** Method of using the grid itself to generate synchronous and 'sinusoidal' waveforms.**
Grid tie inverters are one of the main investments to implement solar energy. It is a complex process of guessing the next steps to produce an AC they synchronized to the AC whose amplitude and frequency are ever fluctuating.
The phenomena were first observed under the use of DAC and ACD components of Arduino to sample and scale down the grid AC into a manageable level. Only recently in the reversed process we are able to eliminate the complex steps of sampling and detections.
To generate waveforms.
Main components:
2 MCT66 ICs.
2 N-transistors (Tip122 or N-Mosfets). - The transistors produce a nicer looking graph.
2 P-transistors (Tip125or P-Mosfets - IRF 4905).
Wires ,jumpers and resistors.
These are simple setups. You may consider to increase the resistance value of the pull up/down resistors (10k?) and/or add 1 or 2 diodes to the pulling downs.
Its produces about +- 80% of the input DC.
Additional suggested equipment to upload power to the grid.
Option 1: (Conventional approaches). -- Connecting your AC and the grid in parallel fashions.
1 Capacitor (as current limiter).
1 Transformers.
Option 2: (Conventional approaches) -- Connecting your AC and the grid in serial and short them up.
2 Capacitor (current limiter).
This terminal to terminal voltage of the system is the sum of the Grid voltage and the produced current. (they were ... because they synchronized to each other)
They may not accept "Option 1" because it may, I said "may" cause "islanding", keeping the line active when the grid are OFF. I stated or its sake only.
Unless you do some more improvement to prevent the incidence occurred.
For those who want to use ACD of Arduino to sample the AC.: Place your 5V or 3.3 V on the DC then you are able to use AnalogRead(...) Instead of feeding it to the transistors (the top MCT66 only.)
Paul_KD7HB:
Has your local power company allowed you to attach your system to theirs?
Paul
You are perfectly right. - As it said. It will become simple by using the gird to generate the waveform.
Getting loose of the cat is the purpose. When the technology out in the open, everyone in the world are able to get it to work, thinking of making the product. People are smart, they are hungry for 'idea' for them to put their innovation into the products by then price will come down serving the community at the end. It may not fit the regulations of the US, but others, somewhere else.
I’m surprised about the grid amplitude and frequency varying . This has all sorts of issues for the power companies as such shifts will generate large currents between generators as their speed changes which is very inefficient and can cause instability ......
Let alone people’s mains driven clocks being inaccurate .
Something is wrong here , frequency is usually regulated by statute too .
I’m not sure what the scope is showing - are you generating bits of a sine wave ? That will create unacceptable harmonics . The waveform looks more triangular than sine wave too
As for connecting other issues are earthing ( sharing with the grid) what happens when the grid fails - loss of frequency control , dangers to workers working on a perceived dead system - there are devices to protect against this but they have to be approved . Different countries will have different regulations
If doubt you’d get permission to use a home made device .
In addition to Hammy's comments, for quite a few years, the frequency of commercial AC power generation has been tied to satellite timing signals, not by magically looking at the incoming power line. The people concerned about a massive solar flare leave this out of their public statements, but it is why the power distribution systems have been failing while there is a flare disturbance.
Paul
hammy:
I’m not sure what the scope is showing - are you generating bits of a sine wave ? That will create unacceptable harmonics . The waveform looks more triangular than sine wave too
The scope shows the result of the 12VDC input. Probed at Cap0 & Cap1 terminals. Regardless the inputs from 3.3V to 24V thy are very much the same.
It's always synchronous to the provided AC, the grid. (most important)
It's simple.
Its curved is depend on the amplitude of the AC. It's analog and smooth.
The raw curves are very much the same independent from voltage DC. Upgrading to a higher DC is just a matter of changing the terminal to terminal capacitor. actually it was placed for showing purposes, Without it the curves have few microseconds resting at cross-zero events.
You are correct at over all hourly, daily level..
For over the years we do have problems to accurately 'predict' the next cross-zero events even with the use of specialized ICs (H11AA1?). In programming we need the accuracy in microsecond or less.
Thanks.
Phi.
The 65.5K resistances were selected right at the border when the curve started rounding its top. The higher the value the lower the hill top making it more sine look.
The 0.1 uf capacitor was selected when it start smoothing the resting period at cross-zero events. Selecting a bigger one 0.5uf? will making it become more sinuous. The higher you input DC the higher the value needed.
If you look at the datasheet of the MCT66 IC (or others optocoupler) the method explores unintended functionality of the chip when they are fed with less than 1 mA. Depend of your objective- Produce the sine like or maximizing the efficiency of the design.
For the benefit of the community, for complete disclosure and for your information.
Previously we use the following method to achieve the 'perfect' grid synchronous wave form. It worked It may fit your purpose. I like this topic better.
Part list:
1 grid to 12VAC transformer.
1 200 ohm? resistor.
1 CT (current transformer)
Op-amps and other resistors to shift the amplify the voltage..
Transistors . . .
With the 12VAC burning a resistor through the CT It generated a fix grid synchronous wave form in both frequency and amplitude . we THEN used the OP amps + Transistor to amplify to the desired voltage and current. It's simple too!
Just an important note:
In the environment when the power is uploading to the grid. Somehow the 'textbook' calculation on the role of the capacitors need to be "reworks" perhaps it works on how much more the voltage of the device is elevated. You may need gradually trial on error to have the desired currents. In our environment an Uf allows u to upload about 0.05 Amp. They are inexpensive/cheap anyway.
Hope this helps
Somehow the images disappeared as the result of the scheduled maintenance of the forum
I post them again.
Note:
Option 1: Using step up transformer to increase the voltage a little above the 110 grid. This is the way they are doing right now. It has to have islanding preventing circuit to be added-on.
Option 2: Direct serially connect to the grid.
The role of the capacitors are the current limiters.
The following is the scope showing the result of the 12VDC with terminal to terminal cap at 0.5uf instead of 0.1 UF (better curve)
