Part Number: TMS320F28379D
Hi Team,
Can you help with implementing phase-shift control for my Triple Active Bridge (TAB) converter?
Each leg of the H-bridges is controlled by a single gate driver with two complmentary outputs, so I only need to provide one PWM signal per leg. The complementary signal and analog dead time are generated internally by the gate driver.
My PWM configuration is as follows:
Port 1: Leg A – EPWM1A, Leg B – EPWM1B
Port 2: Leg A – EPWM2A, Leg B – EPWM2B
Port 3: Leg A – EPWM3A, Leg B – EPWM3B
I also need to control the duty cycle of the generated AC square waveform. For this purpose, I operate each ePWM module in up-down counter mode and generate 50% duty-cycle signals for each individual leg.
For example, for Port 1:
EPWM1A is high from counter zero to TBPRD and low from TBPRD back to zero.
EPWM1B is high from CMPA during up-counting to CMPB during down-counting. For example, CMPA = 0.9 × TBPRD and CMPB = 0.1 × TBPRD.
By controlling the overlap between EPWM1A and EPWM1B, I can therefore control the duty cycle of the resulting AC waveform.
My main question concerns the phase shift among EPWM1, EPWM2, and EPWM3. I use EPWM1 as the master and disable its phase-shift loading. Depending on the power-control command, the phase shifts of Ports 2 and 3 relative to Port 1 may need to be either positive or negative.
Currently, I implement:
EPWM_COUNT_MODE_UP_AFTER_SYNC for a positive phase shift
EPWM_COUNT_MODE_DOWN_AFTER_SYNC for a negative phase shift
The problem occurs when the commanded phase shift of Port 2 or Port 3 changes sign (from negative to positive or vice versa). I then need to change the count direction after synchronization, and this transition appears to cause the loss of one PWM cycle.
Could you please advise me on the proper way to implement a seamless transition between positive and negative phase shifts without losing or disturbing a PWM cycle?
Thanks!
Marvin
