Why DC Bus voltages are used to store in a VFD ?

Why DC Bus voltages are used to store in a VFD with DC Bus Capacitors ?

What's the need of storing the DC Bus voltages , though the input line keeps on coming continuously and the rectifiers keeps on rectifying the input AC supply .....

If I understand right, you are asking why standard VFD inverters are using a constant voltage DC bus? That's in fact not obvious. Besides a voltage source inverter topology, there are also a current source type and other more sophisticated topologies. See https://en.wikipedia.org/wiki/Variable-frequency_drive#Generic_topologies

Nevertheless is the constant voltage bus a straightforward concept that can be easily implemented.

Energy needs to be stored somewhere; either in a capacitor or an inductor, otherwise there will be no power available when the AC input voltage is close to zero.

godfreyl said:

Energy needs to be stored somewhere; either in a capacitor or an inductor, otherwise there will be no power available when the AC input voltage is close to zero.

Click to expand...

so this variation is in almost every cycle as AC alters between positive and negative must then generally be some thing to store power in any circuit

godfreyl said:

Energy needs to be stored somewhere; either in a capacitor or an inductor, otherwise there will be no power available when the AC input voltage is close to zero.

Click to expand...

But if there's no AC input power then any brand or any kind of Drive (VFD) displays the Alarm of UV or LE ......

My question is still unanswerable , why we do need to store the DC Bus with so heavy capacitors ?
What's the advantage of it ? What would happen if we don't use the DC Bus Capacitors or if we don't store it ?

Your questions are basically answered in the link in post #2 and more verbosely in power engineering text books.

The link gives an example of an inverter without energy storage, the cycloconverter that is still used for large drives in the MW scale. It's output voltage is never sinusoidal.

Cycloconverter or matrix converter (MC) topologies (see image): Cycloconverters and MCs are AC-AC converters that have no intermediate DC link for energy storage. A cycloconverter operates as a three-phase current source via three anti-parallel connected SCR-bridges in six-pulse configuration, each cycloconverter phase acting selectively to convert fixed line frequency AC voltage to an alternating voltage at a variable load frequency. MC drives are IGBT-based.


But the drives that i have seen all have IGBTs or IGBT modules in it ....
Would you tell me the below written drives belong to which particular type according to wikipedia link ?

1) Puma RM5G
2) EnyDrive TD 3000 (Emerson Industrial Automation)
3) YASKAWA H1000
4) YASKAWA G7
5) Lenze Servo Drives 93200 & 9326 series
6) ERIC Drive EI - 7001 - 005H

thanks

All small power (< 100 kW or so) industry standard VFD are using a constant voltage bus, it's surely the case for the listed ones.

Are all these VSI or CSI ?