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Evaluating PWM Signals

Experimenter
Experimenter

I am benchmarking the noise and vibration performance of several electric vehicles with induction motors and I would like some way to objectively quantify some characteristics of the PMW control strategies utilize in each vehicle. Do you have any suggestions about how I could at least measure the duty cycle and carrier frequency with Testlab ?

2 REPLIES

Re: Evaluating PWM Signals

Siemens Valued Contributor Siemens Valued Contributor
Siemens Valued Contributor

 

 

Yes …

Using the time signal calculator in Testlab you can quantify the duty cycle and carrier frequency of a PMW control signal.

 

Background

A pulse width modulation (PWM) signal consists of three main components that define its behavior: pulse width, carrier frequency and duty cycle.

 

The pulse width describes the amount time the digital output signal is on

The carrier frequency determines how fast the PWM completes a cycle (i.e. how fast it turns on and off)

The duty cycle describes the amount of time the signal is in an on state as a percentage of the total time of it takes to complete one cycle.

 

 

Q9_P1.png

 

Here are the steps to calculate duty cycle and carrier frequency of a PWM signal using Testlab

 

  • Start Desktop module ( Windows 10 : Start -> all programs-> Sim Center Testlab 18-> Desktop Standard & Advance)
  • Open Time Data Editor add-in ( Tools -> Add-Ins -> Time Signal Calculator -> ) check box on left side of screen then press “OK” to close

 

Q9_P2.png

 

  • Go to Navigator worksheet and right click on PWM signal you want to process then select “Replace Input Basket”

 

Q9_P3.png

 

  • Go to Time Data Selection worksheet and press the “Add” button (above channel list)
  • Below Data Set check box in “View” column to visualized the data

 

Q9_P4.png

 

  • Open function editor by selecting (*fx) icon in fist row of Time Signal calculator and select “PWM_PULSE_TO_CARRIER” function then press “OK” button.

 

 

Q9_P5.png

 

 

 

 

Q9_P6.png

  • Edit formula arguments using dialog box : function1 and cross_level then press “OK” button.

 

Q9_P7.png

 

  • Open function editor again by selecting (*fx) icon in fist row of Time Signal calculator and select “PWM_PULSE_TO_DUTY” function then press “OK” button.

 

Q9_P8.png

 

  • Edit formula arguments using dialog box : function1 and cross_level then press “OK” button.
  • Next press the “Calculate” button to perform calculations

 

Q9_P9.png

 

  • Now save the time data inside the project by pressing the “Save As” button located at lower right hand side of Dataset box. After entering a file name press the “OK” button to save new calculated channels.

 

Q9_P10.png

 

  • Using the “Navigator” tab you can visualize the duty cycle and carrier frequency time histories with a 1x3 display.

 

 

Q9_P11.png

 

  • Additionally, when reviewing PWM data with colormaps it may be useful to utilize an offset order cursor centered at the carrier frequency. In the colormap gif below, the carrier frequency is 2500 Hz
  • To utilize offset order cursor feature right click on colormap and select add single cursor then select order cursor.
  • Next double click on the order cursor then type desired frequency offset into lower parameter box.

 

 

pwm_gif.gif

 

 

 

  • Furthermore, it should be noted that offset order cuts can be generated during throughput processing as well using sections settings.

 

Q9_P12.png

 

 For more information about PWM switching frequencies, see the article: https://community.plm.automation.siemens.com/t5/Testing-Knowledge-Base/Interpreting-Colormaps/ta-p/5...

 

 

 

 

Re: Evaluating PWM Signals

Experimenter
Experimenter

Thanks, this is exactly what I wanted to do ! Also, I ready like the tip about the offset order cursor, that's a really useful feature.