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Currently I am working on an project to feed back the output from a solar panel to the grid. One of the circuits used is the H-bridge. This part is used to convert an arbitrary DC signal to an AC signal. The first circuit was the following:

enter image description here

The 2N2222A are in my case simple N-MOSFETs

The second circuit was the following:

enter image description here

The third circuit was simply using an IC with all the components internally.

The first circuit we could not get to work, but was probably because our shortcoming of knowledge :) .
The second one we did get to work, but was hard to maintain an good signal and was using 2 watt!
Therefore we made the third one to lower the power assumption. This one was using somewhere around 1 watt (it changes from time to time, which is something we have to still found out).

Question:

Currently we have the H-bridge for the DC>AC, but is (still) using 1 watt of power. Is there something (in used chips for example) so we can get the used wattage down in total. Is there maybe another option we can use to make an AC signal which is far more energy efficient.

UPDATE:

1.) The target efficiency is high as possible, every loss on some component is one to many. Of course, you will never get it to 0, but the lower the better.

2.) The VCC of the first circuit has a voltage of 25 volts (INPUT). The four ports (A,A,B,B) are connected to the "grid" (with a 20 volt AC, we first test with a lower voltage). A and A are directly connected and B,B are connected to the grid with an inverter to get a positive voltage over the MOSFETs. The OUTPUT must be at least around 21 volts (so the voltage will be higher then the grid).

3.) In the second circuit the function generator is the grid, with the same specs as the first circuit. The PWM signal is not sure yet and can be varied.
In the third circuit the function generator is a representation of the grid point after the transformer (see point 3 in update 2).
The resistors are all 1k and are just for some security at some points.

UPDATE 2:

1.)

MOFSET: MOSFET N-CH 60V 16A TO-220; part number STP16NF06L For the other parts I will have to look. I can't look them up right now, but the diode is just a simple diode (no Zener).

2.) YES, the 25 volt is the input and the output must be at least 21 volts.

3.) For testing right now we are indeed using an 20V AC transformer between the grid and our circuit. This of course makes a sine wave.

4.) I am living in Europe so the "standard" voltage is 230 volts RMS. The transformer is NOT RMS. So the peak is at 20 volts.

5.) The losses were measured with connecting a voltage supply to the input of the H-bridge (around 25 volt) and the output (the "load" point at the H-bridge) was connected to the transformer with 20 V RMS. The current was measured at the input point of the H-bridge (VCC). The voltage was measured at the voltage source and over the "load". The consumption of the H-bridge was in the second case 2 watt and 1 watt in the third circuit. The first we never got working correctly (still not sure why, so there are no results of that).

6.) The input is an square wave.

7.) The efficiency is not calculated yet, just the loss in watt. I am not currently at the place where it was build so can't give any value on the efficiency.

8.) The whole package in the third case was using around 180mA.

greybeard
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    Efficiency = Output Power / Input Power. You have told us your power loss but have given us no information on supply voltage, current, power or output voltage, current, frequency, power. What efficiency are you hoping for? What efficiency are you getting? Are you trying to generate a sinewave? i.e., You haven't supplied enough information for anyone to answer. – Transistor Jan 22 '16 at 18:48
  • Made an update, hope it is more clear. –  Jan 22 '16 at 18:58
  • Show us your actual circuit.We can't help you if we don't know exactly what components you are using and how they are connected. Is the 20VAC mains power (through a transformer) or something else? What is the expected output power range? – Bruce Abbott Jan 22 '16 at 19:06
  • I think in Update point 2 he's saying he's got 25 V DC and trying to generate 20 V AC - I presume RMS. Point 3 is a bit of a mess. – Transistor Jan 22 '16 at 19:10
  • @user3892683: You didn't answer all the questions. Sinewave? What is your calculated efficiency? Current? What efficiency did your calculations give? How did you measure your losses? – Transistor Jan 22 '16 at 19:11
  • I am still a starter, but provided as much information as I can. :) –  Jan 22 '16 at 19:33
  • but apart from the whole part about the H-bridge are there other options then an H-bridge to get an AC signal from an DC signal. –  Jan 22 '16 at 19:38
  • You need some sort of bridge to flip the polarity, whether it's an H bridge or an amp bridge. – Ignacio Vazquez-Abrams Jan 22 '16 at 20:39
  • One thing to keep in mind is that the MOSFETs draw the least amount of power when they're fully on (or off). If your circuit is switching them on & off slowly, they'll convert more power to heat and deliver less to your load. – kronenpj Mar 23 '18 at 14:58
  • Getting a 230vac output synced to the mains might be tricky. – user361949 Jan 16 '24 at 01:01

1 Answers1

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If you synchronously rectify your "grid" by whatever means you will get a pulsating DC waveform. MOSFETs will be fine for you to use here. This synchronous rectifier bridge runs at power frequencies not PWM frequencies. So there are basically no switching losses here so with readily available low RDS(on) MOSFETs the losses of this section can be well under 1%. Now your PWM could be a Buck convertor or buck-boost or SEPIC or zeta or Ćuk. The key point here is that your losses will be much lower if you take the approach I mentioned. This approach is accepted and it is used by many solar manufacturers. You can now see that you can sleepwalk to 90% efficiency. If you trick up your buck with some switching loss reduction scheme and keep the PWM frequency sane you can crack 95% which is what people want. Because solar cells are not cheap it is worth it to squeeze the last drop of power out of them.

Tim Williams
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Autistic
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  • This sounds really promising! but I can't really follow you. Can you maybe clarify more with a circuit or point to a website? –  Jan 23 '16 at 14:55
  • (The part about rectification looks beside the point considering input is from solar cells.)(I seem to remember HF transformer+secondary H-bridge for 60/50 Hz output.) – greybeard Jan 08 '23 at 09:07
  • I think the OP has "left the building", and the original question severely lacks necessary content for a proper answer. I think this should be closed, or at least just ignored. – PStechPaul Jan 08 '23 at 18:45