This article presents a scalable transformer-coupled open-loop gate-driving technique that enables voltage balancing across series-connected GaN devices. High-voltage pulse generation with short rise times at kilovolt levels is a significant challenge. Conventional solid-state devices such as insulated-gate bipolar transistors and SiC metal–oxide–semiconductor field-effect transistors, though capable of high blocking voltages, are limited in switching speed and cannot reach the nanosecond regime. Gallium nitride (GaN) high-electron-mobility transistors (HEMTs) due to their lateral structure offer low gate charge and ability to switch faster than 50 V/ns, are an attractive potential candidate. However, due to their lateral architecture, GaN HEMTs also have limited voltage-blocking capability, with most commercially available GaN power devices rated up to approximately 650 V, limiting their direct use in fast high voltage waveform generation at kilo-volts level. Series-connecting GaN devices can overcome this limitation but introduces severe voltage-balancing challenges, as even minor gate-signal mismatch at nanosecond timescale can cause destructive imbalance. Conventional closed-loop balancing methods, are difficult to implement at GaN switching speeds due to feedback latency. This article presents a simple open loop technique for driving GaN devices in series with a transformer-coupled gate driver. The proposed gate drive ensures simultaneous turn-on/off with identical gate signals across all devices. An ultrafast full-bridge GaN based inverter excites wideband gate-drive transformers designed to preserve the ultrafast transition speeds of individual devices, while providing high-voltage isolation and near-equal voltage sharing establishing a scalable solution. Experimental results with two series-connected GaN HEMTs confirm nearly balanced voltage sharing at 1 kV across varying loads and currents ... Read more

This paper presents the design and control of 12 kW medium voltage Modular Multilevel Converter (MMC) prototype, providing a general overview on both the component and system levels. A top level functional overview of the sub-module (SM) converter design including features like semiconductor temperature monitoring and protections for over-voltage, overcurrent, and over-temperature to enhance reliability. The paper also offers a comprehensive system overview, utilizing OPALRT as a high-level controller. To demonstrate the effectiveness of the proposed design, a 12-kW, three-phase MMC prototype was constructed, consisting of four full-bridge (FB) SMs in each converter arm. The paper explains communication management and the integration of analog and digital signals between the physical system and the user interface controller. Finally, the system's output under various operating conditions is analyzed and presented. ... Read more