Pmsm3_4: problem in speed control at low rpm

pmsm 3-4 is position control, you want 3-1

with a sensor you should be able to work down to 0 RPM

http://focus.ti.com/general/docs/gencontent.tsp?contentId=67194#dmcs

myself is also working in the same project.

we are done with position control part. earlier we were using incremental feedback, where we were getting problems because of the calibrated angle i.e.offset.

the problem got resolved when we used actual resolver's output with RDC interface (12 bit.)

Now for speed control i.e. build level 5 as per code structure, i am able to control the motor upto say 400 rpm smoothly, but below that the motor is moving in steps and

not quite smoothly. we are using 20KHz ISR i.e. 50us.  if i have to run the motor around 200 rpm, motor will cross 0.06  mechanical degree in one ISR period. but

as the resolution is 12 bit, i am not able to sense below 0.088 degree. will i be able to move my motor below 400 rpm with increased resolution of sensor?

we feel that our Id and Iq loops are ok, as with that only we are running our position loop.

if it would have been a problem with speed loop gains, that should have hampered the high speed operation also. (correct me if i am wrong)

We currently have the Delfino & Piccolo kits for evaluation for a job where we are planning a low speed custom motor (down to zero RPM) using a resolver.  But the PMSM with resolver project in C2000 is listed at TBD.  What is up with this?  When will this status be finalized?

Robert,

We currently have a Piccolo PMSM + Encoder project in the works for the High Voltage Kit, but it's on hold as we work on some other items.

For the resolver, we have an example system for our previous F281x and F280x series, you can find them here

http://focus.ti.com/general/docs/gencontent.tsp?contentId=67194#dmcs

It looks like you already have some experience with motor control systems, so you should be able to pull in the resolver technique into the code for the High Voltage kit.  Are you building your own resolver interface board?

Hello Chris,

A resolver interface board is a distinct possibility.  We would like to avoid a dedicated RDC chip if possible and use the TI code solution for the resolver.

What would be really nice is if TI would pull this old resolver code into controlSUITE C2000, Code Composer 4, for Picolo and Delfino.  C2000 support including the resolver code would also be useful for your high-temp offering F2812-HT and roadmap offering  SM320F28335-HT.

Do you have a reference design for a resolver interface board?

Robert,

From the documentation I referenced:

The schematic design of resolver interface board is taken from the “TMS320F240 DSP Solution

for Obtaining Resolver Angular Position and Speed (SPRA605)”, which can be seen in figure 5.

Have you looked at the code? There is a macro for the resolver calculation, and the implementation is REALLY straight forward.  Once you install the F280x version you can see the source here:

C:\tidcs\DMC\c28\v32x\sys\PMSM3_3_280x\cIQmath\src

We don't have plans to release another resolver solution at this time, we are focusing efforts on additional sensorless implementations.

BTW - for the F2812-HT, there is a working resolver solution available: http://focus.ti.com/docs/toolsw/folders/print/sprc178.html