**6. Conclusions**

The simulation results of the MMC-based PV plant with arm power control are presented specifically when the irradiance is uneven within the arms of the MMC. The consequence of uneven irradiance on each sub-modules of the arm of the MMC is discussed in terms of harmonic distortion and unbalance in the phase currents. It is seen that the MMC-based PV plant is capable of tracking the maximum power at individual sub-module level brining the MPPT granularity to "6· N". This is achieved without any additional *dc-dc* converters.

It is further noticed that, based on the operating conditions, the harmonic distortion in the output currents increases due to residual voltage between the actual inserted arm voltage and the desired arm voltage. The effect of this residual voltage is the increase in THD and the amount of unbalance

in the output current. Though there is no strict requirement on the unbalance, usually a balanced operation is desired for stable operating conditions. Furthermore, there is a strict requirement on the THD of the currents injected into the *ac* grid. It is seen that based on the operating load and irradiance pattern on the PV panels connected to the MMC the THD values can be higher than 5%, which is the allowed limit.

In this paper a modified sorting and tracking algorithm is proposed to the arm power control of the MMC. It enables the effective operation of the MMC-based PV plant even under unequal irradiance patterns across the sub-modules. For the case considered, it is shown that the THD is reduced by 30%, bringing it well within the permitted limit.

**Author Contributions:** Conceptualization, methodology, and validation: A.B.A., formal analysis: R.T. and D.S. Article is written by A.B.A. Article is reviewed by R.T., L.E.N., and D.S. All authors have read and agreed to the published version of the manuscript.

**Funding:** This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie gran<sup>t</sup> agreemen<sup>t</sup> No 845122.

**Conflicts of Interest:** The authors declare no conflicts of interest
