Power Electronics Europe April/May Issue 2022

OPINION 5 www.power-mag.com Issue 2 2022 Power Electronics Europe After the APEC 2022 in Houston the PCIM Europe is one of the major events in power electronics highlighting the new role of wide bandgap semiconductors and particularly Gallium Nitride (GaN). One of the outstandig PCIM sessions is entitled “Advanced GaN Power Electronics”. GaN as a material has various important electrical properties that make it a suitable and promising material for power electronics application. On the other hand, construction of a lateral-current-flowing heterojunction GaN high electron mobility transistor (HEMT) on a Silicon substrate provides additional practical advantages from cost, packaging and switching speed point of view, making it an ideal candidate for high frequency power electronics applications that could not be offered by SiC power devices. Of course there are also some disadvantages of this approach, primarily related to the reliability and scalability to higher voltage/higher power. The presentation of Alex Huang, Professor, University of Texas at Austin, USA will start from a material point view and then focus on GaN device performance comparison, especially with vertical Si and SiC power devices, to highlight the key motivations for adopting GaN. Challenges related to today’s device in terms of dynamic on-resistance, gate drive requirement, short circuit capability and thermal management will be discussed. Future outlook of the device technology will be discussed focusing on bidirectional GaN FET and high voltage (>1200 V) GaN FET. GaN power devices enable dramatically increased switching speed, reduced on-state resistance, and higher operating temperature. However, the decreased turn-on and turn-off transition times can also give rise to undesirable ringing, voltage overshoot, and electromagnetic interference (EMI), if not managed properly. Thus, improvement in power device packaging, gate drive circuitry, printed circuit board (PCB) layout, and new circuit topologies are needed to fully realize the potential of GaN technology. Robert C.N. Pilawa-Podgurski from the University of California outlines the key challenges associated with power electronics design with wide-bandgap power semiconductors, and present solutions that help unleash the true potential of these groundbreaking devices. Many of the early problems of GaN power converters can traced back to this mismatch between power device, package, and circuit implementations. This work will present practical solutions that mitigate many of the key challenges associated with GaN- based power converters, with a focus on technologies to achieve extreme power density designs. The inherent advantages of GaN devices compared to their Silicon counterparts, i.e. absence of reverse recovery charge, lower output and gate charges, etc., allow to operate power electronic systems based on GaN devices at considerably higher switching frequencies, explains Matthias Kasper from Infineon This enables the design of systems with power densities beyond the limits of state-of-the-art Silicon systems, which will be demonstrated at two very different examples: a 240 W mobile charger with two output ports covering very wide output voltages of 5V-48 V, and a three-phase 11 kW on-board charger with an output voltage range of 250 V-800 V. The number of mobile devices such as mobile phones, tablets, and laptops, has increased and driven the need for a versatile adapter that can be used for several devices. Furthermore, the latest increase of USB-PD voltages up to 48 V, together with the 5 A rating of USB cables, opens the possibility to charge devices with up to 240 W. Thus, the current generation of single port USB chargers with 65 W of output power will no longer be sufficient for the consumer market, for which a new generation of higher power adapters with dual USB-PD ports is explored. The challenges to realize such a system are the wide ranges of input voltage (90 – 265 V) and output voltage (5 – 48 V), PFC requirement, and the supply of two independent output ports. In this talk, novel concepts that allow to leverage the advantages of GaN semiconductors in high frequency operation for the next generation of ultra-high density mobile chargers with wide output voltage range and high power level will be presented. As the electric vehicles (EVs) are proliferating, the requirements for on-board chargers (OBCs) are getting ever more demanding, and the original equipment manufacturers (OEMs) are requiring a volume and weight decrease of the OBCs, in order to be able to free space for other components and make the car lighter. The state-of-the-art power density for OBCs on the market now is 2 kW/l, and as WBG devices arrive, the goal is to reach 6 kW/l,, a factor 3 improvement in power density driven by WBG devices. Here an ultra high-density OBC employing a Vienna rectifier PFC providing a regulated split DC-link is used. The split DC-link allows to connect four cascaded dual active bridges (DABs) with 600 V rated GaN HEMTs for output voltage regulation. DABs are inherently bidirectional topologies and are able to operate with ZVS over a wide voltage range, making them the preferred choice for high frequency operation in OBCs. Luca Nela from Swiss EPFL will discuss the future perspectives of GaN devices and propose novel architectures to significantly improve the device performance and address the main challenges of this technology. Investigated are multi-channel devices to improve the on-resistance vs break-down voltage trade-off, reducing conduction losses and resulting in cheaper and more compact power devices. Demonstrated are the potential of monolithically integrating several power devices on the same chip to realize power integrated circuits (ICs) with reduced footprint and high-frequency capabilities. To address the challenging thermal management of high-power density GaN devices and ICs, embedded liquid cooling in the device substrate is proposed, which enables extracting unprecedented heat fluxes. Finally, the potential of GaN for high-frequency soft-switching applications is explored and its performance to existing Si and SiC devices is compared, with a special focus on output-capacitance hysteresis and gate-driving losses in the range of 10 MHz. These papers illustrate the increasing role of GaN – accompanied by new entrants in the market such as start-up Innoscience from China and most recently Japanese ROHM. We have prepared a lot of details on the following pages – also a comparison between GaN and SiC. Achim Scharf PEE Editor Gallium Nitride Takes Off