Capacitor in DC link of the VFD?
Capacitor in DC link of the VFD?
(OP)
can any1 tell me what is the use of Capacitor in DC link of the VFD? How come a capacitor works on DC? also how does a VFD controlled motor gets its required reactive power as it is being supplied directly from an inverter which isn't a source of reactive power?





RE: Capacitor in DC link of the VFD?
All capacitors will work with DC. They work like a fast charging/discharging battery.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Capacitor in DC link of the VFD?
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(2B)+(2B)' ?
RE: Capacitor in DC link of the VFD?
Thnaks @electricpete yes I'm using a PWM inverter. doesn't the DC link capacitor supply the required reactive power in VFD?
RE: Capacitor in DC link of the VFD?
RE: Capacitor in DC link of the VFD?
Consider first principles:
When a voltage is applied to an inductor such as a motor winding the current does not rise instantly. The current rise due to the application of a square wave front follows a curve based on something like (one minus the reciprocal of the base of natural logarithms).
Apply a sine wave and the current curve becomes somewhat more difficult to plot. When the voltage is dropping, the induction tends to keep the current flowing.
Now you can try to calculate the effect of reducing the voltage applied to an inductor on a point to point basis and plot the curve, both when there is a path for the current supplied by the induction coil (the DC link capacitors) and when there is not a path for the current supplied by the inductor (inductive kick).
Or take advantage of a lot of difficult mathematics done in the past by some unsung genius and use the imaginary concept of reactive power (and the DC link capacitors to provide a path for the inductor supplied current).
BTW Does anyone know who developed the concept of reactive power?
Bill
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"Why not the best?"
Jimmy Carter
RE: Capacitor in DC link of the VFD?
I like the obvious and no-nonsense explanation that Pete gave us. A voltage source delivers what the load asks for. Be it active or reactive power - or a mix. No need to try and visualize how power flows in switches and capacitors.
Gunnar Englund
www.gke.org
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Half full - Half empty? I don't mind. It's what in it that counts.
RE: Capacitor in DC link of the VFD?
Bill
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"Why not the best?"
Jimmy Carter
RE: Capacitor in DC link of the VFD?
RE: Capacitor in DC link of the VFD?
I haven't heard anything about these lately. It is an idea that has fizzled?
RE: Capacitor in DC link of the VFD?
This is a good compendium of why I think.
http://www.eurekamagazine.co.uk/design-engineering...
"You measure the size of the accomplishment by the obstacles you had to overcome to reach your goals" -- Booker T. Washington