Project 2 Research Campus Flexible Electrical Networks

The Project 2 of the Research Campus Flexible Electrical Networks focuses on the development of key components for future direct-current (DC) grids covering from the key component DC-DC converter often called the “Edison’s Missing Link” to the sub-components (power electronics devices, gate drivers and transformers) and materials (isolation material). PGS is massively involved several working packages as well as takes the lead of the entire project.


High-Power Multi-Megawatt DC-DC Converter

Open switching cabinet with dc-dc converter Copyright: PGS Prototype of the high-power dual-active bridge DC-DC converter

The work package deals with the development of multi-megawatt DC-DC converter employing Dual-Active Bridge topology that offers a high efficiency and galvanic isolation. The applied medium-frequency transformers are the result of a former collaboration project between PGS and industry partners. Next to the adaptation of the converter for the application in medium-voltage DC campus grid, the research focuses on the extension of the soft-switching area via auxiliary circuits. In optimum cases, the converter losses can be reduced up to a factor of 6 in partial load operation. Furthermore, an enhanced control algorithm is developed to avoid transformer saturation leading to a further reduction of losses in the transformers.


Power Electronics Devices

Schematic image of a hybrid switch Copyright: PGS IETO-IGBT hybrid package

As a key component for DC-DC converters, the project FEN P2 also deals with the investigation of novel power semiconductor concepts for medium-voltage applications. The focus lies on the combination of various device concepts likse the Integrated Emitter Turn-off (IETO) and the Insulated Gate Bipolar Transistor (IGBT) towards a new and optimized device. In this regard, optimization is applied to efficiency, fault handling capability and extension of the Safe Operating Area (SOA). For this purpose, simulations based on FEM and Spice are carried out to gain knowledge about the potentials and improvement possibilities. To verify the results, driver and package prototypes are to be designed, constructed and tested. In the end, a statement regarding the advantages and limitations of the concept should be made.


Intelligent Gate Drive Units

Green printed circuit board with electrical components Copyright: PGS Prototype of a controllable gate drive unit

In this project, the development of a controllable gate drive unit (GDU), safety concepts for the insulated-gate bipolar transistor (IGBT) and the electromagnetic interference transmitted by the IGBT in medium-voltage (MV) applications are the main focus. First, the optimal switching of the IGBT in different applications with the help of a controllable GDU is researched. Hereby, a mitigation of switching loss is the priority. Second, safety concepts and safety circuitry for the IGBT are investigated. A protection regarding overcurrents and overvoltages is the main focus, but also measurement circuitry for the current operating point of the IGBT is researched. As the last point for this work package, the trade-off between EMI during the switching transient and the switching loss is researched. The main for the last point is on the optimal operation of the IGBT regarding these two criteria in different operating points


Medium-Frequency Transformers

Metal casing with measurements Copyright: PGS 2.2 MVA 1 kHz medium-frequency transformer

In the framework of this project, medium-frequency transformers are investigated for the application and operation in high-power dc-dc converters. The major difference between the medium-frequency transformer and a state-of-the art 50 Hz transformer is given by higher operating frequencies and excitation of non-sinusoidal pulsed voltage and current waveforms. With higher frequencies, it is possible to reduce the size and weight of the transformers, but at the same time the power loss density of the windings and magnetic core are increased. Hence, the reduction of used material and costs are limited due to thermal stress and isolation requirements. Furthermore, the required filter inductance of the DC-DC converter is integrated in the design of the medium-frequency transformer. Another aim of the work is the implementation of a suitable mathematical transformer model for circuit simulators, control systems and measurements. The final goal of the project is the construction and commissioning of a three-phase medium-frequency transformer within a multi-megawatt DC-DC converter.


DC Circuit Breakers

Elementwise picture of a switch Copyright: PGS Prototype of a new thyristor-based power electronic switch for DC circuit breakers

The purpose of the work package 4 is to investigate circuit breakers for direct-current grids. Concepts of DC circuit breakers from high and low voltage applications are adapted and their application in medium voltage levels is investigated. Applicable designs are identified for further detailed studies and testing. New power electronic devices for the application in hybrid circuit breakers are investigated. The project aims to develop power electronic devices that can withstand and interrupt high fault currents.

Projectpartners: Infineon, Schaffner, ThyssenKrupp Electrical Steel

Funding: Federal Ministry of Education and Research