Summary
Both AC line reactors and DC chokes are valid passive solutions for reducing harmonics impact.
AC line reactors advantages and drawbacks
Advantages
AC line reactors can be easily added in front of any drive since they are wired on the input lines. This can help reduce ripple voltage when the input voltage is unbalanced.
Since the AC line reactor is located in front of the input rectifier, it builds a low pass filter with the capacitors located on the DC bus at the output of the rectifier and the phase-to-phase capacitors included in the EMC filter. This provides protection for the input rectifier against overvoltage.
Drawbacks
AC line reactors are bigger and more expensive than a DC choke for the same drive input current THDi.
AC line reactors create more DC bus voltage drop than a DC choke for the same input current THDi.
A 3-phase AC line reactor built on the same magnetic core does not help in the drive’s input EMC filter for high-frequency. The common mode inductance is canceled by the coils sharing the common core, making it not effective at blocking the higher frequency common mode noise.
DC chokes advantages and drawbacks
Advantages
DC chokes are smaller and less expensive than AC line reactors for the same input current THDi reduction.
DC chokes create less DC bus voltage drop than an AC line reactor for the same input current THDi.
Splitting the DC choke into two chokes, one on the DC+ and one on the DC-, allows it to work also in reducing high frequency noise. This helps the input EMI filter by filtering some high-frequency emissions coming from the output inverter switching.
Drawbacks
DC chokes do not provide protection of the input rectifier against mains power supply overvoltage.
If it is not integrated into the drive, additional terminals must be provided by the drive in order to insert an external DC choke.