Grid connection technique based on μ theory for a two-stage PV structure

Abstract

There is greater flexibility in selecting the direct-current (DC) bus voltage in a two-stage photovoltaic (PV) grid-connected structure than in a single-stage one. The independent DC/DC and DC/alternating current (AC) control in traditional control methods changes the duty cycle of the first-stage DC/DC, which affects the control of the secondary DC/AC and even stabilises the DC bus voltage between the two stages. Therefore, two-stage converters should be considered and controlled in a unified manner. Here, the authors introduce a robust μ value control method based on the hybrid sensitivity theory to control a two-stage PV power generation system. Considering the effect of parameter perturbation on the modelling of the DC/DC average state model, the proposed method improves the DC bus voltage stability of a PV system and the power quality of the grid-connected current while achieving the maximum power point tracking performance of the PV. MATLAB simulations using three PV operating conditions demonstrate that the proposed control method can effectively reduce the fluctuation of the DC bus voltage between the two stages, the harmonic distortion rate of the grid-connected current, and the power oscillation time when the working conditions change.