Frequency inverter with AC line reactor or DC choke?
Is it AC line reactor more important than DC choke in a frequency inverter? If AC line reactor is missing in the inverter, what are possible impacts to the inverter? And how about DC choke?
Quality frequency inverters incorporate either an AC Reactor or DC Reactor (choke). Their inclusion in the basic design of the frequency inverter allows the design engineer to maximize the advantages of the choke. Their function is to reduce the current distortion caused by the input stage rectifiers by slowing the rate of change of current, and thus charging the internal capacitor at a slower rate over a longer time.
The Harmonic Distortion caused by a frequency inverter is related to its size & load, choke size, and the supply network parameters.
With no AC Reactor or DC Choke, the harmonic distortion will be greater.
Another consideration should be a properly sized source transformer that provides enough impedance. The sized source transformer used as an isolation transformer (although a bit more of an investment) should provide 3 to 5% impedance yet also provides Voltage Transient mitigation with ten to one reduction in impulse peaks, as well as noise reduction through the use of a Delta primary to Wye secondary with center tap ground. It provides additional protection for the frequency inverter front (Converter) end while proper ground of the Source to inverter, frequency inverter to Motor and Motor to Voltage Source assists in mitigating high frequency noise, especially when flat braid is used as the grounding straps. This protects your investment and assists in keeping the variable frequency inverter from generating noise into the supply that can compromise your nearby instrumentation, and PLC power supplies, etc. As well you can tap up the transformer giving you a higher input voltage mitigating the voltage drop issues resulting from the higher impedance.
The DC link assists in mitigating DC Bus Ripple and increasing the input impedance enabling a slower inrush for power on and sudden demand current requirements furthering the life of your capacitors, while a sized supply transformer protects the front end of the frequency inverter drive by providing voltage noise protection and adding input impedance for smoother current and adding a capability to change taps to prevent a voltage drop, while input reactors slow inrush current furthering the life of your input components and capacitors but add no protection from Voltage impulses or noise to the drive converter components, and add voltage drop increasing stress on those components. The important thing to remember is that “Proper” systemic design protects your frequency inverters and system components investment.
