Just went overboard on ADC, better to have too much rather than not enough. I really wanted the simultaneous sampling feature.7circle wrote:Marvelously mezmarizing R-NZy
The ADC at 200ksps could be good with a pair of sample and hold circuits on the two phase current measurements.
Do you need to go to 500k sps for each Current signal or would 100k sps do?
More the merrier, if the AD7862 doesn't blow the budget.
Did you consider an AD with SPI on the Power board near the Current Sensors.
I didn't find an SPI adc with simultaneous sampling that I liked and using one on a parallel bus makes it possible for me to determine exactly when the currents are sampled.
I want to play around with sensor-less vector control so extra performance and control is always a good thing.
The SPI idea would be good for keeping noise from the switching board out of the critical current inputs though by localising the analog signal path.
I figured cost wise the ADC is cheep compared to the MOSFETS and since I would rather the controller be done right than done to a price point. for say a smaller 6-FET controller the micros on chip ADC's could be used but they are quite slow when you have to use a mux on them to get the 2 currents.
Yes I'm targeting 1000Hz operation for sinewave sensorless vector control but I will also probably do a simple sensored trapesium control mode that allows much faster operation.7circle wrote:Marvelously mezmarizing R-NZy
What's your target electrical RPM?
You had mentioned "Turnigy 80-100 to over 8500RPM mechanical (1000Hz) "
I will of course try and go faster but I expect losses in the motor to rise at some point. The 1000Hz means I need to have my software current controller running at a significantly higher rate to get any resemblance of a sinewave and it is this that will limit it in sinewave mode.
Since the electrical RPM supported its is entirely dependent on the processor performance and since I'm estimating this until I have some more control code written its all a bit of a guess. I say 1000Hz electrical as I am confident based on whet I have seen so far with this processor and comparisons to a TI DSP I use at work. It should be able to do better than this.
edit: 1000Hz electrical -> 1000 electrical rev per second -> 60000 RPM electrical.
I have got most the software infrastructure in place to allow easily switching between modes of operation.
I have exposed 2 ADC inputs on the control connector for throttle and ebrake along with a few digital IO lines so it would be a matter of programming to use them for any desired purpose.7circle wrote:Marvelously mezmarizing R-NZy
Will you have other AD inputs on a connector pins
eg Throttle, Brake,
1 wire - Multi button sensor for Cruise Control (1k-Econ/2k-Set/4k-Resume/8k-Acc/16k-Decel)
For my bike I'm planning to do a separate dash controller and to connect it to the motor controller over a CAN bus interface but having the option to use a simple resistive setup could be handy for testing or for less complex setups.
I am concerned about keeping the +vbus and 0vbus well decoupled. I thought about caps above the + side FETS but they may interfere with where I need to build up the traces with braid for the phase outputs.7circle wrote:Marvelously mezmarizing R-NZy
Will your electros be on the Top or bottom with the Fets?
Just wondering about the Stabilty of the Bus for the Left hand side Fets.
You could also allow several small LOW esr cans over the Fets so its distributed.
(Just noticed you new posts on extra Bus Caps)
If the holes are their you can choose to fit them or not. More the merrier.
The electros and leaded MKP caps will be mounted on the top side but the SMD MLCC will be on the bottom side with virtually no track length. I'm hoping the SMD caps are enough to hold things together.
Yes that is planned, I've been leaving that till last but I will expose areas of the phases and the + and - bus polygons once I have no other changes to the board.7circle wrote:Marvelously mezmarizing R-NZy
You might want to leave space with Solder Resist gaps for track thickening.
This is something I'm a bit concerned about. currently the only currents in the inner layers are because of paralleling with the external +bus and -bus polygons but getting the heat out is a problem as you say. I may add a few more vias to help get the heat out. Hopefully using thick copper on the outer layers and beefing them up with braid will prevent issues by providing a lower impedance path than the internal fills or at least altering the current split so most flows on the outside.7circle wrote:Marvelously mezmarizing R-NZy
Be carefull with High currents through middle layer copper.
Vias can help with heat build up and stopping track burnout.
I haven't looked for a standard heatsink bar but I have fund a heatsink that comes in a 100mmx150mmx30mm which would work nicely behind the board.7circle wrote:Marvelously mezmarizing R-NZy
Have you found a Heasink bar thickness that''s standard. Say 10mm x 30mm Bar.
Or as others have suggested, using mini link bars for the twin FETS on the low side that are at U,V &W potential (oh you've got A,B & C)
This way you don't need insulated pads behind the TO247AC (if used) you put them behind the three minibars (... I'm thirsty )
Will the heatsink need to be fastened to the PCB?
There doesn't appear to be any holes for this?
Also the Heastink can be a current path the Tab and center Drain Pins.
But be careful it doesn't make the Drain Leg a main current path to a Capacitor.
Some times happens if battery positive is linked to heatsink.
I decided to avoid the complication of having a bar run along the +ve fets and then having to insulate the bar from the heatsink.
There is a set of pads for standoffs around the edge of the board (3 per side) with a few in the middle that may not have shown up too well in the images I posted that will be used to support the PCB.
My cats not too fond of the skin a cat analogy either7circle wrote:Marvelously mezmarizing R-NZy
As you know too many ways to blow you self up (sick of ...skin the cat analogy)
So please ignore my comments if they bug you. (Splat....*...)
... Don;t ant to drive you crazy with my rants''
It's look ace.
No problem its good to see others views especially since they can sometimes prevent expensive mistakes. Sometimes the mere fact of answering someones question can highlight an issue (happens all the time between me and other software engineers at work).
Since this is by far the highest power electronics I have designed myself there is definitely a chance of design problems.
Hopefully I havent missed anything. If I have or if you have other questions or suggestions fire away