The RHODaS project is advancing the state of the art in high-performance power electronics for heavy-duty electric transport. A central outcome of this effort is the development of a hybrid T-Type multilevel power converter designed to meet the demanding efficiency, power density, and reliability requirements of next-generation electric powertrains.
A new report documents the full design, development, and validation process of the final converter prototype, together with the testing scenarios and procedures defined to assess its performance under realistic operating conditions.
Project Objectives and Technical Ambition
At the core of RHODaS is the objective to deliver a high-power inverter capable of supplying 150 kW of continuous power while achieving a power density of 58.6 kW/l. The new report by the Austrian Institute of Technology traces the evolution of the converter from an initial prototype, which revealed critical design limitations, to a final, robust architecture that satisfies the project’s technical targets and provides a solid foundation for system-level validation.
From Early Challenges to a Robust Final Design
The first prototype of the hybrid T-Type converter exposed several critical issues during testing. These included shortcomings in the mechanical and thermal design, limitations associated with the use of pre-production GaN semiconductors, and insufficient voltage withstand capability. Together, these factors ultimately led to the failure of the initial inverter during experimental validation.
Building on these lessons, the consortium implemented a comprehensive redesign. The final prototype incorporates bottom-side cooled GS66516B-MR GaN transistors, replacing the earlier pre-production devices. The gate driver circuitry was significantly improved through the introduction of a permanent negative gate voltage supply and optimised gate trace routing, enhancing switching robustness and reliability.
Thermal performance was addressed through the integration of a copper heat-spreading plate combined with high-performance thermal interface materials, ensuring effective heat dissipation under high-load conditions. In addition, the converter adopts a modular architecture composed of three identical power stages, simplifying integration, scalability, and maintenance.
Integration and Experimental Validation
The integration of the final prototype involved careful preparation, including heatsink modifications, epoxy resin sealing, and the application of thermal insulation to ensure stable and repeatable operation. The converter was then subjected to extensive laboratory testing at DC bus voltages of 800 V and 1000 V. These tests demonstrated efficiencies of up to 99% in both two-level and three-level operating modes. Thermal measurements confirmed stable operating conditions, with GaN junction temperatures remaining around 82°C during prolonged load tests, highlighting the effectiveness of the revised thermal management strategy.
Testing Framework and Validation Strategy
The report also defines a comprehensive set of testing scenarios and procedures aligned with relevant automotive standards, including ISO 21782-3. These procedures cover efficiency mapping, temperature rise assessments, simulated driving cycles, and maximum power operation, with optional tests such as regenerative braking evaluation and thermal imaging. Final validation of the converter is planned at BOSMAL’s Mechanical Testing Laboratory, where the prototype will be assessed under conditions representative of real-world heavy-duty electric vehicle operation.
Achievements and Next Steps
The final hybrid T-Type power converter represents a major milestone for the RHODaS project. Despite delays caused by the necessary redesign, the project has successfully delivered a reliable, high-efficiency, and high-power-density converter platform ready for final validation. The upcoming testing campaign at BOSMAL will confirm compliance with technical and environmental requirements and support the transition of the technology toward heavy-duty electric transport applications.
Read the full report here >