help required for fixed point conversion

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Gary 2022-6-19

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回答： Gary 2022-7-17

Algo.slx

I am using R14A and I have modelled angle tracking observer algoirthm in simulink. I have simulated model wih floating point and it works well. I used fixed point advisor. Although there are no errors, but the output is zero. Can anybody help us withthis.

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Andy Bartlett 2022-6-21

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Hi Gary,

Please check that the correct parameter values have been supplied.

For example, in the comments below, you mentioned that

Ts=10000

wn=42 rad/s

The sample time Ts is unusually large, especially given that the model stop time is 0.5 seconds.

Given those values the two discrete integrators never execute except at time 0,

but I'm seeing sample times for other blocks being much shorter, so they execute a lot in the 0.5 seconds sim time.

To reduce confusion over reproduction steps, allow me to suppest you define the parameters in a MATLAB script with some name like

init_data_Algo.m

Ts=10000;
wn=42;

then automatically run that script from the model by doing a one time set_param

set_param(bdroot,'PreLoadFcn','init_data_Algo')
set_param(bdroot,'InitFcn','init_data_Algo')

followed by resaving the model.

Then, check the reproduction

% CAUTION: Save all your open models first!!!
%    Next command will close them all without saving.
bdclose all   
clear all
mdl = 'Algo'
open_system(mdl)
sim(mdl)

Whatever you are seeing from that simulation is what others should see when then attempt to reproduce the results.

Finally, upload both the edited Algo.slx and the data initialization MATLAB script, here.

Regards,

Andy

Gary 2022-6-24

Algo.slx

Hi Andy

Please see the file with all modifications suggested. I entered the desired values in the simulink model without creating a seperate script file. Tried to run fixed point advisor. But it gave lot of errors. Please suggest fix or method to fix it

Gary 2022-6-27

Could anybody help me to fix the overflow wraps in the model?

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回答（2 个）

Ayush Kumar Jaiswal 2022-6-19

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编辑：Ayush Kumar Jaiswal 2022-6-19

The problem of getting all the output as zeros could potentially be related to the proposed data type settings which results in overflows. You could verfiy that in the histograms produced after simulation.

Try increasing the word length in the Settings section of the fixed point tool, allowing more room for calculation and hence avoiding overflows.

Thanks

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Ayush Kumar Jaiswal 2022-6-20

Float subsystem also gives zeros as an output. You mean to say that after converting to fixed point both subsystems are giving zeros? Then please share the un-converted model.

Gary 2022-6-21

No. Float system gives perfect output. Fixed point model gives output zero. As I said earlier, I wanted to know the method of troubleshooting the problem. I am unable to find proper tutorials in this regard. All I could find is usage of fixed point advisor and not how to fix the problem when it occurs

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Gary 2022-7-17

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Finally, I got this model working in fixed point. I have learnt two lessons. First increase the size (16,32,48 etc) and secondly reduce the input range. By iterating between these two factors, I could finally get the result. Thank you all for all the help provided