Development of Control Algorithm for Medium Voltage AC to Multi-port Low Voltage DC Converters for Utility-scale Grid Integration of Solar and Storage

Reactive power support is critical in grid voltage regulation, particularly for grid-scale storage and utility-scale renewable systems applications. As per IEEE Standard 1547(2018) Clause 5, around 40-44% of the rated apparent power, is required to support reactive power when the rated active power is drawn or supplied to the grid for voltage regulation. The cascaded multilevel converter configuration is widely adopted across various medium voltage applications due to its modular nature, improved efficiency, and adequate power handling capabilities. However, existing literature on medium voltage AC (MVAC) to low-voltage DC (LVDC) applications lacks discussion on redistributing reactive power among each H-bridge module series connected to the MVAC grid to improve performance. This paper proposes a novel control algorithm for MVAC to multi-port LVDC applications. The algorithm ensures autonomous P Q control for each module cascaded across the MVAC grid and provides a methodology for efficiently distributing the total reactive power demand within each module. The proposed control strategy is validated through PLECS simulations, wherein two H-bridge modules are connected to a 1 kV single-phase (1ϕ) grid in a 10 kVA rated system, with each H-bridge module maintaining a DC voltage of 1.3 kV. Experimental validation is done by flowing 200 W of active power and 200 VAR of reactive power through a 230 V 1ϕ grid connected to two cascaded H-bridge-based systems, maintaining the DC bus voltage at 200 V.