SO the optocoupler gate drives look very appealing but they need 15 volts or greater to run them? Because they use a LED to trigger the out put Mr Colton designed a half bridge drive like this to delay the turn on of each fet so the other fet gets shut off fully first. This is to prevent shoot though events!
Not simple BLDC controller It RUNS! :)
- Thread starter Arlo1
- Start date
Lebowski
10 MW
Some stuff I learned the hard way :? when working with optocouplers: make sure your power transistors are
off when the LED part of the optocoupler is off !
Have you guys thought of using a class D audio driver like this:
http://www.silabs.com/products/audiovideo/class-d-audio-drivers/Pages/Si824x.aspx
if you look at the datasheet you'll see that a class D audio circuit is very (very !) similar
to the circuits that we use to drive one pin of the motor. See the datasheet (under documentation)
figure 38/39 on page 23. A class D amplifier uses square waves (like we do) of a few 100 kHz
to drive a speaker (which is like a linear motor).
With this particular IC the dead-time between the high and low side can be programmed by
chosing an external resistor, everything is taken care of inside the IC.
Interesting bit about this IC is that isolation is obtained not by using optocouplers but
by using radio signals.
off when the LED part of the optocoupler is off !
Have you guys thought of using a class D audio driver like this:
http://www.silabs.com/products/audiovideo/class-d-audio-drivers/Pages/Si824x.aspx
if you look at the datasheet you'll see that a class D audio circuit is very (very !) similar
to the circuits that we use to drive one pin of the motor. See the datasheet (under documentation)
figure 38/39 on page 23. A class D amplifier uses square waves (like we do) of a few 100 kHz
to drive a speaker (which is like a linear motor).
With this particular IC the dead-time between the high and low side can be programmed by
chosing an external resistor, everything is taken care of inside the IC.
Interesting bit about this IC is that isolation is obtained not by using optocouplers but
by using radio signals.
bigmoose
1 MW
Arlo as you get into the dspPIC you can set the dead time in software.
Thanks big moose I already have the IR2113 coming and they run a half bridge each with a Shut down pin as well. So basically exactly what I want. I will run them with isolated 12 volts as well. If you can you are almost always better doing a job with software from my stand point. Then I can program the turn on delay to what ever I want!bigmoose said:
Lebowski said:
Just the other day I was looking at the SI823x line, which uses nearly (exactly?) identical technology to build a family of FET/IGBT gate drivers. What is the difference between a class D audio driver and a high/low phase leg driver? They look identical to me.
Would a guy not be smart to set a max on time as well eg if I build a system that reaches 600 phase amps in 41 uS and 600 phase amps is the max I am aiming for would I not want to program the max on time to 40 uS and try that to start?bigmoose said:
oldswamm
100 W
Arlo, I just discovered this thread.
You should look at the dsPIC30F4011. I don't THINK you lose anything. The extra memory might find a use, it usually does.
The CAN interface is easy to implement, and might be useful for an automotive ap?
The Runner will get 4wd, right?
I love it. I too am jealous.
Bob
You should look at the dsPIC30F4011. I don't THINK you lose anything. The extra memory might find a use, it usually does.
The CAN interface is easy to implement, and might be useful for an automotive ap?
The Runner will get 4wd, right?
I love it. I too am jealous.
Bob
I already ordered 2 dspic30F3010-301/SO and have the 2 pic18f2431 chips in my box. The Road Runner will burn something as long as I can hold out. The SRT4 is gettng hybrid assist electric rear wheels asap. For now this controller is to run collossus in my e-ysr and I want insane power!oldswamm said:
oldswamm
100 W
I know, I read the whole thread. I'm thinking down the road. The CAN would only require 1 8 lead IC added to the boardArlo1 said:
Actually I was going to suggest something similar to that for the Road Runner. It NEEDS front wheel assist, doesn't it?
I knew that to.
The road runner is light in the front and getting lighter and will wheely when Im done! So like a drag bike NO front wheel assist=bad idea! I plan to make it burn hydrogen but the electric revalution comes first!oldswamm said:]
Actually I was going to suggest something similar to that for the Road Runner. It NEEDS front wheel assist, doesn't it?
I knew that to.
