Electronics > Power & Renewable Energy

How to design a single phase inverter (5kW)

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Faringdon:
Hi,
Would you agree that a grid-tied single phase mains inverter (sinusoidal output) is an extremely simple bit of hardware to design?
Lets face it, it connects to the grid voltage, so that essentially defines its output voltage.
Surely all that is needed, is simply to have a DC bus which is higher in voltage than mains peak, and then you simply use sinusoidal PWM and an H bridge, to shovel an AC voltage out towards the grid?……there will obviously be an inductor between the inverter output and the grid wires…and that will limit the di/dt of the current going into the mains. Also, obviously current limiting would be needed.
What is  the most complicated part of it? Its difficult to see where the feedback loop is needed…..there is obviously no control over the output current….just output current limit…..because it’s the load seen by the grid which determines what current is pulled from the inverter?
The bit of control that I can see, is that at any instant in time, the inverter’s output must be higher than the grid voltage, otherwise current wont be able to flow out of the inverter. (when I say “inverter’s output voltage, I mean the voltage on the non-grid side of the inverter’s output inductor.)

fourtytwo42:

--- Quote from: Faringdon on October 02, 2021, 01:27:28 pm ---Would you agree that a single phase mains inverter (sinusoidal output) is an extremely simple bit of hardware to design?

--- End quote ---
Fortunately for mankind a large amount of signal processing software is also required that I believe you have no capability to produce!

Gyro:
Presumably related to his recent solar 'stuff'.

Coming to a house fire near you!  :palm:

Faringdon:
Thanks, i can manage the "sinsoidal PWM bit" into the H bridge.
With a good LCL filter between H bridge and mains, and i'm on the way to supplying current into the mains...(with a current limiter in there aswell).
I mean, there isnt any control over the current drawn from it.......(other than simple limitation), because its the load that decides the current.

So the only thing that would be the changing is the sinsoidal PWM pulses...ie narrowing them down over the entire 10ms half cycle...........i assume the pwm can be changed  pulse to pulse, but all procedding pulses would have to change in line with that i assume.....so i guess thats  where the signal processing comes into it?

At the end of the day,  i believe its simply a case of supplying current into the mains, from a sinusoidally PWM'd H bridge. I mean, its hard to see whats to go wrong...because the mains is a very "stiff" 50Hz voltage source......so its not as if i am going to distort it.....and as long as we have current limitation, then we arenet going to burn out the wiring.
Woudl you agree?

Also, its unusual, that there are no posts on any  forum , anywhere, of anybody asking "How to design a grid tied inverter" . Why is this?

bdunham7:

--- Quote from: Faringdon on October 02, 2021, 01:27:28 pm ---Hi,
Would you agree that a single phase mains inverter (sinusoidal output) is an extremely simple bit of hardware to design?
Lets face it, it connects to the grid voltage, so that essentially defines its output voltage.
Surely all that is needed, is simply to have a DC bus which is higher in voltage than mains peak, and then you simply use sinusoidal PWM and an H bridge, to shovel an AC voltage out towards the grid?……there will obviously be an inductor between the inverter output and the grid wires…and that will limit the di/dt of the current going into the mains. Also, obviously current limiting would be needed.
What is  the most complicated part of it? Its difficult to see where the feedback loop is needed…..there is obviously no control over the output current….just output current limit…..because it’s the load seen by the grid which determines what current is pulled from the inverter?
The bit of control that I can see, is that at any instant in time, the inverter’s output must be higher than the grid voltage, otherwise current wont be able to flow out of the inverter. (when I say “inverter’s output voltage, I mean the voltage on the non-grid side of the inverter’s output inductor.)

--- End quote ---

I would not agree.  I believe that the sections of your statement that I've highlighted in red are all incorrect.  The last part about the inverter output being higher than the grid voltage is probably the wrong way of thinking about it, but I'll leave it for now.

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