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Any way to reduce the start time of DRV10983

Jinzhou Chen
Prodigy 210 points
Other Parts Discussed in Thread: DRV10983

I am testing a motor (12V, 2 pole-pairs, Rs = 0.38, Kt = 29 mV/Hz) with a load disk of 100 g using DRV10983 demo board. Generally speaking, the system works fine but I want the start up time to be shorter. Currently, the start up time of motor from 0 to 500 RPM is about 1.9 second, I want it to be about 0.5 second. Below are my settings in the GUI:

IPD enabled, current threshold 0.6A, advance angle 30 deg, IPD clock 95 Hz, IPD release mode is Brake (IPD works fine and the time is within 0.1 second)

Startup setting: Align time is 0.04 s, First Order Accelerate 9.2Hz/s, second order accelerate 0.66 Hz/s2, Open to Closed Loop threshold 25.6 Hz, Open Loop Current rate 6 VCC/s, Open Loop Current 1.6 A.

The maximum speed of the motor is 9300 RPM with the 100 g load, and the working current is within 1 A.

I adjust the startup settings according the Tuning Guide, the First Order Accelerate and second order accelerate are set to the largest value that the motor can startup. I also tried to reduce the Open to Closed Loop Threshold, but it seems that the startup time becomes even longer (Maybe the BEMF is not high enough).

I also measured the phase current and found that the peak phase current during startup is about 1 A, which is lower than my set value 1.6 A. Is it possible to increase the startup phase current so as to increase the acceleration during startup?

 

Below are saved GUI settings:

DRV10983 0x20 0x2A
DRV10983 0x21 0x28
DRV10983 0x22 0x3C
DRV10983 0x23 0xF
DRV10983 0x24 0xC0
DRV10983 0x25 0xF3
DRV10983 0x26 0x8F
DRV10983 0x27 0xB8
DRV10983 0x28 0xDD
DRV10983 0x29 0xA5
DRV10983 0x2A 0x2F
DRV10983 0x2B 0xC
  • 0
    TI__Guru** 114905 points
    Hi Jinzhou,

    Our experts have been notified and should reply soon.
  • 0 in reply to Rick Duncan
    TI__Expert 3010 points

    Hi Jinzhou,

    Open loop current setting is used to calculate duty cycle based on following equation

    ULimit = ILimit x Rm + Speed(Hz) x Kt

    Refer section 9.4.4 Start-up Current Setting section in datasheet for DRV10983 for more details; So DRV10983 doesn’t set current limit directly.

    I would recommend changing configured values of resistance and Kt and check whether you are able to command more current. The open loop time can be reduced by increasing value ‘First order Accelerate’ and ‘Second order Accelerate’, I see you are using lower value (9.2 Hz/s and 0.66Hz/s^2) than the capability of DRV10983. What happens when you configure higher values of these parameters?

     

    Regards,

    Krushal

  • 0 in reply to Krushal
    Prodigy 210 points
    Hi, Krushal,
    Thank you for your reply. As Rs and Kt are measured realy values, I did not try to regulate these parameters before. But for "First order Accelerate" and "Second order accelerate", I have regulated as suggested in the tuning guide: set the second order accelerate to the minimum, increase the first order accelerate until the motor fail to start up, then set the first order accelerate as the highest value that can start up the motor, then increase the second order accelerate until the motor fail to start up, select the highest value of the second order accelerate that can start up the motor. So these values are already the highest values that can start up the motor.
  • 0 in reply to Jinzhou Chen
    TI__Expert 3010 points

    Hi Jinzhou,

    'First order Accelerate' and 'Second Order Accelerate' are the only parameters available to change the acceleration during startup. As I mention earlier try tweaking motor resistance and Back emf costant Kt; these parameter tends to change from motor to motor and can vary slightly with operating condition

    Regards

    Krushal

     

  • 0 in reply to Krushal
    Prodigy 210 points
    Hi, Krushal,
    I tried to increase the motor resistance and Back emf constant Kt, and then increase the "First order Accelerate", it is true that by this way I can command more current into the motor at start up. However, the start up time can only be reduce to 50% as it triggers over current protection when I want to further increase Rs and Kt to drive more current at start up. The over current lock condition is set to 3.2 A. So this is the fastest start time I can achieve by my current motor and the Demo board, right? Will it damage the Demo board if I uncheck "Current Limit" in "Lock Detect" while I am trying to driving more current into the motor at start up?

    Thank you!
  • 0 in reply to Jinzhou Chen
    TI__Expert 3010 points

    Hi Jinzhou,

    Overcurrent protection is there to prevent excessive current flowing through FETs;So it is not advisable to disable overcurrent fault. Driver has to overcome friction and inertia to start motor from standstill, hence it is not always possible to achieve very fast startup time. Motor Kt, resistance, first order accelerate, second order accelerate are the parameters that will help improve startup time for DRV10983, and if these parameters are already being optimized then I think you you have achieved optimized startup time

    Regards,

    Krushal