VSD Control Platform

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Hi,

I'm about to design the hardware for a new variable speed drive controller.
Since I'm largely targeting high power systems, I certainly don't need to
squeeze the last buck out of the controller.
I am looking for processing power (determinism is very important so I think
I need to steer away from "lighting fast from cache, dog slow otherwise"
processors)
Easy design cycle is also very important

I am a bit out of date on CPU's DSP's etc that are currently widely used, so
if anyone has a better idea I'd be grateful to hear it.

Here is my current basic idea :

Core components sitting on the fast asynchronous memory bus :
    TI TMS320VC33-150 FP DSP
    1024K x 32 bit fast async. SRAM
    EP1C12 Altera Cyclone FPGA

The FPGA does
    Hardware peripherals (PWM, encoder interface, ADC/DAC interface)
    Interface to slower memories (FLASH, NVRAM etc)

Here are some specific questions :

- Does anybody have a better suggestion for the architecture ?
- Where can I source async. SRAM's that will meet better than 9ns access
times, since this is what I need to run the DSP at 75MHz external bus cycle
?

Thanks for your help y'all

Gary



Re: VSD Control Platform

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You didn't indicate the type of motor drive you were looking at but I will
assume 3 phase motor from a 6-switch bridge. When you say high power are we
speaking in kW or MW ranges?.
 
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There are some chips that deal with the complete full vector control of
bridge based drives for three phase motors. These can be interfaced to some
quite simple processors and provide adequate performance. If you prefer not
to be locked into these chips then there are a whole host of processors out
there that have the capability to perform well in such tasks.

If you are just in need of speed and/or torque control then a full vector
controller could even be created in FPGA incorporating a processor core,
some memory and the necessary interlocking logic (to prevent shorting the
psu through two devices down a chain) for the drives and is readily
achievable from freely available core IP.

Before I point you in any specific direction though, perhaps you would care
to reveal some more requirements for these drives that would enable us to
get a better taset of what you are specifically after in the outcome of the
design.

--
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Re: VSD Control Platform
Paul,

Thanks for your input.

100's of kW to several MW's

I don't want to tie down too much in the controller - yes, mostly 3phase AC
via six switches, but certainly also 6 and 12 pulse DC, SR, multi-level etc

This is the reason for the FPGA, so I can give (for example) Vd, Vq and
Angle demands to the FPGA, and it can take Vdc feedback and generate
switching patterns for whatever power bridge is connected.

I plan to steer away from dedicated motor control devices ('2812 would
probably be the favourite here) since they are a bit too specific (and I can
certainly improve on their peripherals in a decent FPGA)

What I'm looking for is a platform that gives me the flexibility to do
high-end motor control (i.e. more than standard vector control  or DTC),
where I can move functions easily from software to the FPGA as appropriate.

I'll also end up with lots of  "user side" needs (function block edited
applications, PLC network connectivity, nice PC front etc etc)

I'm pretty certain about the FPGA side of things, my biggest doubt is the
DSP choice.

I think I'll end up limited by the instruction-fetch speed. If I can get
fast enough async. memories I can run this at 75MHz.

I wondered about the 67x DSP's from TI. However these are quite extensively
cached and I am concerned about this 'cause control code tends to be "do
this bit really fast, then do this other bit really fast" rather than "go
round and round doing this over and over again until you've got an mp3
file". Don't really enough to comment intelligently.

I recently used a monstrous PowerPC ('7457) and never really got the
performance I was expecting (because I always had to go to L3 cache for the
code)

What else is out there for the CPU ?

I'm looking for :
- Lots of MIPS (and / or FLOPS) (Ideally around 100MIPS)
- Really lots of MIPS over quite a lot of code without cache already hot
- Good OCDS (I'm assuming the days of bond-out ICE's are behind us at these
speeds)
- Floating point is a big plus, but not the "be all and end all"

I know I'll have to look carefully at all the candidates myself, but I hoped
to pick up on other peoples' experience from this group.

My plan was to look at :

- Other TI DSP's
- ADI DSP's
- ARM devices (whatever they are)
- Infineon TriCore devices
- Hitachi microcontrollers

Any better ideas ?

Gary












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Re: VSD Control Platform
On Mon, 11 Jul 2005 21:58:44 +0100, "Paul E. Bennett"

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Paul has pushed our RTXcore FPGA solution. According to our use
and evaluation of the RTX CPU core, it still has the best interrupt
response, latency and determinism. Using a 20 MIPS core, you can
do useful work 200ns (4 clocks) after an interrupt arrives.

The RTXcore design was originally done for a client who had a
very sophisticated timing generator that took advantage of the
RTX's determinism. When Intersil obsoleted the commercial and
industrial grades of the RTX2000 device, they found that it was
cheaper to clone it than to change architectures.

By combining the core and any additional peripherals on one
FPGA, the final cost will be lower. You can evaluate the
system using a Xilinx S3 starter kit.

Stephen
P.S. for more details please contact me off line.

--
Stephen Pelc, snipped-for-privacy@INVALID.mpeltd.demon.co.uk
MicroProcessor Engineering Ltd - More Real, Less Time
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Re: VSD Control Platform


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Can you not find a chip with enough on-chip resource for the
CODE memory ?

Look at the Analog  Devices BackFin DSPs, which have fast RAM,
and even this device from ST, which might do the whole thing in one chip
? [DSP.ARM.RAM.FPGA.ADC.DAC...]

http://www.st.com/stonline/prodpres/dedicate/wsinfra/digital/dsp.htm

Freescale also have Motor Controller focused devices.

Do you need CAN / Ethenet / USB ... ?

-jg


Re: VSD Control Platform
Jim :

Thanks for responding.

I guess my OP was misleading - I need a general high grunt CPU - I'll do the
control algorithms and the necessary peripherals in the FPGA myself .

I'm looking for :
- Lots of MIPS (and / or FLOPS) (Ideally around 100MIPS)
- Really lots of MIPS over quite a lot of code without cache already hot
- Good OCDS (I'm assuming the days of bond-out ICE's are behind us at these
speeds)
- Floating point is a big plus, but not the "be all and end all"

I know I'll have to look carefully at all the candidates myself, but I hoped
to pick up on other peoples' experience from this group.

My plan was to look at :

- Other TI DSP's
- ADI DSP's
- ARM devices (whatever they are)
- Infineon TriCore devices
- Hitachi microcontrollers

Any better ideas ?

Gary



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Re: VSD Control Platform
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  I was pointing to devices that have significant on-chip memory, and
that means you get faster operation, and lower EMC/RFI issues, which
probably matters on a large VSD.
  The STW22000 mentioned has a 300MHz ARM _AND_ a 600MHz Dual MAC DSP
and 16MBits of Memory, which I thought was high grunt ?

  The BlackFin devices are in the 300-700MHz range.

-jg


Re: VSD Control Platform
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Please don't toppost.  It means either extensive editing or losing
the context.

I wonder if you should consider two processors.  One has to be
quite fast, and output the precised control timings.  The other
needs to stand back and take a view, but do more computation.  It
can prepare instructions for the i/o processor, and it probably
will not matter if it skips one cycle every so often.  At any rate
you will concentrate the timing problems in the interprocessor
communications.

This doesn't sound like a system where skimping on hardware is
advantageous.  The dual system will also allow for mutual backup
and some fail safe, which I expect will be critical.

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