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Hello, I have a couple of questions regarding control system simulation: -- How could I incorporate different sampling rates in a single feedback system using Simulink ? Can simply having different 'sample time' values (relatively prime) in different blocks solves the problem ? -- Actually I want to simulate a feedback system (multirate) where outer loop time period is an integer multiple of inner loop period. On which rate to discretize the plant (using 'c2d')? -- Has anybody worked on 'lifting a discrete/continuous time signal/system' using Matlab/Simulink ? If yes, then please tell me how ..... (any example). Thanks to all respondents in advance Regards, Sarmad |
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Incorporating different sampling rates.....
Started by ●November 20, 2003
Reply by ●November 21, 20032003-11-21
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Message
See
comments interspersed with your questions.
Yes, you can mix
blocks with different sample rates, even if they aren't harmonically
related. However, as part of your system design you must decide how you
are actually going to merge these disparate input rates. Are you just
using a sample-and-hold? If so, Simulink will do fine with just different
sample rates in the different blocks. If you need better quality,
you'll have to change sample rates using upsampling/downsampling (a.k.a.
resampling).
It depends. If the plant control signal(s) is(are) at the
inner rate only, use the inner rate. If the plant control signal(s)
is(are) at the outer rate only, use the outer rate. If the control
signal(s) can change at either rate, you must either use the highest common
multiple frequency, if it exists; or if the highest common multiple frequency
doesn't exist, you'll have to leave the system as
continuous-time. The highest common multiple frequency of 1Hz and 5.5Hz,
for example, is 11Hz. The highest common multiple frequency of 1Hz and
sqrt(2)Hz doesn't exist. If the highest common multiple frequency is
extremely high compared to the highest-frequency pole/zero in the plant, you may
save execution time going with the continuous-time system, but in most
circumstances the discrete-time system will simulate much more
quickly.
Sorry, I'm not sure what you mean here, so I'm pretty
sure I haven't done it and cannot answer this question off the top of my
head. Anybody else?
Sincerely,
Glen Ragan
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