DC power ripple minimization of LCL filter based distributed generation inverter under unbalanced voltage conditions

This paper presents how to minimize a dc power ripple of the LCL filter based distributed generation (DG) inverter under unbalanced operating conditions. Due to the grid fault, the dc power ripple is generated and influenced the life cycle of renewable energy power plant such as photovoltaic systems or fuel cell stacks. In order to minimize the dc power ripple, a modified dq-axis current control with improved current reference is proposed, because the conventional current reference is acceptable only for the L filter based DG inverter but limited for LCL filter based DG inverters. With the proposed modified dq-axis current loop, the dc power ripple is reduced effectively. The proposed control strategy will reduce the impact to the renewable energy sources from the grid fault. As a result, the constant dc power generation of the DG inverter will enhance the stability and reliability of the renewable energy sources. Theoretical equations of voltage, current, and power are well derived. Simulation and hardware-in-the loop experimental results validated the proposed control method under unbalanced operating conditions.