Need to design and build 250W BLDC inverters for drones.

[cupoftea]

Hi,
We wish to build drones capable of carrying up to say 5kG. Therefore we need four 3 phase BLDC inverters capable
of 250W each.
We must build the inverters ourselves, and not import them in from outside Europe/UK/USA/Australia.
There are very few companys in EU/UK/USA/Australia that build drone inverters, so we need to do this ourselves.

Please offer us any help you can.

The inverter bit looks simple....just a bridge of four suitably heatsunk MOSFETs.

Do you know of inverter control chips for this, or chipsets?
What battery voltage would be best would you think? (we believe 48V is best, with matched series/parallel cells and "stop_when_any_is_full_or_empty"
charging regime.)
they will have 4 propellers, so we need four 250W inverters.
So thats 6 Amps from each battery.

Do you think a microcotnroller would be best to provide the Inverter MOSFETs gate drive
signals?
So we need it to receive the four rotor position sensors, and then push out the drive signals
, and have the four speed inputs.

Please help with this?

 

[D.A.(Tony)Stewart]

1. 1st choose/define a budget for Motors + ESCs + batteries vs qty. and MTBF.
2. Then choose the most efficient motor options for W/gm e.g. 0.16 W/gm @ W/$ @ T rise or lowest gm/W = 6 ? 4?
3. Then compute the stored energy batteries to match energy of trip required plus acceleration losses + margin + thermal losses and derate for weak batteries from 100 to 250 trips.
4. Amortized total cost of ownership / trip depends on stress rates on each component. e.g. junction temp rise and Arrhenius Effects.
5. Define max RPM for noise emissions
6. Then compare performance vs cost.
7. Then design ESC.

This is a simple plan that needs breakdown of tasks to ultimately define Design Specs.

Higher voltage reduces current losses but accelerates battery failure without active BMS during operation and charging as the weakest battery fails faster with more in series. Failure acceleration rate is affected by tolerance on cell capacity deviation and time constant degradation. ESR*C= Tau. C is in kilofarads.

 

[dick_freebird]

Infineon has some interesting-looking BLDC motor control ICs
that appear to be "everything but the switches and the command"
(whatever says how many RPM, or whatever). Maybe there's a
handy reference design for you to work from.

 

[cupoftea]

Thanks, will look at Infineon., Also...
Thanks, this video (build a drone with Arduino) appears to be whats wanted...

....the idea is to build it like this...but replace the so-called "ESC" with our own 3 phase inverter.
Part 6 shows the inverter. I assume thats simple, as all the inverter receives is the gate drive signals.

.it looks like pretty much all the design is done in the vids shown here.
We just need to replace the Inverter with our own....should be easy...then from that point, we can learn how to do the programming aspect of controlling the BLDC inverter from the
pitch and yaw and speed demand values that the flight controller kicks out to us. (ie ultimately we will make our own flight controller, but not yet)
We also need to be able to scale up to drones of a higher power level......presumably thats easy, as the flight controller always first gets connected to the motor and "calibrates" to its characteristics....so it looks like the flight controller will adapt to a drone of any power level.

The code for the flight controller all appears to be dished out to us from the arduino web site. (or the video shown)

So , quite literally, all software is written in the Arduino video, and all that needs to be done, is shovel in our own motors and inverters...the Flight controller will give us the gate drive signals for the inverter FETs...and we simply need to manipulate them to drive the actual FETs via suitable gate drivers.
Would you agree?

 

[D.A.(Tony)Stewart]

Good luck in a 30 kph wind with only 4 props and a 5 kg weight. Any flex > 0 deg in the rotor arms will greatly affect instability, unless you are just dropping packages into the "yard".

6 carbon-fiber props are better if you want heavy-weight control and carbon-fiber rotor arms & body.