Vehicle batteries of electromobility offer the opportunity to increase the flexibility of the energy system and the associated reduction of CO2 emissions. This requires system integration through cost-effective, bidirectional charging systems between: Batteries, grid, local generators and consumers, with high efficiency and high power density. Initial medium power (3-phase, 11 kW) bidirectional DC wallboxes for batteries up to 800 V use expensive 1200 V silicon carbide (SiC) semiconductors, or a higher number of cascaded 650 V transistors. For widespread bidirectional integration of existing battery storage, the cost must be significantly reduced. Gallium nitride transistors on silicon (GaN-on-Si) are inexpensive, but still limited to 650 V dielectric strength. The resulting complex circuit technology does not achieve cost reduction. The overall goal of the project is to demonstrate smart, low-cost, bidirectional charging systems using new semiconductor, device, and system technologies. On the one hand, an off-board DC charging cable of low power (1-phase, 3.4 kW) is demonstrated close to the product. On the other hand, bidirectional device concepts are exploratively investigated for on-board chargers (up to 3-phase, 11 kW). A new GaN semiconductor technology approach with alternative highly insulating carrier substrates (sapphire or QST®) is expected to enable low-cost 1200 V devices, for battery voltages up to 800 V. In addition, a bidirectional lockout GaN circuit breaker will be realized to enable efficient, simple and cost-effective bidirectional charging systems. Increased operating times for V2H and V2G of >60,000 h will be evaluated in terms of reliability. The innovation potential of the technologies is shown by demonstrating cost advantages with simultaneously increased energy efficiency compared to 1200 V SiC for bidirectional on/off-board charging cables and chargers.
Project Description ILH
In the sub-project of the Institute for Robust Power Semiconductor Systems (ILH) at the University of Stuttgart, the focus is on the characterization, modeling and design of bidirectional charging circuits in high-voltage GaN technology. New characterization methodologies for bidirectional power switches will be investigated and a lifetime-oriented design for DC charging circuits will be established.