Editing Dead-time distortion
Your changes will be displayed to readers once an authorized user accepts them. (help) |
Warning: You are not logged in. Your IP address will be publicly visible if you make any edits. If you log in or create an account, your edits will be attributed to your username, along with other benefits.
The edit can be undone.
Please check the comparison below to verify that this is what you want to do, and then save the changes below to finish undoing the edit.
Latest revision | Your text | ||
Line 9: | Line 9: | ||
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 [[ | + | # 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. | ||
Line 19: | Line 19: | ||
==Distortion effects== | ==Distortion effects== | ||
− | [[File:Torqueripple w deadtime distortion.png|300px|thumb|Measured torque ripple as function of time when motor is rotating. Torque [[ | + | [[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 | ||
Line 29: | Line 29: | ||
==Measurements== | ==Measurements== | ||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
− | |||
===Dead time distortion=== | ===Dead time distortion=== | ||
− | + | [[File:Currentripple w deadtime distortion.png|300px|thumb|Distortion correction disabled. Top graph: phase current reference and achieved current. Bottom graph: PWM duty cycle reference]] | |
These graphs show actual distortion on sinusoidal motor currents when [[PWM]] frequency was 17.5 kHz and dead-time length 2 µs. No countermeasures were taken to reduce distortion. | These graphs show actual distortion on sinusoidal motor currents when [[PWM]] frequency was 17.5 kHz and dead-time length 2 µs. No countermeasures were taken to reduce distortion. | ||
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 | + | 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 [[ | + | [[File:Currentripple w deadtime correction2.png|300px|thumb|[[VSD-XR]] distortion correction enabled. Top graph: phase current reference and achieved current. Bottom graph: PWM duty cycle reference]] |
− | + | The bottom image shows the exactly same experiment with the one above but this time [[VSD-XR]] dead time correction was turned on. Notice how dips almost completely disappear and PWM duty cycle reference shows more sine-like waveform. | |
− | + | ||
− | + |