File:Delta PWM.png
Summary
| Description |
English: Principle of the delta Pulse Width Modulation (PWM). |
| Date | |
| Source |
Own work, using gnuplot, python and scipy Category:PNG created with Gnuplot#Delta%20PWM.png |
| Author | Cyril BUTTAY |
| Permission (Reusing this file) |
as licensed |
| Other versions |
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File:Delta PWM.svg is a vector version of this file. It should be used in place of this PNG file when not inferior.Category:Vector version available
File:Delta PWM.png → File:Delta PWM.svg
For more information, see Help:SVG. |
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Licensing
I, the copyright holder of this work, hereby publish it under the following licenses:
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Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled GNU Free Documentation License. |
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This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported license. | |
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| This licensing tag was added to this file as part of the GFDL licensing update. |
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This file was generated using the following python code (requires the module scipy)
#!/usr/bin/python
# this file generates data and the gnuplot file used for the delta pwm plot
# needs python, scipy and gnuplot (4.0 used)
from scipy import *
freq= 0.05 # frequency of the reference signal
step=1e-2 # calculation time step
hysteresis=0.15 # hysteresis of the delta pwm
current_increase=0.5 # rate of increase (or decrease) in the output current
current_decrease=-0.5
direction=0 # direction=0 when output current increase, 1 otherwise
current=[0] # this is the current waveform
pwm=[0] # This vector is the pwm signal
grid=["0"] # this vector contains the x-values at which the pwm signal
# changes state
file = open("data.dat","w") # the data file
for i in range(int(1/(freq*step))):
reference=sin(i*step*freq*2*pi)
high_limit=reference+hysteresis
low_limit=reference-hysteresis
if direction==0:
if current[i]<high_limit: #if current is increasing, but we still
#are under the upper limit, carry on
current.append(current[i]+current_increase*step)
pwm.append(1)
else: #else change pwm state
current.append(current[i]+current_decrease*step)
direction=1
grid.append("%s"%(i*step)) #stores the time value at which the
#pwm changed state
pwm.append(0)
elif direction==1: #if current is decreasing, but we still
#are over the lower limit, carry on
if current[i]>low_limit:
current.append(current[i]+current_decrease*step)
pwm.append(0)
else: #else change pwm state
current.append(current[i]+current_increase*step)
direction=0
grid.append("%s"%(i*step)) #stores the time value at which the
#pwm changed state
pwm.append(1)
file.write('%s\t%s\t%s\t%s\t%s\t%s\n'%(i*step,pwm[i],current[i],
high_limit,
low_limit,
reference))
file.close() # end of data generation
xtics=',"" '.join(grid) # creates a string used for the x-tics
file = open("delta.plt","w") # generates the gnuplot file
file.write("""
# This file is used to generate a plot that explains the
# principle of the delta pwm
# graph configuration
set terminal postscript eps enhanced "Times-Roman" 24 color solid
set encoding iso_8859_15
unset title
set line style 1 lt 3 lw 3 pt 0 ps 0
set line style 2 lt 2 lw 1 pt 0 ps 0
set line style 3 lt 8 lw 2 pt 0 ps 0
set line style 4 lt 4 lw 3 pt 0 ps 0
set border 15 lt 7 lw 4
set grid xtics ytics
set xlabel ""
set format x ""
set bmargin 0
set tmargin 0
set ytics ("0" 0)
set xtics (%s)
set output "delta.eps"
set multiplot
set ylabel "Analog signals"
set origin 0,0.54
set size 1,0.45
plot [0:19][-1.2:1.2] "data.dat" using 1:6 ls 3 title 'Reference' w l,\
'' using 1:4 w l ls 2 title 'Limits',\
'' using 1:5 w l ls 2 title '',\
'' using 1:3 w l ls 1 title 'Output'
set ytics ("0" 0, "1" 1)
set ylabel "PWM signal"
set xlabel "Time"
set origin 0,0.09
plot [0:19][-0.25:1.25] 'data.dat' using 1:2 ls 4 title '' w l
unset multiplot """ %xtics)
file.close() # end of the gnuplot file.
This generates two files, 'data.dat' (data) and 'sigma.plt' (gnuplot source). gnuplot sigma.plt then generates a eps file, which is converted in png using imagemagick.
Category:Power electronic diagrams Category:Pulse width modulation