50Hz 230 volt power in a 60Hz world

[tallgirl]

I did tell you that I can't comment on code requirements

Well, I sort of need something that's Code compliant ...

So what do you think Variable Frequency Drive actually means?

VFDs do NOT create sine waves.

HTH.

Yes, to feed a motor. But run from output to input does not depend on motor characteristics.

Correct. However, if the output side of a VFD doesn't function pretty much like the electric grid, the inverters won't sync and stay synced. In particular, most UL1741 compliant inverters will try to change the behavior of the "grid" to make sure it really is the grid. If that VFD allows the inverter to change the voltage or frequency (which it likely will) of the "grid" (the VFD output), the inverter wil decide it is islanded and disconnect.

HVDC stuffs oodles of the stuff back into the grid. How bad is that??

And yes, not only will work. It does.

Yes, because they are DESIGNED for the purpose.

 

[tallgirl]

Your original post lead us to believe you wanted to recoup wasted energy, and there has been many suggestions doing that, but apparently none of them works for you, sounds like the air in Texas will stay a little warmer!

That's probably about right. Sending it back where it came from is the best thing to do with it and the only compliant solutions I know how to do were rejected last summer.

 

[hurk27]

I think you have a few misconceptions of what a VFD drive is capable of, the PWM is for control of voltage and current not frequency, the motor speed is controlled by frequency and yes VFD's do change the frequency to do this, if you were to just change the duration of the current (which PWM does) you are only changing the RMS or average time the motor sees the current thus changing the voltage and current it also sees but if the frequency is not changed the motor will still try to meet the RPM's based upon the frequency it see's, some VFDs are infact design to dump extra energy back into the grid, and yes in most cases it is a full signwave, and it is synced with the grids frequency other wise things would go boom, so yes a VFD could be designed to take DC and change it to any frequency called for.

I am by no means an expert on VFDs but Besoeker does this for a living as he designs and builds custom VFD's that are much bigger then we tend to use so in my mind he is and expert on them .


But I do know you can use a VFD to run a 3-phase motor from a single phase service and I have heard of one being use to take dirty power and output clean 60hz power for a PLC system once.

But the question would you try to use a VFD for this purpose? I think the answer would be no as there would be much lower cost systems out there that are designed to do what you wish that would be much better at it, all it would take is to send a manufacture the specs you need of the device to accomplish and I'm sure they would design the electronics to fit your needs, so the VFD idea is kind of mute.

When we needed inverters for our transfer cars not many companies were making them that would allow an input voltage range of 100 to 300 volts DC but our engineer sent a manufacture the specs we needed and they made it

 

[kwired]

I think you have a few misconceptions of what a VFD drive is capable of, the PWM is for control of voltage and current not frequency, the motor speed is controlled by frequency and yes VFD's do change the frequency to do this, if you were to just change the duration of the current (which PWM does) you are only changing the RMS or average time the motor sees the current thus changing the voltage and current it also sees but if the frequency is not changed the motor will still try to meet the RPM's based upon the frequency it see's, some VFDs are infact design to dump extra energy back into the grid, and yes in most cases it is a full signwave, and it is synced with the grids frequency other wise things would go boom, so yes a VFD could be designed to take DC and change it to any frequency called for.

I am by no means an expert on VFDs but Besoeker does this for a living as he designs and builds custom VFD's that are much bigger then we tend to use so in my mind he is and expert on them .


But I do know you can use a VFD to run a 3-phase motor from a single phase service and I have heard of one being use to take dirty power and output clean 60hz power for a PLC system once.

But the question would you try to use a VFD for this purpose? I think the answer would be no as there would be much lower cost systems out there that are designed to do what you wish that would be much better at it, all it would take is to send a manufacture the specs you need of the device to accomplish and I'm sure they would design the electronics to fit your needs, so the VFD idea is kind of mute.

When we needed inverters for our transfer cars not many companies were making them that would allow an input voltage range of 100 to 300 volts DC but our engineer sent a manufacture the specs we needed and they made it

I don't know a lot of the finer details of the operation of these either, but would guess some of the base components are the same thing or at least very similar and would just have more details involving controlling those components to accomplish what the OP is looking for.

 

[hurk27]

In particular, most UL1741 compliant inverters will try to change the behavior of the "grid" to make sure it really is the grid. If that VFD allows the inverter to change the voltage or frequency (which it likely will) of the "grid" (the VFD output), the inverter Will decide it is islanded and disconnect.

A little point of view, we don't change the frequency of the power grid nor can we unless we have a much larger source then all the generator stations that supply the grid, this is why we sync with the grid.

Like a motor, a generator outputs a frequency based upon its RPM's and poles it has, a motor operates with a lagging frequency and a generator operates with a leading frequency if it is putting power into the grid, so any time you sync with the grid the amount of lead over the grid frequency will determine how much power you put into the grid just like a motor lagging the the grid will pull more and more power from the grid as it slips or lags more and more.

