Three-phase power imbalance represents a persistent operational challenge for microgrids relying on distributed energy resources, particularly when islanded from the main grid. When photovoltaic arrays, small wind turbines, or other microsources generate unequal power across phases, downstream equipment experiences stress, harmonic distortion increases, and overall system efficiency degrades. Traditional solutions require additional power-conditioning hardware, adding capital expense and complexity.
This research presents an elegant alternative by leveraging the inherent capabilities of modular multilevel converter (MMC) topology. The proposed control strategy redistributes power between phases through deliberate management of direct current circulating currents within the converter arms. Rather than introducing external balancing equipment, the system modulates the virtual voltage of each arm, creating controlled current flows that shift power from over-supplied to under-supplied phases.
The control mechanism operates by measuring real-time output power from each microsource and load demand across all three phases. A dedicated dc circulating current controller then calculates the necessary current injection to equilibrate power flow. This correction signal integrates into the phase modulation indices, adjusting converter switching patterns without affecting output voltage magnitude or system frequency. Energy storage devices, such as batteries, provide compensation by absorbing or supplying the necessary energy adjustments.
Simulation and experimental validation demonstrate that the strategy successfully maintains balanced three-phase power delivery under varying distributed generation scenarios. The approach preserves voltage stability and frequency regulation while dynamically responding to microsource output variations. Because the control exploits MMC's native circulating current capability, no separate power flow controllers or static compensators are required.
For islanded microgrids with diverse renewable resources, this solution improves reliability, reduces equipment thermal stress, and lowers system costs by eliminating dedicated balancing infrastructure. The technique proves particularly valuable in remote communities, industrial facilities, or military installations where resilient, autonomous power systems are essential.
