FOC SDK 3.4 with STM32F303CB

Posted on March 29, 2014 at 04:58

Found the bug that was at fault. I have selected PB5 as the motor 2 phase 3 low side pwm, but the library sets the alternate function register incorrectly. The alternate function for TIM8 on PB5 is 3.

GPIOB_AFRL is set to 0x00244000, it should be 0x00344000.

The problem is with STMCWB, not the library. It generates the following incorrect line in ''Control stage parameters motor 2'':

#define PHASE_WL_GPIO_AF2                GPIO_AF_2

Workaround for now is to edit the template file to GPIO_AF_3

Posted on March 29, 2014 at 20:03

Now that I have it working, I have another question. When I used the STM32F103, I was able to go to much higher pwm values which worked well for my small motor. I found that 32 - 36 kHz worked well.

With SMT32F303 I can only go up to a maximum of 27500 Hz, after which I get an error:

ERR   12:02:09  1       511  Maximum resulting modulation index clamped to minimum allowed (81%) for motor M1

ERR   12:02:09  2       511  Maximum resulting modulation index clamped to minimum allowed (81%) for motor M2

Are there any other parameters I can change to get to a higher PWM, or is this a limitation of using the onboard current sensing amplifiers?

Posted on March 30, 2014 at 22:53

Another question: now that I have 2 motors running I cannot figure out how to get them to run simultaneously. I can start motor 1, but it stops as soon as I start motor 2. I can start motor 2 but it stops as soon as I start motor 1. No errors are received over the UART protocol, just a successful acknowledge of the start command.

The library clearly says simultaneous control of dual motors. What am I missing here? Please help.

Posted on March 31, 2014 at 11:27

Ciao Joevn,

thank for you valuable feedback.

As you probably already understand just two embeded OPAMP are sufficient for the three shunt current sensing because the three inputs are multiplexed inside.

I reported the issue you submited to the WB designer for the next version. The workaround you popose is ok.

The maximum modulation index (MMI) is calculated by WB according PWM freq, Dead time, Tnoise/TRise and selected current sampling time. Is used to avoid the noise caused by the 6-PWM switching. There is a limitation in the minimum MMI supported by WB/Lib. that is 81% and this don't depend on the microcontroller used but by the algorithm. You can try to reduce the mentioned paramenters in order to use higher PWM frequencies.

The behaviour you mention for the dual drive is not the one expected. Dual drive means dual simultaneous. Probably you are facing with some issue related to an high FOC rate, in this case you can try to increase the execution rate to 2 or 3 PWM period. Or it is just an issue related to the serial communication, please verify that the ''All motor'' check box is chceckd in the monitor page of WB.

Ciao

Gigi