2 Three-Phase-Shift (TPS) With Varying Frequency

The operation principle of conventional TPS control is shown in Figure 2-1, where all switches are operating alternatively at almost 50% duty cycle with necessary dead time. Three phase-shift angles are defined here for bidirectional power regulation.

The inner-bridge phase-shift θ1 is defined as the phase-shift by which the driver signal of Q1 leads that of Q3 in the primary-side bridge. The inner-bridge phase-shift θ2 is defined as the phase-shift by which the driver signal of Q6 leads that of Q8 in the primary-side bridge. Thus, the two high-frequency AC voltages are generated due to the existence of internal phase-shift. The external phase-shift φ is defined as the phase-shift by which the driver signal of Q1 leads that of Q8. The external phase-shift φ can also be defined as the phase-shift by which the positive rising edge of VAB from zero to high level leads that of VCD during one switching period.

When the varying frequency is added with TPS control, each bridge still works at 50% duty cycle, but the switching frequency also changes in real time.