I don't have the figures around me but any inverter that is in sync with the grid has to maintain a slight lead in frequency or it will not be putting power into the grid, this is in micro hertz difference of leading, if the inverter was lagging the grid it would be pulling power from the grid just like a motor, the amount of leading is what determines how much power is put into the grid, to much lead and the inverter could be over loaded.

The grids frequency is to rigged for us to change its value, while it is true it does change every so slightly it is very robust that anything we do won't change it, all we can do is intervene and take the grids voltage and frequency and and through electronics change it to what we need, but the grids frequency will still be the same.

 

[tallgirl]

Wayne,

There's a word of difference between what a VFD is designed to do and what must be done to interconnect an inverter to the grid.

The most challenging part of connecting these sorts of inverters to anything that's not the electric grid is that they are required to try and figure out if they aren't connected to the grid. If they aren't, or they can't be fooled well enough, they MUST disconnect.

Sorry -- our posts crossed.

Yes, the inverter has to try to push power to the grid.

If you recall, the suggestion was to use a four-quadrant VFD and have it absorb the power from the inverters, then change the frequency of its input from 50Hz to an output of 60Hz.

What's going to happen on the inverter side is that it will try to change it's output, and then it's going to look and see if it was able to change the grid. As you correctly noted, the grid is too big for a small inverter to move, but is the VFD designed to behalf just like the electric grid, or is it designed to control an electric motor?

 

[hurk27]

I don't know a lot of the finer details of the operation of these either, but would guess some of the base components are the same thing or at least very similar and would just have more details involving controlling those components to accomplish what the OP is looking for.

You could look at it that way but a VFD is more designed to control a motor then it would be a power supply, it has many components that control current frequency and voltage and also timers to ramp up the speed of a motor as well as decelerate the motor, this would not be useful in Tallgirls application as most of this would not apply to her need, yes a VFD is just like a PV system in that is has a DC source to charge batteries, Caps in the case of the VFD, and a inverter that takes the DC and changes it back to an AC current, you could also make the same comparison with a dual conversion UPS system, but again it would be better to find a manufacture who is more knowledgeable in the PV field to design the correct system that she needs,

 

[kwired]

There's a word of difference between what a VFD is designed to do and what must be done to interconnect an inverter to the grid.

True, but that mostly involves differences in control of similar core components doesn't it?

It is still going to be semiconductor devices that take a DC current source and pulse current in a way to simulate an AC waveform. Adding additional components to make a more pure sine wave may be desired in some cases, it just is not necessary to make a perfect sine wave to drive an AC motor, so why add additional components to do so? Adding additional components to sync with the utility is also not something needed with a motor drive.

When I first brought the VFD into the conversation here Wayne asked: "I wonder if any inverter manufacture could design an inverter that could be switched between 50hz and 60hz and the output voltage readjusted for different voltages, kind of a one size fits all inverter?"

I simply replied with why not? We already do the same thing with VFD's. When we change the output frequency of the drive from 60 to 50 Hz, we usually change output voltage proportionally as well.

If we can use a semiconductor based device to do this with a motor why not for your application also? It may need some tweaking but aren't all the basic necessities already there?

 

[hurk27]

Wayne,

There's a word of difference between what a VFD is designed to do and what must be done to interconnect an inverter to the grid.

The most challenging part of connecting these sorts of inverters to anything that's not the electric grid is that they are required to try and figure out if they aren't connected to the grid. If they aren't, or they can't be fooled well enough, they MUST disconnect.

Sorry -- our posts crossed.

Yes, the inverter has to try to push power to the grid.

If you recall, the suggestion was to use a four-quadrant VFD and have it absorb the power from the inverters, then change the frequency of its input from 50Hz to an output of 60Hz.

What's going to happen on the inverter side is that it will try to change it's output, and then it's going to look and see if it was able to change the grid. As you correctly noted, the grid is too big for a small inverter to move, but is the VFD designed to behalf just like the electric grid, or is it designed to control an electric motor?

That one is one Besoeker would have to answer as I always thought a VFD uses the grid as the reference frequency and doesn't have an oscillator that would provide the inverter with a reference, which is where the inverter searches for an oscillation and if it isn't there when it test for it it knows its off grid.

If the VFD mentioned is not connected to a power supply then there is no 50hz reference frequency at that point and the inverter would have to have a switch to run it off grid all the time so it won't hunt for the reference frequency at its output?

Which is why a inverter that can sync up to the utility would not be usable in feeding another inverter, it would be better to obtain and inverter that has the dual functions such as I mentioned before one that has a switch that would change it from a 50hz to a 60hz at the flip of a switch, but this wouldn't make any sense to the application you are after as you are only needing a 50hz end product for you customer and the need for the 60hz is only to find a useful load for the inverter that can be put to work to add savings to your company's cost while it is under test.

