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.
This paper presents a high performance 4-layer communication architecture for a smart micro-grid testbed which consists of a 2 kVA Distributed Energy Resource (DER) inverter with PV and battery channels capable of advanced grid supportive and grid forming functions in the Process layer, a Raspberry Pi computer in the Interface layer, a customized Edge Intelligent Device (EID) in the Sub-station layer, and an end-to-end solar energy optimization platform (e-SEOP) in the Supervisory layer. The Raspberry Pi serves as a communication interface which communicates with the DER inverter using Serial Peripheral Interface (SPI) communication and talks to the EID using Modbus TCP/IP protocol. This paper provides a convenient and comprehensive solution to SPI and Modbus TCP/IP communication implementation in a smart micro-grid. The challenges of coordination between communication and system control and between different communication protocols have been addressed, which leads to a boost in the communication efficiency and makes the system highly scalable, flexible and adaptive. The proposed communication architecture as well as the micro-grid test bench have been validated through hardware experiments. The results indicate a reliable and efficient communication among different layers, which facilitates large-scale status monitoring of edge devices and coordinated control of the entire system.
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