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DRV8312-C2-KIT: How to drive two motors in perfect sync from one 3-phase output of driver board? Also problems with max. speed and power usage readout.

Jörn
Prodigy 70 points

Part Number: DRV8312-C2-KIT

Hello,

I'm working with the InstaSpin_BLDC example project for the DRV8312-C2-Kit. I have 3 issues I hope you can assist me with:

  1. I want to drive two identical sensorless 3-phase permanent-magnet motors in perfect synchronization, i.e. applying the same phase voltages to each phase between the two. I have tried to simply connect the phase output for one motor to both motors (so for the 3 output terminals I stuck in 6 cables in total [MOA goes to phase A1 of motor 1 and phase A2 of motor 2, and so on...]). But when I run the InstaSpin application, the execution crashes early on without spinning the motor (only jumping a few steps by the sound of it) and I need to reset the board. I'm no electrical engineer and have a hard time wrapping my head around these kinds of sensorless motor drivers. I'm not sure how to trouble-shoot this. Is my approach even possible for the InstaSpin driver?
  2. Driving a single motor with the InstaSpin application works fine. I want to read out the power usage of the motor (current draw, voltage), but I am unsure how to calculate those values from the data provided. All I can find is some oddly sized "per-unit" (?) values. Can someone tell me what values I need to transform in which way to receive motor voltage in Volt and current in Amps?
  3. Max. speed problem: when entering high speed values (>0.5), my motor can only ever accelerate to 0.42 speed (~1650 RPM) and holds stable there, even though it is rated for over 4400 RPM. What might be the limiting issue here?

  • 0
    TI__Genius 17175 points
    1) You would be better off to have two DRV8312 chips and duplicating the ePWM set for the first motor to the second motor, and driving each using it's own driver, PWM and ADC. That would represent a true two motor solution, and easy enough if you want to drive them with the same settings. I suggest ordering a LaunchXL-F28069M + 2x BoostXL-DRV8301 and using the InstaSPIN-FOC lab for 2 motor control if you want a pre-packaged 2motor control lab

    2) Per-unit value is based on the current scaling of the board you are using, it represents the current from [-1,1] based on the value presented to the ADC from the current sampling circuit. For DRV8312_revD kit, the ADC full scale current is 17.3A, or +/-8.65A. This means, for a value of I = 0.5 pu, your motor Iq is 8.65A*0.5 = 4.325A.

    3) Can your power supply provide enough power to spin the motor to rated speed?

    Sean