Motors and Drives: Variable Frequency Drive (VFD)--Common Advanced Features

Part 7 of the Variable Frequency Drives Series explains more common advanced features often found on variable frequency drives, including: stall prevention, slip compensation, and dc injection.

Stall Prevention

  • Over voltage – needed for deceling: will stop deceling when dc bus voltage rises too high and will continue to decel when dc bus level falls back to normal

  • Over Current- needed during acceling or heavy loading: will stop acceling when current is too high and continue acceling again when current level returns to normal

Slip Compensation/ Boost–Output frequency increases above setpoint automatically to drive the load closer to the original speed

Auto Torque Boost – will increase current during starting automatically until the load is moving

DC Injection – sometimes holding torque is required for short periods of time during starting and stopping: releasing a mechanical brake is a common use.

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