Industrial drives and inverters often use a six-pulse rectifier feeding a DC bus. Adding inductance can reduce peak charging current, current harmonics, capacitor stress, and upstream distortion. The inductor can be placed on the AC input or in the DC link, but a DC reactor vs AC reactor inverter comparison must consider which electrical stress and protection goals matter.
What an AC line reactor does
An AC reactor is installed in one or all input phases before the rectifier. It limits current rise during line disturbances and rectifier commutation, reduces peak input current, adds impedance against notches, and can provide some protection from utility transients. It also causes voltage drop that depends on load current and system impedance.
Three-phase reactors must maintain balanced inductance and withstand line voltage, fault current, harmonics, and common-mode voltage to core or chassis. An integrated three-phase core can reduce size, but unbalance and zero-sequence behavior need analysis.
What a DC-link reactor does
A DC reactor sits between the rectifier and bus capacitor, either in the positive, negative, or split link depending on topology. It smooths DC charging current and reduces RMS capacitor current and line-current peaks. Because it is after the rectifier, its insulation and waveform differ from an AC line reactor.
The reactor carries DC current with a six-pulse or switching ripple component. The core requires energy-storage capability under bias. A gapped ferrite, powder core, laminated core, or other construction may be appropriate depending on current, ripple frequency, loss, size, and acoustic requirements.
Harmonic reduction is system dependent
Both locations can improve input current waveform, but the result depends on source impedance, bus capacitance, load, rectifier topology, and inductance percentage. An AC reactor affects each phase directly and can reduce commutation notches seen by the supply. A DC reactor may provide strong smoothing with lower line-to-ground insulation complexity in some designs.
Neither option necessarily meets stringent harmonic limits alone. Twelve-pulse arrangements, passive harmonic filters, active front ends, or active filters may be needed. Simulate and measure at the intended source short-circuit ratio and load profile.
Regenerative and active-front-end inverters
An active front end controls bidirectional current and has its own line inductance requirement. A reactor selected for a diode rectifier cannot be assumed suitable. PWM voltage, switching ripple, common-mode stress, control stability, and fault current become central. A DC-link choke may serve a different ripple or decoupling role.
Saturation and transient duty
AC reactors experience phase current and possible DC offset during faults or asymmetrical conditions. DC reactors operate under substantial DC bias and must retain minimum incremental inductance at peak current and temperature. Precharge, capacitor faults, line dips, motor regeneration, and braking events can exceed nominal current.
Saturation current and thermal current are different limits. A short pulse may remain thermally safe but lose inductance and allow excessive semiconductor or capacitor current.
Loss, noise, and cooling
Winding loss includes RMS current and harmonic AC effects. Core loss depends on flux ripple and material. Laminated reactors can produce audible hum from line harmonics and mechanical forces. Gap fringing can heat nearby conductors. Mounting, airflow, enclosure, fan failure, and neighboring heat sources determine final temperature.
Selection checklist
- Define inverter input topology, line voltage, source impedance, and bus capacitance.
- Set harmonic, rectifier-current, capacitor-ripple, and transient-protection targets.
- Model AC reactor, DC reactor, and combined options over load and line range.
- Specify inductance at current and temperature, resistance, fault duty, and insulation.
- Check voltage drop, bus regulation, precharge, regeneration, and control stability.
- Validate harmonic spectrum, temperature, acoustic noise, and protection in the final cabinet.
BaoHui Tech needs line and DC-bus waveforms, current spectrum, source data, inverter topology, target impedance, fault and regenerative duty, cooling, size, insulation, and harmonic limits to design the reactor.
Frequently asked questions
Can both an AC and DC reactor be used?
Yes, but added impedance, voltage drop, cost, heat, and control interaction should be justified by system analysis.
Which location gives lower harmonics?
There is no universal answer. Source impedance, bus capacitance, rectifier, load, and inductance determine the result.