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Grid Tied Inverter, 200W

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Flyback

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Hello,

I have simulated a grid tied inverter by simply having an isolated 400V supply….then having a PWM with a sinusoidally varying duty cycle which switches via a bridge into a Filter to filter out the switching harmonics and leave behind the 50Hz waveform.

Would you say this is a good modus operandi?

Its as in the attached simulation in LTspice
 

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unclejed613

Well-Known Member
Most Helpful Member
Hello,

I have simulated a grid tied inverter by simply having an isolated 400V supply….then having a PWM with a sinusoidally varying duty cycle which switches via a bridge into a Filter to filter out the switching harmonics and leave behind the 50Hz waveform.

Would you say this is a good modus operandi?

Its as in the attached simulation in LTspice
why not simulate an actual inverter using a push-pull pair of transistors and a transformer?
 

crutschow

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Most Helpful Member
Is the inverter operating frequency phase synchronized to the mains.
If not, you will have a very short lived inverter. :eek:
 

tomizett

Active Member
Well, as the others have implied, it rather depends on what kind of inverter you're trying to simulate and why. The basic topology is certainly reasonable - assuming that that's the way your inverter works. As in #3 though, if your simulation also includes an active mains supply then you'll have to consider synchronisation between the inverter and grid.

What's the purpose of the simulation? Are you designing a grid-tie inverter or are you simulating one as part of some larger power system?
 

unclejed613

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i'm not sure what the OP is trying to accomplish here. most UPSs only charge batteries while the incoming line supply is good, and turn on when the AC line drops out. if the device is supposed to act as a current booster, one alternative (and a far simpler one) is to connect an analog amplifier as a Negative Impedance Converter. an NIC would maintain the same phase as the power line because its input IS the power line. if the purpose is to provide a distributed power system, then a system of phase locked diesel generators (or other primary power sources) would be the way to do this. the way that the power grid maintains phase lock, is actually a consequence of the alternators at a power station, also behaving like a motor, more specifically like a synchro motor. this property of the machinery keeps all of the alternators in lockstep.
 

tcmtech

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i'm not sure what the OP is trying to accomplish here. most UPSs only charge batteries while the incoming line supply is good, and turn on when the AC line drops out. if the device is supposed to act as a current booster, one alternative (and a far simpler one) is to connect an analog amplifier as a Negative Impedance Converter. an NIC would maintain the same phase as the power line because its input IS the power line. if the purpose is to provide a distributed power system, then a system of phase locked diesel generators (or other primary power sources) would be the way to do this. the way that the power grid maintains phase lock, is actually a consequence of the alternators at a power station, also behaving like a motor, more specifically like a synchro motor. this property of the machinery keeps all of the alternators in lockstep.

Well put. As someone who has worked on the DIY GTI concept for years I can say for sure that making a massless solid state circuit act anything like a synchronized rotating mass cogeneration unit and feed active power back into the grid is not as easy as it may seem and making it overly complicated just makes things that much worse real fast.

Also there is the realistic practicality aspect of what size of unit is being built and what cost you want to put into it being the ROI tends to become cost prohibitive real fast at low wattages unless it's going to be running day in and day out for years on end.
 

alec_t

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the ROI tends to become cost prohibitive real fast at low wattages
That was my initial thought. What justifies a 200W inverter being grid-tied?
 

tcmtech

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That was my initial thought. What justifies a 200W inverter being grid-tied?
For me it would be to just use up old parts that don't have an real purpose anymore so that they don't end up in the scrap metal bin or trash. Zero investment but a time and I have a lot of that on hand so that's no big deal there either.

Beyond that, basic math says anything built on purpose with all new parts is likely going to have to put in thousands to 10's of thousands of running hours (which could take years to accumulate) just to reach break even especially if labor time cash value is factored into the build.
 

unclejed613

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That was my initial thought. What justifies a 200W inverter being grid-tied?
it could be used as a NIC to service a local load, but the NIC also consumes power. another possibility is having a local solar or wind farm, and wanting to keep sync with the main grid, so that switching between the grid and the local power farm happens with no hiccups, especially if there were a lot of 3-phase motors in use. this is what makes wind/solar power systems for industrial use 3 times as expensive per watt than home systems, 3 phases vs 1 phase.
 

crutschow

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this is what makes wind/solar power systems for industrial use 3 times as expensive per watt than home systems, 3 phases vs 1 phase
I don't follow. o_O
The cost for a given power should be similar since much of the cost is for the panels. You just need a three-phase inverter instead of a single-phase.
 

unclejed613

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I don't follow. o_O
The cost for a given power should be similar since much of the cost is for the panels. You just need a three-phase inverter instead of a single-phase.
you're right about that...
 

unclejed613

Well-Known Member
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a banking equipment company i used to work for de-installed a 3 phase UPS that had been in use at a bank's processing center. with batteries and transformer, the UPS was a big heavy beast that could only be moved with a forklift.
 
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