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SVM Waveform Generator Equation

Dragos Moscalu
Prodigy 170 points

Hello guys,


In his simulation model, of space vector modulation, Dave Wilson used a different method for generating the SV modulated waves (Vmod_a, Vmod_b & Vmod_c).

Where can I find the mathematical equation for that particular implementation ? What are the benefits of using it compared to the classical method of third harmonic injection into the sine wave ?

Thanks !

  • 0
    TI__Guru** 114905 points
    Hi Dragos,

    Dave has been contacted. He should respond soon.
  • 0 in reply to Rick Duncan
    TI__Expert 4760 points

    Hello Dragos,

    I have several SVM simulation examples, but from the variable nomenclature you mentioned, I assume you are talking about the one I did using LTSpice.

    The equations for this technique are found in a book by Ned Mohan called "Advanced Electric Drives, Control, Analysis and Modeling Using MATLAB/Simulink.  You can find more information about this book at:

    http://www.wiley.com/WileyCDA/WileyTitle/productCd-1118485483,subjectCd-EE30.html

    The space vector modulation scheme used in my simulation is actually very similar to 3rd harmonic injection in that they both result in 15% better bus utilization, and can easily implemented in a LUT.  The advantage of using a LUT is that you can easily change the modulation index from 0 to 133% to obtain a gradual and natural transition into the overmodulation range, where 133% corresponds to a trapezoidal waveform.

    But SVM can provide an additional advantage of reducing switching losses by changing around the switching states to create different PWM patterns. This is not possible with third harmonic injection.  For example, there is one SVM pattern where the bottom transistor for one of the phases is turned on continuously while the other two phases are modulating.  Then, 120 degrees later, a different bottom transistor is held on while the other two modulate around it.  Finally, the third bottom transistor is held on for the last 120 degrees,  This results in a 33 % reduction in switching losses compared to third-harmonic injection.

    Best Regards,

    Dave