Hybrid energy storage system adjusts grid fluctuations : Page 2 of 2

March 08, 2018 //By Christoph Hammerschmidt
Hybrid energy storage system adjusts grid fluctuations
With the implementation of the "energy turnaround", the switchover from carbon-based to renewable energy, the proportion of electricity generated from fluctuating renewable sources such as wind and sun increases. This requires the expansion of electricity storage capacities and flexible energy management. Researchers at the Fraunhofer Institute for Solar Energy Systems ISE and partners have developed a hybrid energy storage system consisting of a lithium-ion battery and a super capacitor for short-term performance requirements.

Due to its increased switching frequency, the inverter can react more quickly to fluctuations in the mains supply than commercially available devices. As a result, the system is suitable as a very fast primary reserve that can reduce peak loads and for self-consumption solutions on an industrial scale. Implemented in a 19-inch rack with a height of 125 cm, the inverter is smaller by a factor of 2 to 4 than comparable devices on the market. This has been made possible by the use of modern silicon carbide semiconductors and by optimizing the design of circuit boards, filter elements and cooling methods. In order to be able to realize the extremely fast switching speeds and to limit the resulting overvoltages at the semiconductors, a thick copper conductor board with only film capacitors was developed which has been optimized for this purpose. Cooling is provided by a liquid cooler. In order to make the chokes both compact and low-loss, a high-quality powder core material in tablet form was used.

The control of the power electronics is based on a new model-based predictive scheme. By measuring all relevant currents and voltages in the system and through model-based prediction of future conditions, it is possible to achieve significant performance gains compared with available current regulators.

In addition to power electronics, Fraunhofer ISE researchers also developed the energy management for the hybrid energy storage system, using the "OpenMUC" energy management software framework developed at the institute. The algorithms of the energy management system divide the power between battery and super capacitor in the field test. Two different approaches with different parameters and reloading strategies are examined. Medium-term resource planning is ensured by the project partners by means of a generation and consumption forecast and integration into the platform for controlling the distributed systems.
Other developments from Fraunhofer ISE that will be included in the project are new business models for storage systems, such as solar self-supply, peak shaving - i. e. the reduction of the power price - as well as for control energy markets and the control of power gradients and reactive power supply in the low-voltage grid.

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