AX 300-3 & VLLR


Author Message
Downwind

Guru

Joined: 09/09/2009
Location: Australia
Posts: 2333
Posted: 02:30pm 09 May 2012      

One of the things i have done for some time now, and is a large part of the controller for Phill, is to use RPM limiting.
I dont understand why this is not used more widely, as its only a matter of monitoring RPM and should a pre set speed be reached, then apply the brakes (dumpload), i dub it a "The mill saver".
In high winds there is little point allowing the mill flog its guts out and reach close to runaway speeds, and think it is far better to hit the brakes and pull the mill speed down, then allow it to spin up again then repeat as required.
This also allows for furling that is not 100% correct to be compensated by rpm limiting, as loading the mill heavy can also help pull it harder into furl, as well as it not reaching runaway speeds.

There is no point in allowing it to reach high current outputs in strong wind/gusts, then trying to shut the mill down as this is where damage occurs, the extra bragging rights of the high power peaks that might be gained from high rpm adds little over all power to the daily total, and is far better to loose the absolute top speeds and save the mill to fly for another day. (broken mills make no power)

With design and development testing i had done with Phill for the VLLR, on bench testing here at 24 volt it was able to control the voltage to the battery within less than 1 volt hysteresis.
For example with 15 amp output, 10 amp could be sunk to the fluid and 5 amp supplied to the battery, maintaining a steady battery voltage, allowing for the battery to be full charged or topped off, as the voltage rise the probes would step in slightly shunting more current to the fluid and maintaining the set voltage.
This made for what jokingly got called "The Ducks Nuts" controller as the principle of liquid resistors acting on the 3 phase AC worked so well and so smooth.

From what i have seen thus far, the system Phill has constructed here is really "The Ducks Nuts" of control methods, but we both agree real world testing will prove this true or false with time, as bench testing can only prove concept and mother nature can pose issues that testing dont account for.

Its a lot of work and depends greatly on electronics for control, so not a project for the light hearted amateur.

The control electronics is split between 2 chips to keep response times fast and smooth.
1 chip controls the actuator and monitors the voltage using 16 bit ADC resolution via I2C.
The second chip monitors all other inputs/outputs from limit switches, rpm, temp, serial data in and out from PC, manual switches and any other function, then controls chip 1 accordingly.
Each function received to chip 1 is acknowledged back to the second chip to ensure the command has been received and executed, chip 2 then sends a text message to the PC to be logged in the records of operations preformed.

Pete.


Sometimes it just works