DRV10975: Speed in duty 100%

Hi Masayoshi,

Thanks for posting in E2E forum. I loaded the EEPROM settings into the GUI and here are my observations:

1. The phase to center tap resistance of the motor the customer is using is 16 ohms. However, the recommended resistance range for this device is between 0.3 ohms and 12 ohms. Please check the table below. Can you check with the customer to make sure the resistance is 16 ohms? If yes, then this device will not be able to support the motor. 

2. In order to optimize the control performance, DRV10975 limits the output voltage depending on the Software current limit settings. In this case, the software current limit is set to 0.4A which is too low.This might limit the output voltage and speed depending on the load on the motor. Can you increase the current limit  and try again?

3. Open to closed loop threshold is set to 153.6 Hz which seems too high. If this frequency is greater than the base electrical frequency, then the device will stay in open loop and cause difference in speed performance because in open loop, device doesn't read the Speed command. What is the rated speed and number of pole pairs of the motor?   

Regards,

Vishnu

Hi Vishnu,

Thanks for your advice.

1. I understand the recommended resistance is 0.3 to 12 ohm. I've confirmed the resistance of the motor is 12.2 ohm. It seems violate the spec. Should the customer use other motor?

2. Because of the motor spec, the customer can't increase the current limit. When increase the current limit, the motor can't achieve higher speed.

3. Rated speed is 8000 rpm and number of pole is 12. Could you tell me how much the Open to closed loop threshold is the best to set?

Regards,

Yoshi

Hi Masayoshi,

1. Anything outside the spec is not recommended as it wouldn't be possible to achieve the optimum performance.

2. The reason why motor can't achieve high speed is because when the current limit is increased, motor current increases. When the motor current increases, the voltage drop across the stator resistance increases significantly (because of High Rph) and this drop limits the speed due to low BEMF. 

3. The base electrical frequency of the motor is 800 Hz. So what you have now should be good. Still can you try decreasing it to around 40 Hz?

Regards,

Vishnu

Hi Vishnu,

When the customer decreasing the Open to closed loop threshold to 38.4Hz. The motor didn't start up to spin.

I understood their motor resistance is violated the recommendation spec. But, please let me know if there is any other solution.

Regards,

Yoshi

Yoshi,

Since the BEMF constant is low, you can leave the open to closed loop threshold to 153.6 Hz. Is the supply voltage constant during both attempts? Can you try increasing the align time, first order acceleration and second order acceleration constant? Increasing these parameters gives more time to align the rotor and estimate the BEMF. Once the device operates in closed loop, read the estimated Kt and make sure it matches the programmed Kt.

Please let me know if these recommendations work. If not, then enable all the faults and let me know what fault gets triggered if there are any.

Regards,

Vishnu