**6. Conclusions**

In this paper, the control strategy of the MMC-BESS for rectifier mode operation with capacitor voltage controlled by a battery side DC/DC converter was proposed. The main contributions can be summarized as follows:

• The reason why the rectifier mode control strategy in conventional MMCs invalidates in the MMC-BESS was analyzed in this paper. The ac power and dc power were decoupled by the battery side control, so it was impossible to control dc-link voltage through ac power. According

to the analysis, the control strategy containing dc-link voltage control and SOC equalization was proposed in this paper to achieve the control objective based on battery side capacitor voltage control.

• At battery side, since the capacitor voltage was stabilized by a battery side DC/DC converter, the control strategy of the DC/DC converter was key to the performance of the whole system. Therefore, an improved control strategy for an individual capacitor voltage control was proposed in this paper, enhancing the dynamic performance of capacitor voltage, meanwhile greatly reducing the occupied storage space of the MAF by using a common filter per phase arm. Seen from the simulation and experimental results, the proposed battery side control strategy can satisfy the requirements of rapidity and accuracy, facilitating the application of the MMC-BESS in practice.

**Author Contributions:** Z.W., H.L. and Y.M. conceived and discussed the implementation of the control strategy; Z.W. and Y.M. performed the experiments; H.L. supervised the progress of the project; Z.W. and Y.M. wrote the paper.

**Funding:** This research was funded by National Natural Science Foundation of China gran<sup>t</sup> number 51741703.

**Conflicts of Interest:** The authors declare no conflict of interest.
