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

Abstract

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 hardswitching 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.

A Comprehensive Short-Circuit Protection Scheme for Series-Connected SiC MOSFETs

“…After the SC fault is detected, the STO will be implemented. In this research, the current source gate driver in [11] is used. The gate driver can output a multi-level gate current and has a fast dynamic response, which is proven to have several benefits in series-connected devices.…”

“…Even though the closed-loop voltage balancing methods [11], [12] can achieve V ds voltage balancing, the V ds is still unbalanced during transients and start-up of the closed-loop control. Therefore, the TVS diode for the series-connected SiC MOSFETs is necessary to protect the serial devices from overvoltage.…”

“…The device under test is two series-connected 1.2 kV/30 A SiC MOSFETs C3M0075120K from Wolfspeed [35]. The developed multi-level current source gate driver for the seriesconnected SiC MOSFETs has been elaborated in [11]. A 2 kV DC power supply is used to regulate the dc-link voltage.…”

“…Series connection of single devices is an effective way to achieve higher blocking voltage [9], [10]. One of the major challenges of series-connected devices is the unequal drainsource voltage (V ds ) balancing [11], [12].…”

“…In this case, the V ds of the short-circuit device is zero, and the voltage across the other serial devices will increase, which may cause overvoltage failure of these devices. The transient voltage suppressor (TVS) is commonly implemented in parallel with each serial SiC MOSFET to avoid overvoltage failure [11], [12]. However, monitoring each device in the serial string is still necessary.…”