Systematical Controller Design for Two-stage Grid-connected Photovoltaic Power Conditioning System

In this paper, a systematical controller design method for a two-stage grid-connected photovoltaic power conditioning system (PCS) is proposed. For a pre-stage boost converter to achieve the stable operation in the entire region of solar arrays (SAs), the digital resistive current (DRC) mode controller is proposed. This algorithm is very simple to implement with a digital controller and there is no power stage parameter dependency in the controller design. Also, the advanced incremental conductance maximum power point tracking (MPPT) algorithm is used in the proposed system. This approach has the advantages of good accuracy around the MPP and fast tracking speed due to the variable step size, which is based on the inherent characteristic of the SA. For a post-stage single-phase fullbridge inverter control, a state feedback inner current controller using a sine reference function tracking algorithm and an I-P outer DC-link voltage controller using a notch filter are proposed to control the output inverter current to be in-phase with the grid voltage and to regulate the input DC-link voltage. The current control loop can be systematically designed for the required system specification using the time domain analysis and pole placement approach. Also, the voltage loop with the notch filter can enhance the voltage regulation dynamics by increasing the control bandwidth. From the experiment of the prototype two-stage PCS hardware with a 200W SA, the validity of the proposed control scheme is provided with design guidelines of each controller using the stability issues.