T-Type Inverter total losses

Question

Hi!

I’m doing a study on the three-phase T-Type Inverter, the model of which can be downloaded from PLEXIM. In particular, I have to focus on how the total losses (which can be seen already from the downloaded model) change as phi changes. I have to vary phi from -180 to 180. By taking SVPWM1 Space Vector modulation (or others, like SPWM, THIPWM, THZSPWM), I get smaller losses when phi=0. In Space Vector SVPWM0, however, I have minimal losses at phi=30 (and phi=-150), and not at phi=0, as I expected. I can’t explain the reason why, I would need a little help.
Thank you very much,
Mary

P.S: in attachments, under the name of "T-Type results" I put the Excel table and graph that compares SVPWM1 and SVPWM0.

Comments

There are no attachments, but also we would need your model to understand how you modified the Plexim demo.

---

Sorry, my mistake. Here it is all the needed attachments :)

Thank you for your attention!

Answer 1

I can recreate your findings.  I also assume that by SVPWM1 you're referring to the first option in the 3-Phase Index-Based modulation component, DPWM0.  

If we look at the zero sequence injection shown in the component's help for DPWM0, we can see that the zero sequence injection is phase shifted relative to the fundamental by 30 degrees.  I suspect this is the reason why the loss profile is also shifted for this modulation scheme, as if the current peak occurs during the max/min duty cycle, then there will be less switching losses.

Two of the papers referenced in the demo model (copied below) show the derivation of the theoretical loss profile for different modulation schemes. I would expect a theoretical analysis of the topic will reveal a similar shift in the loss profile.

E. Serban, C. Pondiche, and M. Ordonez, “Power-loss analysis in 3-level TNPC inverters: Modulation effects,” in 2017 IEEE Energy Conversion Congress and Exposition (ECCE), Cincinnati, OH, 2017, pp. 490-497. Click to access online: IEEE Xplore webpage.

E. Serban, C. Pondiche and M. Ordonez, “Modulation Effects on Power-Loss and Leakage Current in Three-Phase Solar Inverters,” in IEEE Transactions on Energy Conversion, vol. 34, no. 1, pp. 339-350, March 2019. Click to access online: IEEE Xplore webpage.

Comments

Refer to Figure 11 or Figure 5.17 of the attached two linked references showing similar behavior.  Note that the DPWM numbering can vary from reference to reference.