AC Drive with DC Bus?

Without smoothing the voltage & stablize the volatge will not possible without the rectfier section

S.Pathan

Some VFDs allow this, some do not. You must check with each manufacturer to see on a case-by-case basis. The problem is whether or not the connection point they provide is before or after the smoothing capacitors and DC bus choke (if there is one). Another issue is where the VFD derives it's control power. For some it is pulled off of the DC bus, so that would be no problem. But for others the control power is taken from a separate SMPS connected to the AC line source, so if you have no AC you have no control power to run the VFD!

You are correct. If you are running your VFD successfully from a DC Bus then the rectifier section is not being used at all.

Its better to connect +DC via the rectifier input terminals then use with -ive commoned as this then utilises the inrush circuit at switch controlling the charge current to a low value.

If supplying more than one inverter trying to bus together to harness regeneration then one is connected as a parasite to the main drive, this must be sized for total load and DC chokes help in this regard.

There are 2 types of VFD's available, they are inverters and converters(in Siemens parlance). 1 takes line voltage, typically 3 phase but some smaller ones will work on single phase, and converts it to DC and then back to AC. The other takes DC and inverts it into AC. This type is often used in multi-motor systems and is particularly useful in a situation where 1 or more motors are being overhauled as the power just gets dumped back on the bus and used by the other drives instead of being dumped into a braking resistor. There is usually a "Front end" consisting of a rectifier and brake chopper that sources the DC for the system.