Energy Management Strategy of Photovoltaic–Energy Storage Converter Under Unbalanced DC-Link Condition

Abstract

Open-end-winding dual-inverter converters are attractive for high-voltage and high-power photovoltaic–energy storage systems because of their multilevel output capability and high DC-link voltage utilization. However, unequal power availability between the independent DC links may cause one inverter to exceed its linear modulation range, resulting in overmodulation and grid-current distortion. This paper proposes a power-sharing strategy based on reference-voltage-vector reconstruction for a dual-inverter system with a DC-link voltage ratio of 2:1. The equivalent four-level output characteristics are analyzed, and the feasible power-sharing range is derived according to the modulation index, DC-link voltages, and inverter voltage limits. Combined with 180° decoupled modulation, the proposed strategy enables flexible power transfer among the photovoltaic unit, energy storage system, and grid while keeping both inverters within the linear modulation region. OPAL-RT results demonstrate stable operation under different power-sharing modes, with the grid-side power maintained at approximately 23.2–24.1 kW. These results verify the effectiveness and feasibility of the proposed strategy.