Current Control Structures for Grid-Connected Photovoltaic System

Abstract

In the present scenario, renewable energy source like solar power is the more convenient source of energy. Sustaining a steady DC link voltage and regulation of grid-current are challenging task in grid-tied photovoltaic (PV) system. These issues are overcome by designing a dual-loop control schemes; outer dc-link voltage loop which generates the reference signal for the inner current loop. The grid-tried inverter is used in photovoltaic (PV) system to inject the current with low total harmonic distortion (THD) into the utility grid by designing the efficient current controller. Generally, proportional-integral (PI) controller, proportional-resonant (PR) controller, dead-beat controller and hysteresis current controller are used in PV system to regulate the grid-current. These controllers are implemented in any one of the reference frames like; synchronous (d-q), stationary (α-β) or natural (a-b-c) reference frame. In this paper, the above-mentioned grid-current controllers are employed in all three reference frames and evaluate the steady-state performance of the controllers in terms of THD. The advantages and disadvantages of all grid-current controllers in each reference frames are briefly discussed and compared. This paper provides the best possible grid-current controller in three different reference frames. Finally, the simulation results from a two-stage 5.5 kW, 440 V (L-L), three-phase grid-tied PV system are provided to confirm the theoretical analysis and effectiveness of the control schemes.