SLLU336A May   2021  – January 2022 MCT8316A

 

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3.3.1 Maximum motor electrical speed (Hz)

Using the motor’s datasheet, the user can input the maximum motor electrical speed in Hz. If this data is not available, the user can input the number of pole pairs and motor mechanical speed in RPM. The GUI will convert the motor mechanical speed in RPM to motor electrical speed in Hz using Equation 1.

Equation 1. fElectrical=nPolePairs∙ωMechanical60    

Where:

  • ωMechanical is the mechanical speed in units revolutions per minute (RPM)

  • fElectrical is the electrical speed in units of hertz (Hz)

  • nPolePairs is the number of motor pole pairs

Configure the abnormal speed threshold [LOCK_ABN_SPEED] to 150% of maximum speed [MAX_SPEED].

Note:

Determining number of motor poles without a motor datasheet:

  1. Use a lab power supply and make sure the current limit is set to less than the motor rated current. Do not turn on the supply

  2. Connect V+ of the supply to phase A and V- of the supply to phase B of the motor. Any 2 of the 3 phases can be chosen at random if they are not labeled

  3. Turn on supply The rotor should have settled at one position with the injecting current.

  4. Manually rotate the rotor until rotor snaps to another settle position. It will have several settle-down positions around one mechanical cycle

  5. Count the number of settle-down positions for one fully mechanical cycle, which is the number of pole pairs. Multiplying by two calculates the number of poles.

Be careful of gearing systems within a motor. The gearing ratio will determine how many rotor revolutions correlate to the shaft’s mechanical revolution.