# BLDC/PMSM controller question



## bart_dood (Sep 2, 2010)

Hi folks,

I am working on converting a bug over to EV, using recycled parts from 2000-2006 honda insight cars. I already have two motors which I'll be splicing together, the mechanical designs for the parts to do this have been finished as far as designs but I'm waiting on fabrication.

In addition to using the motors, I also have the controllers, I'll be using two, one for each motor, one is master and one a dumb slave. The controllers themselves are basically just the high voltage (144v) and high current IGBT's etc so they require an external source to drive them.

This means I have to develop a board with microprocessor to give the right high/low and deadtime switching to power the motor. I have already reversed engineering the inputs to the honda module and I know what PWM frequency and dead time to use.

To save myself some time I purchased a microchip BLDC evaluation board which can drive small motors for testing, when I have everything finished on it I can wire in the honda controllers to power the full sized motor.

There are a number of applications for motor control and I've been looking into which one is the most appropriate. However they all seem based on setting a speed via a pot input. So instead of a 'throttle' as on a gasoline car, the system tries to maintain a constant rpm irrespective of load. Of course there needs to be a current control as it would be easy to overload things without it.

My question is is this how 'normal' automotive BLDC controllers work? or do they output some kind of torque based off throttle position?

I am open to some easier way to accomplish this control box, I know there are a few people working on home brew controllers for BLDC motors, however I haven't seen any complete ones yet and I only need the heart of the system and not the high voltage/current driver section.

Thanks


----------



## major (Apr 4, 2008)

bart_dood said:


> .... they all seem based on setting a speed via a pot input. So instead of a 'throttle' as on a gasoline car, the system tries to maintain a constant rpm irrespective of load. Of course there needs to be a current control as it would be easy to overload things without it.
> 
> My question is is this how 'normal' automotive BLDC controllers work? or do they output some kind of torque based off throttle position?


Yep, you need a torque control. So the throttle pedal input commands the torque output of the motor. I'm familiar with induction motors in EVs and use close loop flux vector for torque control. A similar thing is done with PM motors. But obviously doesn't use slip. I think it is called field oriented control, FOC. The inverter remains the same. It's just the smarts. You should be able to find some literature on the subject.

major


----------



## bart_dood (Sep 2, 2010)

major said:


> Yep, you need a torque control. So the throttle pedal input commands the torque output of the motor. I'm familiar with induction motors in EVs and use close loop flux vector for torque control. A similar thing is done with PM motors. But obviously doesn't use slip. I think it is called field oriented control, FOC. The inverter remains the same. It's just the smarts. You should be able to find some literature on the subject.
> 
> major


FOV is what the software currently uses, but alas like I said it uses fixed speed.
I'm guessing that when you say it should be torque control it really is current? can't measure torque directly and current is the next best thing..

I think re-writing such code might be beyond my abilities...not sure where I go from here...


----------



## major (Apr 4, 2008)

bart_dood said:


> FOV is what the software currently uses, but alas like I said it uses fixed speed.
> I'm guessing that when you say it should be torque control it really is current? can't measure torque directly and current is the next best thing..
> 
> I think re-writing such code might be beyond my abilities...not sure where I go from here...


Check out this thread. http://www.diyelectriccar.com/forums/showthread.php?t=51983


----------



## Harold in CR (Sep 8, 2008)

Check out this E/S thread, in case you are not aware of it. Guy is trying to manipulate the plug in for his Insight. Maybe he can provide some input ??

http://endless-sphere.com/forums/viewtopic.php?f=7&t=22246


----------



## david85 (Nov 12, 2007)

Bart, 

from what I understand, you achive torque control in a BLDC setup with a closed loop current feedback since torque is proportional to current draw through the power stage of the controller.


----------

