TMS320F28069M: Max. possible RPM with a 4 Pole BLDC motor

Hi Sean,

Thank you for clarifying, much appreciated. Which parameters do affect the frequency ?
I mean any parameter, which is configurable in user.h ?
It does not seem obvious to me, as to which parameter would control the motor electrical frequency.
Have a 4 pole motor which can go up to 20,000 RPM; 20,000 x 4/120 = 666 Hz, well within the 2kHz limits at least.

Thanks,
Manu

Correct, the numbers you gave seem reasonable. Keep in mind that sensorless control can be difficult at high frequencies (approaching 2khz). The electrical drive frequency is not a parameter in user.h, it is related to the frequency at which the inverter drives the motor, which in turn is related to the commanded output

Sean

Trying to adapt user.h, got really confused on this line in the instaspin_lab manual:

"Lastly, low inductance motors usually have low flux values also. Make sure that the full scale voltage is set to a value that allows the flux to be identified. Consider this formula when selecting full scale voltage:

Min Flux in V/Hz = USER_IQ_FULL_SCALE_VOLTAGE_V/USER_EST_FREQ_Hz/0.7"
This is on Page 72 of the manual.

Trying to dissect that statement, using the macros from user.h:

#define USER_ISR_FREQ_Hz ((float_t)USER_PWM_FREQ_kHz * 1000.0 / (float_t)USER_NUM_PWM_TICKS_PER_ISR_TICK)
#define USER_CTRL_FREQ_Hz (uint_least32_t)(USER_ISR_FREQ_Hz/USER_NUM_ISR_TICKS_PER_CTRL_TICK)
#define USER_EST_FREQ_Hz (uint_least32_t)(USER_CTRL_FREQ_Hz/USER_NUM_CTRL_TICKS_PER_EST_TICK)

I am unsure about these values, but found them in the accompanying spreadsheet.

USER_NUM_PWM_TICKS_PER_ISR_TICK is it 3 ticks ?
USER_NUM_ISR_TICKS_PER_CTRL_TICK is 1 ?
USER_NUM_CTRL_TICKS_PER_EST_TICK is 1 ?

Are they the right values ?

USER_ISR_FREQ_Hz = 45.0 * 1000/3 = 15000.0
USER_CTRL_FREQ_Hz = 15000.0/1 = 15000.0
USER_EST_FREQ_Hz=15000.0/1 = 15000.0

With the following definitions, calculated using the spreadsheet:
// -- tweaks
#define USER_PWM_FREQ_kHZ (45.0)
#define USER_IQ_FULL_SCALE_FREQ_Hz (1386.0)
#define USER_MOTOR_FLUX_EST_FREQ_Hz (133.0) //(50.0)
#define USER_MAX_ACCEL_EST_Hzps (18.0)
#define USER_IQ_FULL_SCALE_CURRENT_A (18.0)
#define USER_IQ_FULL_SCALE_VOLTAGE_V (34.0)

Min Flux in V/Hz = 34.0/15000.0/0.7 = 0.0032380952380952380952380952381

Now, does it mean to replace

#define USER_MOTOR_RATED_FLUX (0.0340334028)

with this calculated value ? I don't understand where it has to be set ?

Thanks,
Manu

Hi Sean,

Thanks for the clarification.

Thanks,

Manu