© 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.