Stefan,
It was late. The Kpd was my lazy way of writing (Kp*E + Kd*E)
Basically in a velocity control loop, when the actual velocity is equal to the desired velocity, the control signal output is whatever value is required to maintain the current speed. (75% PWM for a speed of say 2000rpm)
In a position control loop the output signal is zero when the desired position is reached.
The I term is there to compensate for the drag in the system when the control voltage is very small as we are almost there. In this case the I term winds up (increases the control signal) until the desired position is reached as the E term is so small.
In a Velocity control system, this problem does not exist as the error value is always added to the current value of the control signal, effectively doing what the I term would do anyway.
If you write out the velocity algorithm fully you will find the the I term is redundant.
Cheers,
Peter
Stefan Trethan wrote:
toggle quoted message
Show quoted text
On Thu, 04 May 2006 15:04:28 +0200, Peter Homann <groups@...> wrote:
Vc = Vc + Kpd*E
Vc = Kpd*E
To me this seems like a PI vs. a P control.
I don't quite see what it has to do with velocity vs. position?
I would say a PID can be used for RPM control as well, what is wrong with integrating the error out to zero here?
ST
Yahoo! Groups Links
--
------------------------------------------------------------------
Web: www.homanndesigns.com
email: homann@...
Phone: +61 421 601 665
www.homanndesigns.com/ModIO.html - Modbus Interface Unit
www.homanndesigns.com/DigiSpeedDeal.html - DC Spindle control
www.homanndesigns.com/TurboTaig.html - Taig Mill Upgrade board
