How does VFD carrier frequency and VFD output frequency affect dVdT filters
Most dv/dt output filters are designed to operate on VFD’S that have a carrier frequency of 2 to 4 KHZ. At higher carrier frequencies from 5 to 20 KHz you must consult with the filter factory to find out if derating is required and, if so, how much.
If the output frequency of the VFD is increased above 60 Hz say up to 120 Hz you must also consult with the filter factory to find out if derating is required and, if so, how much. Higher carrier frequencies are used on applications that require lower noise levels in the drive motor (E.g. ventilation supply and or return fans that are installed inside a building air duct). The higher carrier frequencies increase motor lamination vibrations above the human audibility frequency range.
The higher carrier frequencies also lower the harmonic losses in the motor which will make it run cooler thus extending motor life. On the other hand, higher carrier frequencies and or output VFD frequencies above 60 HZ will increase the VFD IGBT switching losses so the VFD may need to be oversized along with the dv/dt output filter.
