VSI vs CSI VFD topology

[cmelguet]

Hi,

Can someone explain when I should use a CSI (current source inverter) topology for the inverter of the VSD or when to use a VSI (Voltage Source inverter) kind?

Thanks.

 

[Skogsgurra]

It is mostly a question of economy and availability.

CSI is mostly used for large drives while VSI is used all over the power spectrum.

VSI (with PWM output) generates lots of EMI that cannot always be filtered away. But they are easy to control and are therefore used where tight speed or torque control is needed.

CSI is not suitable for drives where fast and precise control is needed because controlling them involves changing current in the huge DC link inductance. But, they do not generate as much EMI as VSI inverters do. And are sometimes more economical than large VSI inverters.

Mains Power Factor *can* be controlled in a VSI inverter but cannot be controlled in a CSI inverter. That alone may be a criterion to select a VSI.

All serious drive manufacturers can help you do the right selection.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[jraef]

Traditionally , CSI topology has a reputation for being "bullet proof". The components are (or at least were) much less susceptible to the vagaries of modern power systems where grid switching, sags and spikes are too common. One such anecdote that a Robicon salesman friend of mine used to spout all the time was when some 2300V 1000HP pumps were flooded, the CSI drives kept pumping power into them under current limit, they only shut down when other equipment in the pump station flooded out and took out the main power. A PWM drive would not have fared so well I think.

But a sometimes negative aspect to CSI technology was that the motors and drives had to be impedance matched. That meant replacing the motor with a spare meant a new commissioning procedure, usually performed by the CSI drive mfr. For some people, the time waiting for that to take place was undesirable.

"Dear future generations: Please accept our apologies. We were rolling drunk on petroleum."
— Kilgore Trout (via Kurt Vonnegut)
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[electricuwe]

Unless special PWM-rectifiers are used, CSI drives suffer from a poor fundamental power factor at speeds below nominal.