Medium Voltage Electronics

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.

R&D Topics

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 and more has to be guaranteed – a real challenge against the background of power electronics existing for only about 35 years.

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.

Control of Multi-level Converters 

One drawback of multi-level topology concepts is the increased number of semiconductor switches to be controlled. Especially for systems with small and medium power, the control effort can represent a significant proportion of the total system cost. Fraunhofer IISB is developing optimized control and communication systems as key elements for cost-efficient multi-level systems. The work is focused on:

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 and more has to be guaranteed – a real challenge against the background that power electronics at all exists for only about 35 years.

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. 

Control of Multi-level Converters 

One drawback of multi-level topology concepts is the increased number of semiconductor switches to be controlled. Especially for systems with small and medium power, the control effort can represent a significant proportion of the total system cost. Fraunhofer IISB is developing 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
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Products & Services

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

Projects & Publications

 

Brochures

 

Related Research Areas at IISB

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