So im looking at the power supplies. The usb chargers will proly be ok unless somone points one better out. I am not sure what to use for the fet driver supply. I ordered these http://www.ebay.co.uk/itm/160460011494?ssPageName=STRK:MEWNX:IT&_trksid=p3984.m1439.l2649 and now Im looking at this DCP021212 http://www.datasheetcatalog.org/datasheet/texasinstruments/dcp021212.pdf which might be better because its smaller and made by someone trust worthy!
As for the fet driver supply I want it iscolated and 12 volts with how much amprage? Where will I supply it from if I feed 5 volts to the brain? It would be nice to find a 110-240 volt ac/12vdc adapter isolated to feed all three fet stages!
As for the fet driver supply I want it iscolated and 12 volts with how much amprage? Where will I supply it from if I feed 5 volts to the brain? It would be nice to find a 110-240 volt ac/12vdc adapter isolated to feed all three fet stages!
oldswamm
100 W
Either that part for dc-dc, or nme1212dc to isolate the high sides, but I still think a good 100-240v 12v supply could work for a cheap dc supply. The 5v regulator can run off this supply with no noticeable efficiency hit.
You might even consider a 40/44 pin PIC. The extra pins can be used for single drop (or multi) 1wire sensors or analogue temp sensors, or whatever you think of later. Like memory, you can find a use for more pins. (And make sure you leave a kluge area to make additions to the prototype easier.)
You might even consider a 40/44 pin PIC. The extra pins can be used for single drop (or multi) 1wire sensors or analogue temp sensors, or whatever you think of later. Like memory, you can find a use for more pins. (And make sure you leave a kluge area to make additions to the prototype easier.)
bigmoose
1 MW
I've used Recom RO-xx12S (4 bucks and change from Future Electronics) before in small/medium applications. They are a little under 100 mA output; but remember the peak driver output comes from the capacitor. You need to do the math on the coulombs dumped from your chosen FET(s) and your PWM rate to get the average current draw. A 5v supply of around 0.5 amps likely will be more than enough.
oldswamm
100 W
Regarding the over current discussion. This is a redundant limit, for an uncommon event, right? You aren't going to run against this limit are you?
Couldn't you use comparators to trip transistors (crowbars) across all 6 gates, plus an interrupt input to the processor, so it could take action. <edit> Forgot you were using drivers with an enable. That's simpler if they will 'disable' quickly enough.<endedit>
This circuit especially should be kept simple. I don't use KISS. I avoid doing anything because it's what stupid people do. I figure that second S probably keeps 'it' from working! I prefer 'Keep it as simple as possible'.
Bob
Oh, the RO part is pin compatible with the nme part I listed, I just couldn't remember 'ro'.
<edit>I was thinking that a separate comparator would be connected to the fault input for 'normal' current limiting. It could be set up with enough delay to keep the pwm off till the interrupt routine could take action.
Couldn't you use comparators to trip transistors (crowbars) across all 6 gates, plus an interrupt input to the processor, so it could take action. <edit> Forgot you were using drivers with an enable. That's simpler if they will 'disable' quickly enough.<endedit>
This circuit especially should be kept simple. I don't use KISS. I avoid doing anything because it's what stupid people do. I figure that second S probably keeps 'it' from working!
I prefer 'Keep it as simple as possible'.Bob
Oh, the RO part is pin compatible with the nme part I listed, I just couldn't remember 'ro'.
<edit>I was thinking that a separate comparator would be connected to the fault input for 'normal' current limiting. It could be set up with enough delay to keep the pwm off till the interrupt routine could take action.
oldswamm
100 W
That last post confused me.
2 comparators, could be on the same shunt, bit more complicated with 2 shunts instead of 3.
<edit>3 shunts? One, optimized for speed, for HW shutdown, the other two optimized for accuracy, for phase current.<endedit>
One comparator would drive the enable pins on the drivers, to off.
The other would be connected to the fault input on the PIC, and would be set to a lower current than the first.
Normally the first wouldn't trip because the fault input would take care of it, and the program would probably temporarily reduce the pulse width so it didn't happen again?
If the first trips, it would probably indicate a 'fault' of some sort, and, if there's an appropriate input, the processor would act accordingly. The fault input keeps the PWM off for the rest of the cycle, so the program would have time without resorting to RC delays like I implied in the last post.
