Losses in power grids and electric devices are between 5% and 7% smaller with direct current than with alternating current.
Direct current also makes it possible to more efficiently feed electric energy from regenerative sources into power grids and energy storage and to improve grid stability; with direct current it would be possible to build much more compact electric devices.
The lack of efficient and cost-effective circuit breaker technologies has made it impossible to fully exploit the potentials of direct current, e.g. in distribution grids in data centre, photovoltaics and telecommunication systems or in on-board grids for aviation and shipping, electric vehicles and railway technology.
The only electromechanical circuit breakers available today implicate the risk of arcing when switching direct current and voltages; they are also slow to react, heavy, unwieldy and expensive.
Funded by the German Federal Ministry of Education and Research (BMBF), the research project called “NEST-DC” aims to investigate the foundations of a semiconductor-based and completely electronic circuit breaker for DC power grids and applications.
The new circuit breaker should be able to switch direct current on, and most importantly switch it off, as quickly and safely as possible at voltages of up to 1,500V. Among other things NEST-DC will explore innovative semiconductor components such as the over current blocking field effect transistor (OCB-Fet).
New structure and connection technologies and switching topologies for the circuit breakers that will use OCB-Fets are to be formulated and tested. There will be demonstrators for the project results in on-board aviation grids, electromobility and photovoltaics, as well as for direct current distribution networks.
The NEST-DC research partners represent the complete value creation chain from the semiconductor chip all the way to the DC power grid system. The team includes the University of Bremen’s Institute for Electrical Drives, Power Electronics, and Devices (IALB) and the four companies Airbus Group, E-T-A Elektrotechnische Apparate GmbH, Siemens AG and Infineon Technologies AG (project co-ordination). Support is also being provided by the European Center for Power Electronics e.V. (ECPE), headquartered in Nuremberg, Germany.
Within the project, the IALB will handle investigation and simulation of novel semiconductor structures for use in the OCB-Fets, static and dynamic measurement of the newly developed circuit breakers and testing their thermal behavior and destruction limits. Airbus Group Innovations will define the requirements for aviation applications, researching a suitable topology and developing a demonstrator together with the NEST-DC partners. The hardware tests will be carried out by Airbus Group in Ottobrunn, Germany.
Siemens will concentrate on the structure and connection technologies of the circuit breakers. E-T-A Elektrotechnische Apparate will define the requirements for industrial applications and, together with the partners, will validate the circuit breakers for voltage classes up to 1,500V. Infineon is leading the project, contributing its power semiconductor expertise and researching power semiconductors intended for use in the OCB-Fets.
The NEST-DC research project is receiving about €2.3m in support from the BMBF in the context of the funding focus area ‘Power Electronics for Increasing Energy Efficiency’. The project began in October 2013 and will run for three years. NEST-DC abbreviates the German for ‘Innovative Electronic Direct Current Circuit Breakers for Renewable Energies and On-Board Power Networks’.