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Motor Inductance

Valid for S300, S400, S600, S700

General

Minimum and maximum motor inductance is given in the technical data of the instructions manuals of the servo amplifiers. Depending on the mains supply voltage different values are given. If motor induction is too high, the required motor current cannot be delivered in the required time. An inductance too low has the result, that current is given too fast to the motor.

Minimum motor inductance

The minimum load inductance has been researched empirically.
Target: current ripple (rated current and rated voltage at 8 kHz) should be maximum 10%

What happens if motor inductance is too low

  • Current ripple and power loss increase.
    • motor temperature rises
    • control behavior becomes bad
    • motor runs not as smooth as before, trembling 
  • F14 (power stage fault) may occur in extreme cases 
  • Motor becomes loud 

Possible measures

  • S300 and S700: set FILTMODE to 2 (Smith Predictor)
  • S300/S400/S600: set PWM to 16 kHz
  • use a motor choke

Check recommendation

  • A test is recommended, if the given minimum value of the motor inductance remains under
  • A test is required,
    • if operational torque is near the motor torque limit
    • in case of long motor cables (approx. >10m)
    • if very smooth running is required

Maximum motor inductance

The maximum load inductance has been researched empirically.
Target: current should be delivered (with rated mains voltage) within 3 cycles of the current control circuit.

What happens if motor inductance is too high

  • control performance becomes bad
  • current rises slow / torque rises slow
  • high frequent oscillations cannot be controlled

Check recommendation

  • A test is recommended
    • if the given maximum value of the motor inductance in exceeded
    • in case of strongly oscillating systems
    • if highest dynamic is required (acceleration to target velocity in some ms)