"Your impossibility may just be my day to day routine." -- tcmtech

 

Val, you do nice work, neat and professional, but... (maybe it's just me?) it seems really overcomplicated.

What about simplifiying to the very minimal hardware requirements?

1. Low voltage DC to HV 1/2 sine SMPS (generate the HV half sine in real time by PWM at the low volts DC side)

2. Four HV IGBT to commutate the half sine to a full sine and connect it to mains

3. one optocoupler to measure mains voltage (and phase), maybe you could use 2

4. one optocoupler to measure dc current drawn from the 1/2 sine circuit.

That reduces the whole circuit to 1 microcontroller or 494, couple of LV FETs, 4 IGBT, few diodes etc.

Re your question on measuring current, the mains can't supply current to the HV section of the circuit because its a high voltage dc supply which is a cap fed by diodes. It is only possible for the rmains to draw current, which can be measured on a simple shunt resistor on the HV dc ground rail.

My personal preference (I posted in another thread) would be to make the circuit "output current regulated", so the PWM controller feeds out current to the mains based on the instantaneous mains voltage, so if the mains waveform is 50v it feeds in 0.5A to the mains, if mains is 120v it feeds in 1.2A and so on.

This mimics a resistive load (but in reverse) so it naturally follows the mains waveform itself, so the PWM controller does not need to measure it's own output voltage or generate a sine voltage output etc (this will be automatic) which really simplifies things.

It also gives some easy protection for not feeding any current to the mains if the mains goes down, and can control phasing, so it kills a few birds with one stone.

 

Go to my Tutorial on Grid Tied or Grid Connected Inverters. After reading some of the messages on this subject in this Forum, I feel compelled to share this information.

Grid Connected Inverter

One must understand the powerplay at work with this technology. Many forces are at work to resist or halt the development and commercial availability of this technology, both by Commercial concerns and by Governments who are under the influence of Lobbyists answering to special interests like Energy Fuels Companies and Power Utilities especially to resist inverter Net-Grid-Connection. Also, the manufacturing companies of low power Grid Tied Inverters, those below 500 Watts, have been swallowed up by International Corporations and subsequently closed down. The low power Grid Tied Inverter is available no more.

There is the additional issue of the Intelligent or Smart-Grid which will eleiminate the "Islanding" problem, and the safety hazard of live grids after disconnect.

 

Thanks for commenting.

Yes, my design looks complicated. I'm all for simplicity. However, this is as simple as I know how to make it. My goal was to maintain complete isolation both from the mains and also from the PV array. I've been involved with many designs that ultimately had to obtain VDE, UL, CSA approval. It's not easy. The schematic design is not the only thing they look at. The physical packaging is also very important. They will look at such things as... if a wire connected to the high voltage circuits got loose, could it come in contact with the low voltage circuits that humans could access.

I can't quite make out the circuit topology you are advocating. Perhaps it would help if you would illustrate with a sketch.

The design I am proposing is not new. I think you will find that most commercial units use this circuit topology. Xantrex publishes a partial schematic of their circuit topology in their manuals of their high power 3-phase inverters.

On the issue of back feeding from the mains to the inverter... the AC from the mains sees a resistor in series with a capacitor. The capacitor gets charged and discharged each cycle. Since there is resistance in the circuit from the wiring, some power is dissipated due to this current flowing in the resistance and not returned to the mains.

The PWM signal on the H-bridge induces a voltage on the filter components so that the voltage of the AC waveform is higher than the voltage from the mains. Power will then flow from the inverter to the grid. I still haven't been able to determine what components to use for the filter circuit.

I have thought about the question of islanding (not feeding power to the grid when there is a power outage). I hope to achieve shutdown in two ways. My power supply is getting power from the mains. If it goes down, so will my power supply no matter how much my inverter tries to keep the power alive. Secondly, the micro will keep monitoring the zero-crossing signal and shut everything down if it finds one pulse missing. I don't know if this will do the trick or whether some more sophisticated method needs to be employed.

 

Jsalsburg -nice web page! Typical small grid tie inverter. Are you saying that nobody is selling commercial small grid tie units any more??

Val Gretchev -on back feeding mains current into the inverter, this should not happen for reasons we both said. Surely you don't need to measure the few mW of the charge/discharge of your filter cap??

In the interest of absolute minimalisation (which always amuses me) I have just put up a minimalist micro grid tie topology design up on my web page you can see it here;
Micro Grid-Tie; solar panel tied to the mains grid

I look forward to comments.

 

Hi all... I have been reading all 10 pages BUT Im still missing the point..maybe?!

I have some set of questions hoping to get answered:

but this one first...

#1 what is the difference between an switching inverter (DC-DC then fed to H-bridge,chopped square wave to approximate sine) and a Grid Tie inverter?

I have here in the works, an inverter(12Vdc battery as input), using Hbridge using IRF840 mosfets..im using a PIC to do complementary "pulsed" modified sine SQUARE WAVE..... but still building on my DC-DC(maybe ill use a 494 or 3525 for this/push-pull)

goal: 220Vac @60Hz

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