SLVAFO8A April   2024  – May 2024 DRV8214 , DRV8234

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction: Need for Sensorless Designs
  5. 2Ripple Counting − Concept
    1. 2.1 Ripple Counting Algorithm Details
  6. 3Case Study: Robotic Wheel Drive
    1. 3.1 Robotic Wheel Motor Operating Conditions
    2. 3.2 Tuning Parameters for Ripple Counting
      1. 3.2.1 Resistance Parameters
      2. 3.2.2 KMC and KMC_SCALE
        1. 3.2.2.1 Tuning KMC_SCALE
        2. 3.2.2.2 Tuning KMC
    3. 3.3 Robotic Wheel Motor with Ripple Counting
      1. 3.3.1 Inrush and Steady State Performance
        1. 3.3.1.1 Motor Speed Calculation
      2. 3.3.2 Soft Start
      3. 3.3.3 Loaded Conditions
  7. 4Challenges and Workarounds
    1. 4.1 Low Average Currents
    2. 4.2 Motor Inertia During Stop
    3. 4.3 Inrush
    4. 4.4 High Load Conditions
  8. 5Summary
  9. 6References
  10. 7Revision History

4.4 High Load Conditions

During high load torque conditions, the ripple counting algorithm fails to detect a few current ripples. At these operating conditions, the motor speed is usually too slow for the algorithm to estimate accurately. Furthermore, at such low speeds, any error in the motor resistance value compounds multifold to the actual speed estimation by the algorithm. The workaround here is to turn off the error corrector (if already on) by setting DIS_EC to 1b. The recommendation is to program the MCU to detect motor current with the IPROPI pin or the IMTR register. Switch off the error corrector once the motor current value crosses 50% of full load (stall) current. Turn the error corrector back on when the motor current value is below 50%.

Accuracy calculation is shown in Table 4-2.

Table 4-2 Accuracy at High Loads
Parameter Error Corrector ON Error Corrector OFF
50% Load (650mA) 60% Load (780mA) 70% Load (910mA) 50% Load (650mA) 60% Load (780mA) 70% Load (910mA)
Encoder Counts 40 32 20 40 32 20
RC_OUT Counts 60 36 15 60 48 30
Accuracy 100% 75% 50% 100% 100% 100%
Error Corrector ON (50% Load)Figure 4-10 Error Corrector ON (50% Load)
Error Corrector ON (60% Load)Figure 4-12 Error Corrector ON (60% Load)
Error Corrector ON (70% Load)Figure 4-14 Error Corrector ON (70% Load)
Error Corrector OFF (50% Load)Figure 4-11 Error Corrector OFF (50% Load)
Error Corrector OFF (60% Load)Figure 4-13 Error Corrector OFF (60% Load)
Error Corrector OFF (70% Load)Figure 4-15 Error Corrector OFF (70% Load)