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Steinau an der Strasse, Germany

Wagner M.,TU Dresden | Kolb S.,ENASYS GmbH
2013 15th European Conference on Power Electronics and Applications, EPE 2013

Resistance spot welding uses direct current in the range of 1 kA to more than 100 kA to join sheet metals. The current is provided by an inverter that is connected a dc-link capacitor and transformer with a high turns ratio. The current is rectified at the secondary side of the transformer. Since the voltage between the tips of the welding electrodes is in the range of only a few Volts the voltage drop across the rectifier diodes contributes to high losses and therefore to a low efficiency. This paper presents a new high frequency transformer optimized for welding applications, which consists of submodules of planar transformers with integrated synchronous rectification, allowing size reduction and improved controllability of the welding process while reducing the transformer size and losses thus increasing the overall system efficiency. The potential of the new welding transformer is shown through experimental results. © 2013 IEEE. Source

Engelhardt P.,Oel Waerme Institute GmbH | Maximini M.,Oel Waerme Institute GmbH | Beckmann F.,Inhouse Engineering GmbH | Brenner M.,Behr GmbH and Co. KG | Moritz O.,ENASYS GmbH
International Journal of Hydrogen Energy

Polymer electrolyte fuel cells (PEFC) combined with diesel fuel processors offer a great potential for auxiliary power units (APU) in mobile applications. In a joint research project with partners from industry, Oel-Waerme-Institut GmbH is developing an integrated modular fuel cell system for mobile power generation in caravans and yachts. The system includes a steam reforming fuel processor that allows the operation of low-temperature (LT-) as well as high-temperature (HT-) PEFC. In the presented work the coupled operation of the fuel processor and LT-PEFC and HT-PEFC stacks is demonstrated using logistic diesel from a gas station. For LT-PEFC operation, a single-stage preferential oxidation reactor (PROX) was applied to achieve the required CO concentration. Long-term coupled operation was carried out at a reformer temperature of 780 °C using both diesel surrogate (sulfur content <2 wt. ppm) and logistic diesel from a gas station (sulfur content <10 wt. ppm). In contrast to diesel surrogate, an increase in residual hydrocarbon concentration in the reformate was measured using logistic diesel, which is related to the catalyst deactivation from sulfur. Consequently, during LT-PEFC operation cell voltage remained stable using the diesel surrogate, but decreased over operating time using logistic diesel due to deactivation of both reformer and fuel cell catalyst. At a reformer temperature of 800 °C, residual hydrocarbon concentration and cell voltage of the LT-PEFC remained stable during operation with logistic diesel. It was concluded that residual hydrocarbons deactivate the LT-PEFC catalyst more severely than sulfuric compounds. During HT-PEFC operation, cell voltage remained stable in spite of an increasing hydrocarbon concentration. The HT-PEFC showed no indication of anode catalyst deactivation during operation with reformate from steam reforming of logistic diesel and therefore has great potential for coupling with the fuel processor without the need for a PROX reactor. © 2014 Hydrogen Energy Publications, LLC. Source

Maximini M.,Oel Waerme Institute GmbH | Engelhardt P.,Oel Waerme Institute GmbH | Brenner M.,Behr GmbH and Co. KG | Beckmann F.,Inhouse Engineering GmbH | Moritz O.,ENASYS GmbH
International Journal of Hydrogen Energy

Fuel cell systems based on liquid fuels are particularly suitable for auxiliary power generation due to the high energy density of the fuel and its easy storage. Together with industrial partners, Oel-Waerme-Institut is developing a 3 kWel PEM fuel cell system based on diesel steam reforming to be applied as an APU for caravans and yachts. The start-up time of a fuel cell APU is of crucial importance since a buffer battery has to supply electric power until the system is ready to take over. Therefore, the start-up time directly affects the battery capacity and consequently the system size, weight, and cost. In the presented work a novel start-up strategy for the steam reforming fuel processor is introduced. The new approach includes the reactive heating of WGS reactors by using reformate from oxidative steam reforming (OSR) instead of the sequential heating of the fuel processor. The start-up procedure is demonstrated on a 10 kW steam reformer and a parameter study is carried out. Subsequently, the new procedure is tested on the complete fuel processor. Here, the OSR operation starts after 15:20 min and provides reformate for reactive heating of the WGS reactors. Steam reforming operation can be started after 23:40 min, which is 9 min earlier than applying sequential heating of the fuel processor. Until SR operation, the total energy consumption sums up to up to 5.9 MJ fuel and 13 Ah (12 V) electric energy. © 2014 Hydrogen Energy Publications, LLC. Source

Wagner M.,TU Dresden | Bernet S.,TU Dresden | Kolb S.,ENASYS GmbH

Resistance spot welding is a commonly used industrial process. A low efficiency of the inverter, transformer and rectifier lead to high operation costs and a bulky cooling system. This work investigates a new transformer with integrated synchronous rectification that significantly increases the system efficiency and decreases system size and weight, and therefore offers lower costs for energy, the cooling system, transformer and rectifier. A modulation scheme for the synchronous rectifier is proposed and the high efficiency and the thermal behavior of the transformer are presented. © 2013 IEEE. Source

Ditmanson C.,TU Dresden | Kolb S.,ENASYS GmbH
2014 16th European Conference on Power Electronics and Applications, EPE-ECCE Europe 2014

Distributed control solutions are being pursued for new modular converter topologies. In this paper, a novel distributed control system is presented for a modular wind turbine drive with 12 parallel converter modules, where each module has a local control platform and two central control units are used, one active and one redundant unit. A comparison is done of ring versus star network topologies, and it is concluded that the star topology has the advantages of lower latency, higher bandwidth, and better synchronization and the drawbacks of a complex central controller and lower scalability. Analysis is done for fault-tolerant, synchronized operation with a redundant star network topology using 100BASE-TX Ethernet for communications. Furthermore, small custom Ethernet data packets transmitted at regular intervals are used which provides benefits of ensured data integrity, low signal latency, and simple synchronization. Experimental results demonstrate ca. 20 ns synchronization precision, and interruption-free fault tolerance. © 2014 IEEE. Source

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