Medium Voltage Electronics

The unique selling point of the working group is the combination of competence about semiconductors, topologies, control, thermal design and system development.

Our research topics include:

• Test of extraordinary devices under tests at 200 m² medium voltage test bench up to 30 kV an 1.6 MW
• Self-developed and self-constructed 10 MW modular multilevel inverter with flexible control for special test setups with up to 20 kV
• Topology studies and realization of 2-level, 3-level and multilevel inverters for renewable energy, railway and ship applications
• “Honest” Digital Twins: Simulation and verification by measurements
• FPGA control and SoC development: Auto code generation for automated control
• Thermo-electrical semiconductor characterization and modeling: Si, SiC and GaN up to 10 kV with four customized double pulse setups
• Direct cooling of power electronic systems: Simulation and measurement of novel mechatronic concepts

With the rapid increase of power electronic systems in electrical energy grid applications multi-level topologies gain in importance. These converters allow overcoming the specific weak points of high-blocking voltage semi­conductors with respect to their static and dynamic properties.

Multi-level systems are therefore the key technology for efficient and cost-effective power electronic systems in high- and medium-voltage applications.

Multi-level systems also provide better EMC performance, which allows the reduction of system size and costs. The low line perturbations of these systems, and a general “grid-compatible” behavior become more important with increasing dominance of power electronic systems in the electrical energy grid.

Based on these specific characteristics, multi-level converters are used in many areas of electrical energy conversion. The term “multi-level” comprises various converter topologies. Depending on the specific application, different power electronic topologies represent the optimal solution. Today, in the electrical energy grid, the well-known three-level NPC inverters are widely used for small and medium power solar inverters and a new family based on the modular multi-level (MMC/M2C) principle has found its way into high-power and high-voltage transmission systems (HVDC, SVC).

Besides grid tied systems, many other applications can be covered by multi-level converters, for example high-performance drives for industrial, railway, or naval systems.

In order to test power converters in the medium voltage range of 1 kV up to 30 kV, a specialized testing room with isolated measuring equipment and safety precautions is required. For this purpose, we established our Medium Voltage and Megawatt Power Test Lab in 2019.

The 220 m² medium voltage test bench at Fraunhofer IISB allows for the testing of medium voltage components and systems by offering DC and AC voltage power supplies and sinks up to 30 kV and 3.2 MW. A 900 kW water cooling supply can be used to cool the device under test or evaluate the device performance at elevated temperatures deliberately. Furthermore, a modular multilevel grid simulator with power hardware in the loop concept allows for testing under realistic conditions with arbitrary disturbances like frequency variations or voltage dips.

Check out the 360° virtual lab tour of our extensive testing infrastructure.

For additional information please see our brochure.

The outsanding efficiency of our 1000 V 450 kW railway traction inverter is achieved by a FEM optimized heatsink, a customized DC link design and paralleled SiC power modules. The boundary conditions for railway applications like insulation co-ordination and emergency breaking are considered. Further hardware in the loop (HiL) test setups are available.

Compared to traditional two-level topologies, multi-level systems have special requirements regarding the power modules. On the other hand, several of these topologies provide additional degrees of freedom. 

In order to optimize the complete converter system, Fraunhofer IISB is developing and qualifying new specific power modules. These power modules are required to utilize the full potential of modern power semiconductors in multi-level systems. By using specially adopted joining technologies the system lifetime is increased compared to state-of-the-art modules. New application-specific power module con­cepts allow the integration of protection mechanisms to improve the converter behavior and availability in case of system or device failures.

The work is focused on:

• Innovative communication concepts for cell based multi-level systems
• Development of control boards and decentralized control solutions
• Optimized IGBT and MOSFET drivers with special functions for multi-level control

Our special focus lies on:

• System evaluation and topology benchmarking
• Customer-specific designs, including construction, assembly, and characterization of prototypes
• Technical benchmarking of systems to evaluate the current market situation for new customer product definitions
• Design of optimized power modules for multi-level converters
• Rapid prototyping for the benchmarking of new technology approaches close
  to the target application  
• High-power converters for medium- and low-voltage drive applications