HomeFAQWhat is the trouble with using a filter for treating the VFD waveform?

What is the trouble with using a filter for treating the VFD waveform?

Cost, heat and space. The question really becomes is it necessary? Inverter duty motors are designed specifically to accept the less than perfect waveforms to a certain level. That level is a combination of the particular variable frequency drive being used, the motor and the cable length/capacitance of the system.

In general, a very low-inductance load will increase the DC bus ripple current and increase heating of the capacitor bank. In general, using a general-purpose VFD with a NEMA design or inverter-rated motor should be no problem, but if you rig up an R-L load for testing purposes, make sure there's enough inductance. Otherwise you could damage the DC bus capacitors.

In the past, if I just wanted to load an inverter to check the hardware, I have disassembled a general-purpose induction motor and removed the rotor. The stator makes a nice R-L load. They're not needed in most cases (AFAIK, I'm not a variable frequency drive user or installer), I just mentioned a case in which they are actually needed (i.e. multiple inverters in parallel).

About the "empty" induction motor, as an R-L load, I wanted to do the same (recently it was for testing dead-time compensation, since the motion induced back-EMF would have added some "noise" to my measurements), but I expected the inductance to be orders of magnitude lower than with the rotor.

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