© KIT / Walter Frasch

Research project: Modular storage increases flexibility and battery life

Flexibly combining different energy storage technologies and connecting the battery modules to the power grid via a grid-friendly inverter is the concept behind the LeMoStore project. In the newly launched joint project, the Karlsruhe Institute of Technology (KIT) is cooperating with partners from science and industry. LeMoStore aims to maximize the lifetime of the battery modules and to provide a stable power supply with a high share of renewable energy.

Researchers investigate new approach: strategically dividing charging and discharging power

Conventional storage concepts in the public power grid with established technologies such as lithium-ion batteries combine many battery cells to form a large energy storage system. Similar to photovoltaic systems, this is connected to the power grid via an inverter that converts direct current into alternating current.

The research project “Lifetime-optimized integration of modular energy storage systems in power grids” (LeMoStore) under the leadership of KIT is pursuing a new approach. The concept envisages flexibly combining several small battery modules based on different storage technologies and efficiently connecting them to the power grid via a grid-friendly inverter. “Charging and discharging power are strategically divided in order to achieve the maximum service life of the battery modules and at the same time meet the application-specific requirements on the power grid,” says Professor Marc Hiller, member of the institute management at KIT’s Electrotechnical Institute (ETI).

In the LeMoStore joint project, KIT cooperates with the Technical University of Aschaffenburg (TH AB) and the industrial partners BMZ Germany GmbH, BATEMO GmbH, Hottinger Brüel & Kjær GmbH, Linde Material Handling GmbH, KION Battery Systems GmbH (KBS), and Mainsite GmbH & Co. KG. The three-year project was launched on 1 June 2021. The Federal Ministry for Economic Affairs and Energy (BMWi) is funding LeMoStore with around 1.7 million euros.

Modular multi-level inverter enables individual combination of various battery modules

The scientists are focusing on a modular construction kit with new types of Power Electronic Storage Blocks (PESB), which can be used to combine battery modules individually. This allows a high degree of flexibility, says Professor Marc Hiller from KIT. For this purpose, the researchers use a so-called Modular Multilevel Converter (MMC), which consists of numerous power electronic modules (MMC cells). In combination with a battery, an MMC cell forms a PESB. The interconnection and control of the individual PESBs creates a converter system that can convert direct current to alternating current and vice versa with high efficiency. At the same time, the desired power consumption and output of the individual battery modules can be precisely controlled. Therefore, used battery modules (for example from electric vehicles) can also be used without having to reduce the performance of the overall system.

Researchers model the entire system and test it under a wide range of operating conditions

In order to determine the optimal energy distribution in real time, the scientists model an entire system. The hardware used enables them to simulate a realistic network environment and to simulate AC networks up to 1 kV and DC networks up to 1.5 kV. The researchers can thus test the LeMoStore demonstrator in all occurring operating conditions and validate and verify its functionality.