Medium Voltage Electronics

To develop holistic solutions for our partners, we combine our expertise in the areas of 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 and 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 (T-Type, NPC, Sparse) 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 and static characterization
  • Direct cooling of power electronic systems: Simulation and measurement of novel mechatronic concepts

With the increasing use of power electronic systems in electrical energy grid applications, multi-level topologies are also becoming more important. These converters make it possible to overcome the specific critical points of high-blocking voltage semi­conductors with regard 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. They also provide better EMC performance, which allows the reduction of system size and costs. These systems show low grid perturbations and a generally “grid-compatible” behavior.

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 offer the optimum solution. Today, in the electrical energy grid, the well-known three-level NPC inverters are widely used for small and medium power solar inverters. A new type based on the modular multi-level (MMC/M2C) principle has been introduced into high-power and high-voltage transmission systems (HVDC, SVC). Besides grid-related systems, many other applications can be covered by multi-level converters, for example high-performance drives for industrial, rail or naval systems.

Virtual 360° tour of our Medium Voltage and Megawatt Power Test Lab

© Daniel Karmann / Fraunhofer IISB
Panoramic view of our medium voltage test bench

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.

1000 V 450 kW Motor Drives for Railway Traction

Our 1000 V 450 kW railway traction inverter: 50 % smaller and 30 % lower losses compared to state-of-the-art inverters with efficiencies up to 99.4 %.


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.

6 kV 1.2 MVA Ship Traction Inverter

Novel drive inverter for cruise ships with up to 6 kV and 1.2 MVA with superior output voltage quality for distributed DC grids.

The goal of the publicly funded project MVDC4S is to establish DC medium voltage distribution grids and drivetrains for the environmentally friendly operation of cruise ships. Fraunhofer IISB focuses on the development of next-generation medium voltage drive inverters as an alternative to conventional three level converters.

Power Modules for Multi-level Converters

State-of-the-art multi-level converter systems make use of power semiconductors in industrial standard-packages with isolated baseplates. For applications in the energy grid, a system lifetime of 40 years or more must be guaranteed – a real challenge given that power electronics have only been around for only about 40 years.

Compared to conventional two-level topologies, multi-level systems place special demands on the power modules. However, several of these topologies offer 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 necessary to exploit the full potential of modern power semiconductors in multi-level systems. By using specially adapted 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 converter behavior and availability in the event of system or device failures.

Control of Multi-level Converters

One drawback of multi-level topology concepts is the increased number of semiconductor switches to be controlled. Especially in systems with low and medium power, the control effort can account for a considerable proportion of the total system cost. Fraunhofer IISB develops optimized control and communication systems as key elements for cost-efficient multi-level systems.

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

Products & Services

At Fraunhofer IISB, we develop multi-level systems optimized for customer-specific applications in all power and voltage ranges. Teams of engineers with many years of industrial back­ground and experience from numerous pro­jects support you in a wide area of power electronics related issues.

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