So unless you can find a load to use like some computers, TV's or other loads that will like the 50hz it maybe just cost effective to dump it into a heater element put in your water heater, or furnace, keep in mind that many electronics today are design to be used world wide so many will operate just fine from 100 to 240 volts with no problem and at 50 or 60hz, but make sure you check the device before trying it,

 

[Besoeker]

Well, I sort of need something that's Code compliant ...

VFDs do NOT create sine waves.

Those with active front end where the juice is stuffed back into the grid do. Such beasts do exist and are in use throughout the world thus, one might reasonably conclude, are code compliant. If it isn't your area of expertise that's fine.

Correct. However, if the output side of a VFD doesn't function pretty much like the electric grid, the inverters won't sync and stay synced.

It isn't the output configuration that matters.

Yes, because they are DESIGNED for the purpose.

For the most part they are mains commutated inverters. Being connected to an AC sine wave grid provides the mains commutation.
The technology used is used for the majority is thyristor (SCR) and works in the same way as a regenerative DC variable speed drive. The regenerative circuit can take any level of DC from zero up to about 1.15 times the AC supply voltage and stick it back into the grid. Easy peasy. Rectify your 50Hz and you then have a simple way to use it rather than losing it.

 

[Besoeker]

That one is one Besoeker would have to answer as I always thought a VFD uses the grid as the reference frequency ,

Mains commutated inverters do. As a rule, variable frequency inverters don't. The low impedance DC link effectively decouples input and output frequencies - regardless of direction of power flow.

 

[tallgirl]

Those with active front end where the juice is stuffed back into the grid do. Such beasts do exist and are in use throughout the world thus, one might reasonably conclude, are code compliant. If it isn't your area of expertise that's fine.

Understood. But so far you're convincing me that PV isn't your area of expertise.

It isn't the output configuration that matters.

For the most part they are mains commutated inverters. Being connected to an AC sine wave grid provides the mains commutation.
The technology used is used for the majority is thyristor (SCR) and works in the same way as a regenerative DC variable speed drive. The regenerative circuit can take any level of DC from zero up to about 1.15 times the AC supply voltage and stick it back into the grid. Easy peasy. Rectify your 50Hz and you then have a simple way to use it rather than losing it.

Both "ends" -- input and output -- of this hypothetical VFD must perform a very specific role: the 60Hz end has to be UL 1741 / IEEE 1547 and the 50Hz end has to behave enough like an electric grid that it can fool a UL 1741 compliant device into believing it is attached to a 50Hz, 230 volt grid.

Think of it as a bridge -- if the 50Hz array needs additional power (which it does at night, during cloud passage, in the middle of a rainstorm, etc.) power must flow from the 60Hz supply (grid) to the 50Hz load (development array). Once the sun comes out, or the clouds go away, power has to flow from the 50Hz side to the 60Hz side, and it has to do it in a way that the 50Hz inverters can't tell they aren't connected to a 50Hz grid.

 

[Besoeker]

Understood. But so far you're convincing me that PV isn't your area of expertise.

It doesn't matter where the DC comes from.

Both "ends" -- input and output -- of this hypothetical VFD must perform a very specific role: the 60Hz end has to be UL 1741 / IEEE 1547 and the 50Hz end has to behave enough like an electric grid that it can fool a UL 1741 compliant device into believing it is attached to a 50Hz, 230 volt grid.

The 50Hz is what you are generating and want to load if I understand you correctly.
That would go where the motor on a VFD would be connected or rectified and put into the DC side of a regenerative DC drive. The inverter stage, whether an active front end or a mains-commutated unit then puts the power into your fixed frequency 60Hz grid.
There is nothing ground breaking about this sort of power circuit.

 

[tallgirl]

It doesn't matter where the DC comes from.

Why do you keep talking about DC power that doesn't exist?

 

[hurk27]

Why do you keep talking about DC power that doesn't exist?

While not trying to answer for Besoeker, most who have a simple understanding of the theory's of how PV systems work understand that the PV cells produce DC to which the inverters change to AC whether it be 50hz or 60hz the DC from the PV cells can be used for not only supplying the DC voltage to the inverters but also batteries for back up power if so designed, if the grid is used as the back up as systems have more or less gone that route then the DC is left at the point to the first inverter which is now common to be up on the cell array with nothing but the AC brought down to the control system, I believe the latter is what your are testing and this is why you are trying to find a use for the AC (50hz) as the DC is left at the array, if the DC was brought down from the cell array then it would be just a matter of using a 60hz grid tie inverter to put the extra power back into the grid or using the 60hz for local loads, but that wouldn't solve the problem of testing the whole system including the 50hz grid tie inverter as it would only test the cell array.

