WHERE DID ALL THE TIME GO!?
IGBTs! IGBTs! IGBTs!
LOOK AT THESE IGBTs!
Current limited by the package leads, among other things, these are the perfect candidate for some pulsed, hard-switched, power dense goodness.
And so the journey to building a QCW bus modulator begins.
In essence, the modulator portion of your QCW coil is just a buck converter capable of producing arbitrary waveforms across the bus of your DRSSTC.
The tried and true control scheme for these guys is hysteresis (bang-bang) control, which involves turning on the high side of your buck converter when the sense voltage falls below your hysteresis band and turning the high side on when your sense falls below the hysteresis band.
In lieu of a microcontroller, I opted to make my control loop out of op-amps for noise immunity and beardy-weirdy cred.
|Troller Schematic. Forgive me, for I have text overlap up the wazoo.|
The outputs of the comparators are then fed to an SR latch so that the hysteresis thing happens.
|Squiggles of Science|
Special notes: the input signal is actually taken from an opto, which is filtered by an LC to reproduce the desired waveform. It's like L-C filterception. Additionally, this allows me to send square wave pulses optically, instead of an analog signal through a long length of coax, which is bound to
The boards are now split up into three sections: a DC-chopper motherboard, controller daughterboard, and DRSSTC with filter LC.
|Can't have too much bus cap (a work in progress)|
The addition of the driver daughterboard would allow me to send out for plenty of driver revisions without having to spend a fortune on the whole 5.5" x 5.5" board. Oh, and did I mention how small everything is? :3
Current limiting is implemented on the driver side as desaturation detection: in an over-current state, the voltage drop across the switches increases to well above the typical ~2.0V, which is detected by the drivers, which do some fancy soft-turn off to prevent voltage spikes induced by the typically high dI/dt. The gate drivers also conveniently have built-in opto-isolated inputs.
IN OTHER NEWS:
Bluescooter got an overhaul to make it more of a reliable commuter vehicle than junkyard scrapper on the verge of collapse.
After eating through a current modded controller, a few things were changed:
1) Motor upgrade!
An especially squat, low kv motor, perfect for squeezing into the tiny 4" u-channel frame.
But everything changed when
I was forced to look beyond Ye' Old Hobbyking, and found a cheaper, dare I say, better option:
Even with expedited shipping, the SDSHobby motor lends itself to be a good $20 cheaper than the Hobbyking equivalent, the only downside from ordering from SDSHobby being their rather small selection of EV-sized motors.
2) The controller with the infinite heatsink
Some fresh thermal grease, three holes, and some cap screws later, a happier 'troller was born.
Even on especially hot days, I've yet to find the area around the FETs go more than 5°C above ambient.
3) It has a new caddy.
|Structural Hot Glue|
Made entirely out of