> Anders, can You suggest, how to implement that (preferably a simple > and easy way, so that even child or golden retriever :) would > understand)? The scheme in my IRAMS datasheet suggests using Shunt > resistors for that, but I suspect that something else should also be > needed, but I have no idea, how these things actually work.
I don't know the details. You/we should encourage M.Martsola of granitedevices, or M.Freimanis of geckodrive, or linuxcnc's own P.Wallace of Mesa to give comments on the details of the design and/or share an open-hardware servodrive design. So without going into details: - shunt-resistor on the phase where you want to measure current. Make sure the resistor can handle the power. - in principle it is enough to measure 2 phases, and the third current can be deduced from the other two (Kirchoff!). At least for the popular Y-connection. Not sure about delta/Wye connection. - The voltage drop across the shunt is going to be small (we don't want a lot of power wasted in the shunt), so it needs amplification. - The differential amp that monitors the voltage drop needs to be able to handle high common-mode voltage, possibly up to the maximum DC voltage of the drive if the shunts are 'before' the motor windings (called high-side-sensing). - The amp also needs to handle noise and voltage spikes well. The inductance of the motor windings will filter the PWM to some extent, but a lot of the PWM-frequency and its higher harmonics will remain. Maybe add low-pass filtering on the amp-output also. - For fault-protection the amp-output should be compared to a pre-set current-limit, and the result used to shutdown the IRAMS. Possibly this fault-condition should also connect a braking resistor across the motor windings. - For continuous current-sensing the signal should be digitized. To save input pins on the fpga a serial format (pwm, pulse-frequency, I2C?) would probably be best. Back in 2006 I tried using IRF's own IR2175 for this http://www.anderswallin.net/wp-content/2006_06servo/proto_powerstage.pdf but somehow this wasn't working very well, and if my control-logic would command full power from the IRAMS then frying the drive without tripping the current-limit was possible. I'd encourage any new design to use fast hard-wired current-sensing/limiting solution to make the power-stage as fool-proof as possible (user & programming errors will happen!) Anders ------------------------------------------------------------------------------ Virtualization & Cloud Management Using Capacity Planning Cloud computing makes use of virtualization - but cloud computing also focuses on allowing computing to be delivered as a service. http://www.accelacomm.com/jaw/sfnl/114/51521223/ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
