DRV10970EVM: DRV10970 RPM stability

Hello 

I am usign EVM board as is with the onboard PWM signal. 

To be totaly exact the problem is thrue all of the range of motor speed. I set a "desired" frequency of the motor and that it jumps +- 5Hz. The issue is that this is more problematic on the LOW range of the frequency where we will be running the motor most of the time. I checked the PWM and it looks stable to me.

Is there some more parameter that can be tweaked to get more stable frequency of the motor ? 

What is the expected stability that we can achive with this controler ? 

Thank you for you answers Joze

Hello Joze,

Is there a specific reason why you have the drive adjusted to specifically 5°? One thought, I would recommend floating the DAA pin to use adaptive drive angle adjustment. This monitors the U-phase current and U-phase hall signal in order to align them properly. If the 5° alignment differs from 30Hz vs 60Hz this should hopefully address this issue if this is the problem.

Another idea would be to try the trapezoidal mode with 0° hall placement to see if this provides better speed stability. The stability is not defined by the driver since this is greatly dependent on the motor that is being used.

Best,

Isaac

Hello Isaac 

The reason for 5° is testing that I did and here i got the best results. In case of floatin ( adaptive DAA ) motor frequency stability is even worse.. it jums +-10Hz  but in case of 5° it "only" jumps +- 5Hz. The same "bad"resault I get if I select 10° DAA.

WE have managed to get the specification of the motor from the producer .. can this provide more info to you ? 

1 Nominal voltage UN                                               12 V

2 Terminal resistance, phase-phase R                     6,95Ω

3 Efficiency, max. ηmax.                                           73 %

4 No-load speed n0                                                  6 500 min-1

5 No-load current, typ. (with shaft o 3 mm) I0          0,039  A

6 Starting torque MA                                                29,1 mNm

7 Speed constant kn                                                561 min-1/V

8 Back-EMF constant kE                                         1,78 mV/min-1

9 Torque constant kM                                              17  mNm/A

10 Current constant kI                                             0,0588 A/mNm

11 Slope of n-M curve Δn /ΔM                                229 min-1/mNm

12 Terminal inductance, phase-phase L                 884 μH

13 Mechanical time constant τm                             7,92 ms

14 Rotor inertia J                                                    3,3 gcm2

15 Angular acceleration αmax.                               88,2 103rad/s2

20 Mass                                                                   25,5 g

21 Direction of rotation                                            electronically reversible

22 Speed up to nmax.                                             10 000 min-1

23 Number of pole pairs                                           7

24 Hall sensors                                                        digital

They claim that the HALL placement is 120°

I have tried the trapezioadal mode but the frequency is even worse.

With testing i have found out that the best combo for stability in low end of frequency is sinusoidal operation
mode with 30° Hall placement with 5° drive angle adjustment, here i get +- 2hz BUT i dont have linear speed control .. it goes from 20Hz to 60Hz .. that wihth MIN PWM change it goest to 100Hz .. and it goes up-to 160 Hz only 

Do you have any more advice how to make this work.

Thank you in advance.

BR joze

Hi Joze,

We are working on assistance to tune these motor parameters, please allow us another day to look over this data. 

Thanks,
Aaron

Hi Joze,

I think this issue is due to the Hall placement. DRV10970 supports 0 deg and 30 deg hall placements only. Also, this device has 5 deg and 10 deg lead angle adjustments only so nothing much can be done. I would recommend you to check MCT8316Z which is a sensored trapezoidal control device with more lead angle settings.

Regards,

Vishnu 

HI 

I would like to get teh evaluation baord for this driver .. but is not available. Do you have any idea when it will be ? 

Is there any other option available from TI ?

br Joze

Hi Joze,

You can place an order from the below link.

https://www.ti.com/tool/DRV10970EVM#order-start-development

Regards,

Vishnu

Hi Joze,

Do you need more assistance with this thread or can we close it?

Thanks,
Aaron

HI 

The issue is that i dont know .. i would like to order EVM 

https://www.ti.com/tool/MCT8316ZTEVM#order-start-development

but the problem is that is not availabe .. so i can not test.

Do you have any idea when it will be back on order ? 

br joze