The invention is an excellent example of the intense collaboration between Siemens and universities. The original idea for the new converter comes from Prof. Rainer Marquardt, who holds the chair in power electronics at the University of the Bundeswehr (German armed forces) in Munich. Around six years ago, Sommer and Prof. Marquardt coauthored a study conducted by the chair about this idea. “I thought that this could possibly be something for Siemens,” recalls Sommer. He was intrigued by idea of a modular system that can be built using the same components for a wide range of applications. Whereas a number of different devices are typically needed to cover the entire application spectrum, the M2C concept calls for identical components to be connected in series and used as necessary for low to high outputs throughout the medium voltage range.

Like most new ideas, the lion’s share of the work goes into solving a slew of individual problems. Sommer, a specialist for drive technology, received support from Hiller, who as an assistant to the chair was involved in the development of the Modular Multilevel Converter from the very beginning. Together the two worked meticulously on the open and closed-loop control methods, tested various configurations, and applied for patents on a number of the results. Sommer has 18 inventions covered by 11 granted individual patents to his credit; Hiller boasts 14 inventions and two granted individual patents. The two achieved the decisive breakthrough two years ago: “We were the first in the world to get a prototype of this new system up and running in the lab,” explains Sommer.

After years of groundwork, it was now clear that the new converter had a future. The inventor team does not work in a basic research department, however, but rather in a product development department. “The advantage of this is that I have a very good feel for what can be successful on the market,” says Sommer. Sommer and Hiller worked on their invention parallel to their product development duties.

They are convinced that their system will be a success. “There are a lot of converters, but no device combines as many advantages as the M2C,” declares Hiller confidently. The new topology can be used for network applications such as network couplings as well as for drives for compressors or pumps. The system requires no additional filters for power grids, saves space, and increases unit efficiency. Whereas other converter systems fail if one element does not function, the M2C can continue to work even after the loss of a module.  The design of the Multilevel Converter also eliminates the need for redundant systems, reducing both investment and maintenance costs. “The system is highly available,” says Hiller. The Multilevel Converter is currently being explored as an interesting option for the low-loss feed of the energy from offshore wind farms into existing power grids.

Both researchers were interested in tinkering with electric equipment even as children. Model railroads were Sommer's favorite hobby, and Hiller was fascinated by model airplanes. Today they dedicate the little free time that they have to their families.