Editing Dead-time distortion

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Description of the image:
 
Description of the image:
 
# Schematic: typical single phase half-bridge PWM power output consisting two transistors and an inductive load (inductor). In 3 phase motor drives there are 3 pcs of this kind of circuits excluding inductor (which is replaced by a motor coil).
 
# Schematic: typical single phase half-bridge PWM power output consisting two transistors and an inductive load (inductor). In 3 phase motor drives there are 3 pcs of this kind of circuits excluding inductor (which is replaced by a motor coil).
# Desired load voltage waveform: the distortion free waveform [[setpoint signal]] on load that we would want to see.  
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# Desired load voltage waveform: the distortion free waveform [[Reference signal|reference signal]] on load that we would want to see.  
 
# PWM to top transistor: PWM signal that is controls when the top side transistor is in conductive state.
 
# PWM to top transistor: PWM signal that is controls when the top side transistor is in conductive state.
 
# PWM to bottom transistor: PWM signal that is controls when the bottom side transistor is in conductive state.
 
# PWM to bottom transistor: PWM signal that is controls when the bottom side transistor is in conductive state.
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==Distortion effects==
 
==Distortion effects==
[[File:Torqueripple w deadtime distortion.png|300px|thumb|Measured torque ripple as function of time when motor is rotating. Torque [[setpoint signal|setpoint]] was constant so in ideal case this curve would be flat but instead it shows significant drops in torque periodically. No DTD distortion correction was used.]]
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[[File:Torqueripple w deadtime distortion.png|300px|thumb|Measured torque ripple as function of time when motor is rotating. Torque [[Reference signal|reference]] was constant so in ideal case this curve would be flat but instead it shows significant drops in torque periodically. No DTD distortion correction was used.]]
 
Some of most notable motion control problems caused by DTD:
 
Some of most notable motion control problems caused by DTD:
 
* Unwanted ripple in torque that may reduce motion smoothness
 
* Unwanted ripple in torque that may reduce motion smoothness
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| image1    = Currentripple w deadtime distortion.png
 
| image1    = Currentripple w deadtime distortion.png
 
| alt1      = Before dead time correction
 
| alt1      = Before dead time correction
| caption1  = No distortion correction. Top graph: phase current setpoint and achieved current. Bottom graph: PWM duty cycle setpoint
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| caption1  = No distortion correction. Top graph: phase current reference and achieved current. Bottom graph: PWM duty cycle reference
  
 
| image2    = Currentripple w deadtime correction2.png
 
| image2    = Currentripple w deadtime correction2.png
 
| alt2      = After dead time correction
 
| alt2      = After dead time correction
| caption2  = [[Argon (servo drive)]] distortion correction enabled. Top graph: phase current setpoint and achieved current. Bottom graph: PWM duty cycle setpoint
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| caption2  = [[Argon (servo drive)]] distortion correction enabled. Top graph: phase current reference and achieved current. Bottom graph: PWM duty cycle reference
 
}}
 
}}
 
===Dead time distortion===
 
===Dead time distortion===
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Notice the current dips in otherwise sinusoidal signal. There are 6 dips per sine cycle because in this experiment the test was done on a 3 phase motor which has 3 sine currents with 60 degree phase angle differences. Only one phase is displayed but distortion of two remaining phases will induce dips also in the neighbor phases.
 
Notice the current dips in otherwise sinusoidal signal. There are 6 dips per sine cycle because in this experiment the test was done on a 3 phase motor which has 3 sine currents with 60 degree phase angle differences. Only one phase is displayed but distortion of two remaining phases will induce dips also in the neighbor phases.
  
Also notice how PWM duty cycle setpoint from drive [[Torque controller|torque/current controller]] jumps up/down trying to compensate dead time errors. However, no current controller alone is fast enough to completely eliminate current ripples.
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Also notice how PWM duty cycle reference from drive [[Torque controller|torque/current controller]] jumps up/down trying to compensate dead time errors. However, no current controller alone is fast enough to completely eliminate current ripples.
  
 
===Distortion elimination===
 
===Distortion elimination===
The bottom image shows the exactly same experiment with the one above but this time [[Argon (servo drive)]] dead time correction was turned on. Notice how dips almost completely disappear and PWM duty cycle setpoint shows more sine-like waveform.
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The bottom image shows the exactly same experiment with the one above but this time [[Argon (servo drive)]] dead time correction was turned on. Notice how dips almost completely disappear and PWM duty cycle reference shows more sine-like waveform.
[[Category:Technology]]
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[[Category:Glossary]]
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[[Category:Argon features]]
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