Installation manual

Geo Direct PWM Amplifier
PWM Frequency 36
PWM FREQUENCY
The minimum PWM frequency of a system is based on the time constant of the motor. In general, the
lower the time constant, the higher the PWM frequency should be. The motor time constant is calculated
dividing the motor inductance by the resistance (phase-phase). The minimum PWM Frequency is then
determined using the following relationship:







;






=>








Example: A motor with an inductance of 6.1 millihenries (mH), and a resistance of 11.50 Ohms (
phase-phase) yields a time constant of 0.53 milliseconds. Therefore, the minimum PWM Frequency is
about ~6000Hz (6.0 KHz).
Note
Systems with very low time constants (needing higher PWM
frequencies) may require the addition of chokes or in-line inductive
loads to obtain a good current loop bandwidth.
Note
The maximum PWM frequency for each model of the Geo Direct
PWM Drives is listed in the electrical specifications.