This is just from what I could gather from the post so it might not be correct?

I had to do some thinking and read between the lines sort of speak myself as the setup was not described very clear so forgive me if I have it wrong

Sometimes I can have great comprehension and other times I just get things muddled up

 

[hurk27]

I should add as I have posted before a VFD takes the AC changes it to DC which feeds the inverter section that changes it back to AC, the input to the VFD can be designed for your 50hz AC because it is nothing but a AC to DC conversion like a battery charger sort of speak, then this DC feeds an inverter that would create the 60hz you are looking for.

A simpler method would be to just let the 50hz AC from your inverter supply a DC power supply that would in turn feed a 60hz grid tie inverter which would be more common to you, this way you would be loading both the array and the 50hz inverter and the rest will be nothing more then a load that would have some usefulness in putting some power back into the grid instead of going to waste, yes there would be some loss so the power put back into the grid would be less then it would if the 50hz could be put into the grid, but at the same time it would provide a load that could be tested and recorded at the 50hz output of the inverter your are testing that would provide useful info.

The only thing you wouldn't be able to test is the 50hz inverters abilities to detect the grid as it would have to be run as an off grid inverter using the above load, or any load, which you have that problem now with just using a resistor/heater bank as a load.

Simulating a 50hz grid frequency at the output of the inverter is not an easy task as this is an input to the output of the inverter that the inverter looks for, and the load has to supply this 50hz signwave which most loads would not supply, and there lies your problem as you would have to have another 50hz source that would mimic the grid, it could be done but not in an easy way that would also provide a load for the inverter to dump into without the inverter changing the frequency of the simulated grid as it would not be stiff enough, a 60hz generator running at a reduced speed for 50hz would provide this reference but would be a more costly test method and as a load is applied the generator would fluctuate in speed as the load is applied and turned off this will cause a change in frequency as the RPM's of the generator changes.

Maybe a generator with a large flywheel might work, but it would have to be tested, FYI any two pole generator(alternator) ran at 3000 RPM's will produce 50hz, 3600 RPM's for 60hz.

Ok how about this, use a 220 volt 5kw motor powered from the inverter, that runs two alternators one at 3000 RPM's and one at 3600 RPMs, have the output of the inverter also connected to the 3000 RPM alternator, and use the 3600 RPM alternator to feed other loads, this at least would provide both things you would be looking for a load and a source to simulate the grid, the motor pulleys as well as the alternators would have to be sized to have the alternators run at the correct RPM's.

Ok maybe I'm over thinking this LOL

 

[hillbilly1]

My line of thought was instead of trying to sell it back to the utility, utilize it locally. I don't know many KW you have to play with, but what about running things such as the exhaust fan that removes the heat from the load bank, if a freq drive will not met specs, change the motor to 50 hz. Lighting would not be that good unless you have electronic ballast, but there are probably other loads around the lab that are presently run off the 60 HZ system, that might also work on 50 HZ.

 

[hurk27]

In re-thinking the above altenator load system I think there would be a problem unless some kind of load govenor was used, because since a grid tie inverter tries to lead the frequency of the grid, this would speed up the motor which then the inverter again would try to lead which again would speed up the motor until the inverter would turn off when the frequency limit is reached, if there is no limit the whole thing would run away I think?:blink:

 

[weressl]

Wayne,

It's for product development. We have a 60Hz product and want to manufacture a product for parts of the world that use 50Hz.

That's one of the things that's most interesting about PV -- all the different systems in use out there. For example, Mexico is mostly 127/240 Wye, as I understand it. Any country that's small (and doesn't get along with its neighbors ...) or is an island has unstable voltage and frequency.

Your suggestion that the power be converted on a DC bus is what I'd suggested -- some vendors inverters can be AC coupled (one inverter backfeeding the output of another) and that can be used for frequency or voltage conversion. Stick batteries in the middle and DC output of one AC coupled inverter can be DC coupled to another with a completely different frequency system.

The 50Hz system would be 380/220V, 3 phase. Single phase is used as 220V derived from the 3 phase system grounded wye to phase, unlike the US where 240/120V single(two) phases are supplied with center ground.

 

[hurk27]

The 50Hz system would be 380/220V, 3 phase. Single phase is used as 220V derived from the 3 phase system grounded wye to phase, unlike the US where 240/120V single(two) phases are supplied with center ground.

Not in Mexico, they have a 127/220 volt WYE and even use the same receptacles we use for the 127 volts although I thought it was 60hz like us?:?

Just checked with a few international voltage charts, and yes Mexico is 127/220 Wye and they also use 277/480 with a frequency of 60hz for both

Monaco uses a 127/220 WYE at 50hz as does Morocco and the Netherlands Antilles to name a few, the rest can be found HERE