TMS320F28335: Phase-Shifted Pulse Width Modulation

Hi Noah,

My expertise is not in using a FCMLI, but if you can please send some information/diagram of what you would want the EPWM signals to output/look like then I can provide some information on if the EPWM configuration is possible and tips on how to implement it!

Best Regards,

Allison 

Hi Allison,

Please see the attached diagram. Basically phase shift each gate signal by some phase related to the number of levels of the flying capacitor multilevel inverter. Each gate signal has the same phase shift relative to the first gate signal.

Regards,

-Noah

Hi Noah,

Thanks for the info and diagram! This configuration looks possible- a few follow-up questions: would the phase shift of the EPWMs and the frequency of EPWMs remain constant and only the duty cycles change? And what information/input would be used to determine the duty cycles of the EPWMs? 

Best Regards,

Allison

The phase shift is always constant in the configuration when the Inverter is operational. We do not intend to vary the number of levels of the FCMLI on the fly. The frequency would remain constant during the changing duty cycle. The data that is input is typically a sinusoid interpreted using a digital interface most likely SPI data.

Thank you,

-Noah

Hi Noah,

There are a few ways you could implement multiple PWMs with constant phase shift and varying duty cycle. Here's are some general ideas at a high-level:

• Implement phase shift with the Time-Base submodule (TBPHS), and then adjust duty cycles by updating Counter Compare values (CMPx) based on your input data
• Both account for phase shift and adjust duty cycles when updating Counter Compare values (CMPx) based on your input data and calculations (e.g. if you wanted a phase shift of 10 for EPWM2, increase the CMPx of EPWM2 accordingly in your calculations)
• Use the Dead Band submodule to implement phase shift and vary the duty cycles with rising and falling edge delays updated based on your input data

Let me know if you have any follow-up questions! A good place to start would be referencing some of the C2000Ware software examples that we have, such as the example {C2000Ware}\device_support\f2833x\examples\epwm_updown_aq or epwm_up_aq. You could also look around the digital power or motor control SDKs as well to see more application-based examples.

Best Regards,

Allison

Hi Noah, while we do not have specific reference designs for a Flying Capacitor Multi-level Inverter, we do have reference designs for a three-level, three-phase ANPC inverter (TIDA-010210) and bidirectional three-phase three-level (T-type) inverter (TIDA-01606) - I know your question is just on specific EPWM functionality for FCMLI but wanted to link those in case you have any interest in these other topologies

Best Regards,

Allison