Development of a module selection algorithm for a modular multilevel converter with integrated batteries

  • Motivation

    At the ETI, a modular multilevel converter (MMC) with integrated battery modules is being investigated for storing renewable energies. It consists of a large number of individual MMC cells, which are designed as a full-bridge modules with an additional energy storage in the form of a battery module.

    A cascaded control structure is used, in which a central control specifies the six branch voltages. This is converted into control signals for the MMC cells by the signal processing units in the individual branches on the associated branch FPGAs.

    In a classic MMC, the algorithm for the arm voltage generation by selecting the cells to be switched only takes into account the voltages of the individual cells in addition to the branch power. For modules with integrated battery modules - especially when combining different battery types within one branch - it makes sense to also take the battery current into account in order not to put too much strain on the batteries and thus age them excessively. At the same time, other factors such as the ripple of the branch current and the switching losses must be taken into account.



    As part of this work, an algorithm for generating the voltage of an MMC with integrated batteries will be developed. The selection of the modules involved in voltage generation should take particular account of the current load. To do this, the following steps should be carried out:


    • Familiarize yourself with existing algorithms
    • Develop and simulate an algorithm in MATLAB/Simulink
    • Implement the algorithm on the arm FPGA
    • Test the algorithm using the existing arm of the prototype MMC