Various aspects of home brew inverters


Author Message
poida

Guru

Joined: 02/02/2017
Location: Australia
Posts: 1382
Posted: 10:56pm 12 Feb 2021      

- why is the high voltage inverter not used in the amateur field?

my first answer is to be sure not to handle DC at 310 or more volts.
I assume that the sketch nano1 can safely drive through drivers
with adequate dead time, a high voltage H bridge.
if safety and efficiency are not the problem, what would improve using the output transformer?


I am sure others can answer this much better than I can.
The transformer type (I call it LF for low frequency) has shown to be easy
to build and robust. Peak power levels into 10kW and well beyond are quite
common in systems built by people who run their entire houses.
When unskilled builders make 10kW power electronics, I think we all
want to be exposed to 50V DC only. We can usually safely construct
the 240V AC output wiring using common sense and widely available components
obtained from nearby hardware stores.

The high voltage inverter (or HF) does not need the heavy LF transformer.
But it requires a DC supply of the AC output peak voltage.
For 240V AC output, that means 340V DC or likely about 20% more than this.
I do not like working with 400V DC and I like even less working with 400V DC
backed up by large capacitors.
In my view, I will never build or attempt to repair a HF inverter.

Efficiency of a well built LF inverter can be 95% over a wide range of output power
levels. In most cases our builds have the idle power loss to be around 10W.
Our builds are from 2kW to 6kW and larger. This is good idle power loss.

Other losses are DC resistance through the primary and secondary winding of the transformer. Since we build the transformer, we can limit these losses to very low levels. Usually commercial transformers are designed and build to be near the onset of saturation at their operating frequencies. We can build a transformer that will be far away from any amount of saturation under operation because we can oversize
the core and the two winding copper conductor cross sectional areas.
Sometimes this is done to nearly humurous degrees.

There are also Rds(on) losses in the MOSFETs when they are switched ON.
This is not insignificant but it is small compared to the larger loss
due to the switching from ON to OFF or OFF to ON the MOSFETs are required to do
at 20kHz. These two losses can amount to 100s of Watts and necessitate large
heatsinks and good cooling fans.

All of the above can be managed easily by system builders of varying degrees
of electrical, electronic and mechanical engineering skills.