A Closed-Loop Current Source Gate Driver With Active Gate Current Control for Dynamic Voltage Balancing in Series-Connected GaN HEMTs

The voltage rating of commercial Gallium Nitride (GaN) power semiconductors is limited to 600/650 V because of the lateral structure. Stacking low-voltage switches is an effective way to block higher dc-link voltage. However, unbalanced voltage sharing can occur even with well-matched gate drivers and semiconductors due to the device-to-ground displacement currents. As a result, the low-voltage switches may suffer from over-voltage breakdown. This study presents a novel closed-loop current source gate driver to address the unbalanced dynamic voltage sharing issue. Additional compensation current is actively injected into the switch gate to counteract the voltage imbalance brought by the device-to-ground displacement currents. Compared with the conventional voltage source gate driver-based active gate control method, the proposed current source gate driver tunes the switch turn-off timing and dv/dt more accurately because the switch gate current is directly regulated. Meanwhile, since both the pulse width and amplitude of the compensation gate current can be adjusted, the proposed active gate control is more flexible for adapting to different operating conditions. Moreover, without employing snubber circuits or extra Miller capacitors, the switching speed and switching energy of the GaN devices are not compromised. By implementing the proposed gate driver and voltage balancing schemes, well-balanced voltage sharing can be obtained for both soft-switching and hard-switching scenarios. A series-connected GaN-based multiple pulse tester (MPT) is built to prove the effectiveness of the proposed approach under different load and different switching speed (dv/dt) conditions.