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

3.2.2.1 Tuning KMC_SCALE

Ripple Frequency Calculation Figure 3-1 Ripple Frequency Calculation
  1. From section 8.2.3.1.2.2.1.1, the first step in tuning KMC_SCALE is to obtain the value of actual ripple speed in rad/s. For this method, the motor was connected to DRV8234 at 11V at no-load conditions. The motor current waveform was observed on the oscilloscope using a current probe to obtain the ripple frequency in Hz as shown in Figure 3-1. The number of ripples (54) observed was divided by the time (90ms) to obtain ripple frequency as 600Hz. Using Equation 1, the ripple frequency in rad/s was calculated as 3769.91 rad/s. Let OBS_SPEED = 3770 rad/s.
  2. The next step is to select the lowest value of KMC_SCALE, 00b and set KMC to the highest possible value, 255.
  3. The next step is to set W_SCALE set to a value under which maximum allowable ripple speed is more than OBS_SPEED. In this example, W_SCALE was set to 00b (allowing a maximum value of 4080 rad/s)*, for example, 16 rad/s.
  4. Following the next steps as mentioned in the data sheet, we find that the tuned value of KMC_SCALE for this example is 10b. Figure 8-3 (KMC_SCALE Tuning Procedure) in the data sheet for DRV8234 displays a flowchart for tuning KMC_SCALE. The iterative steps for tuning KMC_SCALE in this example are summarized in Table 3-3.
Table 3-3 KMC_SCALE tuning
Iteration KMC_SCALE KMC SPEED W_SCALE EST_SPEED (rad/s) OBS_SPEED (rad/s) Decision
1 00b 255 0x0F (15) 00b 240 3770 EST<OBS
2 01b 255 0x1E (30) 00b 480 3770 EST<OBS
3 10b 255 0xF0 (240) 00b 3840 3770 EST>OBS