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TIDA-010062: A totem pole state machine issue

Part Number: TIDA-010062

Hi team,

Here's an issue from the customer may need your help:

Customers have questions about the state machine in the demo program for totem-pole bridgeless PFC: 

In totem-pole PFC, the upper tube of the high-frequency tube acts as the control tube for the PFC and the lower tube acts as a complementary tube for the negative half cycle. When the negative half-cycle condition is implemented with the DSP, the output of the input inductor current is the duty-cycle-generated input.

When setting PWM: Clear at CAU, set at CAD, PWM from AQ is fed to DB module, and EPWMA is sent to the upper tube and the complimentary EPWMB is given to the lower tube.

However, in the TI state machine, the EPWMA and EPEMB are swapped at NZC2 using TTPLPFC_enable_swap_dead_output(TTPLPFC_high_FREQ_PWM_base). The state after NZC2 is NZC3, and enters into negative half after NZC3.

Then the PWM signal that the EPWMA would have been going to the control pipe (i.e. the upper tube of the HF leg) is going to the sync tube (i.e. the lower tube of the HF leg) for the negative half of the cycle, so that the polarity of the control is reversed?

The code for the TI state machine is as follows: 

The state machine is as follows: 

Could you help check this case? Thanks.

Best Regards,

Cherry

  • Hi Cherry,

    This is because the upper switch and bottom switch swap their roles in each half AC cycle. At positive AC cycle, the upper switch is boost switch and be controlled by D, the bottom switch is sync switch and be controlled by 1-D. At negative AC cycle, the bottom switch becomes boost switch and upper switch becomes sync switch, therefore we need to swap EPWMA and EPWMB so that the boost switch is controlled by D and sync switch is controlled by 1-D.

    Regards,

    Bosheng