4 How to Capture the Phase Difference and Period of Multiphase Totem Pole PFCs

Due to the large current ripple with TCM control mode, a multiphase TCM totem pole PFC is required for high-power applications. Generally, interleaved control has two designs: open-loop control and close-loop control [1]. Since the open-loop control implements a specific ratio of the switching period of the master phase to the slave phase, the control cannot verify if the slave phase is operating in the ZVS condition all the time because of the parameter variations among different phases. For close-loop control, turn-on instances of different phases are decided by the ZCD signals separately to make sure ZVS is operating with better efficiency and stability.

To achieve the expected phase shift relationship, additional logic is required to capture the phase difference among different phases and the period of the master, so that the phase difference can be further adjusted to the expected phase by changing the on-time of the slave phases in order.

Generally, ECAP modules can be used, but two modules are required for two phases, and at least three modules are required for three phases. This is not an efficient method and the amount of ECAP modules is limited for some C2000 devices.

Figure 4-1 shows a simplified design to capture the phase difference and periods of multiphase PWM output simultaneously. An auxiliary PWM output is designed to reflect the two rising edges of the different phase PWM outputs. The auxiliary PWM output actions are controlled by the T1 and T2 events, where the T1 event refers to the rising edge of phase 1 PWM, and the T2 event refers to the rising edge of the phase 2 PWM. In this way, the single capture module is enough to obtain the phase differences (duty cycle of auxiliary PWM) and period, instead of using two modules. In this way, even for three phase interleaved totem pole PFCs, only two capture modules are required.