In BLDC Motor in general, how to estimate capacitance needed to mitigate voltage pumping (limit to say 20%-30% from power rails) cause by motor reversal or activate braking. What the general methodology to model this and useful guideline to work this out.
The BLDC Motor is being used as servo actuator where it expected to spin forward and backward in accordance to position (or angle) feedback. The postential energy of mechnical elements (mass, gear, etc) will be transulated back to electrical energy which lead to voltage pumping. The role of the capacitor is to absorb these energy. The driven voltage is 24V and would like to limits voltage pumping by 20-30% from 24V.
Becasue the capacitor is absorbing these energy, it expected to get hot.
The General formula for energy absorption by a capacitor is 1/2 CV2..Hope that would help you to calculate the capacitor required.
Hi Mr Kumar, how to define energy from the system to determine the 1/2 C.V2 Please expand that or link to paper?
Hi Richard,
The capacitance value depends on the:
You may wish to check out some details from this Application Notes on the L6235 driver from the ST Microelectronics. The power controller you intend to use may be a different one, but this should give you a good idea about the selection:
http://www.st.com/content/ccc/resource/technical/document/application_note/42/69/71/8a/39/26/44/c9/CD00004396.pdf/files/CD00004396.pdf/jcr:content/translations/en.CD00004396.pdf
With best wishes.
-Sanjay
Hi Roy
Thank for the link. but the paper does not address voltage pumping when motor become generator due to reversal direction or active breaking. This paper only discuss power supply decoupling.
That is true, Richard.
You need an active braking solution. By the way, do you necessarily wish to recover the excess energy from the capacitor. Or will some form of dissipative braking do ?
Also, will it perhaps be possible for you to share a diagram of your exact configuration ?
-Sanjay
Well you mentioned about voltage, if you know max current rating or power rating,you can calculate energy Energy=power* time.Here energy is nor constant instead it is transient.Hence if you take care of initial values rest will follow inherently.
Roy, thank for reply and no it is not for regenerative purpose, more in line of dissipative braking but I'm operating at extereme temperature (150C) so Pd has to be managed.
Oops !
Thanks Richard, for that vital detail !!
Let me give it some thought.
-Sanjay