Ultra-Low Inductance Phase Leg Design for GaN-Based Three-Phase Motor Drive Systems
A vertical power loop design is proposed and shown in Figure 1. GaN devices are mounted on both sides of the PCB board and figure 1 shows the current loop and gate loop in the proposed design, where the power loop is folded to increase the mutual coupling between the current through the two devices and the decoupling capacitor is mounted near the devices as close as possible, therefore the current commutation loop inductance can be reduced significantly compared with the reference design, For lateral GaN devices, the current conducts along the devices, therefore the proposed vertical layout is more suitable for lateral devices compared with vertical devices. The parasitic loop inductance estimation through Q3D extraction shows that the power loop inductance is reduced 10 times as compared with the reference lateral power loop layout design. Figure 1(b) also indicates that the gate loop is perpendicular to the current loop which can also reduce the near field coupling due to the high di/dt in the current commutation loop. Moreover, the DC input and AC output terminals are separated in the proposed layout, which reduces the interaction between input and output noise. The thermal design is more challenging in the proposed layout since the devices are overlapping each other and the heat has to dissipate along the PCB board. The heat dissipation can be improved by implementing the power loop with direct bonded copper (DBC) or by using the newly-released top-cooled devices.