The big question is 'how fast is the enable pin based shutdown compared to the fault input on the processor'. I find no delay specs for the fault input on the dsPIC30F4012. OK, I did find it in the 3011 pdf, 50ns.
I think maybe I'm still confused. Is redundant fault protection needed, or is the driver delay the problem, or just in case of processor or firmware faults.
2 comparators, could be on the same shunt, bit more complicated with 2 shunts instead of 3.
<edit>3 shunts? One, optimized for speed, for HW shutdown, the other two optimized for accuracy, for phase current.<endedit>
One comparator would drive the enable pins on the drivers, to off.
The other would be connected to the fault input on the PIC, and would be set to a lower current than the first.
Normally the first wouldn't trip because the fault input would take care of it, and the program would probably temporarily reduce the pulse width so it didn't happen again?
If the first trips, it would probably indicate a 'fault' of some sort, and, if there's an appropriate input, the processor would act accordingly. The fault input keeps the PWM off for the rest of the cycle, so the program would have time without resorting to RC delays like I implied in the last post.
The big question is 'how fast is the enable pin based shutdown compared to the fault input on the processor'. I find no delay specs for the fault input on the dsPIC30F4012. OK, I did find it in the 3011 pdf, 50ns.
I think maybe I'm still confused.
Is redundant fault protection needed, or is the driver delay the problem, or just in case of processor or firmware faults.
Lebowski
10 MW
cool stuff 8) let us know how you get on with the included course, I'm very curious as to how good and elaborate it is.
oldswamm
100 W
Does this refer to the software, or getting it into the PIC?Njay said:It's a piece of cake Arlo, you'll see
<edit rather than make a new post>
Just wanted to mention to those who don't realize it, the ADCs on the PICs Arlo intends to use can do 2 simultaneous conversions at 500khz. Up to 4 @ 250khz. (Actually samples, the conversions are at 1mhz.)
Lebowski
10 MW
Njay said:It's a piece of cake Arlo, you'll see
Well,
, in a 16F88 I run a control loop to control the current through a motor (so a currentbased throttle control). This comprises a 1st order integrator implemented with 16 bit fixed point
math (including fixed point multiplications and in addition to this, for speed, an eeprom table),
this runs at 4 kHz sample freq. On top of this (via interrupts) it runs a noise shaper at 10 kHz sample frequency.
Definately not a piece of cake
but lots of fun (and definately a case of: you can make stuffas complicated as you want)
Lebowski
10 MW
Njay said:I was referring to learning to develop software
Lebowski, try an AVR, you'll like the 4x+ speed increase over the PIC
With the AVR I really dislike their datasheets, impossible to read while those of PIC
are very clear. Plus I didn't find any programmer on their site, same for good
assembler design environment...
Plus Microchip gives you free PIC's if you ask nicely, haven't found this option
on the AVR site...
By the way, with the 30F2011 and a standard motor stage (using only 2 out of 3 motor wires)
you can build a wickedly powerfull (kilowatt) audio amplifier
bigmoose
1 MW
Njay, I would recommend a "system comparison." For a complex PWM controller we are looking for a combination of system features. First a PWM section optimized for 3 phase control. Deadtime inputs, period centering, etc.; then we need a good, fast AtoD, then some decent DSP features in single cycles for the PID loops, followed by user interfaces like free input pins RS232, USB, CAN features. Take the device I recommended and do a relevant feature comparison to your AVR's (which honestly I am not experienced with as one head can only hold so much manufacturer data... :| ) I am open to new an better devices!
BigM, my "AVR try" suggestion was only a comment on Lebowski's PIC16F88 project. I could rebate all of your points except the free samples Lebowski (which is the only advantage 8bit PICs have over 8bit AVRs, not considering some special peripheral a certain PIC model might have better over AVRs), but I suspect that would leads to kind of an avr vs pic argument
Nevertheless I guess this project already has a platform picked up, Arlo already invested in one. In the end I guess there won't be relevant BLDC control hw differences in comparable platforms.
Nevertheless I guess this project already has a platform picked up, Arlo already invested in one. In the end I guess there won't be relevant BLDC control hw differences in comparable platforms.