A novel strategy for improving power quality of islanded hybrid AC/DC microgrid using parallel-operated interlinking converters

Abstract

The hybrid AC/DC microgrid (HM), which combines the advantages of both AC and DC subgrids, is a promising structure. However, the penetration of a large number of non-linear loads and single-phase/unbalanced loads in the HM can degrade the power quality of the HM. Therefore, this paper proposes a novel control of parallel-operated interlinking converters (ILCs) to integrate power quality compensation, which is able to improve the power quality effectively. In the proposed strategy, an ILC with the largest capacity is selected to be controlled into the voltage source mode, which is referred to as the master ILC, to achieve a balanced and harmonic-free AC bus voltage. Moreover, by introducing virtual impedance to regulate the equivalent impedance, the master ILC is capable of operating in different compensation modes according to the different power quality requirements of HM. Other ILCs are called slave ILCs and are controlled in current source mode to eliminate DC bus voltage ripple by controlling the pulsating power transmitted by multiple ILCs counteracting each other. The proposed control strategy makes full use of the remaining capacity of the ILCs to integrate the power quality compensation in HM without adding additional hardware, thus reducing the power quality control cost of the system and achieving balanced and harmonic-free AC bus voltage as well as DC bus voltage ripples-free simultaneously. Finally, the simulation results verify the effectiveness and feasibility of the proposed ILC power quality control method.