Is there a way to control AC flow to only flow in one direction.

[jerryls]

is there a way to control AC power flow to only flow in one direction? Maybe using IGBT's or other semiconductors? I know it can be done with a power meter and relay but I want to be able to do it within one or two cycles.
Thanks

 

[schmitt trigger]

I'm not familiar with the power meter and relay method, but I assume that if one senses reverse power (with the meter) one then drives the relay, which somehow changes the connections -this is the part that I don't know how to do-.

But if you know how it is done, and then post a simple schematic, other people may suggest at ways to replace the relay with power semiconductors.

On the power meter, I know that many of the power meter ICs from Analog Devices have a "reverse power" signal which you could use.

Is this single phase or three phase?

 

[JanIan]

I'm not familiar with the power meter and relay method, but I assume that if one senses reverse power (with the meter) one then drives the relay, which somehow changes the connections -this is the part that I don't know how to do-.

I think it's doable just switching the relay on if amplitude is negative only (positive respectively). The result is a chopped DC current, isn't it? Just half duty cycle somehow?

But if you know how it is done, and then post a simple schematic, other people may suggest at ways to replace the relay with power semiconductors.

As the result of this 'one-direction flow' is just DC it simply is a rectifier where one amplitude is skipped. Don't know why we should do this, but okay. Each rectifier can be done using semiconductors. If we replace diodes with MOSFETs we just have to switch them according to the amplitude (the direction) of the AC. Usually this is done if the current (power in general) is high, such that losses using diodes because of voltage drop just would be way too much.

On the power meter, I know that many of the power meter ICs from Analog Devices have a "reverse power" signal which you could use.

If it's accessible somehow ...

Is this single phase or three phase?

Couldn't we just build/design it for one phase and then stack it together for the other phases separately (I mean building it three times, handling each phase separately - but I'm not sure).

 

[schmitt trigger]

Jan;
at first I thought what you also thought...a rectifier.

But then, I remembered than in wind generators which use an induction generator connected across the line, if the air is not blowing hard enough the generator becomes a motor....it consumes power, instead of producing power...this is called a power reversal.

I assume this is what the original poster is talking about, but he needs to provide more information before he can be helped.

 

[JanIan]

Yes dude, really that must be it. Stopping AC to flow back to the generator.
Good you mentioned that, currently also planning a wind and micro hydro site using AC generators/induction AC motors (squirrel cage type, i.e. without permanent magnets in the rotor; using capacitors for initial induction of flux instead). Thanks.

Wonder if there is a easy, simple straight forward solution without using ICs?

The only solution I can think of is that the supply line has to be cut (by a switch, i.e. relay|mosfet|igbt, AC component!? or is any DC component AC usable too?).

• Measure produced voltage of the generator using a secondary winding on the power line e.g.?
• If voltage drops to zero switch off the power line.

Think it's doable using a p-channel MOSFET or triac feeding back the voltage through a voltage divider such that the voltage never exceeds the maximal gate rating, huh?
The question is what is the simplest solution. And what if we have 3-phase AC?

 

[schmitt trigger]

You may be right, the solution could be as simple as cutting out the line with a Triac, when sensing reverse power.

We have to wait on the OP to give us more details....

 

[jerryls]

Sorry I haven't replied sooner but it was just a curiosity and I have been busy with other things. However, I do appreciate all the answers and dialog.
. The application is for solar generation tied into the grid power. The utility companies are now limiting the backflow(called net metering) or in some cases not allowing any because they say it trips there old relay equipment that was designed 80 years ago for power to only flow in one direction. I could not find and commercial products that will only allow one way power other then relay types. The utility claims relays are not fast enough and their protection circuits will trip.

 

[mtwieg]

Sorry I haven't replied sooner but it was just a curiosity and I have been busy with other things. However, I do appreciate all the answers and dialog.
. The application is for solar generation tied into the grid power. The utility companies are now limiting the backflow(called net metering) or in some cases not allowing any because they say it trips there old relay equipment that was designed 80 years ago for power to only flow in one direction. I could not find and commercial products that will only allow one way power other then relay types. The utility claims relays are not fast enough and their protection circuits will trip.

So is your goal to put something between the grid tie inverter and the grid that will prevent the GTI from providing so much power that it reverses the net power direction into the grid? What a waste of capacity!

It's possible in principle, but simply putting a big switch between the inverter and the grid probably isn't a good way to do it. Implementing the limit by controlling the GTI itself would be a much better solution, though exactly how that is done would depend on how the GTI is built. You would also need a power measurement at the main feed to which the GTI is connected.