Abstract
The voltage rating of the commercial Gallium Nitride (GaN) power devices are limited to 600/650 V due to the lateral structure. Stacking the low-voltage rating devices is a straightforward approach to block higher dc link voltage. However, the unbalanced voltage sharing can occur due to the discrepancies in the gate driving loops, the device parameter tolerance and the device-to-ground displacement currents for the series-connected devices in the stack. The voltage imbalance may cause the over-voltage breakdown, in particular for GaN devices, which do not have the avalanche breakdown mechanism. In this article, a novel controllable current source gate driver is proposed, which addresses the voltage imbalance issue of series-connected GaN HEMTs for both hard switching and soft switching scenarios. The proposed current source gate driver controls the device switching timing and the dv/dt with fine accuracy by directly regulating the device gate current. Without the employment of the lossy snubber circuit or the external Miller capacitor, the switching energy and the switching speed are almost not compromised for each individual device. Meanwhile, the current mirror circuits are utilized as the discontinuous pulsed current sources, which produce negligible additional gate driving loss. A series-connected GaN-based multiple pulse tester is built to validate the proposed current source gate driver and the voltage balancing strategies. It is demonstrated that the drain-to-source voltage difference of the series-connected GaN devices is below 10% for different load current and different switching speed (dv/dt) conditions. Moreover, it is found that the series-connected GaN solution can save 33.6% switching energy compared with the benchmark SiC solution under the same operating condition.
Highlights
Medium voltage (MV) dc is considered an enabling and promising technique in future power distribution grid, microgrids, shipboard power system, offshore wind farms, highpower drive systems and electric vehicle (EV) charging stations [1]–[5]
The small current sources on the secondary side compensate the voltage sharing difference caused by the displacement currents flowing through the device-toground parasitic capacitances
The experimental results coincide with the theoretical analysis pretty well for both soft switching and hard switching scenarios
Summary
Medium voltage (MV) dc is considered an enabling and promising technique in future power distribution grid, microgrids, shipboard power system, offshore wind farms, highpower drive systems and electric vehicle (EV) charging stations [1]–[5]. In MV dc systems, Silicon Carbide (SiC) devices are gradually replacing Si-IGBTs due to the much reduced switching energy and the high operating temperature capabilities. The reverse recovery loss of the intrinsic body diode of the SiC devices is still inevitable. Though external SiC Schottky diode can be paralleled with the SiC MOSFETs to cut down the reverse recovery loss, the costs will be increased. Gallium Nitride (GaN) power devices offer low specific onstate resistance, fast switching speed and high operating temperature capabilities compared with Silicon (Si) counterpart. All of these are beneficial for the efficiency, power density, specific power, as well as the reliability of power electronics converters [6]. Though Silicon Carbide (SiC) excels in hightemperature applications, the material characteristics of GaN
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call