A novel second harmonic current reduction method for dual active bridge used in photovoltaic power system

Dual active bridge (DAB) converter is widely used in photovoltaic power system. It usually works as an interface between DC voltage bus and storage units with its main function of balancing the power flow of the entire system through maintaining the bus voltage stable. However, due to the pulsating output power of the inverter, there will be an ac current pulsating at twice the output frequency in its input current, which will penetrate to the DAB converter. As a result, the current flowing through the power switches and storage units contains second harmonic current (SHC), leading to reduction of conversion efficiency and doing harm to storage units. Considering the difficulty of applying dual-loop control for DAB, this paper proposes a novel SHC reduction method which only requires a voltage-loop control. The proposed method can reduce SHC in DAB effectively. Besides, it won´t sacrifice dynamic performance of the DAB converter. A 6-kW photovoltaic power system has been built in laboratory, and the experimental results verify the effectiveness of the proposed method.