Maurice Kowal

Circuit breaker concepts for future high-power DC-applications

The development of advanced transmission and distribution technologies is steadily gaining interest. Especially the large number of wind farms leads to a demand for new and innovative solutions. Considering the interconnection of offshore wind farms, new technologies must be investigated. One promising solution for an interconnection is a DC distribution system which is also discussed for new (onshore) medium-voltage distribution systems. Beside the advantages of DC distribution (low losses, no reactive power), DC has major disadvantages concerning control and switching actions. Since present circuit breakers are not able to switch large DC currents, new solutions must be found. After a brief introduction of the fundamental principles for switching DC currents, different concepts of DC circuit breakers are presented and compared in this paper. Furthermore, this analysis is accomplished for different voltage levels and all solutions are compared under technical and economical aspects.

A highly integrated drive inverter using DirectFETs and ceramic dc-link capacitors for open-end winding machines in electric vehicles

A highly integrated inverter for open-end winding machines is designed and build. This paper presents the design of a 6-phase full-bridge inverter for driving an open-end winding machine for electric vehicles. The inverter consists of six full-bridge phase modules that are arranged in a hexagonal shape inside the motor housing. DirectFETs with double-side cooling are used as switching elements. Each module has its own bank of ceramic capacitors. A low-inductive layout allows continuous operation in the nominal operating point at a dc-link voltage of 145V, which is extremely close to the breakdown voltage of the DirectFETs of 150V. In the nominal operating point with a dc-link voltage of 125V, a maximum efficiency of η = 97% is reached.