Re: PID question

hondgm@xxxxxxxxx wrote:

Actually, I have an ADC that reads the load current. I also have one
that reads load voltage, which is a little redundant. The micro is 16
bit, with a 100ksps A/D and a some DSP type functionality. It seems to
handle it ok; it's just that some loads causes the voltage output to
jump all over the place. For example, pure resistive loads are fine.
If I put a small motor on as a load with some current limiting, it has
problems. The voltage output jumps all over.

Just to add a few thoughts. If your A/D can sample at 100k samples per second, you'll have 10us sampling time (assuming no s/w overhead). You must also take into account that, since you have a discrete-time closed-loop system, you must allocate several samples to your desired response time, so as not to de-stabilise the loop. That will slow it down, but may still be acceptable for what you want to do. My very rough guess would be a response (settling) time of at least 100us, probably a lot more (for a very stable loop).

If/when you have the circuit and PIC code working, please post the current limiter speed of response you get to a load step change.

--
Regards,
Costas
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