You might take a look at this application note for some ideas: http://jrkerr.com/pssc_irams.zip.
>________________________________ > From: Anders Wallin <anders.e.e.wal...@gmail.com> >To: Enhanced Machine Controller (EMC) <emc-users@lists.sourceforge.net> >Sent: Saturday, March 3, 2012 8:38 AM >Subject: Re: [Emc-users] IRAMS Plan > >> 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 >Emc-users@lists.sourceforge.net >https://lists.sourceforge.net/lists/listinfo/emc-users > > > ------------------------------------------------------------------------------ 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
